Selective Attention and Perceptual Load in Autism Spectrum Disorders

Background: When we focus our attention on an aspect of the environment it is important to be able to ignore potentially interfering distractors (selective attention). Ignoring distractors though is not always something that can be done at will, and it does seem that under some circumstances we process distractor information whether we like it or not (e.g. we hear our own name mentioned in a conversation we are not focusing on at a cocktail party). Recent research by Lavie (1995) has shown that the degree to which distractors are processed depends on how much of our finite attentional resource is allocated to the task we are focussing on (perceptual load theory).
Our previous research has examined the effect of perceptual load on selective attention within Autistic Spectrum Disorders (ASD). Previous studies suggest that individuals with ASD might find it difficult to ignore distractors (Burack et al 1994), although no studies have yet taken into account the perceptual load of the focus task. Our results showed that individuals with ASD continue to be affected by distractors at higher levels of perceptual load than typically developing controls. This suggests that there may be increased perceptual capacity in individuals with ASD
Objectives: Our previous studies use indirect measures (effect on reaction times) to draw conclusions regarding the extent of irrelevant distractor processing at differing levels of perceptual load. Such measures, however, cannot be used to infer whether the task-irrelevant stimuli are consciously perceived. This study aimed to investigate this by using a dual-task paradigm (Macdonald & Lavie, 2008) to examine how the increased distractibility within ASD relates to conscious perception and awareness.
Methods: Young adults with ASD and typically developing adults, matched for chronological age and non-verbal IQ, performed a dual-task paradigm where it was necessary to detect the presence of an expected critical stimulus that was presented offset from a central visual search task. The perceptual load of the central task was varied.
Results: Preliminary results suggest that individuals with ASD are able to consciously perceive the critical stimulus at higher levels of load than typically developing control individuals.
Conclusions: These findings reinforce the view that individuals with ASD have a greater perceptual capacity and imply that they can consciously perceive a larger number of visual stimuli at any given time.