Characterization and Measurement of Sensory Seeking and Avoidance Behaviors in Autism: A Comprehensive Review

1. Introduction: Sensory Processing in Autism Spectrum Disorder

Atypical sensory processing has emerged as a ubiquitous feature of autism spectrum disorder (ASD), with research indicating that over 90% of individuals with ASD demonstrate abnormal responses to sensory stimuli . The significance of these sensory processing differences has been increasingly recognized, culminating in their inclusion as a diagnostic criterion in the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5)[1]. The DSM-5 specifically acknowledges sensory abnormalities as diagnostic criteria in ASD, with approximately 90% of ASD individuals experiencing atypical sensory responses, including both hyper- and hypo-reactivity to stimuli[2]. This formal recognition underscores the need for adult questionnaires investigating basic sensory functioning, which has become increasingly important in light of the emphasis placed on sensory reactivity in diagnostic procedures[3].

The incidence of sensory reactivity differences in autism significantly exceeds that observed in the neurotypical population. While the basis of sensory processing disorders in autism is multifactorial, sensory integration and processing concerns appear to play a fundamental role in the manifestation of behavioral differences[4]. Research into sensory processing in ASD has been approached from two primary perspectives: the first focuses on characterizing symptoms that manifest in response to real-world sensory stimulation, while the second examines the neural pathways and mechanisms underlying sensory processing. This dual approach has contributed significantly to our understanding of sensory differences in ASD, though these perspectives have largely developed independently, creating separate theories and methodologies[5].

The current multidisciplinary approach to understanding sensory processing in ASD, while valuable, must evolve toward an interdisciplinary model to advance knowledge in this field. Integration of sensory symptoms research with neuroscience perspectives will inevitably lead to a better understanding of the biological basis of these symptoms and enhance the potential for translation to early identification and treatment. This integrative approach is essential for advancing our understanding of sensory processing in ASD[5].

This review synthesizes the literature on how sensory seeking and avoidance behaviors associated with autism are characterized and measured, highlighting key assessment tools, neurophysiological correlates, and emerging research directions. By examining both behavioral manifestations and underlying mechanisms, this review aims to provide a comprehensive understanding of sensory processing differences in individuals with ASD.

2. Conceptual Framework and Characterization of Sensory Processing in Autism

2.1 Sensory Hyper- and Hypo-Responsivity

Individuals with autism commonly present with atypical patterns of sensory responsiveness, which are generally categorized into three main patterns: hyporesponsiveness (diminished response to sensory stimuli), hyperresponsiveness (exaggerated response to sensory stimuli), and sensory seeking (craving or fascination with certain sensory experiences)[6]. These sensory-based behaviors represent a fundamental aspect of ASD and have been extensively studied through various neuroimaging techniques, including electroencephalography (EEG), magnetoencephalography (MEG), and functional MRI. These investigations examine both unimodal sensory processing and multisensory integration, as well as the influence of covert and overt attention on sensory processing[7].

Research has consistently demonstrated greater sensory hypersensitivity in individuals with ASD compared to controls. However, the traditional scoring of sensory assessment tools often fails to differentiate between hyper- and hyposensitivity, making it difficult to determine whether individuals with ASD might also show differences in hyposensitivity[8]. When more refined measurement approaches are employed, studies reveal that individuals with ASD report significantly more hypersensitivity, but not necessarily more hyposensitivity, compared to control groups. Higher hypersensitivity scores have been shown to positively correlate with increased autistic traits, suggesting a relationship between sensory processing differences and core features of autism[8].

Sensory overresponsiveness is highly prevalent in individuals with ASD and typically persists into adulthood. Research has found associations between sensory avoiding behaviors (a manifestation of overresponsiveness) and levels of anxiety and loneliness in adults with ASD. Individuals who experience sensory avoiding more frequently report higher anxiety and feelings of loneliness, with loneliness mediating the relationship between sensory avoiding and anxiety[9]. These findings highlight the far-reaching effects of sensory processing differences on emotional well-being and social functioning.

2.2 Specificity of Sensory Profiles in Autism

Sensory processing differences are not exclusive to ASD but are common across various neurodevelopmental disorders. Research comparing sensory processing, praxis, and social participation in children with ASD, Attention Deficit Hyperactivity Disorder (ADHD), combined ASD+ADHD, and typically developing children has employed measures such as the Sensory Processing Measure (SPM) to evaluate these domains in both home and classroom contexts[10]. Findings suggest that difficulties in proprioception appear more characteristic of ADHD, while social difficulties are more characteristic of ASD. Interestingly, context-specific differences in sensory processing were uniquely observed in the ASD group, potentially relating to contextual hyperselectivity, an inherent feature of autism[10].

Research has also distinguished between sensory processing differences in children with ASD and those with Sensory Processing Disorders (SPD) who do not meet criteria for an ASD diagnosis. Children with SPD show atypical sensory behaviors to the same or greater degree as ASD children, and neuroimaging studies have revealed impaired white matter microstructure in SPD that correlates with atypical sensory behavior[1]. Diffusion tensor imaging studies indicate that both ASD and SPD cohorts demonstrate decreased connectivity in parieto-occipital tracts involved in sensory perception and multisensory integration. However, only the ASD group shows impaired connectivity in temporal tracts associated with social-emotional processing, suggesting distinct neural patterns underlying sensory differences in these populations[1].

2.3 Tactile Processing and Somatosensory Function

Tactile sensitivity has received particular attention in ASD research, with studies consistently documenting abnormal reactions to tactile stimulation. Investigations have addressed both neurobiological bases of tactile sensitivity and clinical implications, with a specific focus on tactile processing deficits through various methodological approaches[2]. Research examining tactile cortical processing in young children with autism has utilized electroencephalography (EEG) to investigate somatosensory-evoked potentials (SEPs) during passive tactile fingertip stimulation, comparing these responses between autistic children and neurotypical peers. These studies have assessed potential links between neural measures and "real-world" parent-reported tactile reactivity[11].

Structural neuroimaging studies have revealed reduced integrity in both thalamocortical and intrainsular tracts in children with ASD compared to typically developing children. These structural differences correlate with behavioral observations, where children with ASD exhibit impaired tactile discriminative ability, increased tactile defensiveness, and more sensory seeking behaviors (characterized by enthusiastic play or repetitive engagement with specific tactile stimuli). A significant relationship exists between intrainsular tract integrity and tactile seeking behaviors, with the direction of this relationship differing between ASD and typically developing groups[12].

Qualitative research has provided valuable insights into the subjective experience of sensory differences in autism. Studies employing focus groups with autistic adults have characterized visual sensory experiences, documenting a range of visual hypersensitivities including sensitivity to light, motion, patterns, and particular colors. These sensory experiences contribute to distraction and are frequently part of a wider multisensory processing issue[13]. Such experiences significantly impact personal wellbeing and daily life, with participants reporting fatigue, stress, and hindrances to daily activities like travel and social engagement. The degree of understanding individuals have about their sensory experiences influences their emotional response, with greater understanding reducing concern. While various coping strategies are employed to manage these sensory experiences, their effectiveness varies considerably[13].

3. Measurement Methods and Assessment Tools

3.1 Parent/Caregiver Report Measures

Assessment of sensory processing characteristics requires a comprehensive approach that includes standardized tests, caregiver questionnaires, and clinical observations. Numerous tools have been developed to identify different patterns of sensory processing, with fifteen tests having established psychometric properties, primarily for the US population. Nine of these tools are applicable to children from preschool through grade 12[14]. A review of various studies reveals that the most commonly used assessment tools are the Sensory Integration and Praxis Test, the Sensory Processing Measure, and the Sensory Profile[14].

Questionnaire-based studies suggest atypical sensory perception in over 90% of individuals with autism spectrum conditions (ASC). While most sensory questionnaire-based studies record parental reports of children's sensory experiences, less is known about sensory reactivity in adults with ASC. The inclusion of sensory reactivity in the DSM-5 criteria for ASC has highlighted the need for adult questionnaires investigating basic sensory functioning. To address this gap, researchers have developed and validated tools such as the Sensory Perception Quotient (SPQ), which assesses basic sensory hyper- and hyposensitivity across all five sensory modalities[3].

Sensory abnormalities are recognized as diagnostic criteria in autism, and atypical responses to sensory input are increasingly identified as a common feature of ASDs. The inclusion of sensory aspects in autism diagnosis in the DSM-5 reflects the prevalence of sensory dysfunctions in this population. Various tools investigate these sensory domains, primarily through rating scales that complement other assessment methods and help define the clinical picture and individual trajectory, ultimately improving diagnosis and intervention approaches[15].

Despite the proliferation of sensory assessment tools, a systematic review of the psychometric properties of self and caregiver report measures used to assess sensory features in ASD revealed substantial differences in the specific sensory features defined across assessment tools. When evaluated against quality psychometric evidence criteria, only five assessments were identified as "appropriate with conditions," with no sensory assessment tools having sufficient quality psychometric evidence to receive a recommendation of "Appropriate" for measuring sensory features in ASD. These findings highlight potentially significant shortcomings in current methods used to measure sensory features in ASD and suggest the need for more rigorous development of psychometrically sound assessment tools for this population[16].

3.2 Direct Observational Assessments

While researchers and practitioners typically use parent-report measures or informal clinical observations to understand the presence and nature of sensory interests, repetitions, and seeking behaviors (SIRS), direct observational measures provide valuable complementary information. The Sensory Processing Assessment for Young Children, an observational measure, has been used to characterize SIRS across children with ASD, developmental delays, and typical development[17]. These assessments have identified group differences in the frequency and intensity of overall SIRS, complexity of SIRS, and incidence of particular types of SIRS (including posturing, sighting, proprioceptive seeking, and spinning). Interestingly, facial affect during engagement in SIRS is primarily neutral across all groups, providing insight into the emotional context of these behaviors[17].

The need for reliable measures to understand the biological underpinnings of sensory processing differences has led to the development of scoring methodologies specific to auditory over-responsivity (AOR) and tactile over-responsivity (TOR). Studies have established cohorts based on sensory over-responsivity using both parent report measures (such as the Short Sensory Profile) and direct assessment measures (such as the Sensory Processing-Three Dimensions: Assessment)[18]. In studies of children with neurodevelopmental disorders, direct assessment has identified auditory over-responsivity in 31% and tactile over-responsivity in 27% of participants. The inter-test agreement between parent report and direct observation has shown moderate overlap (65% for AOR and 50% for TOR), suggesting that a combination of questionnaire and direct observation measures should be employed in both clinical and research settings[18].

Research examining the relationship between sensory processing atypicalities and social functioning in young children with ASD has employed both parent-reported measures of sensory processing and precise measures of social attention deployment using custom-designed eye-tracking tasks depicting naturalistic social scenes[19]. Within ASD populations, higher intensities of sensory issues correlate with more prominent social difficulties and lower adaptive functioning. Children with ASD who have more sensory issues show visual exploration patterns of social scenes that significantly deviate from those of typically developing children, highlighting the impact of sensory processing on social perception[19].

3.3 Neurophysiological and Psychophysiological Approaches

Auditory sensory modulation difficulties are common in ASD and may stem from a faulty arousal system that compromises the ability to regulate optimal responses. Neurophysiological studies have employed techniques such as magnetic field recordings to examine correlates of auditory sensory modulation difficulties in children with ASD. Analysis of components like the P100m, which is the most prominent component of the auditory magnetic field response in children, may reflect preattentive arousal processes. Studies have shown that this component is rightward lateralized in typically developing children but not in children with ASD, who show a tendency toward P100m reduction in the right hemisphere[20].

The atypical P100m lateralization in individuals with ASD is associated with greater severity of sensory abnormalities as assessed by tools like the Short Sensory Profile, as well as with auditory hypersensitivity during the first two years of life. The absence of right-hemispheric predominance of the P100m in ASD children suggests disturbance of the right hemisphere ascending reticular brainstem pathways and/or their thalamic and cortical projections, which may contribute to abnormal arousal and attention. The correlation between sensory abnormalities and atypical P100m lateralization suggests that reduced preattentive processing in the right hemisphere and/or its shift to the left hemisphere may contribute to abnormal sensory behavior in ASD[20].

Abnormalities in cortical connectivity and evoked responses have been extensively documented in ASD, though specific signatures of these cortical abnormalities remain elusive, with data pointing toward both increased and reduced response amplitudes and functional connectivity. Some researchers have proposed that functional connectivity in ASD is reduced in the feedback (top-down) direction but increased in the feedforward (bottom-up) direction. Studies assessing the onset, feedforward-driven component of responses to vibrotactile stimuli in the somatosensory cortex of individuals with ASD have used novel methods to measure the spatio-temporal divergence of cortical activation[21]. These investigations have revealed that, relative to typically developing participants, individuals with ASD show an increase in the initial onset component of the cortical response and a faster spread of local activity. These findings suggest increased thalamocortical feedforward connectivity in ASD, offering a plausible mechanism for previously observed increased response variability and tactile processing abnormalities associated with the disorder[21].

Sensory processing can be studied along multiple dimensions, with two of the most basic being the examination of instantaneous sensory responses and how these responses change over time, corresponding to dimensions of 'sensitivity' and 'habituation'. While research indicates that autistic individuals do not differ systematically from controls in sensory acuity/sensitivity, data from studies of habituation have been more equivocal[22]. Studies using galvanic skin response (GSR) and magnetoencephalography (MEG) to assess habituation in autism have revealed consistent patterns of reduced habituation in autistic participants. These results suggest that autism compromises a fundamental aspect of sensory processing, at least in the auditory domain, which may have implications for understanding sensory hypersensitivities, a hallmark feature of autism, and potential relevance for early detection of autism risk[22].

4. Neural Underpinnings of Sensory Processing Differences

4.1 Brain Structure and Connectivity

Sensory dysfunction is a core symptom of ASD, and while these abnormalities can be extremely debilitating, relatively little is known about the underlying neuroanatomical and neurophysiological factors that lead to sensory abnormalities in ASD. Investigation into these aspects could lead to significant advancements in understanding ASD and provide targets for treatment and diagnostic procedures. Research examining the covariation of volumes of brain structures involved in abnormal sensory processing, measured through structural magnetic resonance imaging, has provided insights into the connectivity of these brain regions[23].

Studies quantifying the structural covariation of sensory-related cerebral cortical structures, the cerebellum, and the amygdala have revealed decreased structural covariation between sensory-related cortical structures in individuals with ASD, especially between the left and right cerebral hemispheres. Conversely, these individuals present with increased structural covariation of structures in the right cerebral hemisphere. Additionally, sensory-related cerebral structures exhibit decreased structural covariation with functionally identified cerebellar networks, while the left amygdala shows significantly increased structural covariation with cerebral structures related to visual processing. These patterns suggest altered connectivity both within and between cerebral cortices and other brain structures related to sensory processing[23].

White matter microstructural pathology has been demonstrated in children with Sensory Processing Disorders (SPD), correlating with atypical sensory behavior. Diffusion tensor imaging (DTI) fiber tractography has been used to evaluate the structural connectivity of specific white matter tracts in children with ASD and SPD, relative to typically developing children. This approach defines white matter tracts using probabilistic streamline tractography and assesses the strength of tract connectivity using mean fractional anisotropy[1]. Both SPD and ASD groups demonstrate decreased connectivity relative to controls in parieto-occipital tracts involved in sensory perception and multisensory integration. However, the ASD group alone shows impaired connectivity in temporal tracts thought to subserve social-emotional processing, highlighting distinct neural signatures for these conditions[1].

4.2 Neurochemical Factors

Individuals with ASD often exhibit abnormal processing of sensory inputs from multiple modalities and higher-order cognitive/behavioral responses to those inputs. Several lines of evidence suggest that altered γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain, is a central characteristic of the neurophysiology of ASD. To understand the relationship between GABA levels in specific brain regions and atypical sensory processing in ASD, researchers have employed 1H magnetic resonance spectroscopy (1H-MRS) to examine whether GABA levels in brain regions critical to higher-order motor and/or multiple sensory functions are associated with abnormal sensory responses[24].

Studies measuring GABA levels in regions including the primary visual cortex, left sensorimotor cortex, left supplementary motor area (SMA), and left ventral premotor cortex (vPMC) have found greater sensory hyper-responsiveness in individuals with ASD relative to controls. Reduced GABA concentrations have been observed in the left SMA of individuals with ASD, though no differences were found in other regions of interest. Correlation analyses have revealed a negative association between left vPMC GABA levels and the severity of sensory hyper-responsiveness across all participants and specifically within the ASD group. These findings suggest that reduced inhibitory neurotransmission (reduced GABA) in higher-order motor areas, which modulate motor commands and integrate multiple sensory modalities, may underlie sensory hyper-responsiveness in ASD[24].

4.3 Genetic Contributions

Contactin genes CNTN5 and CNTN6 code for neuronal cell adhesion molecules that promote neurite outgrowth in sensory-motor neuronal pathways. Mutations of these genes have been reported in individuals with ASD, though little is known about their prevalence and clinical impact. Studies have identified CNTN5 and CNTN6 deleterious variants in individuals with ASD[25], with both deletions and private coding sequence variants of CNTN6 being significantly enriched in individuals with ASD compared to controls. Among the rare CNTN6 variants identified, some deletions were transmitted by fathers diagnosed with ASD, and certain mutations were either transmitted from mothers to sons with ASD or found de novo in children with ASD[25].

Clinical investigations of patients carrying CNTN5 or CNTN6 variants have shown that they were hypersensitive to sounds (a condition called hyperacusis) and displayed changes in wave latency within the auditory pathway. These results reinforce the hypothesis of abnormal neuronal connectivity in the pathophysiology of ASD and provide new insights into the genes that increase risk for abnormal sensory perception in ASD[25].

Activity dependent neuroprotective protein (ADNP) syndrome is one of the most common single-gene causes of autism spectrum disorder and intellectual disability. Research examining the sensory reactivity phenotype in children and adolescents with ADNP syndrome has employed comprehensive clinical evaluations including standardized observations, caregiver interviews, and questionnaires[26]. Sensory reactivity symptoms have been observed and reported in all participants with ADNP syndrome, revealing a syndrome-specific phenotype characterized by high levels of sensory seeking across tactile, auditory, and visual domains. Tactile hyporeactivity, characterized by pain insensitivity, is reported in the majority of these individuals. Importantly, sensory symptoms are identified across individuals regardless of age, sex, IQ, adaptive ability, genetic variant, and most significantly, ASD status, suggesting that sensory reactivity is a core feature of the syndrome rather than simply a manifestation of comorbid ASD[26].

5. Developmental Considerations and Individual Differences

5.1 Age-Related Changes in Sensory Processing

Atypicalities in tactile processing are reported in both autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), though it remains unknown if these precede and associate with traits of these disorders emerging in childhood. Research investigating behavioral and neural markers of tactile sensory processing in infants at elevated likelihood of ASD and/or ADHD compared to infants at typical likelihood has provided insights into the early development of these sensory differences[27]. Using behavioral and EEG responses to pairs of tactile stimuli, along with concurrent parental reports of tactile responsiveness, studies have found no effect of infants' likelihood status on behavioral markers of tactile sensory processing. However, increased ASD likelihood has been associated with reduced neural repetition suppression to tactile input. Reduced neural repetition suppression at 10 months significantly predicts ASD traits at 24 months across the entire sample but does not predict ADHD traits[27].

The nature of sensory processing differences across development has been examined in studies comparing children with and without autism across a wide age range (8-18 years). Comprehensive clinical batteries including multiple measures of sensory responsiveness, core features of autism, adaptive behavior, internalizing behaviors, cognitive ability, and language ability have been employed to characterize these differences[6]. Significant group differences have been consistently observed across all three patterns of sensory responsiveness (hyporesponsiveness, hyperresponsiveness, and sensory seeking). While some indices of core and related autism features are robustly associated with all three patterns of sensory responsiveness (e.g., restricted and repetitive behaviors), others are more strongly associated with discrete patterns (e.g., internalizing problem behaviors with hyperresponsiveness, language with sensory seeking). These findings extend prior work to show that differences in sensory responsiveness linked with core and related features of autism persist in older children and adolescents on the spectrum, suggesting developmental continuity in these relationships[6].

5.2 Individual Variability and Subtypes

Hierarchical cluster analysis of atypical sensory functioning in adults with ASD has identified distinct clusters based on sensory reactivity patterns. In one study, three clusters were identified: a low frequency group characterized by relatively low subscale scores, particularly for atypical sensory/motor reactivity; an intermediate group with significantly elevated hyperreactivity, sensory interests, and sensory/motor issues relative to the first group, but not hyporeactivity; and a high frequency subgroup with significantly elevated scores across all subscales and evident co-occurrence of hyper- and hyporeactivity[28]. Similar patterns have been observed in the general population, with clusters of low scorers and high scorers relative to other clusters. The identification of these distinct patterns of atypical sensory reactivity is important for targeting appropriate support interventions[28].

Research investigating clinical features not included in standard diagnostic criteria for Asperger Syndrome (AS) has compared individuals with AS to controls without AS. The prevalence of face recognition difficulties was found to be 46.6% in individuals with AS compared to 10.7% in the control group. Similarly, subjectively reported aberrant sensibilities were present in 91.4% of those with AS versus 46.6% of controls, sleeping disturbances in 48.3% versus 23.2%, and aberrant eating habits in 60.3% versus 14.3%. These findings suggest that aberrant processing of sensory information is a common feature in AS, and the impact of these clinical features that are not incorporated in standard diagnostic criteria may have been underestimated in our understanding of the condition[29].

The relationship between atypical sensory processing and adaptive functioning in individuals with and without autism has been examined using twin studies to explore genetic and environmental influences. In a clinically enriched twin sample, researchers investigated associations between the quadrants of the Adult/Adolescent Sensory Profile (low registration, sensory sensitivity, sensation seeking, and sensation avoiding) and adaptive functioning[30]. Sensory sensitivity and sensation avoiding were associated with reduced adaptive functioning across individuals but not within twin pairs. An interaction effect was found between sensation seeking and ASD diagnosis, showing a negative association between sensation seeking and adaptive functioning only in individuals diagnosed with ASD. These results suggest that atypical sensory processing is associated with reduced adaptive functioning and that familial factors influence this link. Additionally, sensation seeking behaviors might specifically interfere with adaptive functioning in individuals with ASD[30].

6. Implications for Intervention and Future Directions

6.1 Translational Applications and Intervention Approaches

Research examining the relationship between sleep concerns and sensory processing differences in autistic individuals has found that investigators frequently report multiple sleep concerns such as bedtime resistance, sleep anxiety, delayed sleep onset, night awakening, and short sleep duration in this population. Identified sensory concerns focus on reactivity, with both hyper- and hypo-reactivity as well as sensory seeking observed across sensory domains. The co-existence of sleep concerns and sensory integration/processing differences is frequently reported, suggesting a potential relationship between these domains[4]. Few intervention studies have shown a clear sensory focus; those that have emphasized pressure, movement, touch, and individual sensory preferences/needs. Programs such as swimming and massage have shown promising results, though none of the studies were of high quality. The relationship between poor sleep and sensory integration/processing differences appears complex and multi-faceted, requiring additional research with greater rigor and purposeful use of sensation and sensorimotor supports as components of intervention[4].

Dr. A. Jean Ayres was the first occupational therapist to conceptualize Sensory Integration (SI) theories and therapies to address sensory deficits in autism. Her work, which was based on neurological knowledge from the 1970s, has been revisited in light of advancements in neuroimaging techniques that provide better understanding of the brain areas underlying sensory processing deficits in ASD. Current research explores Ayres' postulates (e.g., registration, modulation, motivation) through the lens of neuroimaging literature by reviewing the neural underpinnings of sensory processing and integration in ASD[31]. Many aspects of Ayres' hypotheses about the nature of sensory processing disorder have been found to be highly consistent with current literature on sensory processing in children with ASD, though some discrepancies exist across various methodological techniques and ASD developmental trajectories. With additional characterization, neurophysiological profiles of sensory processing in ASD may serve as valuable biomarkers for diagnosis and monitoring of therapeutic interventions such as SI therapy[31].

Innovative approaches to supporting children with autism in managing sensory experiences include the development of socially assistive robot companions that utilize tactile sensing. Based on literature review and interviews with experienced autism specialists, researchers have identified the importance of understanding touch-seeking and touch-avoiding behavior in autistic children, their individual differences and customization needs, and the potential roles of touch-perceiving robots in facilitating positive interactions[32]. Requirements for such technology include attention to robustness and maintainability, sensing range, feel, gesture identification, spatial and temporal attributes, and adaptation capabilities. These technological innovations offer promising avenues for future intervention approaches that address the sensory needs of children with autism in a personalized manner[32].

6.2 Methodological Advances and Future Research Directions

Atypical sensory processing in autism spectrum disorders frequently cascades into behavioral alterations such as isolation, aggression, indifference, anxious/depressed states, or attention problems. Predictive machine learning models offer refined statistical explorations of the associations between sensory processing abilities and behavioral outcomes. Using parent-report measures such as the Sensory Profile 2 (SP2) and the Child Behavior Checklist (CBCL), researchers have developed supervised machine learning regression models to predict behavioral outcomes based on sensory processing scores[33]. The most reliable predictions have been found for total behavior problems (using items in the SP2 touch scale as inputs), anxiety/depression (using avoiding quadrant scores), social problems (using registration scores), and externalizing scales, revealing important relationships between sensory processing and behavioral outcomes. These machine learning approaches highlight the utility of advanced statistical models in studying the predictive value of sensory processing impairments on specific behavioral alterations in ASD[33].

A notable characteristic of ASD is the co-occurring deficits in low-level sensory processing and high-order social interaction. While evidence suggests detrimental cascading effects of sensory anomalies on higher-order cognitive functions in ASD, the exact pathological mechanism underlying their atypical functional interaction across the cortical hierarchy has not been systematically investigated. Research addressing this gap has assessed the functional organization of sensory and motor areas in ASD and their relationship with subcortical and high-order transmodal systems using advanced techniques such as connectopic mapping[34]. Findings have revealed topological anomalies in motor and visual areas in individuals with ASD, with patterns in motor areas showing associations with the symptom severity of restricted and repetitive behaviors. Diverging patterns of ASD-related connectivity abnormalities have been observed, including decreased functional connectivity within sensory/motor areas but increased connectivity between sensory and subcortical structures. The proportion of decreased connectivity tends to increase along the cortical hierarchy, suggesting more dysconnectivity in higher-order functional networks. Importantly, the association between low-level sensory/motor connectivity and clinical symptoms in ASD is mediated by high-order transmodal systems, suggesting pathogenic functional interactions along the cortical hierarchy[34].

The relationship between caregiver-reported sensory processing abnormalities and physiological measures of sensory responsiveness has been investigated by examining acoustic startle response (ASR) measures in children with autism spectrum disorders and typical development. Studies analyzing mean ASR magnitudes in response to stimuli of varying intensities (65-105 dB) and average peak startle latency have provided insights into the physiological correlates of sensory behaviors[35]. Low-threshold scores on the Sensory Profile auditory section have been found to relate to ASR magnitudes at moderate intensities (75 and 85 dB) but not to lower intensities (65 dB). Peak startle latency and ASR magnitudes at low-stimuli intensities have shown significant relationships with low-threshold quadrants (sensory sensitivity and sensation avoiding) and the high-threshold quadrant of sensation seeking. These findings suggest that physiological assessment provides valuable information regarding auditory over-responsiveness to less-intense stimuli and its relationship to caregiver-observed sensory processing abnormalities in everyday situations[35].

7. Conclusion

This review has synthesized the current literature on the characterization and measurement of sensory seeking and avoidance behaviors in autism spectrum disorder. The evidence clearly indicates that sensory processing differences are a cardinal feature of ASD, with distinct patterns of hyper-responsivity, hypo-responsivity, and sensory seeking behaviors observed across sensory modalities. These sensory patterns demonstrate relationships with core autism features, adaptive functioning, and emotional well-being, highlighting their central importance in understanding the autism phenotype.

Measurement approaches have evolved from parent/caregiver reports to include direct observational assessments and sophisticated neurophysiological techniques, though psychometric limitations in current assessment tools remain a challenge. Neuroimaging studies have revealed structural and functional brain differences associated with atypical sensory processing in ASD, providing insights into the neural mechanisms underlying these behaviors. Genetic studies have identified specific gene variants associated with sensory processing differences, further elucidating the biological basis of these features.

The field has progressed from simply documenting sensory abnormalities to understanding their developmental trajectory, individual variability, and relationship to other domains of functioning. This increased understanding has informed intervention approaches, though more high-quality research is needed to establish effective treatments targeting sensory differences. Advanced methodologies, including machine learning and connectomic mapping, offer promising avenues for future research that may lead to more personalized approaches to assessment and intervention.

Future research should focus on developing psychometrically sound assessment tools, integrating behavioral and neurophysiological measurement approaches, and conducting longitudinal studies to better understand the developmental course of sensory processing differences in ASD. Additionally, more rigorous intervention studies are needed to establish effective treatments for sensory symptoms that may, in turn, positively impact broader areas of functioning for individuals with autism.