The Effect of Visual Perceptual Load on Auditory Detection Sensitivity in ASD

Background: According to the increased perceptual capacity account (Remington et al. 2009), individuals with ASD have an enhanced capacity for processing perceptual information. When the perceptual load of a task is high, capacity is exhausted in neurotypical controls and task-irrelevant stimuli are not processed. In contrast, individuals with ASD have spare capacity automatically processing task-irrelevant stimuli under conditions of high perceptual load.  This has been demonstrated in the visual domain with studies measuring response competition effects (Remington et al, 2009), detection sensitivity (Remington, Swettenham & Lavie, 2012) and rates of inattentional blindness (Swettenham et al. 2014). Recently, we have also demonstrated that increased perceptual capacity in ASD operates across sensory modalities. Increasing the perceptual load of a visual search task reduces awareness of an unexpected auditory stimulus to a lesser extent in children with ASD than in typically developing (TD) children (Tillmann et al. 2015).  

Objectives: The current study investigated whether increasing the perceptual load in a visual search task has less of an effect on detection sensitivity for an expected (present on 50% of trials) auditory stimulus in ASD compared to TD individuals.  Our previous study used an inattentional deafness paradigm, which involves awareness of a single, unexpectedly presented auditory stimulus, and a manipulation of perceptual load by altering the subtlety of a line discrimination task (Tillmann et al. 2015).  Here we used a different measure of perceptual load (increasing visual search set-size) and asked participants to indicate the presence/absence of a tone on each trial, allowing us to measure detection sensitivity.  

Methods: 20 TD adolescents and 19 adolescents with ASD matched for chronological age and non-verbal ability performed a visual search task (responding to target letter X or N in a search array) while simultaneously detecting presence/absence of an auditory tone embedded in noise (see Figure 1). Perceptual load was manipulated by increasing the number of additional visual stimuli in the search display (i.e. increasing the search set size). The intensity level of the auditory stimulus was just above each individual’s pre-established auditory perceptual threshold, thus controlling for individual differences in perceptual sensitivity.  

Results: When the perceptual load of the visual task was low (one or two items in the central search array), detection sensitivity for the auditory stimulus did not differ between groups. However, when the perceptual load was higher (four items in the search array) auditory detection sensitivity was significantly reduced in TD individuals compared to individuals with ASD, who maintained a high level of detection. At even higher levels of perceptual load, there was no difference in detection sensitivity between groups (see Figure 2).   

Conclusions: The finding that auditory detection sensitivity in the ASD group was less affected by increasing the perceptual load of the visual task provides further support for the hypothesis that individuals with ASD have an increased perceptual capacity. We have also demonstrated that increased capacity affects processing across modalities, and that these effects cannot be explained by differences in response criteria (e.g. always responding “stimulus present”).