Non-Spatial Auditory Information Does Not Improve Complex Visual Search for Persons with Autism and Asperger Syndrome : « Pip » but No « Pop »

Background: Searching for a visual target from among a spatially complex environment is facilitated when an auditory tone or « pip » is presented in synchrony with a visual change in the target's attribute (i.e., color change). This « pip and pop » effect (van de Burg et al., 2008) is argued to result from the integration between temporally synchronized changes in auditory (non-spatial auditory « pip ») and visual (target color change) events, resulting in a salient multi-modal feature that typically draws attention to the target. This paradigm is well-suited to test the hypothesis that persons with autism integrate input from multiple sensory modalities less efficiently (Iarocci & McDonald, 2006). Such hypotheses are congruent with findings of atypical pattern of neural connectivity between specific brain areas that are sensitive to information from different sensory modalities in autism.

Objectives: To assess audio-visual integration abilities for non-social information in person with autism and Asperger syndrome by assessing whether they benefit from the synchronous presentation of auditory and visual events (manifest a « pip and pop » effect) during a demanding visual search task.

Methods: Twelve high-functioning autistic, 10 non-autistic, and 11 participants with Asperger syndrome matched for chronological age, full-scale IQ, gender and handedness were asked to complete a difficult visual search task. Participants searched for a horizontally- or vertically-oriented line segment (target) from among 24, 36 or 48 obliquely-oriented distracters (van de Burg et al., 2008; Exp.1). At random intervals, a random number of distracters changed color, between red and green. The target's color also changed, never coinciding with the distracter color change - it was the only changing item. In the tone-absent condition, participants were instructed to search for either the vertical or the horizontal target and to respond as quickly and accurately as possible to its orientation. In the tone-present condition, the task was the same except that the visual (color) target change was simultaneously accompanied by a short auditory « pip ».

Results: ANOVAs revealed that visual search times for the control group decreased significantly for the tone-present compared to the tone-absent condition (p < 0.05), reflecting the beneficial result of audio-visual integration. However, the performance of participants in both the autism and Asperger groups was unaffected by the presence of the auditory tone (p > 0.05), suggesting that target saliency was not increased by integrative audio-visual processes. Between-group differences were not evidenced for the tone-absent visual search conditions (p > 0.05).

Conclusions: The present findings suggest than persons with autism or Asperger syndrome do not necessarily benefit from typically facilitatory multimodal integration during a demanding visual search task. The absence of the « pip and pop » effect in these groups is suggestive of atypical/impaired integration of low-level perceptual cues originating from different sensory modalities. The lack of superior autistic performance on the tone-absent conditions may be related to the complexity (dynamic and spatial changes) of attributes defining the target and distracter search items. The results are discussed within the context of perceptual and cognitive theories in ASD.