There is a growing body of literature describing unusual sensory processing patterns in individuals with Autism Spectrum Disorder. A proliferation of writing from individuals with ASD such as Temple Grandin, Donna Williams and others have noted sensory processing impairments as one of the key elements that interferes with their ability to carry out daily tasks and engage in successful social interactions. The incidence of sensory processing impairments in individuals diagnosed with ASD reported in the literature range from 42% to 95% (Baranek, 2002,; Kientz & Dunn, 1997; Le Couteur et al., 1989; Volkmar, Cohen & Paul, 1986; Watling et al., 2001, Tomchek and Dunn, 2007).
The “Sensory Integration” originated from Dr. Jean Ayres’s research in the mid 1960’s. In her book, Sensory Integration and the Child, Dr. Ayres noted that some children’s atypical behaviour, problems with learning and physical clumsiness stemmed from sensory-based deficits and began to develop what is now known as Ayres’ Sensory Integration Theory. However, there has been some confusion and controversy around the term ‘sensory integration’. Occupational Therapists most often refer to such dysfunction using the umbrella term of Sensory Processing Disorder (SPD).
There is accumulating research to support the presence of such deficits in ASD. Differences in auditory processing are one of the more commonly reported sensory processing impairments in children with ASD (Greenspan & Weider, 1997). Tomchek and Dunn (2007) reported that in a sample of 281 children ages 3-6 years, diagnosed with ASD, 95% demonstrated some degree of sensory processing dysfunction, and this was most notable in the areas of under-responsivity, auditory filtering and tactile sensitivities. In a follow-up study (Ben-Sasson et al, 2007), extreme sensory modulation behaviors in toddlers with autism spectrum disorders (ASD) were investigated. Parental report of sensory behaviors in 101 toddlers with ASD was compared to 100 toddlers who were typically developing matched on chronological age and 99 toddlers matched on mental age. Children with ASD were different from typically developing children in their high frequency of under-responsiveness and avoiding behaviours. The findings were interpreted as pointing to an early onset of an “extreme sensory profile in ASD.” Crane et al (2009) recently reported that up to 94% of adults continue to present with severe sensory difficulties in at least one domain of the Sensory Profile suggesting that sensory differences persist across the life span. In a meta-analysis (a form of systematic review) of 14 studies, Ben-Sasson et al (2009) reported a significant difference in the presence/frequency of sensory symptoms between ASD and typical groups, with the greatest difference in under-responsiveness, followed by over-responsiveness and sensation seeking.
Dysfunction of both sympathetic and parasympathetic systems have been observed in children who experience sensory processing difficulties and results from small studies measuring electrodermal responses (a measure of sympathetic nervous system activity) have also suggested that children with ASD are physiologically under-responsive to sensory input (Miller et al. 2001) However, one should keep in mind that behavioural ratings by parents demonstrated significant sensory over-responsivity in the tactile, taste, smell, visual and auditory domains. Possible genetic etiologies to sensory processing deficits have also started to be explored (Goldsmith et al 2006)
Identification of sensory processing difficulties is particularly important in the context of recent data suggesting a relationship between sensory difficulties and core symptoms, adaptive function and maladaptive behaviors. In a recent study (Hilton et al 2010), the relationship between sensory responsiveness and social severity in children with high functioning autism was examined. Significant relationships were found between the social responsiveness scale (SRS) scores and the six sensory profile sensory system (SPSS) scores, suggesting that the relationship between sensory responsiveness and other autism related traits is more important than previously recognized, and addressing sensory modulation issues in children with autism may be more critical than previously thought. Two very recent studies (Boyd et al 2010 and Gal et al 2010) examined the relationships of repetitive behaviors to social deficits and reported significant associations between the two domains, in particular over-responsiveness and stereotypy, possibly suggesting a shared neurobiological mechanisms for over-responsive sensory symptoms and repetitive behaviors, a fact that may have implications for both diagnosis as well as intervention. In addition, recent data by Lane et al 2010 presented a “clear predictive association” between sensory processing deficits and communication skills and maladaptive behavior, supporting the use of sensory based interventions in the treatment of communication and behavioral difficulties in this population. Lastly, Ashburner et al (2008) documented that a pattern of sensory difficulties that included auditory filtering deficits, sensory under-responsiveness, and sensory seeking behaviors was associated with academic underachievement. Specifically, children with ASD who found it difficult to process verbal instructions in a noisy environment or were focused on sensory-seeking behaviors, were more likely to underachieve academically, again highlighting the need for therapeutic intervention for sensory difficulties.
Occupational Therapists with training in Ayres’ Sensory Integration Theory aim to understand each child’s sensory needs in different environments and the function of sensory seeking behaviors. Although sensory seeking behaviors often relate to sensory differences in children with autism, one should keep in mind that such behaviors also have the potential to result in extra attention by the child’s caregivers and therefore may be used by the child as a communication tool or to seek such attention. For example, a child may bite his hand not as a way of seeking sensation but as a way of protesting a change in his routine. This issue highlights the need for multidisciplinary approach to sensory issues and collaborations between occupational therapists and behavioral consultants can be particularly fruitful.
Once sensory-based maladaptive behaviors are identified, one is confronted with the need to make appropriate therapeutic recommendations. In a review of sensory interventions, Baranek (2002) identified pilot studies of sensory integration intervention with children with autism and reported that although sensory integration interventions were associated with improvements in social interaction, purposeful play, and decreased sensitivities, the studies included small sample size and lacked control groups, so that the evidence to support such intervention still remains weak and requires further research. Sensory-based interventions, such as those that provide therapeutic touch, have been proposed to decrease maladaptive behaviors, hyperactivity, self-stimulation and stereotypic movements, and possibly improve attention and focus. Two randomized controlled trials have examined the effects of massage on children with ASD. Field et al. (1997) compared a group of boys with ASD who received massage for 2 days a week for 4 weeks to boys with ASD who played a game for the same amount of time. The children who received massage showed decreased aversion to touch, off-task behavior, and stereotypic behavior. However, the study lacked standardized measures. Escalona et al. (2001) compared children with ASD who received massage by their parents every night for a month to a control group whose parents read to them every night. The children who received massage demonstrated less over-responsivity, impulsivity and stereotypy, and improved on-task behaviors. Therapy approaches that use the auditory system (e.g., therapeutic listening and auditory integration training-AIT) to improve organization of the central nervous system have recently become more controversial. In a Cochrane systematic review of AIT, Sinha et al. (2004) reported that the evidence for AIT effectiveness was weak and inconclusive.
A “sensory diet” is one of the most commonly used tools by Occupational Therapists to help children maintain the just-right state needed for optimal function. It is called a “sensory diet” because, like a nutritional diet, the child may need main “sensory meals” as well “sensory snacks” throughout the day to maintain a just right state. The sensory diet uses sensory-based activities to modulate arousal and alertness levels that are carefully chosen by the occupational therapist to best meet each child’s sensory needs both at home and school. While there are few studies that focus specifically on sensory diets, there are several studies that evaluate various components that may be included in a sensory diet, but controlled research is still lacking.
Most scholars recommend the use of sensory-based interventions as one component of a comprehensive intervention that uses a variety of methods to promote performance (Baranek, 2002; Greenspan & Wieder, 1997). Although some positive benefits from sensory-based treatment have been documented, it is still not clear how these interventions affect the child’s overall functional and educational outcomes. Future research studies need to include measurement of both effects on physiological markers and core symptoms and global functioning, to elucidate the mechanisms by which sensory-based interventions may influence outcomes in children with ASD.
In summary, sensory differences in children with ASD have now been well documented. However, sensory deficits do remain an under-investigated symptom domain in ASD. We are in urgent need for research both to understand the nature of sensory deficits in ASD and to provide evidence-based interventions.
Moira Pena, OT, is an Instructor at the Holland Bloorview Kids Rehabilitation Hospital, which is affiliated with the University of Toronto. You may contact Moira by phone at (416) 425-6220 ext 3625 or by email – mpena@hollandbloorview.ca
