The Effect of Visual Perceptual Load on Auditory Awareness in Autism Spectrum Disorder

Background: This study investigated cross-modal selective attention in individuals with Autism Spectrum Disorders (ASD) by applying Lavie’s Load theory of attention and cognitive control (Lavie, 2005). Load theory asserts that the extent to which task-irrelevant stimuli are processed depends on the level of perceptual load of the task (e.g. subtle (high load) vs. gross (low load) line discrimination). Previous results demonstrated that when visual perceptual load increases, adults with ASD continue to process task-irrelevant visual stimuli whereas control participants do not. These findings may reflect an increased perceptual capacity in ASD (Remington et al., 2009, 2012; Swettenham et al, in press). Perceptual load has also recently been identified as a critical factor in cross-modal selective attention in neurotypical adults using an “inattentional deafness” paradigm (Macdonald & Lavie, 2011). Awareness rates for an unexpected and task-irrelevant auditory stimulus on a critical trial were significantly reduced under high visual load compared to low visual load.

Objectives: The present study examined, for the first time, the effect of visual perceptual load on awareness of an auditory stimulus in children with ASD.

Methods: 26 children diagnosed with ASD (Mean age 10y 4m) and 44 typically developing children (TD) (Mean age 10y 2m), matched for chronological age and non-verbal IQ (Raven’s), took part in the study. All participants were checked for normal or corrected-to-normal vision and normal hearing. The task was adapted from Macdonald & Lavie (2011) and involved participants judging which line of a briefly presented cross (110ms) was longest (horizontal vs. vertical). Participants were randomly assigned to either the high load (subtle line discrimination) or low load condition (gross discrimination). On the critical 7^th trial, an unexpected, task-irrelevant auditory stimulus was played concurrently with the visual stimulus. Participants were then asked whether they had noticed anything else on that trial. On a subsequent control trial, participants were told to ignore the cross stimulus. Only those participants who successfully identified the auditory stimulus on the control trial and made correct line judgments on at least 5 out of 7 trials (including the critical trial), were included in further analyses.

Results: As predicted by load theory, TD children were more likely to notice the auditory stimulus in the low visual load vs. high visual load task, x² (1) = 7.747, p = .005. This was not the case however for children with ASD, who demonstrated similar detection rates across perceptual load conditions, x² (1) = 0.016, p = .899, yet reported greater awareness than controls in the high perceptual load condition, x²(1) = 8.474, p = .004.

Conclusions: Awareness rates for an auditory stimulus were reduced for TD controls under high visual perceptual load, but remained unaffected in children with ASD. These findings extend the hypothesis that individuals with ASD have an increased perceptual capacity to contexts involving cross modal selective attention.