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In the months following injury or stroke, most patients receive traditional treatment for a few hours per day. Among other exercises, patients practice the repetition of words and phrases. Mechanisms are also taught in traditional treatment to compensate for lost language function such as drawing and using phrases that are easier to pronounce.
Emphasis is placed on establishing a basis for communication with family and caregivers in everyday life. Treatment is individualized based on the patient's own priorities, along with the family's input.
A patient may have the option of individual or group treatment. Although less common, group treatment has been shown to have advantageous outcomes. Some types of group treatments include family counseling, maintenance groups, support groups and treatment groups.
Melodic intonation therapy was inspired by the observation that individuals with non-fluent aphasia sometimes can sing words or phrases that they normally cannot speak. "Melodic Intonation Therapy was begun as an attempt to use the intact melodic/prosodic processing skills of the right hemisphere in those with aphasia to help cue retrieval words and expressive language." It is believed that this is because singing capabilities are stored in the right hemisphere of the brain, which is likely to remain unaffected after a stroke in the left hemisphere. However, recent evidence demonstrates that the capability of individuals with aphasia to sing entire pieces of text may actually result from rhythmic features and the familiarity with the lyrics.
The goal of Melodic Intonation Therapy is to utilize singing to access the language-capable regions in the right hemisphere and use these regions to compensate for lost function in the left hemisphere. The natural musical component of speech was used to engage the patients' ability to produce phrases. A clinical study revealed that singing and rhythmic speech may be similarly effective in the treatment of non-fluent aphasia and apraxia of speech. Moreover, evidence from randomized controlled trials is still needed to confirm that Melodic Intonation Therapy is suitable to improve propositional utterances and speech intelligibility in individuals with (chronic) non-fluent aphasia and apraxia of speech.
A pilot study reported positive results when comparing the efficacy of a modified form of MIT to no treatment in people with nonfluent aphasia with damage to their left-brain. A randomized controlled trial was conducted and the study reported benefits of utilizing modified MIT treatment early in the recovery phase for people with nonfluent aphasia.
Melodic Intonation Therapy is used by music therapists, board-certified professionals that use music as a therapeutic tool to effect certain non-musical outcomes in their patients. Speech language pathologists can also use this therapy for individuals who have had a left hemisphere stroke and non-fluent aphasias such as Broca's or even apraxia of speech.
Two important principles of constraint-induced aphasia therapy are that treatment is very intense, with sessions lasting for up to 6 hours over the course of 10 days and that language is used in a communication context in which it is closely linked to (nonverbal) actions. These principles are motivated by neuroscience insights about learning at the level of nerve cells (synaptic plasticity) and the coupling between cortical systems for language and action in the human brain. Constraint-induced therapy contrasts sharply with traditional therapy by the strong belief that mechanisms to compensate for lost language function, such as gesturing or writing, should not be used unless absolutely necessary, even in everyday life.
It is believed that CIAT works by the mechanism of increased neuroplasticity. By constraining an individual to use only speech, it is believed that the brain is more likely to reestablish old neural pathways and recruit new neural pathways to compensate for lost function.
The strongest results of CIAT have been seen in patients with chronic aphasia (lasting over 6 months). Studies of CIAT have confirmed that further improvement is possible even after a patient has reached a "plateau" period of recovery. It has also been proven that the benefits of CIAT are retained long term. However, improvements only seem to be made while a patient is undergoing intense therapy. Recent work has investigated combining constraint-induced aphasia therapy with drug treatment, which led to an amplification of therapy benefits.
In addition to active speech therapy, pharmaceuticals have also been considered as a useful treatment for expressive aphasia. This area of study is relatively new and much research continues to be conducted.
The following drugs have been suggested for use in treating aphasia and their efficacy has been studied in control studies.
The most effect has been shown by piracetam and amphetamine, which may increase cerebral plasticity and result in an increased capability to improve language function. It has been seen that piracetam is most effective when treatment is begun immediately following stroke. When used in chronic cases it has been much less efficient.
Bromocriptine has been shown by some studies to increase verbal fluency and word retrieval with therapy than with just therapy alone. Furthermore, its use seems to be restricted to non-fluent aphasia.
Donepezil has shown a potential for helping chronic aphasia.
No study has established irrefutable evidence that any drug is an effective treatment for aphasia therapy. Furthermore, no study has shown any drug to be specific for language recovery. Comparison between the recovery of language function and other motor function using any drug has shown that improvement is due to a global increase plasticity of neural networks.
In transcranial magnetic stimulation (TMS), magnetic fields are used to create electrical currents in specified cortical regions. The procedure is a painless and noninvasive method of stimulating the cortex. TMS works by suppressing the inhibition process in certain areas of the brain. By suppressing the inhibition of neurons by external factors, the targeted area of the brain may be reactivated and thereby recruited to compensate for lost function. Research has shown that patients can demonstrate increased object naming ability with regular transcranial magnetic stimulation than patients not receiving TMS. Furthermore, research suggests this improvement is sustained upon the completion of TMS therapy. However, some patients fail to show any significant improvement from TMS which indicates the need for further research of this treatment.
It has been proven that, among all types of therapies, one of the most important factors and best predictors for a successful outcome is the intensity of the therapy. By comparing the length and intensity of various methods of therapies, it was proven that intensity is a better predictor of recovery than the method of therapy used.
In most individuals with expressive aphasia, the majority of recovery is seen within the first year following a stroke or injury. The majority of this improvement is seen in the first four weeks in therapy following a stroke and slows thereafter. However, this timeline will vary depending upon the type of stroke experienced by the patient. Patients who experienced an ischemic stroke may recover in the days and weeks following the stroke, and then experience a plateau and gradual slowing of recovery. On the contrary, patients who experienced a hemorrhagic stroke experience a slower recovery in the first 4–8 weeks, followed by a faster recovery which eventually stabilizes.
Numerous factors impact the recovery process and outcomes. Site and extent of lesion greatly impacts recovery. Other factors that may affect prognosis are age, education, gender, and motivation. Occupation, handedness, personality, and emotional state may also be associated with recovery outcomes.
Studies have also found that prognosis of expressive aphasia correlates strongly with the initial severity of impairment. However, it has been seen that continued recovery is possible years after a stroke with effective treatment. Timing and intensity of treatment is another factor that impacts outcomes. Research suggests that even in later stages of recovery, intervention is effective at improving function, as well as, preventing loss of function.
Unlike receptive aphasia, patients with expressive aphasia are aware of their errors in language production. This may further motivate a person with expressive aphasia to progress in treatment, which would affect treatment outcomes. On the other hand, awareness of impairment may lead to higher levels of frustration, depression, anxiety, or social withdrawal, which have been proven to negatively affect a person's chance of recovery.
Expressive aphasia was first identified by the French neurologist Paul Broca. By examining the brains of deceased individuals having acquired expressive aphasia in life, he concluded that language ability is localized in the ventroposterior region of the frontal lobe. One of the most important aspects of Paul Broca's discovery was the observation that the loss of proper speech in expressive aphasia is due to the brain's loss of ability to produce language, as opposed to the mouth's loss of ability to produce words.
The discoveries of Paul Broca were made during the same period of time as the German Neurologist Carl Wernicke, who was also studying brains of aphasiacs post-mortem and identified the region now known as Wernicke's area. Discoveries of both men contributed to the concept of localization, which states that specific brain functions are all localized to a specific area of the brain. While both men made significant contributions to the field of aphasia, it was Carl Wernicke who realized the difference between patients with aphasia that could not produce language and those that could not comprehend language (the essential difference between expressive and receptive aphasia).
Aphasiology is the study of language impairment usually resulting from brain damage, due to neurovascular accident—hemorrhage, stroke—or associated with a variety of neurodegenerative diseases, including different types of dementia. It is also the name of a scientific journal covering the area. These specific language deficits, termed aphasias, may be defined as impairments of language production or comprehension that cannot be attributed to trivial causes such as deafness or oral paralysis. A number of aphasias have been described, but two are best known: expressive aphasia (Broca's aphasia) and receptive aphasia (Wernicke's or sensory aphasia).
Acute aphasias are often the result of tissue damage following a stroke.
Lesions exclusively to Broca's area (the foot of the inferior frontal gyrus) do not produce Broca's aphasia, but instead mild dysprosody and agraphia, sometimes accompanied by word-finding pauses and mild dysarthria. Not much is known about what other areas must be damaged in order to produce Broca's aphasia, but some maintain damage to the inferior pre-Rolandic motor strip (the motor cortex region responsible glossopharyngeal muscle control) is also necessary.
A fascinating corollary of this has come from research on aphasias in deaf users of sign language, who show deficits in signing and comprehension analogous to Expressive and Receptive aphasias in hearing populations. These studies demonstrate that the grammatical functions of Broca's area and the semantic functions of Wernicke's area are indeed deep, abstract properties of the language system independent of its modality of expression.
Another less commonly known aphasia is global aphasia, which generally manifests itself after a stroke affecting an extensive portion of the brain occurs, including infarction of both divisions of the middle cerebral artery and generally both Broca's area and Wernicke's area. Survivors with global aphasia may have great difficulty understanding and forming words and sentences, and generally experience a great deal of difficulty when trying to communicate. With considerable speech therapy rehabilitation, global aphasia may progress into expressive aphasia or receptive aphasia.
A person with anomic aphasia have word-finding difficulties. Anomic aphasia, also known as anomia, is a non-fluent aphasia, which means the person speaks hesitantly because of a difficulty naming words and/or producing correct syntax. The person struggles to find the right words for speaking and writing. Subjects tend to use circumlocutions, in which they speak around the word they can not find, to make up for their loss. People also with anomic aphasia tend to know how to use an object, but rather can not name the aforementioned object. Any damage in or near the zone of language can result in anomic aphasia. Other forms of aphasia often transition into a syndrome of primarily anomic aphasia in the process of recovery.
Conduction Aphasia is a rare form of aphasia in which fibres in the arcuate fasciculus and superior longitudinal fasciculus are damaged. These fibres are the link between the Wernicke's and Broca's area. Damage to the area connecting comprehension and expression together has the following symptoms: fluent speech, good comprehension, poor oral reading, repetition is poor and transpositions of sounds within words is very common.
Primary progressive aphasia is a rare disorder where people slowly lose their ability to talk, read, write, and comprehend what they hear in conversation over a period of time. It was first described as a distinct syndrome by Mesulam in 1982. There are three variants: progressive nonfluent aphasia (PNFA), semantic dementia (SD), and logopenic progressive aphasia (LPA).
MMN refers to the mismatch response in electroencephalography (EEG); MMF or MMNM refer to the mismatch response in magnetoencephalography (MEG).
The auditory MMN was discovered in 1978 by Risto Näätänen, A. W. K. Gaillard, and S. Mäntysalo at the Institute for Perception, TNO in The Netherlands.
The first report of a visual MMN was in 1990 by Rainer Cammer. For a history of the development of the visual MMN, see Pazo-Alvarez et al. (2003).
The auditory MMN can occur in response to deviance in pitch, intensity, or duration. The auditory MMN is a fronto-central negative potential with sources in the primary and non-primary auditory cortex and a typical latency of 150-250 ms after the onset of the deviant stimulus. Sources could also include the inferior frontal gyrus, and the insular cortex. The amplitude and latency of the MMN is related to how different the deviant stimulus is from the standard. Large deviances elicit MMN at earlier latencies. For very large deviances, the MMN can even overlap the N100.
The visual MMN can occur in response to deviance in such aspects as color, size, or duration. The visual MMN is an occipital negative potential with sources in the primary visual cortex and a typical latency of 150-250 ms after the onset of the deviant stimulus.
As kindred phenomena have been elicited with speech stimuli, under passive conditions that require very little active attention to the sound, a version of MMN has been frequently used in studies of neurolinguistic perception, to test whether or not these participants neurologically distinguish between certain kinds of sounds. The MMN response has been used to study how fetuses and newborns discriminate speech sounds. In addition to these kinds of studies focusing on phonological processing, some research has implicated the MMN in syntactic processing. Some of these studies have attempted to directly test the automaticity of the MMN, providing converging evidence for the understanding of the MMN as a task-independent and automatic response.
MMN is evoked by an infrequently presented stimulus ("deviant"), differing from the frequently-occurring stimuli ("standards") in one or several physical parameters like duration, intensity, or frequency. In addition, it is generated by a change in spectrally complex stimuli like phonemes, in synthesised instrumental tones, or in the spectral component of tone timbre. Also the temporal order reversals elicit an MMN when successive sound elements differ either in frequency, intensity, or duration. The MMN is not elicited by stimuli with deviant stimulus parameters when they are presented without the intervening standards. Thus, the MMN has been suggested to reflect change detection when a memory trace representing the constant standard stimulus and the neural code of the stimulus with deviant parameter(s) are discrepant.
The MMN data can be understood as providing evidence that stimulus features are separately analysed and stored in the vicinity of auditory cortex (for a discussion, please see the theory section below). The close resemblance of the behaviour of the MMN to that of the previously behaviourally observed "echoic" memory system strongly suggests that the MMN provides a non-invasive, objective, task-independently measurable physiological correlate of stimulus-feature representations in auditory sensory memory.
The experimental evidence suggests that the auditory sensory memory index MMN provides sensory data for attentional processes, and, in essence, governs certain aspects of attentive information processing. This is evident in the finding that the latency of the MMN determines the timing of behavioural responses to changes in the auditory environment. Furthermore, even individual differences in discrimination ability can be probed with the MMN. The MMN is a component of the chain of brain events causing attention switches to changes in the environment. Attentional instructions also affect MMN.
The MMN has been documented in a number of studies to disclose neuropathological changes.
Presently, the accumulated body of evidence suggests that while the MMN offers unique opportunities to basic research of the information processing of a healthy brain, it might be useful in tapping neurodegenerative changes as well.
MMN, which is elicited irrespective of attention, provides an objective means for evaluating possible auditory discrimination and sensory-memory anomalies in such clinical groups as dyslexics and patients with aphasia, who have a multitude of symptoms including attentional problems. Recent results suggest that a major problem underlying the reading deficit in dyslexia might be an inability of the dyslexics' auditory cortex to adequately model complex sound patterns with fast temporal variation. According to the results of an ongoing study, MMN might also be used in the evaluation of auditory perception deficits in aphasia.
Alzheimer's patients demonstrate decreased amplitude of MMN, especially with long inter-stimulus intervals; this is thought to reflect reduced span of auditory sensory memory. Parkinsonian patients do demonstrate a similar deficit pattern, whereas alcoholism would appear to enhance the MMN response. This latter, seemingly contradictory, finding could be explained by hyperexcitability of CNS neurones resulting from neuroadaptive changes taking place during a heavy drinking bout.
While the results obtained thus far seem encouraging, several steps need to be taken before the MMN can be used as a clinical tool in patient treatment. A focus of research in the late 1990s aimed to tackle some of the key signal-analysis problems encountered in development of clinical use of MMN and challenges still remain. Nevertheless, as it stands, clinical research employing the MMN has already produced significant knowledge on the CNS functional changes related to cognitive decline in the aforementioned clinical disorders.
A 2010 study found that MMN durations were reduced in a group of schizophrenia patients who later went on to have psychotic episodes, suggesting that MMN durations may predict future psychosis.
The mainstream "memory trace" interpretation of MMN is that it is elicited in response to violations of simple rules governing the properties of information. It is thought to arise from violation of an automatically formed, short-term neural model or memory trace of physical or abstract environmental regularities. However, other than MMN, there is no other neurophysiological evidence for the formation of the memory representation of those regularities.
Integral to this memory trace view is that there are:
i) a population of sensory afferent neuronal elements that respond to sound, and;
ii) a separate population of memory neuronal elements that build a neural model of standard stimulation and respond more vigorously when the incoming stimulation violates that neural model, eliciting an MMN.
An alternative "fresh afferent" interpretation is that there are no memory neuronal elements, but the sensory afferent neuronal elements that are tuned to properties of the standard stimulation respond less vigorously upon repeated stimulation. Thus when a deviant activates a distinct new population of neuronal elements that is tuned to the different properties of the deviant rather than the standard, these fresh afferents respond more vigorously, eliciting an MMN.
A third view is that the sensory afferents are the memory neurons.
The bi-directional hypothesis of language and action proposes that the sensorimotor and language comprehension areas of the brain exert reciprocal influence over one another. This hypothesis argues that areas of the brain involved in movement and sensation, as well as movement itself, influence cognitive processes such as language comprehension. In addition, the reverse effect is argued, where it is proposed that language comprehension influences movement and sensation. Proponents of the bi-directional hypothesis of language and action conduct and interpret linguistic, cognitive, and movement studies within the framework of embodied cognition and embodied language processing. Embodied language developed from embodied cognition, and proposes that sensorimotor systems are not only involved in the comprehension of language, but that they are necessary for understanding the semantic meaning of words.
The theory that sensory and motor processes are coupled to cognitive processes stems from action-oriented models of cognition. These theories, such as the embodied and situated cognitive theories, propose that cognitive processes are rooted in areas of the brain involved in movement planning and execution, as well as areas responsible for processing sensory input, termed sensorimotor areas or areas of action and perception. According to action-oriented models, higher cognitive processes evolved from sensorimotor brain regions, thereby necessitating sensorimotor areas for cognition and language comprehension. With this organization, it was then hypothesized that action and cognitive processes exert influence on one another in a bi-directional manner: action and perception influence language comprehension, and language comprehension influences sensorimotor processes.
Effects of Language Comprehension on Systems of Action.
Language comprehension tasks can exert influence over systems of action, both at the neural and behavioral level. This means that language stimuli influence both electrical activity in sensorimotor areas of the brain, as well as actual movement.
The ability of language to influence neural activity of motor systems also manifests itself behaviorally by altering movement. Semantic priming has been implicated in these behavioral changes, and has been used as evidence for the involvement of the motor system in language comprehension. The Action-Sentence Compatibility Effect (ACE) is indicative of these semantic priming effects. Understanding language that implies action may invoke motor facilitation, or prime the motor system, when the action or posture being performed to indicate language comprehension is compatible with action or posture implied by the language. Compatible ACE tasks have been shown to lead to shorter reaction times. This effect has been demonstrated on various types of movements, including hand posture during button pressing, reaching, and manual rotation.
Effects of Systems of Action on Language Comprehension.
The bi-directional hypothesis of action and language proposes that altering the activity of motor systems, either through altered neural activity or actual movement, influences language comprehension. Neural activity in specific areas of the brain can be altered using transcranial magnetic stimulation (TMS), or by studying patients with neuropathologies leading to specific sensory and/or motor deficits. Movement is also used to alter the activity of neural motor systems, increasing overall excitability of motor and pre-motor areas.
Lesions of sensory and motor areas have also been studied to elucidate the effects of sensorimotor systems on language comprehension. One such example of this is the patient JR; this patient has a lesion in areas in the auditory association cortex implicated in processing auditory information. This patient showcases significant impairments in conceptual and perceptual processing of sound-related language and objects. For example, processing the meaning of words describing sound-related objects (e.g., "bell') was significantly impaired in JR as compared to non-sound-related objects (e.g., "armchair"). These data suggest that damage of sensory regions involved in processing auditory information specifically impair processing of sound-related conceptual information, highlighting the necessity of sensory systems for language comprehension.
Movement has been shown to influence language comprehension. This has been demonstrated by priming motor areas with movement, increasing the excitability of motor and pre-motor areas associated with the body part being moved. It has been demonstrated that motor engagement of a specific body part decreases neural activity in language processing areas when processing words related to that body part. This decreased neural activity is a feature of semantic priming, and suggests that activation of specific motor areas through movement can facilitate language comprehension in a semantically-dependent manner. An interference effect has also been demonstrated. During incompatible ACE conditions, neural signatures of language comprehension have been shown to be inhibited. Combined, these pieces of evidence have been used to support a semantic role of the motor system.
Movement can also inhibit language comprehension tasks, particularly tasks of verbal working memory. When asked to memorize and verbally recall four-word sequences of either arm or leg action words, performing complex, rhythmic movements after presentation of the word sequences was demonstrated to interfere with memory performance. This performance deficit was body-part specific, where movement of the legs impaired performance of recall of leg words, and movement of the arms impaired recall of arm words. These data indicate that sensorimotor systems exhibit cortically specific "inhibitory casual effects" on memory of action words, as impairment was specific to motor engagement and bodily association of the words.
Relating cognitive functions to brain structures is done in the field of cognitive neuroscience. This field attempts to map cognitive processes, such as language comprehension, onto neural activation of specific brain structures.The bi-directional hypothesis of language and action requires that action and language processes have overlapping brain structures, or shared neural substrates, thereby necessitating motor areas for language comprehension. The neural substrates of embodied cognition are often studied using the cognitive tasks of object recognition, action recognition, working memory tasks, and language comprehension tasks. These networks have been elucidated with behavioral, computational, and imaging studies, but the discovery of their exact organization is ongoing.
A Jabberwocky sentence is a type of sentence of interest in neurolinguistics. Jabberwocky sentences take their name from the language of Lewis Carroll's well-known poem "Jabberwocky". In the poem, Carroll uses correct English grammar and syntax, but many of the words are made up and merely suggest meaning. A Jabberwocky sentence is therefore a sentence which uses correct grammar and syntax but contains nonsense words, rendering it semantically meaningless.
A second study by Silva-Pereyra et al. showed that preschoolers at the age of 36 months demonstrate similar processing patterns compared to adults when processing normal sentences with phrase structure violations, showing ERP activity analogous to the N150 and P600 in adults, but shifted later in time. When presented with phrase-structure violations in Jabberwocky sentences, however, preschoolers demonstrate activity analogous to a N400, typically associated with the extraction of meaning from words in adults, along with a diminished P600. This implies that semantics plays a role in syntactic processing in children and provides neurobiological evidence for interactive theories over modular theories of semantic and syntactic processing.
The motor theory of speech perception is the hypothesis that people perceive spoken words by identifying the vocal tract gestures with which they are pronounced rather than by identifying the sound patterns that speech generates. It originally claimed that speech perception is done through a specialized module that is innate and human-specific. Though the idea of a module has been qualified in more recent versions of the theory, the idea remains that the role of the speech motor system is not only to produce speech articulations but also to detect them.
The hypothesis has gained more interest outside the field of speech perception than inside. This has increased particularly since the discovery of mirror neurons that link the production and perception of motor movements, including those made by the vocal tract.
The theory was initially proposed in the Haskins Laboratories in the 1950s by Alvin Liberman and Franklin S. Cooper, and developed further by Donald Shankweiler, Michael Studdert-Kennedy, Ignatius Mattingly, Carol Fowler and Douglas Whalen.
The hypothesis has its origins in research using pattern playback to create reading machines for the blind that would substitute sounds for orthographic letters. This led to a close examination of how spoken sounds correspond to the acoustic spectrogram of them as a sequence of auditory sounds. This found that successive consonants and vowels overlap in time with one another (a phenomenon known as coarticulation). This suggested that speech is not heard like an acoustic "alphabet" or "cipher," but as a "code" of overlapping speech gestures.
Initially, the theory was associationist: infants mimic the speech they hear and that this leads to behavioristic associations between articulation and its sensory consequences. Later, this overt mimicry would be short-circuited and become speech perception. This aspect of the theory was dropped, however, with the discovery that prelinguistic infants could already detect most of the phonetic contrasts used to separate different speech sounds.
The behavioristic approach was replaced by a cognitivist one in which there was a speech module. The module detected speech in terms of hidden distal objects rather than at the proximal or immediate level of their input. The evidence for this was the research finding that speech processing was special such as duplex perception.
Initially, speech perception was assumed to link to speech objects that were both
This was later revised to include the phonetic gestures rather than motor commands, and then the gestures intended by the speaker at a prevocal, linguistic level, rather than actual movements.
The "speech is special" claim has been dropped, as it was found that speech perception could occur for nonspeech sounds (for example, slamming doors for duplex perception).
The discovery of mirror neurons has led to renewed interest in the motor theory of speech perception, and the theory still has its advocates, although there are also critics.
If speech is identified in terms of how it is physically made, then nonauditory information should be incorporated into speech percepts even if it is still subjectively heard as "sounds". This is, in fact, the case.
If people can hear the gestures in speech, then the imitation of speech should be very fast, as in when words are repeated that are heard in headphones as in speech shadowing. People can repeat heard syllables more quickly than they would be able to produce them normally.
Evidence exists that perception and production are generally coupled in the motor system. This is supported by the existence of mirror neurons that are activated both by seeing (or hearing) an action and when that action is carried out. Another source of evidence is that for common coding theory between the representations used for perception and action.
The motor theory of speech perception is not widely held in the field of speech perception, though it is more popular in other fields, such as theoretical linguistics. As three of its advocates have noted, "it has few proponents within the field of speech perception, and many authors cite it primarily to offer critical commentary".p. 361 Several critiques of it exist.
Speech perception is affected by nonproduction sources of information, such as context. Individual words are hard to understand in isolation but easy when heard in sentence context. It therefore seems that speech perception uses multiple sources that are integrated together in an optimal way.
The motor theory of speech perception would predict that speech motor abilities in infants predict their speech perception abilities, but in actuality it is the other way around. It would also predict that defects in speech production would impair speech perception, but they do not. However, this only affects the first and already superseded behaviorist version of the theory, where infants were supposed to learn "all" production-perception patterns by imitation early in childhood. This is no longer the mainstream view of motor-speech theorists.
Several sources of evidence for a specialized speech module have failed to be supported.
As a result, this part of the theory has been dropped by some researchers.
The evidence provided for the motor theory of speech perception is limited to tasks such as syllable discrimination that use speech units not full spoken words or spoken sentences. As a result, "speech perception is sometimes interpreted as referring to the perception of speech at the sublexical level. However, the ultimate goal of these studies is presumably to understand the neural processes supporting the ability to process speech sounds under ecologically valid conditions, that is, situations in which successful speech sound processing ultimately leads to contact with the mental lexicon and auditory comprehension." This however creates the problem of " a tenuous connection to their implicit target of investigation, speech recognition".
It has been suggested that birds also hear each other's bird song in terms of vocal gestures.
The coining of the term "neurolinguistics" is attributed to Edith Crowell Trager, Henri Hecaen and Alexandr Luria, in the late 1940s and 1950s; Luria's book "Problems in Neurolinguistics" is likely the first book with Neurolinguistics in the title. Harry Whitaker popularized neurolinguistics in the United States in the 1970s, founding the journal "Brain and Language" in 1974.
Although aphasiology is the historical core of neurolinguistics, in recent years the field has broadened considerably, thanks in part to the emergence of new brain imaging technologies (such as PET and fMRI) and time-sensitive electrophysiological techniques (EEG and MEG), which can highlight patterns of brain activation as people engage in various language tasks; electrophysiological techniques, in particular, emerged as a viable method for the study of language in 1980 with the discovery of the N400, a brain response shown to be sensitive to semantic issues in language comprehension. The N400 was the first language-relevant event-related potential to be identified, and since its discovery EEG and MEG have become increasingly widely used for conducting language research.
Neurolinguistics is closely related to the field of psycholinguistics, which seeks to elucidate the cognitive mechanisms of language by employing the traditional techniques of experimental psychology; today, psycholinguistic and neurolinguistic theories often inform one another, and there is much collaboration between the two fields.
Neurolinguistics research is carried out in all the major areas of linguistics; the main linguistic subfields, and how neurolinguistics addresses them, are given in the table below.
Neurolinguistics research investigates several topics, including where language information is processed, how language processing unfolds over time, how brain structures are related to language acquisition and learning, and how neurophysiology can contribute to speech and language pathology.
Much work in neurolinguistics has, like Broca's and Wernicke's early studies, investigated the locations of specific language "modules" within the brain. Research questions include what course language information follows through the brain as it is processed, whether or not particular areas specialize in processing particular sorts of information, how different brain regions interact with one another in language processing, and how the locations of brain activation differ when a subject is producing or perceiving a language other than his or her first language.
Another area of neurolinguistics literature involves the use of electrophysiological techniques to analyze the rapid processing of language in time. The temporal ordering of specific patterns of brain activity may reflect discrete computational processes that the brain undergoes during language processing; for example, one neurolinguistic theory of sentence parsing proposes that three brain responses (the ELAN, N400, and P600) are products of three different steps in syntactic and semantic processing.
Another topic is the relationship between brain structures and language acquisition. Research in first language acquisition has already established that infants from all linguistic environments go through similar and predictable stages (such as babbling), and some neurolinguistics research attempts to find correlations between stages of language development and stages of brain development, while other research investigates the physical changes (known as neuroplasticity) that the brain undergoes during second language acquisition, when adults learn a new language.
Neuroplasticity is observed when both Second Language acquisition and Language Learning experience are induced, the result of this language exposure concludes that an increase of gray and white matter could be found in children, young adults and the elderly.
Ping Li, Jennifer Legault, Kaitlyn A. Litcofsky, May 2014.
Neuroplasticity as a function of second language learning: Anatomical changes in the human brain
Cortex: A Journal Devoted to the Study of the Nervous System & Behavior, 410.1016/j.cortex.2014.05.00124996640
Neurolinguistic techniques are also used to study disorders and breakdowns in language, such as aphasia and dyslexia, and how they relate to physical characteristics of the brain.
Since one of the focuses of this field is the testing of linguistic and psycholinguistic models, the technology used for experiments is highly relevant to the study of neurolinguistics. Modern brain imaging techniques have contributed greatly to a growing understanding of the anatomical organization of linguistic functions. Brain imaging methods used in neurolinguistics may be classified into hemodynamic methods, electrophysiological methods, and methods that stimulate the cortex directly.

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