Necker cube = reversible figure


Penrose triangle = unrealizable object


Kanizsa triangle = illusory contours


Ponzo illusion in a purely schematic form and, below, with perspective clues


A person  glassblowing .


Comparison between a healthy eye versus one with a  Cataract .


Pictured here is a slit lamp. When used with a  binocular microscope , the ophthalmologist can examine the eye with a small beam (slit) of light. The slit of light can accentuate features of the eye when directed at an angle. The microscope used in combination with the slit lamp allows for greater magnification (10 - 25 times) than typical handheld devices.


A posterior chamber intraocular lens prior to insertion. This is inserted during cataract surgery after the cloudy eye's natural lens is removed.


The holochroal eye of  Paralejurus  sp.


Holoptic  Anisoptera


Holoptic eyes of a male syrphid ( Eristalinus taeniops )


Ewald Hering's model, published 1899, of how a Vernier acuity stimulus is coded by a receptor array. Receptors marked  c  signal a different position code along the horizontal direction from either the position  a  code or the position  b  code. [ 1 ]


Acuity/Resolution versus Hyperacuity/Localization  Top: Two stars imaged on the mosaic of retinal receptor cells can be resolved only if their separation leaves at least one intervening mosaic element with a detectably different intensity, otherwise the pattern is indistinguishable from a single elongated star.  Bottom:  Two targets can be localized relative to each other to values transcending the spacing of the mosaic units; the hyperacuity mechanism achieves this by identifying,  with sub-pixel precision, the light center of each target, across all the pixels it covers


A phakic IOL


Before surgery (natural crystalline lens, left). After surgery (implanted PCIOL, right).


An anterior chamber IOL (ACIOL)


A posterior capsular opacity (PCO) around a posterior chamber IOL (as seen on retroillumination in a  slit lamp )


Acrylic MICS-IOL in holder


Plaque at  St Thomas' Hospital  – site of first permanent insertion of an intraocular lens, 8 February 1950


A patient in front of a  tonometer


Diaton transpalpebral tonometer


Scallops have up to 100 simple eyes


Flushing the nasolacrimal duct in a cat.


The nictitating membrane of a  masked lapwing  as it closes over the left eye, originating from the  medial   canthus


The  plica semilunaris of conjunctiva  is a vestigial remnant of a nictitating membrane in humans.


Two  American  soldiers pictured during the  2003 Iraq War  seen through an  image intensifier .


The  electromagnetic spectrum , with the  visible portion  highlighted


Normalised  absorption spectra  of the three human photopsins and of human rhodopsin (dashed). Drawn after Bowmaker and Dartnall (1980). [ 5 ]


The pupil of the eye dilates in the dark to enhance night vision. Shown here is a pupil of an adult naturally dilated to 9 mm in diameter in  mesopic  light levels. The average human eye is not able to dilate to this extent without the use of mydriatics.


USMC  M3 Sniperscope assembled on a  M3 Carbine . Introduced during the  Korean War , it was an early active infrared night vision equipment powered by a large 12 volt battery that was carried in a rubberized canvas backpack.


An  M60 tank  with an infrared searchlight mounted on the cannon.


Binocular night vision goggles on a flight helmet. The green color of the objective lenses is the reflection of the light interference filters, not a glow.


Appearance  of figure changes on 45-degree rotation


Discrimination of length (top) and orientation (bottom) for a line at various orientations around the clock


Human eye .


Biological processes that might be active in the tear fluid, based on  Gene Ontology  data. From de Souza et al., 2006. [ 7 ]


Licking eyeballs may cause viral  conjunctivitis  (pictured).


A schematic of the oculometer, depicting the arrangement of the light source, objective lens, beam splitter, two polarizing lenses, detector, and eyepiece.


Ommatidium: A – cornea, B – crystalline cone, C & D – pigment cells, E – rhabdom, F – photoreceptor cells, G – membrana fenestrata, H – optic nerve


Ommatidia of a  krill


Large optic pit (fluorescein angiography)


3D model of orbit with surrounding bones


The seven bones that form the orbit: yellow =  Frontal bone green =  Lacrimal bone brown =  Ethmoid bone blue =  Zygomatic bone purple =  Maxillary bone aqua =  Palatine bone red =  Sphenoid bone teal =  Nasal bone  (illustrated but not part of the orbit)


Tear system : a. tear gland / lacrimal gland, b. superior lacrimal punctum, c. superior lacrimal canal, d. tear sac / lacrimal sac, e. inferior lacrimal punctum, f. inferior lacrimal canal, g. nasolacrimal canal


Eye bags  – minor periorbital puffiness usually detectable below the eyes only.


Periorbital  edema .


The 1931 CIE photopic  luminosity function . The horizontal axis is wavelength in nm.


The head of a  mantis  showing the black pseudopupil in its compound eyes


The eye of a  mantis shrimp  has three regions, each with its own pseudopupil.


Monocular PD can be measured during an eye test.


PD measurement using an app (PD+ by Zernike)


Pupillary distance measurement with iPad app


Diagram of light and four Purkinje images [ 1 ]


An eye with Purkinje images


A demonstration of red-eye correction


Diagram of the eye, the retina, and location of the various retinal implants. Retinal layers, from bottom to top: retinal pigment epithelium (RPE), photoreceptors (PR), horizontal cells (HC), bipolar cells (BC), amacrine cells (AC), ganglion cells (RGC), nerve fiber layer (RNFL).


Summary of pervasive effects of light


Cattle rhodopsin


The  visual cycle  follows the renewal of the retinal chromophore. It runs in parallel to the phototransduction pathway.


Trace of saccades of the human eye on a face while scanning


Saccadic main sequence, showing single saccades from a participant performing a visually-guided saccade task. It is called "main sequence" because it looks like the  main sequence  in astrophysics.


J. Paul Getty , one of the twelve famous people  George Ohsawa  claimed were suffering from sanpaku because of visible  sclerae  under their  irises . [ 1 ]


The CIE 1951 scotopic  luminosity function . The horizontal axis is  wavelength  in  nm .


Head of  Polistes  with two compound eyes and three ocelli ( circled )


This  jumping spider 's main ocelli (center pair) are very acute. The outer pair are "secondary eyes" and other pairs of secondary eyes are on the sides and top of its head.


Head of a  wasp  with three  dorsal  ocelli (centre), and the upper part of its  compound eyes  (left and right)


Moth larva about to moult; the new stemmata are visible behind the old head capsule


An example of a sawfly larva. It has just a single pair of stemmata, and they are set higher on its head than the position of stemmata on the heads of  lepidopteran  larvae.


The larva of one of the  Acherontia  species shown here, is typical of the order Lepidoptera. The head of the larva bears more than one pair of stemmata, all of which are set low down and are far more widely placed than the mouthparts.


A  Scolopendra  species ( Chilopoda ) with stemmata incompletely aggregated into compound eyes


A man squinting on a sunny day


Howard-Dolman test.


Example of a Snellen-like depth test


Stye of the upper eyelid


8-year-old boy with an external hordeolum of lower lid


Internal stye of upper eyelid


Pupillary response


Human tears


Anatomy of lachrymation, showing  a) Lacrimal gland b) Superior lacrimal punctum c) Superior lacrimal canal d) Lacrimal sac e) Inferior lacrimal punctum f) Inferior lacrimal canal g) Nasolacrimal canal


A toddler producing tears due to emotional stress or pain


Crying boy


Queen  Maria II of Portugal  shedding tears and hugging a bust of her late father  King Pedro IV  (also Emperor of Brazil as Pedro I), 1836


The two eyes converge to point to the same object.


Right eye diverging while left eye remains relatively stable – an example of partial divergence


The retina image topography is maintained through the visual pathway to the primary visual cortex. [ 9 ]


Frog gland anatomy–  A: Mucous gland (alveolus), B: Chromophore, C: Granular gland (alveolus), D: Connective tissue, E: Stratum corneum, F: Transition zone (intercalary region), G: Epidermis (where the duct resides), H: Dermis


Anatomy of the human skin


A portion of human skin exhibiting goosebumps.


A patient receiving therapeutic hyperthermia as a treatment option against advanced cancer.


Discoloured pale fingers associated with abnormally low skin temperature, resulting from Raynaud's.


Artificial skin made by Integra composed of an outer silicone film and inner matrix of cross linked fibers.


Stork bite


Port-wine stain visible on the head of  Mikhail Gorbachev , one of the most famous individuals with such a birthmark


Afghan children with light complexion


Pork scratchings served in an English  gastropub


Taxidermied  skin of  Lolong , coined as the largest crocodile in captivity by  Guinness World Records , at Philippine National Museum


Red Crocodile Kelly Bag


The rough-textured scutes of crocodile hide present in the back cut.


The prominent skin folds of  Telmatobius culeus  increase surface area for cutaneous gas exchange


Finger degloving and amputation


Computed tomography (CT) image of the pelvis depicting a closed internal degloving injury (Morel-Lavallée lesion). CT is shown in the  axial plane . The white dotted lines and white arrows indicate a collection of blood inside the lesion. A  fracture  of the left  iliac wing  is also visible on the CT. [ 10 ]


Drawings depicting the types of Morel-Lavallee lesions from the Mellando-Bencardino classification.


Table listing the qualities used to categorize Morel-Lavallée lesions based on MRI.


The magician  Harry Houdini  with  Joaquin María Argamasilla  known as the "Spaniard with X-ray Eyes".


A slab of donkey-hide gelatin


The donkey or ass


Figure 1. Polymerization scheme for formation of polyimine-based self-healing electronic skin.


Figure 2. Self-healing material based on hydrogen bonding and interactions with micro-structured nickel particles.


Figure 3. Recycling process for conductive polyimine-based e-skin.


Figure 4. A stretchable and self-healing semiconducting polymer-based material.


Michelangelo 's  The Last Judgment  -  St Bartholomew  holding the knife of his martyrdom and his flayed skin; it is conjectured that Michelangelo included a self-portrait depicting himself as St Bartholomew after he had been flayed alive.


Assyrians  flaying their prisoners alive


Shield showing three flaying knives, symbol of  Bartholomew the Apostle


Apollo flaying Marsyas  by  Antonio Corradini  (1658–1752),  Victoria and Albert Museum ,  London


The  Flaying of Marsyas  after challenging  Apollo . Painting by  Titian .


The Judgement of Cambyses , part 2, half of a  diptych  painted by  Gerard David  in 1498.


Marco Antonio Bragadin , Venetian commander of  Famagusta  flayed alive by the Turks after a year's  defense of the city  in 1571


Depiction of the human body and bacteria that predominate


Scanning electron microscope  image of  Staphylococcus epidermidis  one of roughly a thousand  bacteria  species present on  human skin . Though usually not  pathogenic , it can cause  skin infections  and even life-threatening illnesses in those that are  immunocompromised .


Ecology of the 20 sites on the skin studied in the Human Microbiome Project


A  dragonfly  in its radical final moult, metamorphosing from an aquatic  nymph  to a winged adult.


A juvenile  king penguin  moulting out its brown chick down and growing its first dark grey and white adult feathers


A young  Mediterranean House Gecko  in the process of moulting.


A pinching gesture


Polymorphous light eruptions on the face of a 6-year-old girl, with scarring from past eruptions


A bowl of pork rinds in Thailand


Uncooked  pork belly  with rind attached


A selection of fried pork rind and crackling products at a shop in Florida.


Khaep mu  (in the bowl at the bottom of the image) served as one of the starters in this selection of northern Thai dishes.


Traditional Portuguese  bolo de torresmos


Pork scratchings served in an English  gastropub


Pork scratchings for sale at the  Great British Beer Festival  2016


A  pilgrim  with prayer bump photographed outside  Masjid al-Haram .


The arms of  octopus  are  muscular hydrostats


left- and right-handed helices


Closeup image of the skin of a marbled eel


Closeup of the skin of the longnose gar


Drawing of the bat wing skin showing the fibers of "mesh like scaffolding"


A closeup view of the felt like fiber pattern seen in elephant skin


Active parachuting mechanism


Passive parachuting mechanism


The wing of a woodpecker


The large scutes on the right side cover the ventral, or belly side of the snake. The smaller scales cover the rest of the snake. Note how the scales overlap.


The variation of scale colors as caused by different chromatophores, located on the dorsal (top) surface of a Garter snake.


Exposed integument of the garter snake after the overlying scales have been removed.


Exposed integument from the underside of a scute of a garter snake.


Close up of garter snake scales. Note the presence of soft integument, or skin, between the scales and how they overlap.


Close-up of a patterned beige and brown snakeskin leather used to make a cigarette case


Preparation of spray-on skin using a  ReCell  device


Newborn baby immediately after birth, covered in vernix


Wrinkles on the face and hands are a typical sign of aging


A woman of European origin with facial wrinkles


A wrinkled finger after a warm bath


Adult sole showing water immersion wrinkling


A man receiving a botox injection


Effects of xeroderma on the hand


The cupula is the onion-shaped structure surrounded by endolymph in the ampulla.


The middle ear


The outer ear receives sound, transmitted through the  ossicles  of the middle ear to the  inner ear , where it is converted to a nervous signal in the  cochlear  and transmitted along the  vestibulocochlear nerve .


The  otic placode  on a developing embryo (about four weeks old)


The ear develops in the lower neck region and moves upwards as the  mandible  develops (six weeks).


Stretching of the earlobe and various cartilage piercings


Primate  ears Human and  crab-eating macaque ( Darwin's tubercle  highlighted)


Pinnae of  bats


Half-Lop Rabbit Illustration by Charles Darwin, 1868


Arizona Eye Model. "A" is accommodation in diopters.


A detailed medical illustration of the eye


MRI  scan of the human eye


Schematic diagram of the human eye. It shows a horizontal section through the right eye.


The outer parts of the eye


Side-view of the human eye, viewed approximately 90° temporal, illustrating how the iris and pupil appear rotated towards the viewer due to the optical properties of the cornea and the aqueous humour


The pupil of the human eye can range in size from 2 mm to over 8 mm to  adapt  to the environment


Dilation and constriction of the pupil


The light circle is the  optic disc  where the optic nerve exits the retina


The two eyes converge to point to the same object.


A brown iris


A light brown iris with limbal ring


Amber eye


Hazel eye


Blue eye


Gray eye Northern Italy


Conjunctival infection, or redness of the sclera surrounding the iris and pupil


Diagram of a  human eye  ( horizontal section  of the right eye)  1.  Lens , 2.  Zonule of Zinn or Ciliary zonule , 3.  Posterior chamber  and 4.  Anterior chamber  with 5.  Aqueous humour  flow; 6.  Pupil , 7.  Corneosclera or Fibrous tunic  with 8.  Cornea , 9.  Trabecular meshwork  and  Schlemm's canal . 10.  Corneal limbus  and 11.  Sclera ; 12.  Conjunctiva , 13.  Uvea  with 14.  Iris , 15.  Ciliary body  (with a:  pars plicata  and b:  pars plana ) and 16.  Choroid ); 17.  Ora serrata , 18.  Vitreous humor  with 19.  Hyaloid canal/(old artery) , 20.  Retina  with 21.  Macula or macula lutea , 22.  Fovea  and 23.  Optic disc  →  blind spot ;  24.  Visual axis (line of sight) . 25.  Optical axis . 26.  Optic nerve  with 27.  Dural  sheath, 28.  Tenon's capsule or bulbar sheath , 29. Tendon.  30.  Anterior segment , 31.  Posterior segment .  32.  Ophthalmic artery , 33.   Artery  and  central retinal vein  → 36. Blood vessels of the retina;  Ciliary arteries  (34.  Short posterior ones , 35.  Long posterior ones  and 37.  Anterior ones ), 38.  Lacrimal artery , 39.  Ophthalmic vein , 40.  Vorticose vein .  41.  Ethmoid bone , 42.  Medial rectus muscle , 43.  Lateral rectus muscle , 44.  Sphenoid bone .


posterior segment ora serrata ciliary muscle ciliary zonules Schlemm's canal pupil anterior chamber cornea iris lens cortex lens nucleus ciliary process conjunctiva inferior oblique muscle inferior rectus muscle medial rectus muscle retinal arteries and veins optic disc dura mater central retinal artery central retinal vein optic nerve vorticose vein bulbar sheath macula fovea sclera choroid superior rectus muscle retina


Diagram of a human eye; note that not all eyes have the same anatomy as a human eye.


Eyelids and eyelashes are a unique feature of mammalian eyes, and primarily serve to protect the eyes. However, the lids also play a role in nonverbal communication, and the lashes in human culture and sexuality.


Light from a single point of a distant object and light from a single point of a near object being brought to a focus on the retina


The  visual system  and the  somatosensory system  are active even during  resting state fMRI


Activation and response in the sensory nervous system


The  human eye  is the first element of a  sensory system : in this case,  vision , for the  visual system .


Human  ear


Human nose


Human  tongue


Disability-adjusted life year  for sense organ diseases per 100,000 inhabitants in 2002. [ 29 ]      no data      less than 200      200-400      400-600      600-800      800-1000      1000-1200      1200-1400      1400-1600      1600-1800      1800-2000      2000-2300      more than 2300


A circular tympanum near the eye of a male North  American bullfrog .


Well-developed accessory auricle on the side of the neck


An intermediate power of a microscopic view of an accessory auricle.


Anatomy of the human ear. (The length of the auditory canal is exaggerated in this image.)    Brown is  outer ear .      Red is  middle ear .      Purple is  inner ear .


The AR-15 pattern rifle used by Crooks in the assassination attempt. The  stock  is damaged.


Approximate locations, including Secret Service counter-sniper teams [ 78 ] [ 79 ]


Trump standing alongside Corey Comperatore's fire department uniform while delivering his July 18 acceptance speech at the  2024 Republican National Convention


Photographs of Crooks taken by a sniper approximately one hour before the shooting [ 130 ]


Trump wearing a bandage on his ear at the 2024 Republican National Convention


Thomas Crooks' car trunk with two  improvised explosive devices  inside


The  fennec fox  uses its distinctive oversized pinnae to radiate excess heat and to amplify the sound of small prey burrowing under the desert sand.


To an impala, the pinna is useful in collecting sound.


Cauliflower ear in an MMA fighter


A  rugby union  player wearing a tiger-print  scrum cap , a form of headgear used for shock absorption and protection to the head.


A mild auricular hematoma after drainage


Depiction of cauliflower ear in the  Boxer of Quirinal , circa 100–50 BC


The wide field view of the endoscope allows "looking around the corner" while utilizing the natural ear canal access to cholesteatoma.


Right chorda tympani nerve, viewed from lateral side


3D model of cochlea and semicircular canals


Structural diagram of the cochlea showing how fluid pushed in at the oval window moves, deflects the cochlear partition, and bulges back out at the round window.


CT-volume-rendered images  of the major openings for the cranial nerves and blood vessels of the holotype braincase of  Sarahsaurus aurifontanalis . Crista interfenestralis ("ci") is visible in the upper images. [ 2 ]


Darwin's tubercle (helix)


Scan of Figure 2, from Darwin's Descent of Man, second edition, illustrating Darwin's tubercle


Antibiotic ear drop


Person administering ear drops


Person with otitis externa


Ear hair protruding from the  external auditory meatus  in a middle-aged male. Note the fine  vellus hair  growth on the  antitragus  and  helix .


Ear hair protruding from the  external auditory meatus  in a middle-aged male.


Strand of human hair at 200× magnification


Royal Navy   admiral  Michael Denny  with ear hair


Ear drops are commonly used to treat  swimmer's ear .


A ear-picking session in  Chengdu , China


Clint Eastwood , who has an extreme form of attached ear lobe.


Stretched earlobe piercing, Ethiopia


Earwax in ear


Dry-type human earwax


World map of the distribution of the A allele of the single nucleotide polymorphism rs17822931 in the  ABCC11  gene associated with dry-type earwax. The proportion of A alleles (dry-type earwax) in each population is represented by the white area in each circle.


An ear-cleaner, attending to a man's ear. Gouache painting, Delhi, 1825.


Post contrast T1 weighted MRI demonstrates intense enhancement of both the eye and the endolymphatic sac tumor in patient with VHL.


CT in patient with VHL syndrome through the petrous ridge demonstrates bone erosion at the site of the endolymphatic sac tumor, typical of the locally aggressive behavior of this tumor (curved arrow).


An intermediate power image of an endolymphatic sac tumor with bone (upper left).


A high power image of an endolymphatic sac tumor showing clear cytoplasm in cuboidal cells lined up along papillae.


Upper respiratory system, showing  entrance to auditory tube  near middle


The Eustachian tube has recently been redefined as the  fibrocartilaginous structure connecting the air cell system of the temporal bone to the nose. What was thought of as the bony tube is really part of the air cell system of the temporal bone. [ 4 ]


3D reconstruction of the right Eustachian tube from Valsalva CT. Note the sac like shape of the structure.


3D reconstruction of the air cell system of the temporal bone including the Eustachian tube and its narrowest area in close proximity to the ear, the isthmus


Hearable generic illustration


Global Revenue from Smart Wearables and hearables


Uncoiled cochlea with basilar membrane


Outer hair cell and Deiter's cell


Cartoon representation of healthy vs damaged hair cells


Green fluorescent protein image of the mouse cochlea


Mastoid cells


The middle ear matches mechanical impedance, like a lever.


Graph of a simple  sine wave


Flowchart of sound passage - outer ear


Flowchart of sound passage - middle ear


Flowchart of sound passage - inner ear


Levels of transmission of neural auditory signals


Cross-section through the spiral organ of Corti at greater magnification, showing position of the hair cells on the basement membrane.


Image showing the  outer ear ,  middle ear , and  inner ear , and how sound is conducted through the outer ear, to the  ossicles  of the middle ear, through to the inner ear and the cochlea, where the organ of Corti sits.


Anatomy of the three ossicles


The utricle (left) is approximately horizontally oriented; the saccule (center) lies approximately vertical. The arrows indicate the local on-directions of the hair cells; and the thick black lines indicate the location of the striola. On the right you see a cross-section through the otolith membrane.


An  electrocoagulation  machine


A bamboo ear pick with a down puff


A metal ear pick


A southern bushpig


An  anime -style elven archer with pointed ears


Boy with otapostasis.


Father and son with otapostasis


Insertion of the  tensor tympani muscle  onto the malleus. . AA’ (two fibrous collagenic layers); B epidermis; C mucous membrane; D head of malleus; E incus; F stapes; G tensor tympani; H lateral process of malleus; I Manubrium of malleus; J  stapedius  muscle.


Examples of the onset and recovery of the acoustic reflex measured with a  laser Doppler velocimetry  system


Inner ear , showing utricle near centre


The establishment of  Georgia  in 1733 raised tensions by threatening Spanish possessions in the Caribbean Basin


Ruins of the fortress of San Jeronimo, Portobelo


Spanish Admiral Don  Blas de Lezo  1741


Fortress of San Lorenzo el Real Chagres


Castillo San Felipe de Barajas  ( Cartagena ). This fortress, though incomplete during the war, was integral to Spain's effort to maintain the link with its colonies via the Atlantic  sea lanes .


British operations in the Caribbean Sea during the War of Jenkins' Ear


George Anson's  capture of the  Manila galleon , painted by  Samuel Scott  before 1772


Commodore  Charles Knowles  in armour, one hand gestures to fortifications and a burning ship


A monument in  Georgia  commemorating the  Battle of Bloody Marsh


Floral Badge of Great Britain


Active electrolocation. Conductive objects concentrate the field and resistive objects spread the field.


Nervous system organization - the motor and sensory systems


An illustration of the route of ASMR's tingling sensation [ 1 ]


Virginia Woolf's novel  Mrs Dalloway  contains a passage describing something that may be comparable to ASMR.


Animal grooming has been interpreted as a form of bonding.


Search Examples of bitter compounds in BitterDB


A  2-D model  of cortical  sensory  homunculus


A 2-D cortical  motor  homunculus


3-D sensory and motor homunculus models at the  Natural History Museum, London


Flotation tank with flip top lid opened


The  elephantnose fish  is a weakly electric  mormyrid  fish which generates an  electric field  with its  electric organ  and then uses its electroreceptive  knollenorgans  and mormyromasts to locate nearby objects by the distortions they cause in the electric field. [ 1 ]


Hans Lissmann  discovered electroreception in 1950 through his observations of  Gymnarchus niloticus . [ 2 ]


Electric eels  create  electric fields  powerful enough to stun prey using modified  muscles . Some weakly electric knifefishes appear to mimic the electric eel's discharge patterns; this may be  Batesian mimicry , to deceive predators that they are too dangerous to attack. [ 20 ]


The  platypus  is a  monotreme  mammal that has secondarily acquired electroreception. Its receptors are arranged in stripes on its bill, giving it high sensitivity to the sides and below; it makes quick turns of its head as it swims to detect prey. [ 37 ] [ 38 ]


Foot showing features of HMSN:  pes cavus  and clawing of the toes


Arthropods  like these  northern prawn , and some mammals, detect water movement with sensory hairs such as  whiskers ,  bristles  or  antennae


Lateral line on an  Atlantic cod


Tactile receptors.


A child bites into a  watermelon , experiencing mouthfeel sensations such as juiciness


Schematic diagram of the experimental set-up in the rubber hand illusion task.


Superior colliculus


Light microscope photograph of a muscle spindle. HE stain.


Prismatic reversing glasses (upside down goggles with two prisms)


Modern version of inverting mirrors with harness


Mechanism of nociception via  sensory afferents


This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for pain, proprioception, thermoception, and chemoception to their relevant endpoints in the human brain. Click to enlarge.


Example of a hot plate assay performed on a rat


Example of a traditional set-up for the tail flick assay


A US  Food and Drug Administration  sensory analyst sniffs  canned mackerel  to check for spoilage.


Portrait of  René Descartes  by  Jan Baptist Weenix , 1647–1649


Regions of the cerebral cortex associated with pain


Mechanism of nociceptive pain


The  breaking wheel  was a torture method used for  public execution  by breaking the bones of a criminal or  bludgeoning  them to death.


The  Mawé people  of Brazil intentionally use  bullet ant  stings as a  rite of passage  into manhood.


The second neuron in the figure depicts an encapsulated nerve ending.


The image on the left side depicts the dorsal column pathway for vibration perception.


The peripheral nervous system with an enlarged depiction of an afferent neuron.


The central nervous system


The  Necker cube  and  Rubin vase  can be perceived in more than one way.


Humans are able to make a very good guess on the underlying 3D shape category/identity/geometry given a silhouette of that shape.  Computer vision  researchers have been able to build computational models for perception that exhibit a similar behavior and are capable of generating and  reconstructing 3D shapes  from single or multi-view depth maps or silhouettes. [ 1 ]


Cerebrum lobes


Anatomy of the human ear. (The length of the auditory canal is exaggerated in this image.)    Brown is  outer ear .      Red is  middle ear .      Purple is  inner ear .


Though the phrase "I owe you" can be heard as three distinct words, a  spectrogram  reveals no clear boundaries.


Law of Closure. The human brain tends to perceive complete shapes even if those forms are incomplete.


Spinal cord tracts - tracts of the DCML pathway shown upper right.


Neural connections in the DCML pathway.


The first-order neuron is a  pseudounipolar neuron  (shown left), with a single  axon  originating from the  cell body  then splitting into two branches. The body is situated in the dorsal root ganglion, with one axon traveling peripherally to tissue, and one traveling into the dorsal column. On the right is a  bipolar neuron .


Prepulse inhibition: preceding stimulus attenuates the  startle response .


PPI and startle reflex apparatus for mice


PPI measurement in human.


Prey have adaptations such as  cryptic coloration  in this  Alaskan hare  which help them  avoid predators .


Experiments on  blue jays  suggest they form a search image for certain prey.


This  ladybeetle  ( Calvia decemguttata ) is easily spotted, but its conspicuous colors are a sign of its  unpalatability , with which experienced predators would probably be familiar.


Schematics and images of types of limb proprioceptor neurons in mammals (top) and insects (bottom) [ 1 ]


Graphical representation of  range fractionation . In this diagram, 10 sensory neurons respond to fraction of the entire range of intensities of stimulus (blue, bottom). Together, all 10 of these neurons comprise the range of perceived stimuli", which is all of the discernable stimulus intensities to the system. Neuron response is indicated by "Sensory Neuron Activity" (or, Action Potential Firing Rate). The range of a single sensory neuron is indicated in yellow. In this depiction, low-intensity stimuli (light blue, left) would activate a single sensory neuron, whereas high-intensity stimuli (dark blue, right) may activate 3-4 neurons. The collective firing pattern of the sensory neurons will inform the nervous system about the stimulus properties.


On center and off center  retinal ganglion cells  respond oppositely to light in the center and surround of their receptive fields. A strong response means high frequency firing, a weak response is firing at a low frequency, and no response means no action potential is fired.


A computer emulation of "edge detection" using retinal receptive fields. On-centre and off-centre stimulation is shown in red and green respectively.


Neurons of a convolutional layer (blue), connected to their receptive field (red)


CNN layers arranged in three dimensions


Sensation consists of signal collection and transduction.


Human power exponents and Steven's Power Law


Philippe Mercier -  The Sense of Taste - Google Art Project


The sense of smell. Bequest of  Mrs E.G. Elgar , 1945  Museum of New Zealand Te Papa Tongarewa .


Balance skill development in children


Balance training using  medicine balls


Diagram of  vestibular system


This figure shows nerve activity associated with rotational-induced  physiologic nystagmus  and spontaneous nystagmus resulting from a lesion of one labyrinth. Thin straight arrows show direction of slow components, thick straight arrows show direction of fast components, and curved arrows show direction of  endolymph  flow in the horizontal  semicircular canals . The three semicircular canals are marked AC (anterior canal), PC (posterior canal), and HC (horizontal canal).


This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for balance and acceleration to their relevant endpoints in the human brain.


Another diagram showing neural pathway of  vestibular /balance system. Arrows show the direction of information relay.


Illustration of the flow of fluid in the ear, which in turn causes displacement of the top portion of the hair cells that are embedded in the jelly-like cupula. Also shows the  utricle  and  saccule  organs that are responsible for detecting linear acceleration, or movement in a straight line.


Vestibular sense system, the "sixth sense"


Sensory inclusive bag for people with  sensory processing disorders


Sensory inclusive bag contents:  Noise-cancelling headphones ,  KultureCity  VIP tag,  fidget toy  and verbal cue card


A subject wearing an electroencephalography cap, a conventional technique for measuring one's reactivity using sensory gating.


Ad hoc  use of  sensory deprivation ; using a  kippah  to block light during an unexpected moment of hypersensitivity.


The vestibular system is stimulated through hanging equipment such as tire swings.


CT scan  slice of the brain showing a right- hemispheric   ischemic  stroke (left side of image).


The cortical homunculus, or the visual representation of how your brain sees your body, was discovered by Wilder Penfield


The  visual system  and the  somatosensory system  are active even during  resting state fMRI


Activation and response in the sensory nervous system


The  human eye  is the first element of a  sensory system : in this case,  vision , for the  visual system .


Human  ear


Human nose


Human  tongue


Disability-adjusted life year  for sense organ diseases per 100,000 inhabitants in 2002. [ 29 ]      no data      less than 200      200-400      400-600      600-800      800-1000      1000-1200      1200-1400      1400-1600      1600-1800      1800-2000      2000-2300      more than 2300


1:posterior segment 2:ora serrata 3:ciliary muscle 4:ciliary zonules 5:Schlemm's canal 6:pupil 7:anterior chamber 8:cornea 9:iris 10:lens cortex 11:lens nucleus 12:ciliary process 13:conjunctiva 14:inferior oblique muscule 15:inferior rectus muscule 16:medial rectus muscle 17:retinal arteries and veins 18:optic disc 19:dura mater 20:central retinal artery 21:central retinal vein 22:optic nerve 23:vorticose vein 24:bulbar sheath 25:macula 26:fovea  27:sclera 28:choroid 29:superior rectus muscle 30:retina


Diagrammatic vertical section through the eye of teleost fish. Fish have a  refractive index  gradient within the lens which compensates for  spherical aberration . [ 4 ]  Unlike humans, most fish adjust  focus  by moving the lens closer or further from the  retina . [ 5 ]  Teleosts do so by contracting the retractor lentis muscle.


A  three-spined stickleback  with stained neuromasts


The shape of the  hammerhead shark 's head may enhance olfaction by spacing the nostrils further apart.


Electromagnetic field receptors (ampullae of Lorenzini) and motion detecting canals in the head of a shark


Active electrolocation. Conductive objects concentrate the field and resistive objects spread the field.


Hooked  sailfish


This figure depicts an example of combination of a forward model and an inverse model. Here the reference input is the target sensory state that controller (inverse model) will use to compute a motor command. The plant ( motor unit ) acts out the motor command which results in a new sensory state. This new sensory state can be compared to the state predicted by the forward model to  obtain an error signal. This error signal can be used to correct the internal model or the current movement.


Sensory-specific satiety is illustrated when diners at a buffet eat a larger quantity of food than those eating a single dish, even when the single dish is provided in quantities as much as the diner desires.


The sexual dimorphism in Bibionidae eyes is prominent, with the large dorsal eyes of the male (left) entirely absent in the female (right)


Parts of human spinal cord          1    central canal      2    posterior median sulcus      3    gray matter      4    white matter      5    dorsal root (left), dorsal root ganglion (right)      6    ventral root      7    fascicles      8    anterior spinal artery      9    arachnoid mater      10    dura mater


Sectional organization of spinal cord


Diagram of the spinal cord showing segments


Spinal cord segments and  spinal nerves , spinal cord detail, and spinal  meninges  and  conus medullaris


Spinal cord enlargements


Spinal cord seen in a midsection of a five-week-old embryo


Spinal cord seen in a midsection of a three-month-old fetus


Spinal cord tracts ascending tracts shown in blue


The anterior and lateral spinothalamic tracts labelled at lower right as tracts of the anterolateral system.


Location of visual, auditory and somatosensory perception in the superior colliculus of the brain. Overlapping of these systems creates multisensory space.


Schematic diagram of the human eye.


Diagram of the human ear.


The prominent barcode pattern on this  Ferrari F10   Formula 1  car served as advertising for  Marlboro .


Taste bud


The diagram above depicts the signal transduction pathway of the sweet taste. Object A is a taste bud, object B is one taste cell of the taste bud, and object C is the neuron attached to the taste cell. I. Part I shows the reception of a molecule. 1. Sugar, the first messenger, binds to a protein receptor on the cell membrane. II. Part II shows the transduction of the relay molecules. 2. G Protein-coupled receptors, second messengers, are activated. 3. G Proteins activate adenylate cyclase, an enzyme, which increases the cAMP concentration. Depolarization occurs. 4. The energy, from step 3, is given to activate the K+, potassium, protein channels.III. Part III shows the response of the taste cell. 5. Ca+, calcium, protein channels is activated.6. The increased Ca+ concentration activates neurotransmitter vesicles. 7. The neuron connected to the taste bud is stimulated by the neurotransmitters.


The diagram depicts the signal transduction pathway of the sour or salty taste. Object A is a taste bud, object B is a taste receptor cell within object A, and object C is the neuron attached to object B.  I. Part I is the reception of hydrogen ions or sodium ions.  1. If the taste is sour, H +  ions, from acidic substances, pass through H +  channels. Depolarization takes place  II. Part II is the transduction pathway of the relay molecules. 2. Cation, such as K + , channels are opened.  III. Part III is the response of the cell.  3. An influx of Ca +  ions is activated.  4. The Ca +  activates neurotransmitters.  5. A signal is sent to the neuron attached to the taste bud.


The diagram depicted above shows the signal transduction pathway of the bitter taste. Bitter taste has many different receptors and signal transduction pathways. Bitter indicates poison to animals. It is most similar to sweet. Object A is a taste bud, object B is one taste cell, and object C is a neuron attached to object B. I. Part I is the reception of a molecule.1. A bitter substance such as quinine, is consumed and binds to G Protein-coupled receptors.II. Part II is the transduction pathway 2. Gustducin, a G protein second messenger, is activated. 3. Phosphodiesterase, an enzyme, is then activated. 4. Cyclic nucleotide, cNMP, is used, lowering the concentration 5. Channels such as the K+, potassium, channels, close. III. Part III is the response of the taste cell. 6. This leads to increased levels of Ca+. 7. The neurotransmitters are activated. 8. The signal is sent to the neuron.


Taste buds and papillae of the human tongue


Taste receptors of the human tongue


Signal transduction  of taste receptors


Active brain areas in taste perception


This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for taste to their relevant endpoints in the human brain.


Thalamic nuclei.  Metathalamus  labelled MTh. (Left thalamus viewed from left.)


Nuclei of right thalamus (viewed from above right)


Medial nuclei of the left thalamus.  Key: CeM  Central Medial . CL  Central Lateral . CM  CentroMedian . MD  Medial Dorsal . MV MedioVentral= Reuniens . Pf  Parafascicular . (Lateral view shows sagittal section through left thalamus)


Lateral nuclei of the left thalamus.  Key: VA  Ventral Anterior . VL  Ventral Lateral . VM  Ventral Medial . VPI Ventral PosteroInferior. VPL  Ventral PosteroLateral . VPM  Ventral PosteroMedial . (Medial view shows sagittal section through left thalamus.)


The thalamus is connected to the spinal cord via the  spinothalamic tract


Positions of the pit organs (arrowed in red) on a python, relative to its nostril (black arrow)


The Thinker  by  Auguste Rodin  (1840–1917) in the garden of the  Musée Rodin , Paris


Man thinking on a train journey


A muscle spindle, with γ motor and Ia sensory fibers


Human vestibular system of the  semicircular canals  in the inner ear


Cochlea and vestibular system


Push-pull system of the semicircular canals, for a horizontal head movement to the right.


The vestibulo-ocular reflex. A rotation of the head is detected, which triggers an inhibitory signal to the  extraocular muscles  on one side and an excitatory signal to the muscles on the other side. The result is a compensatory movement of the eyes.


Neural pathway  of the vestibular system


This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for vision to their relevant endpoints in the human brain. Click to enlarge the image.


Representation of optic pathways from each of the 4 quadrants of view for both eyes simultaneously


The  human eye  (horizontal section) The image projected onto the retina is inverted due to the optics of the eye.


S. Ramón y Cajal ,  Structure of the  Mammalian  Retina, 1900


Information flow from the  eyes  (top), crossing at the  optic chiasma , joining left and right eye information in the  optic tract , and layering left and right visual stimuli in the  lateral geniculate nucleus .  V1  in red at bottom of image. (1543 image from  Andreas Vesalius '  Fabrica )


Six layers in the  LGN


Scheme of the  optic tract  with image being decomposed on the way, up to simple cortical cells (simplified)


Visual cortex :  V1; V2; V3; V4; V5 (also called MT)


Visual cortex is active even during  resting state fMRI .


Intraparietal sulcus  (red)


Visual pathway lesions    From top to bottom:   1. Complete loss of vision, right eye   2.  Bitemporal hemianopia    3.  Homonymous hemianopsia    4.  Quadrantanopia    5&6. Quadrantanopia with  macular sparing


Scheme showing sympathetic and parasympathetic innervation of the pupil and sites of lesion in a Horner's syndrome.


Pathways in the Ciliary Ganglion. Green = parasympathetic; Red = sympathetic; Blue = sensory


Diagram illustrating the locations of extraocular muscles and ocular cranial nerves. Paresis of the oculomotor nerve (CNIII) reduces the strength of  medial rectus ,  superior rectus ,  inferior rectus , and  inferior oblique  muscles, while trochlear nerve (CNIV) and abducens nerve (CNVI) paralysis affect  superior oblique muscle  and  lateral rectus muscle  respectively.


Physical examination showing ophthalmoplegia affecting the left eye. The central image represents forward gaze while other images represents different direction of gaze. Drooping of eyelids  (ptosis ) and nonaligned eyes ( strabismus ) are observed, showing paresis of CNIII, CNIV and CNVI.


A depiction of the ultrasound signals emitted by a bat, and the echo from a nearby object


Spectrogram  of  Pipistrellus pipistrellus  bat vocalizations during prey approach. The recording covers a total of 1.1 seconds; lower main frequency c. 45 kHz (as typical for a common pipistrelle). About 150 milliseconds before final contact time between and duration of calls are becoming much shorter ("feeding buzz"). Corresponding audio file:


Auditory cortex of a bat  A  FM-FM area    B  CF-CF area    C  Amplitude-sensitive area    D  Frequency-sensitive area    E  DSCF area


Diagram illustrating sound generation, propagation and reception in a toothed whale. Outgoing sounds are cyan and incoming ones are green.


A Palawan swiftlet ( Aerodramus palawanensis ) flies in complete darkness inside the Puerto Princesa subterranean river cave.


The especially long tails on the hindwings of the  African moon moth , a  Saturniid , oscillate in flight, deflecting the hunting bat's attack to the tails and thus enabling the moth to evade capture. [ 94 ]


The moth  Bertholdia trigona  is one of several moth species known to jam the echolocation of its predator


Five people, each exercising one of the five senses. Coloured lithograph after L.-L. Boilly.


A python (top) and rattlesnake illustrating the positions of the pit organs. Arrows pointing to the pit organs are red; a black arrow points to the nostril.


Diagram of the Crotaline pit organ.


Feather tickling can intensify a sexual feeling. [ 1 ]


Neck licking is a form of light sensual play.


A woman tickled sensually (1869)


Nipple biting (1799)


The four known paintings


A Pedlar Selling Spectacles (Allegory of Sight)


Three Singers  (Allegory of Hearing)


Unconscious Patient (Allegory of Smell)


Stone Operation  (Allegory of Touch)


Street art illustrating the illusion of form-continuity from a particular viewpoint


The Ambassadors , 1533, Hans Holbein the Younger


The Ambassador's Skull: detail when viewed from the accidental viewpoint (from  The Ambassadors  – Hans Holbein the Younger)


Peepshow with Views of the Interior of a Dutch House – Samuel van Hoogstraten


In this picture, the aerial perspective effect is emphasized by a range of mountains at different distances, photographed in a nearly  contre-jour  condition.


Aerial perspective as viewed towards a sunset, with the colour shifting toward red as a result of  rayleigh scattering


Dai Jin , "Landscape in the Style of Yan Wengui", early  Ming Dynasty  (1368–1644); a Chinese landscape painting using atmospheric perspective to show recession in space


Frans Koppelaar ,  Landscape near Bologna , 2001; a painting featuring atmospheric perspective: distant objects appear paler, of lower contrast, and bluer than nearer objects.


Affective haptic devices worn on a human body


HaptiHug: haptic display for communication of hug over a distance


Structure of HaptiHug


The iFeel_IM! architecture


EmoHeart object on the avatars’ chest vividly and expressively represents the communicated emotions


The design of tea cups and a teapot suggest their respective functions


A  door knob  shaped to reflect how it is used, an example of perceptible affordance


Affordance is one of several design principles used when designing graphical user interfaces.


A simple classification scheme for ASC. Sleep and dream states are distinguished from waking consciousness since they account for substantially different ways of the ability of memory formation and retrieval. Psychiatric diseases that go along with persistent changes of consciousness, like  schizophrenia , are covered with the term "pathological conditions". In contrast, the classification scheme includes intended and induced ASCs as well as general fluctuations of  neurotransmission , which are reversible and short-termed. One step further the graph suggests splitting induced ASCs in persistent and reversible states. Translated from German Schmidt & Majic. [ 7 ]


This figure can be seen as a young woman or an old woman; see  My Wife and My Mother-in-Law .


Rubin's vase  utilizes the concept of  Negative space  to create ambiguous images: the vase or two opposing faces.


The  rabbit–duck illusion


Rare example of an ambiguous image that can be interpreted in more than two ways: as the letters "KB", the mathematical inequality "1 < 13" or the letters "VD" with their mirror image. [ 7 ]


"Kanizsa Triangle". These spatially separate fragments give the impression of illusory contours (also known as modal completion) of a triangle.


Law of Proximity


Schroeder's stairs


The Necker Cube: a wire frame cube with no depth cues.


Verbeek's strips could be seen differently when viewed upside down. This image will flip upside-down automatically.


Arcand on  This Week in Science  in 2016 with Megan Watzke hosted by  Kiki Sanford


Arcand inside Brown University YURT, or VR CAVE, during testing of the headset and application. [ 11 ]


Tape recorders  allow backward recording in  recording studios .


The  compact disc  made finding backward messages difficult, causing interest in backmasking to decline.


After being accused of Satanic backmasking,  Styx  included an actual backmasked message in  Kilroy Was Here : " Annuit cœptis ,  Novus ordo seclorum ".


The manual for the popular sound program  SoX  advised that the "reverse" option could be used "for finding Satanic subliminals".


Frank Zappa  used backmasking to avoid censorship.


Blind men and the elephant, 1907 American illustration.


Blind Men Appraising an Elephant  by Ohara Donshu, Edo Period (early 19th century), Brooklyn Museum


The blind men and the elephant   (wall relief in Northeast Thailand)


Seven blind men and an elephant parable at a Jain temple


Blind monks examining an elephant , an  ukiyo-e  print by  Hanabusa Itchō  (1652–1724).


"Blind men and elephant", from the  Holton-Curry Reader  (by  Martha Adelaide Holton  &  Charles Madison Curry , 1914). [ 22 ]


Blind men and elephant


Schematic diagram of the experimental set-up in the rubber hand illusion task. LH = left hand; part = partition; RH = right hand; Ru = rubber hand.


Example frequency-rate plot for 10 trials over increasing stimulation frequencies. Hypothetical data (which reflects established concepts in ICSS procedures) is plotted as the percent maximum responses for any given trial during a sequence. The blue line represents hypothetical data at baseline, while the black line represents hypothetical data following administration of 10 mg/kg cocaine to the subject. This reflects the characteristic "left-shift" of the frequency-rate curve following administration of a drug that increases dopaminergic transmission in the reward pathway.


Chemokinesis


Chemotactic selection


Capillary tube assay for chemotaxis. Motile prokaryotes sense chemicals in their environment and change their motility accordingly. Absent chemicals, movement is completely random. When an attractant or repellent is present, runs become longer and tumbles become less frequent. The result is net movement towards or away from the chemical (i.e., up or down the chemical gradient). The net movement can be seen in the beaker, where the bacteria accumulate around the origin of the attractant, and away from the origin of the repellent.


Correlation of swimming behaviour and flagellar rotation


Domain structure of chemotaxis receptor for Asp


Signalling pathways of E.coli


float


Difference of gradient sensing in prokaryotes and eukaryotes


Chemotaxis related migratory responses


Structure of chemokine classes


Three dimensional structure of chemokines


Chemotactic range fitting


The process of chemotaxis can be demonstrated using a capillary tube assay (shown above). The motile prokaryotes can sense chemicals in their environment and change their motility accordingly. When no chemicals are present, movement is completely random. When a repellent or attractant chemical is present, the motility changes; runs become longer and tumbles become less frequent so that the net movement towards or away from the chemical can be achieved. The net movement can be seen in the beaker, where the bacteria accumulate around the attractant, and away from the repellent.  The beaker used in this illustration is from Wikimedia Commons - " Laboratory Glassware - Beaker " by Amanda44.


Chemotaxis assays with agar plates


Chemotaxis chamber assays


Other chemotaxis assay techniques


A timeline of the sensation and perception of chronostasis within the context of a student in a classroom


Figure 1: An example of the Chubb illusion. The center areas of two rectangular fields are identical, but appear different because the background fields are different.


Figure 2: Illustration of simultaneous contrast


Figure 3: The Chubb Illusion


Spectrum of a paradoxical constant spectrum melody


Simultaneous contrast


Metacontrast and paracontrast


The checker shadow illusion


Map showing countries and territories according to the Corruption Perception Index, 2023, in ascending order:           Score higher than 89      Score equal to or between 80 and 89      Score equal to or between 70 and 79      Score equal to or between 60 and 69      Score equal to or between 50 and 59      Score equal to or between 40 and 49          Score equal to or between 30 and 39      Score equal to or between 20 and 29      Score equal to or between 10 and 19      Score less than 10      Data unavailable


"An  ostrich  only thinks he 'covers up'."


The Ottoman government attempted to ban foreigners from taking photographs such as this one of  Armenian genocide  victims in an effort to cover up the genocide. [ 4 ]


Old Thirty Nine shaking hands with his good brother the  Pope of Italy , or covering up versus sealing up the Bible, 1819  by  George Cruikshank . ("39 articles" refers to the  Church of England )


Front page of the newspaper  L’Aurore  of Thursday 13 January 1898, with the famous open letter  J'Accuse…!  written by  Émile Zola  to the President of France about the  Dreyfus Affair . The headline reads "I accuse! Letter to the  President of the Republic ". See  J'accuse...! , the whole text on Wikisource


Perception underestimates the distance between successive taps to the skin. Stimuli are illustrated in the upper panels, along with their perception (forearm sketches). Corresponding human data and Bayesian model fits are plotted in the lower panels. For details, see Goldreich & Tong (2013). [ 24 ]


Objects in space are evaluated on different points of the retina. Binocular disparity is crucial for the brain to develop a cyclopean image.


Émile Boirac


An example of an fMRI brain scan


A diagram of the formation of an atherosclerotic plaque. Note the blue vascular smooth muscle cells, which migrate from the tunica media into the tunica intima, where the stiff plaque is forming.


Andreas Vesalius  Fabrica, published in 1543, showing the base of the human brain, including  optic chiasma ,  cerebellum ,  olfactory bulbs , etc.


Cross-section of human cerebellum, showing the  dentate nucleus , as well as the  pons  and  inferior olivary nucleus


Saint John the Baptist , ca. 1600–1605, an example of El Greco's elongated style.


An  artistic interpretation  of  mirror neurons , the overactivity of which is a possible explanation for hyperempathy, active in two  human brains


Groups where individuals are more proximal are proposed to be perceived as more entitative.


Groups where individuals share visual similarity are perceived as more entitative.


A collection of individuals moving in sync can increase perceptions of entitativity.


Group members that share similar physical appearances, such as color, are perceived to have more entitativity.


Symbols, such as flags, can increase entitativity perceptions of a group.


People are more likely to donate to support endangered animals when they are depicted with greater entitativity.


The pictorial measure of entitativity from Gaertner & Schopler (1998)


The  universe  is everything that exists theoretically. ( Hubble Ultra-Deep Field  image of distant galaxies pictured)


Johari window


In this map, Germany is the most clearly recognizable figure, with everything else (the "faded part") being ground. However, secondary (less prominent but still recognizable and usable) figures include the European Union, the land, the ocean, and the inset map, each with its unique corresponding ground. Some features do not have clear figure-ground contrast, such as Europe (dark green+light green+dark gray vs. light gray+white), and can be difficult to perceive unambiguously.


In this map, figures like Oman and the Arabian Sea are less obvious due to a lack of differentiation. The land and the ocean have strong differentiation, but can be difficult to recognize which is figure because neither is closed.  Closure  and  centrality  make Oman easier to isolate as a figure than India.


The  Rubin vase  illusion, where it is ambiguous which part is the figure and which the ground


Shapes which can be read as a word once the viewer recognises them as being the isolated negative spaces of a word


Man and crane,  Mimbres culture  pot, c. 1000 -1150 AD


Figure-ground  ambigram   tessellation  displaying the words Liar / Jail alternatively, using negative space.


Type 2: The ground itself is the figure.


When steadily fixating the central dot for many seconds, the peripheral annulus will fade and will be replaced by the colour or texture of the background.


Mach bands = visual illusion of brightness (intensive property)


Illusions of position (Poggendorff), orientation (Zöllner) and, below, length (Müller-Lyer)


Hering Illusion of curvature


Delboeuf Illusion of size: left inner circle and right outer circle are actually equal


Vertical–horizontal illusion


Shifted-chessboard illusion


Necker cube = reversible figure


Penrose triangle = unrealizable object


Kanizsa triangle = illusory contours


Ponzo illusion in a purely schematic form and, below, with perspective clues


Two cases of two interrelated geons, What does the reader imagine in each case?


Reification


The  Necker cube  and the  Rubin vase , two examples of  multistability


Invariance


Law of proximity


Law of similarity


Law of closure


Law of symmetry


Law of continuity


Several grouping principles are employed in this map: similarity allows the reader to selectively isolate cities, rivers, or state boundaries; closure allows the dashed boundary lines to be perceived as continuous borders; proximity makes the collection of river segments appear as a single watershed; and continuity helps the reader "see" whole states even when boundaries are obscured under rivers.


Trajectory of a rat through a square environment is shown in black. Red dots indicate locations at which a particular entorhinal grid cell fired.


Grid cells derive their name from the fact that connecting the centers of their firing fields gives a triangular grid.


Spatial autocorrelogram of the neuronal activity of the grid cell from the first figure.


A hexagonal lattice.


A scatter plot of the type used in the game. This scatterplot displays a correlation of r=.24


Exo-Skin Soft Haptic exoskeletal interface


The word "FAKE" hidden within an AI-generated image of a naval battle


Taj Mahal in warm light from a low elevation sun.


Taj Mahal in the cold light from a high elevation sun.


An optical illusion. Square A is exactly the same shade of grey as Square B. (See  Checker shadow illusion .)


Example of an Illusory Conjunction between two different shapes of different colors forming an entirely new object


The human eye's red-to-green and blue-to-yellow values of each one-wavelength visible color  [ citation needed ]


Human color  sensation  is defined by the  sensitivity curves   (shown here normalized)  of the three kinds of  cone cells : respectively the short-, medium- and long-wavelength types.


By staring at a "fatigue template" for 20–60 seconds, then switching to a neutral target, it is possible to view "impossible" colors.


Some people may be able to see the color "yellow–blue" in this image by letting their eyes cross so that both + symbols are on top of each other. In this image, both  RGB  and  Natural Color System  color pairs are provided. It may be necessary to zoom to adjust the image.


Some people may be able to see the color "red-green" in this image by letting their eyes cross so that both + symbols are on top of each other. In this image, both  RGB  and  Natural Color System  color pairs are provided. It may be necessary to zoom to adjust the image.


Most people see very bright colored concentric circles in this pattern, if it is printed and rotated at around 150–300 rpm.  Alternate version  with inverse contrast yields opposite effect.


Representation of the  pitch class  circle with respect to tone height


The framed line test


Joseph Banks ' account of the  HMS  Endeavour 's entry into  Botany Bay  may be the basis for the myth.


Painting of the grounding of the Endeavour on Australia's  Great Barrier Reef  in June 1770


The Weber-Fechner law illustrated:      1.   Circles in the upper row grow in arithmetic progression: each one is larger by 10 units than previous one. They make an impression of growing initially fast and then slower and slower (the difference between 10 and 20 seems larger than between 60 and 70).      2   Circles in the lower row grow in geometric progression: each one is larger by 40% than previous one. They make an impression of growing by the same amount at each step.


Woodlouse  activity decreases as humidity increases.


The legend to this puzzle reads "Here is a class of a dozen boys, who, being called up to give their names were photographed by the instantaneous process just as each one was commencing to pronounce his own name. The twelve names were Oom, Alden, Eastman, Alfred, Arthur, Luke, Fletcher, Matthew, Theodore, Richard, Shirmer, and Hisswald. Now it would not seem possible to be able to give the correct name to each of the twelve boys, but if you practice the list over to each one, you will find it not a difficult task to locate the proper name for every one of the boys." [ 4 ]


A mother and her child in 1912.  Mothers who better understand their infant's signals are said to have higher maternal sensitivity.


Children whose mothers have higher levels of maternal sensitivity are generally happier, healthier, smarter, and better behaved.


Study talked about in fMRI paragraph


The  hamadryas baboon  is one primate species that fails the mirror test.


European magpies  have demonstrated mirror self-recognition.


A human child exploring his reflection


An example of a simple letter detection task


The  dorsal stream  (green) and  ventral stream  (purple) are shown.  They originate from a common source in visual cortex.  The dorsal stream is responsible for detection of location and motion.


Example of  Beta movement , often confused with  phi phenomenon , in which a succession of still images gives the illusion of a moving ball [ 5 ]


Demonstration of phi phenomenon using two black bars ( SOA  = 102 ms,  ISI  = −51 ms)


The aperture problem. The  grating  appears to be moving down and to the right,  perpendicular  to the orientation of the bars. But it could be moving in many other directions, such as only down, or only to the right. It is impossible to determine unless the ends of the bars become visible in the aperture.


Reichardt model


Examples of visually ambiguous patterns. From top to bottom:  Necker cube ,  Schroeder stairs  and a figure that can be interpreted as black or white arrows.


Fig. 1. Actual views (top), "circle's" perception of views (middle), "triangle's" perception of views (bottom). (Modeled after similar illustrations found in Robinson et al., 1995, and Ross & Ward, 1996.)


In many cultures, the color  black  is associated with nothingness.


This diagram shows the medieval understanding of  spheres  of the  cosmos , derived from  Aristotle , and as per the standard explanation by  Ptolemy . It came to be understood that at least the outermost sphere (marked " Primũ Mobile ") has its own intellect, intelligence or  nous  – a cosmic equivalent to the human mind.


The earliest surviving text that uses the word  nous  is the  Iliad .  Agamemnon  says to  Achilles : "Do not thus, mighty though you are, godlike Achilles, seek to deceive me with your wit ( nous ); for you will not get by me nor persuade me." [ 7 ]


Anaxagoras


An example of the numerosity adaptation effect


Appearance  of figure changes on 45-degree rotation


Discrimination of length (top) and orientation (bottom) for a line at various orientations around the clock


Observing the air traffic in  Rõuge ,  Estonia


Ocular microtremor tracing with burst sections underlined


P300 latency and amplitude trajectories across the lifespan as obtained from the cross-sectional dataset . Dots represent scores from individual participants. From  From P300 Development across the Lifespan: A Systematic Review and Meta-Analysis . [ 1 ]  The latency and amplitude of the P300 response may vary as a function of age.


The P300 response of different healthy subjects in a two-tone auditory oddball paradigm. The plots show the average response to oddball (red) and standard (blue) trials and their difference (black). From  Surprise response as a probe for compressed memory states . [ 2 ]  These examples show the significant individual variability in amplitude, latency and waveform shape across different subjects.


The P300 response as a function of the oddball probability. From  Surprise response as a probe for compressed memory states . [ 2 ]  The ERP shows a larger P300 response magnitude to oddball stimuli and a lower P300 response to standard stimuli as the oddball probability decreases.


Insertion of electrode during  deep brain stimulation  surgery using a  stereotactic frame


Image showing the breakdown of common geometric shapes (geons)


A simple seriation task involving arranging shapes by size


Brain animation highlighting the fusiform face area, thought to be where facial processing and recognition takes place


Whale ,  submarine  or  sheep ?


Forager honey bee flying back to the hive with pollen and nectar


Perceptual map of competing products


Perceptual map of ideal points and clusters


Perceptual map of competing products with ideal vectors


Example of a multi-dimensional perceptual map


In musical notation, the different vertical positions of notes indicate different  pitches .   Play top:  Play bottom:


Note frequencies, four-octave C major diatonic scale, starting with  C 1 .


Conceptual Schematic of Predictive Coding with 2 levels


This image shows a priming web built from different types of priming. The lines in this web indicate associations that an individual might have. If two words are more closely linked in the web, then they are more likely to be more quickly recognized when primed with a nearby word. The dotted lines indicate morpheme primes, or primes from words that sound similar to each other, while the straight lines indicate semantic primes or words that have meanings or associations that relate to each other.


The  extrastriate cortex  (shown in orange and red) is believed to be involved in perceptual priming.


Law of Proximity


Law of Similarity


Law of Closure


Law of good continuation


Law of common fate—a  flock of birds


Principle of good form


Simulated example of a psychometric function, showing how the proportion of correct detections may increase with increasing luminance of the stimulus.


Tajōmaru the bandit and the wife of a samurai, two characters who offer different perspectives of events in the film  Rashomon


Breakdown of objects into geons


Factors of risk perceptions


Picture 1. A picture taken of the Rod and Frame apparatus originally sold by the Stoelting company, and now owned by the Rochester Institute of Technology.


Picture 2. An image showing a 10-degree frame angle and a 7-degree rod angle. Observers using the apparatus see the rod as vertically oriented. The frame of the page, image border, etc. make it appear tilted here.


Image [ 3 ]  generated from a database of  segmented  leaves that simultaneously registers natural images (scene information) with the exact locations of leaf boundaries (information about the physical environment).  Such a database can be used to study across-domain statistics.


A 1921 cartoon representation a person's self-image compared to their reality


Image of a real apple (left), and plastic  food model  apple (right). The fake apple is a simulacrum.


Mole  & Thomas,  Human Statue of Liberty  (1919)—12,000 people in the flame of the torch, 6,000 in the rest of the shape. Plato was referring to an optical illusion such as this in his discussion of simulacra.


The spinning dancer is a kinetic, bistable optical illusion resembling a  rotating  female dancer


This  positron emission tomography   scan  of a woman has a similar effect when viewed spinning


Excited audience members in Australia


Naming the displayed color of a printed word is an easier and quicker task if the word matches the color (top) than if it does not (bottom).


Examples of the three stimuli and colors used for each of the activities of the original Stroop article: [ 2 ] color words in black text color words in incongruent colors colored squares


Figure 1 from Experiment 2 of the original description of the Stroop Effect (1935). 1 is the time that it takes to name the color of the dots while 2 is the time that it takes to say the color when there is a conflict with the written word. [ 2 ]


The anterior cingulate gyrus shows increased activity when viewing conflicting stimulus. [ 8 ] : 454


An observer may be able to instantly judge how many red circles are present without counting them, but would find it harder to do so for the greater number of blue circles.


Ponzo illusion : Top line is perceived as larger than the bottom line, though they are identical in size.


Shape constancy: One would perceive the object to be a rectangular door opening but, if it were to be drawn out, it is in fact made up of varying shapes


Taste Exhibit at the 1931  AAAS  meeting. Visitors were invited to "try this harmless substance and learn whether you are a taster or a non-taster."


Tongue colored with blue food dye revealing the  fungiform papillae .


Pseudounipolar bipolar neurons


WVSOM Meissner's corpuscle


2-point orientation discrimination (2POD) compared to traditional two-point discrimination (2PD)


Common Keypad with Braille


Early robotic prosthetic hand, made in 1963. On open public display at the main shopping mall in Belgrade.


A  sand timer  uses the flow of  sand  to measure the passage of time.


Horizontal  sundial  in Canberra


24-hour clock face in Florence


A contemporary  quartz watch , 2007


Chip-scale  atomic clocks , such as this one unveiled in 2004, are expected to greatly improve  GPS  location. [ 35 ]


Scale of time in  Jain  texts shown  logarithmically


Time's mortal aspect is personified in this bronze statue by  Charles van der Stappen .


Two-dimensional space depicted in three-dimensional spacetime. The past and future  light cones  are absolute, the "present" is a relative concept different for observers in relative motion.


Relativity of simultaneity : Event B is simultaneous with A in the green reference frame, but it occurred before in the blue frame, and occurs later in the red frame.


Views of spacetime along the  world line  of a rapidly accelerating observer in a relativistic universe. The events ("dots") that pass the two diagonal lines in the bottom half of the image (the past  light cone  of the observer in the origin) are the events visible to the observer.


Philosopher and psychologist  William James


Tone variator by  Max Kohl , Chemnitz, Germany


Tone variator with rack and pinion design.


Two sets of arrows that exhibit the  Müller-Lyer illusion . The set on the bottom shows that all the shafts of the arrows are of the same length.


This painting by  Diego Velázquez  known as the  Rokeby Venus  is likely to produce a Venus effect.


Virtual fixtures: Used to enhance operator performance in the telerobotic control of Fitt's Law peg-board task.


Virtual Fixtures used for Augmented Reality Surgery, enables enhanced surgical dexterity.


Example of a forbidden regions virtual fixture


Example of a guiding virtual fixture


The stiffness of a virtual fixture can be soft or hard. A hard fixture completely constrains the motion to the fixture while a softer fixture allows some deviations from the fixture.


Vision capture aids in the illusion that a dummy is talking in  ventriloquism . To the right of it is  Terry Fator .


The visual  dorsal stream  (green) and  ventral stream  (purple) are shown. Much of the human  cerebral cortex  is involved in vision.


Leonardo da Vinci : The eye has a central line and everything that reaches the eye through this central line can be seen distinctly.


Eye movement first 2 seconds ( Yarbus , 1967)


feature based search task


Conjunctive based search task.


A photograph that simulates foveation


A plot of the saccades made while reading text. The plot shows the path of eye movements and the size of the circles represents the time spent at any one location.


A pseudo-color image showing activation of the primary visual cortex during a perceptual task using functional magnetic resonance imaging (fMRI)


Visual search primarily activates areas of the parietal lobe.


Henri Rousseau,  Jungle with Lion


The retina image topography is maintained through the visual pathway to the primary visual cortex. [ 9 ]


LIGHTNESS, VISUAL WEIGHT AND CENTER OF GRAVITY OF AN IMAGE


An illustration of the Weber–Fechner law. On each side, the lower square contains 10 more dots than the upper one. However the perception is different:  On the left side, the difference between upper and lower square is clearly visible. On the right side, the two squares look almost the same.


Threshold increment versus background luminance for various target diameters (in arcmin). Data from tables 4 and 8 of Blackwell (1946), plotted in Crumey (2014).


Choroidal blood flow revealed with ICG-angiography (Spectralis, Heidelberg) and  laser Doppler imaging [ 6 ]


A visual field map of the primary visual cortex and the numerous extrastriate areas


The lingual gyrus is the hypothetical location of V4 in macaque monkeys. In humans, this area is called hV4.


The fusiform gyrus is the hypothetical location of V4α, a secondary area for colour processing.


fMRI showing activity in the primary visual cortex V1


Simulation of cerebral achromatopsia


Hexagonal cells of corneal endothelium visualized by  specular microscopy .


Eyeball lengths: emmetropic, near-sighted (myopic) and far-sighted (hyperopic)


Eye of a  European bison


Human eye , a refractive  cornea  type eye.


The eyes of a mantis shrimp (here  Odontodactylus scyllarus ) are considered the most complex in the whole animal kingdom.


A refractive cornea type eye of a human. The cornea is the clear domed part covering the  anterior chamber of the eye .


Eyelids  and  eyelashes  are a unique characteristic of most mammalian eyes, both of which are evolutionary features to protect the eye.


An image of a house fly compound eye surface by using  scanning electron microscope


Anatomy of the compound eye of an insect


Arthropods such as this  blue bottle fly  have compound eyes.


Evolution of the  mollusc eye


The eye of a  red-tailed hawk


Chinese characters similar to those used in Fu et al., which elicit a response in the FFA


Grassmann expressed his first law with respect to a circular arrangement of spectral colors in this 1853 illustration. [ 4 ]


Simulated stages of a greyout.


Depiction of predictions for refoveating Müller's stimulus with eyes moving independently or eyes following Hering's law of equal innervation.      Line of sight      Visual direction       Vergence


Hering's demonstration of his law of visual direction.


Hering's window demonstration of his law of visual direction. Both eyes fixate a point on the window. The right eye sees Captain Haddock's curses book behind the fixation, the left eye sees the French press behind the fixation point. With both eyes open and fixating the book and the French press appear superimposed and straight ahead.


Arizona Eye Model. "A" is accommodation in diopters.


A detailed medical illustration of the eye


MRI  scan of the human eye


Schematic diagram of the human eye. It shows a horizontal section through the right eye.


The outer parts of the eye


Side-view of the human eye, viewed approximately 90° temporal, illustrating how the iris and pupil appear rotated towards the viewer due to the optical properties of the cornea and the aqueous humour


The pupil of the human eye can range in size from 2 mm to over 8 mm to  adapt  to the environment


Dilation and constriction of the pupil


The light circle is the  optic disc  where the optic nerve exits the retina


The two eyes converge to point to the same object.


A brown iris


A light brown iris with limbal ring


Amber eye


Hazel eye


Blue eye


Gray eye Northern Italy


Conjunctival infection, or redness of the sclera surrounding the iris and pupil


Diagram of a  human eye  ( horizontal section  of the right eye)  1.  Lens , 2.  Zonule of Zinn or Ciliary zonule , 3.  Posterior chamber  and 4.  Anterior chamber  with 5.  Aqueous humour  flow; 6.  Pupil , 7.  Corneosclera or Fibrous tunic  with 8.  Cornea , 9.  Trabecular meshwork  and  Schlemm's canal . 10.  Corneal limbus  and 11.  Sclera ; 12.  Conjunctiva , 13.  Uvea  with 14.  Iris , 15.  Ciliary body  (with a:  pars plicata  and b:  pars plana ) and 16.  Choroid ); 17.  Ora serrata , 18.  Vitreous humor  with 19.  Hyaloid canal/(old artery) , 20.  Retina  with 21.  Macula or macula lutea , 22.  Fovea  and 23.  Optic disc  →  blind spot ;  24.  Visual axis (line of sight) . 25.  Optical axis . 26.  Optic nerve  with 27.  Dural  sheath, 28.  Tenon's capsule or bulbar sheath , 29. Tendon.  30.  Anterior segment , 31.  Posterior segment .  32.  Ophthalmic artery , 33.   Artery  and  central retinal vein  → 36. Blood vessels of the retina;  Ciliary arteries  (34.  Short posterior ones , 35.  Long posterior ones  and 37.  Anterior ones ), 38.  Lacrimal artery , 39.  Ophthalmic vein , 40.  Vorticose vein .  41.  Ethmoid bone , 42.  Medial rectus muscle , 43.  Lateral rectus muscle , 44.  Sphenoid bone .


Brodmann area 17 (red) and higher order visual areas, Brodmann area 18 (orange) and Brodmann area 19 (yellow), are part of the visual cortex.


Cells with on-centre receptive fields fire when the excitatory centre is illuminated and are inhibited when the surround is illuminated.  Off-centre cells respond to the opposite pattern of light.


Simple cells are sensitive to the orientation of a visual stimulus.  A simple cell will fire weakly or not at all if both excitatory and inhibitory regions are activated (a), but will fire optimally if the stimulus is oriented within the excitatory region only (b).  Orientation selectivity is produced by multiple centre-surround receptive fields aligned at a certain angle (c).  A complex cell responds to moving stimuli and is sensitive to direction as well as orientation (d).


The hypercomplex cell above is stopped at one end (i.e. the right).  As the length of the stimulus increases, it enters the antagonistic region, and causes a decrease in response (depicted as single-cell recording signals on the right).  Note this cell is also sensitive to orientation, motion, and direction.


Top: End-stopped cells can detect curves.  Note the properly oriented curve lies within the activating region but recedes and rotates before it enters the antagonistic regions.  This cell is stopped at both ends and will not respond to lines that are not oriented 180˚.  Bottom: End-stopped cells, like those that are stopped at one end, can also detect corners.  The response of the cell will be stronger when the corner is only in the activating region (left image) and weaker when the corner enters the antagonistic region (right image).


Schematic diagram of the primate LGN. Koniocellular neurons not labeled, but are present between the layers.


M P and K cells


Nuclei of the Thalamus


Relative locations of the M-, P-, and K-layers (macaque monkey)


Schematic diagram of the primate LGN.


Visual representation of the parvocellular and magnocellular pathways


Human visual pathway


The memory color of a strawberry is recognisable to most viewers even when, as here, a photograph of them has been manipulated so that the red is literally gray


Black words vs. Colored words


Figure 2  Transformations of the visual field toward the visual map on the primary visual cortex in vertebrates.  U=up; D=down; L=left; R=right; F=fovea


A  fundus photograph  showing the back of the retina. The white circle is the beginning of the optic nerve.


Right superior  quadrantanopia . The areas of the visual field lost in each eye are shown as black areas.  This visual field defect is characteristic of damage to  Meyer's loop  on the left side of the brain.


Horizontal optokinetic nystagmus.


3D model of orbit with surrounding bones


The seven bones that form the orbit: yellow =  Frontal bone green =  Lacrimal bone brown =  Ethmoid bone blue =  Zygomatic bone purple =  Maxillary bone aqua =  Palatine bone red =  Sphenoid bone teal =  Nasal bone  (illustrated but not part of the orbit)


Tear system : a. tear gland / lacrimal gland, b. superior lacrimal punctum, c. superior lacrimal canal, d. tear sac / lacrimal sac, e. inferior lacrimal punctum, f. inferior lacrimal canal, g. nasolacrimal canal


The primary visual cortex (V1) is located in the  occipital lobe . This is the region where orientation columns are found.


Pinwheel formations in the primary visual cortex with singularities in the center. Each color represents an orientation column of a specific line phase. Adapted image from fMRI studies. [ 11 ]


An example of a Moiré interference pattern. The offset of the two lattices creates a dipole of retinal ganglion cells. This dipole is orientated in various directions that correspond to a specific orientation.


A sketch of a parasol cell (right) alongside a midget cell (left) for size comparison


Golgi stain of a neuron.


Schematic diagram of the primate LGN.


An artist's representation of how some people may see phosphenes by retinal stimulation


Overview of the retina photoreceptors. ipRGCs labelled at the top-right.


An ipRGC, shown here as a complied image of the retina from proximal inner nuclear layer to the ganglion cell layer with fluorescent labeling of melanopsin


Spectral sensitivities of the photoreceptors in the human eye. [ 4 ]


Melanopsin structure


Synaptic inputs and outputs of ipRGCs and their corresponding location in the brain


Inputs and outputs to ipRGCs involved in the pupillary light reflex


Pupillary constriction resulting from the pupillary light reflex is mediated by the olivary and posterior pretectal nuclei.


Illustration of color metamerism: In column 1, a ball is illuminated by monochromatic light. Multiplying the spectrum by the cones' spectral sensitivity curves gives the response for each cone type. In column 2, metamerism is used to simulate the scene with blue, green and red LEDs, giving a similar response.


Section of retina


Rods, cones, and nerve layers in the retina: The front (anterior) of the eye is on the left. Light (from the left) passes through several transparent nerve layers to reach the rods and cones (far right). Chemical changes in the rods and cones send a signal back to the nerves. The signal goes first to the  bipolar  and  horizontal cells  (yellow layer), then to the  amacrine cells  and  ganglion cells  (purple layer), then to the optic nerve fibres. The signals are processed in these layers. First, the signals start as raw outputs of points in the rod and cone cells. Then, the nerve layers identify simple shapes, such as bright points surrounded by dark points, edges, and movement. (Based on a drawing by  Ramón y Cajal , 1911)


Illustration of the distribution of cone cells in the fovea of an individual with normal colour vision (left), and a colourblind (protanopic) retina. The center of the fovea holds very few blue-sensitive cones.


Distribution of rods and cones along a line passing through the fovea and the blind spot of a human eye [ 14 ]


Time-Domain OCT of the macular area of a retina at 800 nm, axial resolution 3 μm


Spectral-Domain OCT macula cross-section scan


Macula histology (OCT)


Fundus photograph  showing the blood vessels in a normal human retina. Veins are darker and slightly wider than corresponding arteries. The  optic disc  is at right, and the  macula lutea  is near the centre.


On-centres and off-centres of the retina


A false-color image of a flat-mounted rat retina viewed through a fluorescence microscope at 50x magnification. The optic nerve was injected with a fluorophore, causing retinal ganglion cells to fluoresce.


Illustration of the distribution of cone cells in the fovea of an individual with normal color vision (left), and a color blind (protanopic) retina. Note that the center of the fovea holds very few blue-sensitive cones.


Retinotopic maps with explanation


Location and visuotopic organization of marmoset primary visual cortex (V1)


Apparatus. Refreshable Braille cells are embedded in an inclined surface (left). A sliding potentiometer supports two semicylindrical cradles forming a guide that can be relocated on a Velcro surface to accommodate the participants' anatomical differences.


Eye patches may strengthen the weaker eye but fail to stimulate binocular vision and stereopsis, which may sometimes be recovered by different means.


Oliver Sacks  was the first to make the story of Susan Barry, whom he nicknamed "Stereo Sue", known to the general public.


Although stereoblind, Bridgeman used polarized glasses in a 3D cinema and could suddenly see in 3D.


Tetris  is a popular video game from the 1980s. A modified version of the game (not shown here) has been used for dichoptic training.


Prism lenses (here unusually thick) are used for pre-operative prism adaptation.


Section of mid-brain at level of superior colliculi.


Hind- and mid-brains; postero-lateral view. Superior colliculus labeled in blue.


Schematic circuit diagram of topographic connections between the optic tectum and the two parts of nucleus isthmii.


H&E stain  of chicken optic tectum at E7 (embryonic day 7) showing the generative zone (GZ), the migrating zone (MZ) and the first neuronal lamina (L1). Scale bar 200 μm. From Caltharp et al., 2007. [ 57 ]


The brain of a  cod , with the optic tectum highlighted


Drawing by  Ramon y Cajal  of several types of Golgi-stained neurons in the optic tectum of a sparrow.


Close-up of a trichromatic in-line  shadow mask   CRT display , which creates most visible colors through combinations and different levels of the three  primary colors : red, green and blue


Normalised  responsivity  spectra of human cone cells


Illustration of color metamerism: In column 1, a ball is illuminated by monochromatic light. Multiplying the spectrum by the cones' spectral sensitivity curves gives the response for each cone type. In column 2, metamerism is used to simulate the scene with blue, green and red LEDs, giving a similar response.


comprehension of the phrase 'my cat' in the extended version of Hickok and Poeppel's dual pathway model


repetition of the phrase 'what is your name?' in the extended version of Hickok and Poeppel's dual pathway model


Visual cycle


The classical image on the shape and size of the visual field by Harry Moss Traquair in his book  Clinical Perimetry  (1938; modified to show the essentials). It shows that the visual field is considerably larger on the temporal side than the often quoted 90° extent. Similar limits were already reported in the 19th century.


Bjerrum's area and types of scotomas on the visual field


Visual pathway lesions    From top to bottom:   1. Complete loss of vision in the right eye   2. Bitemporal hemianopia   3. Homonymous hemianopia   4. Quadrantanopia   5. & 6. Quadrantanopia with  macular sparing


Representation of molecular steps in photoactivation (modified from Leskov et al., 2000 [ 4 ] ). Depicted is an outer membrane disk in a rod.  Step 1 : Incident photon (hν) is absorbed and activates a  rhodopsin  (likewise  photopsin ) by conformational change in the disk membrane to R*.  Step 2 : Next, R* makes repeated contacts with transducin molecules, catalyzing its activation to G* by the release of bound GDP in exchange for cytoplasmic GTP, which expels its β and γ subunits.  Step 3 : G* binds inhibitory γ subunits of the phosphodiesterase (PDE) activating its α and β subunits.  Step 4 : Activated PDE hydrolyzes cGMP.  Step 5 : Guanylyl cyclase (GC) synthesizes cGMP, the second messenger in the phototransduction cascade. Reduced levels of cytosolic cGMP cause cyclic nucleotide gated channels to close preventing further influx of Na +  and Ca 2+ .


The absorption of light leads to an isomeric change in the retinal molecule.


George Wald with wife  Ruth Hubbard  in 1967


Wald plotted the absorbance of rod pigment (black curve), then later the absorbance of cone pigments (red, green, and blue curves).


Early robotic prosthetic hand, made in 1963. On open public display at the main shopping mall in Belgrade.


Robots at the RoboCup 2019


Figure 1. Polymerization scheme for formation of polyimine-based self-healing electronic skin.


Figure 2. Self-healing material based on hydrogen bonding and interactions with micro-structured nickel particles.


Figure 3. Recycling process for conductive polyimine-based e-skin.


Figure 4. A stretchable and self-healing semiconducting polymer-based material.


Lidar-derived image of Marching Bears Mound Group,  Effigy Mounds National Monument ,  United States


A  frequency addition source of optical radiation  (FASOR) used at the  Starfire Optical Range  for lidar and  laser guide star  experiments is tuned to the  sodium D2a line  and used to excite  sodium  atoms  in the upper atmosphere .


This lidar may be used to scan buildings, rock formations, et cetera, to produce a 3D model. The lidar can aim its laser beam in a wide range: its head rotates horizontally; a mirror tilts vertically. The laser beam is used to measure the distance to the first object on its path.


Click image to see the animation.  A basic lidar system involves a laser range finder reflected by a rotating mirror (top). The laser is scanned around the scene being digitized, in one or two dimensions (middle), gathering distance measurements at specified angle intervals (bottom).


Lidar scanning performed with a multicopter  UAV


Airborne Lidar Bathymetric Technology-High-resolution multibeam lidar map showing spectacularly faulted and deformed seafloor geology, in shaded relief and coloured by depth


This  mobile robot  uses its lidar to construct a map and avoid obstacles.


Lidar is used to analyze yield rates on agricultural fields.


Cruise Automation  self-driving car with five  Velodyne Lidar  units on the roof


Forecast 3-D Laser System using a SICK LMC lidar sensor


Lidar imaging comparing old-growth forest (right) to a new plantation of trees (left)


A typical workflow to derive forest information at individual tree or plot levels from lidar point clouds [ 109 ]


Near range lidar at Institute of Geophysics, Warsaw, Poland


This  TomTom  mapping van is fitted with five lidar sensors on its roof rack.


A point cloud generated from a moving car using a single  Ouster  OS1 lidar


Lidar scanner on a  4th generation iPad Pro


Figure 1.  plume  modeling


Figure 2. Triangulation method


Types of  robot  sensors ( Light  and  Sound  sensors)


Eurofighter  sensor fusion


Artist's concept of a  Mars Exploration Rover , an example of an unmanned land-based vehicle. Notice the stereo cameras mounted on top of the rover.


The  optical flow  vector of a moving object in a video sequence


VIO is widely used in commercial quadcopters, which provide localization in GPS denied situations.


Egomotion estimation using  corner detection


Inferior alveolar nerve


Neumann KU 100 microphone used to record binaural sound


The key constituents that cause the 3D stereo effect: timing, loudness and  timbre . Sound coming from the left arrives first to the left ear and microseconds later to the right ear. Head muffles the sound making the sound louder to the left ear than to the right ear. The head and other parts of the body deflect the sound thus changing the sound's frequency spectrum along its way from the left side to the right side. The human brain interprets these differences and automatically causes a sensation of a certain location for the sound to the listening person. [ 16 ]


Brüel & Kjær head and torso simulator (HATS)


Plaque commemorating  Samuel Holberry ,  Peace Gardens ,  Sheffield [ 5 ]


Jubilee scroll - Sgrôl y Jiwbilî (7294582196) - Given to Queen Elizabeth on her Diamond Jubilee


The Llandybie Millennium Stone This stone from a local quarry was erected on Llandybie square in 2000. The calligraphy is by Rees


The cupula is the onion-shaped structure surrounded by endolymph in the ampulla.


Eye-tracking device (ETD)


Eye-tracking device on ISS


Cosmonaut with the ETD on ISS Expedition


Outline of the principal system components The reconfigurable digital processing circuitry (FPGA) also facilitates inline optimisation of the front-end, time-critical processes. [ 2 ]


ETD graphic user interface


Cochlea and vestibular system


Drawing of the statocyst system


Statocysts (ss) and statolith (sl) inside the head of sea snail  Gigantopelta chessoia


Pictures G-N show the tip links connecting the stereocilia.


Inner ear , showing utricle near centre


Diagram of the vestibular system, the structures whose dysfunction can benefit from vestibular rehabilitation


Touch is a crucial means of receiving information. This photo shows tactile markings identifying stairs for visually impaired people.


This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for touch to their relevant endpoints in the human brain.


Gray's Anatomy , figure 759: the sensory tract, showing the pathway (blue) up the spinal cord, through the somatosensory thalamus, to S1 (Brodmann areas 3, 1, and 2), S2, and BA7


Gray's Anatomy , figure 717: detail showing path adjacent to the  insular cortex  (marked insula in this figure), adjacent to S1, S2, and BA7


Touch can result in many different physiological reactions such as laughing at being  tickled .


The  cortical homunculus , a map of somatosensory areas of the brain, was devised by  Wilder Penfield .


Cortical map representation of a dog by David Ferrier


Cerebrum lobes


Initial stages of cortical development


Referred pain : Conscious perception of visceral sensations is referred to specific regions of the body that are not sources of the sensations.  Some referred pain due to visceral sensations refer to dermatomes that send fibers to the same level of spinal cord.


Dermatomes of the lower limb (modified, from Fender, after Foerster)


The magician  Harry Houdini  with  Joaquin María Argamasilla  known as the "Spaniard with X-ray Eyes".


Mammalian tendon organ showing typical position in a muscle (left), neuronal connections in spinal cord (middle) and expanded schematic (right). The tendon organ is a stretch receptor that signals the force developed by the muscle. The sensory endings of the Ib afferent are entwined amongst the musculotendinous strands of 10-20 extrafusal muscle fibers. [ A ] [ 3 ]  See an  animated version .


A  baby  wearing many items of soft  winter  clothing:  headband ,  cap , fur-lined  coat ,  scarf  and  sweater


Different shaped  stress balls , including a cube, a star, and a sphere


Primary somatosensory cortex labeled in green  S1


Traditional two-point discrimination compared to two-point orientation discrimination.


This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for olfaction to their relevant endpoints in the human brain.


Action potential propagated by olfactory stimuli in an axon.


Details of olfaction system


1:  Olfactory bulb  2:  Mitral cells  3: Bone 4:  Nasal epithelium  5:  Glomerulus  6:  Olfactory receptor cells


Vesalius '  Fabrica , 1543.  Human   Olfactory bulbs  and Olfactory tracts outlined in red


According to the docking theory of olfaction, cinnamaldehyde, a main odorant in cinnamon, would have weak, non-covalent interactions with several different olfactory receptors (symbolized by the shapes in blue).


Human olfactory system. 1:  Olfactory bulb  2:  Mitral cells  3:  Bone  4: Nasal  epithelium  5:  Glomerulus (olfaction)  6:  Olfactory receptor cells


Bones of the nose and septal cartilage


Roof of the mouth showing position of palatine bones making up the floor of the nose, and forming the  posterior nasal spine  for the attachment of the  musculus uvulae .


Nasal cartilages


Anatomy of the nasal cavity.  Nasal-associated lymphoid tissue  labelled NALT


Paranasal sinuses


Nose shapes used in  Topinard's  nasal index.


Carotid arteries


Multiple arteries supply blood to the nose; the nasal septum, shown here is supplied by the anterior and posterior ethmoidal arteries at top; the sphenopalantine artery at the back, and the anterior ethoidal artery and the superior labial artery over the cartilage. These arteries join at  Kiesselbach's plexus .


The  developing head  at about four weeks. The olfactory pit can be seen at the top.


Air enters the upper respiratory tract through the nose. The nasal conchae can be seen in this image.


The cells lining the nose involved in smell ( olfaction ) are shown here


Saddle nose  ( congenital syphilis )


Prosthetic nose  from 17th century Europe.


Nasal cavity anatomy


CT scan  in the  coronal plane , showing the ostiomeatal complex (green area)


3D medical animation still shot depicting a human nose


The nose of a tapir


Elephants  have  prehensile  noses.


Coronal image of  mouse  main olfactory bulb cell nuclei. Blue  – Glomerular layer;  Red  – External Plexiform and  Mitral cell  layer; Green  – Internal Plexiform and  Granule cell  layer. Top of image is  dorsal  aspect, right of image is  lateral  aspect.  Scale, ventral to dorsal, is approximately 2mm.


Flow of olfactory information from receptors to glomeruli layer