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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 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.