Abstract
Sensory, in particular visual processing is recognized as often perturbed in individuals with Autism Spectrum Disorder (ASD). However, in terms of the literature pertaining to visual processing, individuals in the normal intelligence range (IQ = 90–110) and above, are more frequently represented in study samples than individuals who score below normal in the borderline intellectual disability (ID) (IQ = 71–85) to ID (IQ < 70) ranges. This raises concerns as to whether or not current research is generalizable to a disorder that is often co-morbid with ID. Thus, the aim of this review is to better understand to what extent the current ASD visual processing literature is representative of the entire ASD population as either diagnosed or recognized under DSM-5. Our recalculation of ASD prevalence figures, using the criteria of DSM-5, indicates approximately 40% of the ASD population are likely to be ID although searching of the visual processing literature in ASD up to July 2016 showed that only 20% of papers included the ASD with-ID population. In the published literature, the mean IQ sampled was found to be 104, with about 80% of studies sampling from the 96–115 of the IQ range, highlighting the marked under-representation of the ID and borderline ID sections of the ASD population. We conclude that current understanding of visual processing and perception in ASD is not based on the mean IQ profile of the DSM-5 defined ASD population that now appears to lie within the borderline ID to ID range. Give the importance of the role of vision for the social and cognitive processing in ASD, we recommend accurately representing ASD via greater inclusion of individuals with IQ below 80, in future ASD research.
Highlights
We conclude that current understanding of visual processing and perception in Autism Spectrum Disorder (ASD) is not based on the mean IQ profile of the DSM-5 defined ASD population that appears to lie within the borderline intellectual disability (ID) to ID range
With the release of the DSM-5 in 2013, previously discrete diagnostic categories such as Asperger’s Disorder and Pervasive Developmental Disorder (PDD)—Not Otherwise Specified were collapsed into a single diagnostic category termed Autism Spectrum Disorder (ASD)
A feature in need of closer research scrutiny is the contribution of intelligence to the literature relating to social, cognitive and sensory processing of individuals with ASD as currently there is an over-representation of normal (IQ = 90–110) to above (IQ >111) intelligence in samples chosen for most studies
Summary
Pre DSM-5, autism was clinically considered a disorder predominantly characterized by a comorbid diagnosis of ID (Edelson, 2006). Other studies (Chakrabarti and Fombonne, 2001; Icasiano et al, 2004; Baird et al, 2006; Charman et al, 2011) that included DSM-IV diagnosed autism, and PDD and Asperger Syndrome populations that are recognized by the DSM-5 as ASD report ASD with-ID prevalence figures between 25 and 46%. This left only 14 ASD visual processing studies present in the with-ID search results compared with 79 studies in without-ID search results These two searches give a gross overview of the sampling trends that are present in this literature and indicate that only 20% of visual research relating to individuals with DSM-5 defined ASD, include individuals with a comorbid diagnoses of ID. Wechsler’s child and adult intelligence scales (WAIS, WISC) (Wechsler, 2003, 2014) was chosen for this analysis for scale consistency and because of the frequency with which Wechsler’s measure has TABLE 1 | Summary of two systematic literature searches for ASD with-ID (Search 1) and ASD without-ID (Search 2) in the ASD visual processing literature
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