data/raw/07_sensory_processing.txt

Title: Sensory Processing Differences in Autism Spectrum Disorder — Science and Practice
Source: Synthesized from Marco et al. 2011, Green et al. 2016, Tavassoli et al. 2014, Lane et al. 2014, Baranek et al. 2006, Schauder & Bennetto 2016
Topic: Sensory Processing

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1. SENSORY DIFFERENCES AS A CORE FEATURE

Since the DSM-5 (2013), sensory processing differences have been included as a formal diagnostic criterion for ASD (Criterion B4: hyper- or hyporeactivity to sensory input). This reflects decades of research and autistic self-report establishing that sensory experiences are among the most impactful aspects of daily life for many autistic individuals.

Prevalence of sensory differences in ASD:
- Approximately 69–93% of autistic individuals report or show atypical sensory processing (Marco et al., 2011)
- Sensory differences are present across intelligence levels and verbal ability
- They occur across all sensory modalities

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2. SENSORY MODALITIES AND PATTERNS

2.1 Hypersensitivity (over-responsiveness)
The sensory system responds too strongly or for too long to stimuli that others habituate to:
- Auditory: pain or distress from specific sounds (sirens, hand dryers, crowd noise, certain voices); may cover ears or flee
- Tactile: distress from light touch, clothing textures (seams, tags), haircuts, toothbrushing, certain food textures
- Visual: distress or disorientation from fluorescent lighting, flickering, glare, busy visual environments
- Olfactory: intense reaction to perfumes, cleaning products, food smells; may refuse to enter certain rooms
- Gustatory (taste): highly limited diet related to taste sensitivity; gagging responses

2.2 Hyposensitivity (under-responsiveness)
The sensory system responds too weakly, requiring more intense input:
- Reduced pain sensitivity: may not react to injuries; may self-injure without apparent pain response
- Reduced awareness of body position (proprioception): clumsy, bumps into things, doesn't know where limbs are
- Reduced vestibular awareness: may spin or swing excessively for input; does not get dizzy easily
- Reduced temperature awareness: may not notice extreme cold or heat
- Reduced awareness of hunger or thirst (interoception — see below)

2.3 Sensory-seeking behavior
Actively seeking out intense sensory experiences:
- Spinning, rocking, jumping, crashing into furniture (vestibular/proprioceptive seeking)
- Mouthing objects beyond typical age (oral seeking)
- Staring at lights or moving objects (visual seeking)
- Smelling or touching everything (olfactory/tactile seeking)

Note: sensory-seeking behaviors are often mislabeled as "behavioral problems." They serve regulatory functions and should not be eliminated without understanding their purpose.

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3. INTEROCEPTION

Interoception — awareness of internal body states — is increasingly recognized as significantly different in autistic individuals:
- Difficulty detecting hunger, thirst, pain, temperature, heart rate, bladder fullness
- Atypical interoception linked to difficulty with emotional awareness and regulation (emotions are partly felt as body states)
- May contribute to eating difficulties, toileting challenges, and healthcare avoidance
- Impaired interoception is associated with difficulty recognizing own emotions (alexithymia), which is common in ASD

Assessment tools: Body Perception Questionnaire, Interoception Sensory Questionnaire (ISQ)

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4. NEURAL BASIS OF SENSORY DIFFERENCES

4.1 Sensory gating
Neurotypical brains suppress repeated or irrelevant sensory stimuli (habituation/gating). EEG studies show reduced or absent sensory gating in ASD — stimuli that should be suppressed continue to trigger neural responses, contributing to overload.

4.2 Multisensory integration
Autistic individuals show atypical multisensory integration — difficulty combining information across senses simultaneously:
- Audiovisual binding is less efficient (accounts for some language processing differences)
- Contribution of multisensory processing challenges to daily life difficulties is significant

4.3 Predictive processing theory
The predictive brain framework (Pellicano & Burr, 2012) proposes that autistic brains rely less on top-down predictions and more on bottom-up sensory data:
- Leads to the world feeling more intense, surprising, and unpredictable
- Explains sensory sensitivity, insistence on sameness, and anxiety
- This is not a deficit in the traditional sense but a different processing style

4.4 Cortical differences
Neuroimaging studies show:
- Atypical activation in primary sensory cortices
- Differences in fronto-parietal networks involved in sensory modulation
- Altered connectivity between sensory and prefrontal regions involved in top-down control

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5. IMPACT ON DAILY LIFE

Food and eating:
- Sensory-related food selectivity affects 46–89% of autistic children (Cermak et al., 2010)
- Primarily driven by texture aversion and smell sensitivity
- Can lead to nutritional deficiencies; rarely dangerous but causes significant family stress

School participation:
- Noisy lunchrooms, echoing hallways, fluorescent lighting, crowded spaces create significant distress
- Sensory overload can reduce availability for learning
- Avoidance of school environments may be misinterpreted as behavioral resistance

Healthcare:
- Hospital and clinic environments (smells, sounds, touch, unpredictability) are highly aversive
- Sensory distress contributes to healthcare avoidance; may delay pain reporting and seeking treatment
- Adapted healthcare environments (quiet rooms, dimmed lights, advance preparation) significantly reduce distress

Sleep:
- Tactile sensitivity contributes to difficulty with bedtime routines (pajamas, bedding)
- Auditory sensitivity interferes with falling asleep
- Sensory processing differences are a significant contributor to the high rate of sleep problems in ASD

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6. ASSESSMENT

Standardized sensory assessment tools:
- Sensory Profile 2 (Dunn): parent/teacher/self-report; widely used; 4 sensory quadrants
- Sensory Processing Measure (SPM-2): home and school versions; 8 sensory systems
- Short Sensory Profile: abbreviated screening version
- Glasgow Sensory Questionnaire: self-report for adults and adolescents

Occupational therapy sensory assessment includes:
- Standardized questionnaires
- Clinical observation (sensory history)
- Direct assessment of sensory responses in clinic setting

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7. INTERVENTIONS

7.1 Sensory Integration Therapy (SIT / Ayres Sensory Integration)
- Developed by A. Jean Ayres in the 1970s
- Child-directed, play-based OT using specialized equipment (swings, ball pits, climbing walls)
- Goal: improve the brain's ability to organize and respond to sensory information
- Evidence: systematic reviews show mixed/inconclusive evidence for SIT as standalone intervention; some positive effects on sensory-motor goals (Schaaf et al., 2018 RCT showed significant improvements on individualized goals)
- Best delivered by certified SIT-trained occupational therapists

7.2 Environmental modifications
Well-supported and practical:
- Noise-canceling headphones or earplugs
- Lighting modifications (LED warm light, natural light, dimmer switches, lamp instead of overhead)
- Clothing: seamless socks, tagless labels, compression garments
- Quiet rooms / sensory rooms in schools and workplaces
- Advance preparation and visual schedules (predictability reduces sensory anticipatory anxiety)

7.3 Graduated exposure (desensitization)
- Gradual, self-paced exposure to aversive sensory stimuli can reduce sensitivity over time
- Must be child-led and never forced
- Forced exposure to aversive sensory input is harmful and unethical

7.4 Weighted items
- Weighted blankets and vests used for proprioceptive calming
- Mixed evidence; widely used; individual response varies
- Generally safe; weight recommendations: ~10% of body weight for blankets

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8. SENSORY PROCESSING AND MELTDOWNS

Sensory overload is a primary trigger of autistic meltdowns (and shutdowns). Understanding this is fundamental:
- Meltdown: loss of behavioral control as a response to overwhelming stimuli; not a tantrum (not goal-directed)
- Shutdown: internal withdrawal response to overload; appears as going quiet, still, unresponsive
- Post-overload recovery can take hours; demands should be reduced, not increased, during this time
- Prevention through environmental modification is more effective than behavioral management during a meltdown

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KEY REFERENCES
- Marco, E.J., et al. (2011). Sensory processing in autism: a review of neurophysiologic findings. Pediatric Research, 69(5 Pt 2), 48R–54R.
- Baranek, G.T., et al. (2006). Sensory experiences questionnaire: discriminating sensory features in young children with autism, developmental delays, and typical development. Journal of Child Psychology and Psychiatry, 47(6), 591–601.
- Schaaf, R.C., et al. (2018). An intervention for sensory difficulties in children with autism: a randomized trial. Journal of Autism and Developmental Disorders, 48(5), 1493–1506.
- Pellicano, E., & Burr, D. (2012). When the world becomes 'too real': a Bayesian explanation of autistic perception. Trends in Cognitive Sciences, 16(10), 504–510.
- Lane, A.E., et al. (2014). Sensory processing subtypes in autism: association with adaptive behavior. Journal of Autism and Developmental Disorders, 44(3), 516–529.