Susceptibility to Relative Saliency in Processing Hierarchical Figures Among Adolescents with ASD

Background: One of the consistent characteristics of individuals with Autism spectrum disorders (ASD) is hypersensitivity to small details in their surroundings. It has been previously claimed that while typically developing (TD) individuals exhibit a perceptual bias towards processing of the 'whole' over the small details, individuals with ASD favor the processing of small/local elements. However, findings from studies that used hierarchical figures (HF) with individuals with ASD are inconsistent. One possible reason for such discrepancies is the differences between the stimuli’s physical characteristics that were employed in previous studies which can affect the relative saliency of the global and local levels.

Objectives: The present study aimed at examining the effects of relative saliency of the global/local aspects of HF (by manipulating the size of the local elements of compound figure, with fixed distance between the elements) on local and global perception among adolescents with ASD compared to TD adolescents. We hypothesized that the perceptual bias of participants with ASD will be influenced by relative saliency.

Methods: Participants were 51 adolescents aged 15-20. Twenty-six were high functioning individuals with ASD (22 males, 3 females) and 25 (21 males, 4 females) were TD participants. To assess global and local perception we used hierarchical numerals (i.e., large numeral comprised of small numerals). We manipulated the saliency of each level relative to the other level by changing the visual angle of the stimuli. Three sizes were employed: small – the global level was more salient than the local level; medium – both levels were equally salient; large –the local level was more salient than the global level.

Results: Participants from both groups were influenced by the saliency manipulation as was evidenced by a triple interaction between Level, Size and Congruency. In addition, triple interaction between Group, Level and Size indicated that TD participants showed global precedence with small figures (where global level was more salient than local level), whereas participants with ASD exhibited global precedence with small figures and local precedence with large figures (when local level was more salient than global level). Importantly, with medium figures no Level effects were obtained. Also, an interaction between Group and Congruency revealed that ASD participants exhibited larger congruency effects compared to TD participants.

Conclusions: Participants with ASD were more sensitive to saliency manipulations compared to TD participants. Furthermore, while global bias was demonstrated by TD adolescents, no level preference was recorded among adolescents with ASD. Rather, ASD participants were equally biased towards salient information regardless of level of processing. Moreover, they exhibited increased difficulty in filtering irrelevant information compared to TD adolescents. Taken together, our results do not corroborate the notion of superior local processing among individuals with ASD but instead consistent with the idea that participants with ASD do not develop efficient perceptual organization mechanisms, which may further impair top-down suppression of irrelevant information. The results of the present study may have clinical implications such as developing computerized perceptual and cognitive training programs for improving visual perceptual organization and better cognitive control among individuals with ASD.