Spatial and Temporal Effects on Visual Filtering in Autism Spectrum Disorder

Background:  

The ability to filter irrelevant visual stimuli in order to attend to meaningful sources of information is crucial to all aspects of adaptive functioning, as real-life environments involve innumerable and consistently moving and changing stimuli. Among persons with autism spectrum disorder (ASD), visual filtering efficiency has been portrayed in two apparently conflicting ways – increased distractibility (e.g., Burack, 1994) and overfocused attention (Mann & Walker, 2003). According to the increased distractibility hypothesis, persons with ASD are particularly susceptible to distraction by stimuli that are so visually peripheral that they do not affect the processing of typically developing persons, whereas according to the overfocused hypothesis persons with ASD process information within a restricted range regardless of its importance.  

Objectives:  

The aim of the study was to investigate the effect of temporal and distance manipulations of distracters on target identification among children with ASD. The timing of target and flanker onsets was manipulated to determine whether asynchronous onset of the flankers and target facilitated or disrupted target identification, while the proximity of the flankers to the target was varied to assess the participants’ ability to narrow and broaden the focus of attention.

Methods:  

The participants included school-aged children with ASD (n= 13) and TD children (n= 13) matched on mental age (mean MA = 8.6 years; F(1,24) = .008, p> .05). A modified version of the flanker paradigm (Eriksen & Eriksen, 1974) was used, in which participants responded to a ‘target’ stimulus presented at the centre of a computer screen with distracting ‘flanker’ stimuli presented to the left and right along the same horizontal plane that varied in shape (similar or dissimilar to target), distance from targets (1.16°, 3.46°, or 6.89° of visual angle), and in temporal onset relative to target onset (simultaneous, or 150ms, 300ms, or 450ms after target). 

Results:  

Both groups of children displayed faster RTs when flankers were similar to targets than when they were dissimilar. The children with ASD also displayed faster RTs when the flankers and target were presented simultaneously than with onset asynchrony of 150ms (p = .002), 300ms (p= .000), and 450ms (p= .001). Unlike the TD children who had faster RTs when flankers were farther from the targets than when flankers were at an intermediate (p=.000) or closer (p= .000) distances, the participants with ASD showed similar performance regardless of the distance of the distracters from the target. 

Conclusions:  

The findings related to both spatial and temporal distracter manipulations support the notion of increased distractibility among persons with ASD, but are inconsistent with the overfocused hypothesis.