NORMAL LOW-LEVEL AUDIOVISUAL INTERACTION IN ADULTS WITH AUTISM: THE DOUBLE FLASH ILLUSION

Background: Some clinical interventions for people with autism target sensory processing, under the assumption that low-level sensory processing forms the foundation for higher levels required for social interaction and cognition (Ayres, 2005). Integration of vision and hearing is particularly important for social-communicative abilities, and thus a good candidate for investigation in autism. Objectives: To determine whether low-level auditory and visual stimuli are integrated similarly in adults with versus without autism. Methods: Low-level audiovisual integration was characterized in a group of eight high-functioning adults with autism and eight controls (matched for age and IQ) using a paradigm (Shams et al., 2002) in which multiple beeps presented concurrently with a single flash evoke the illusory percept of multiple flashes. In a second experiment, the temporal window of this cross-modal influence was explored by incrementally increasing the time separating the onsets of the auditory stimuli. Results: The autism group reported perceiving illusory flashes similarly to controls at short (< 80 msec) temporal windows. At longer temporal windows (> 80 msec), the illusory effect disappeared in the control group but persisted in the autism group (t= 2.68; p=0.03). Persistent illusory perception at these longer intervals was significantly correlated with autism severity on the social domain of the ADI-R (r = -0.764 (p =.027), and strongly negatively correlated with IQ in both groups (autism: r = -0.574, p =0.137; control: r = -.842, p =0.009). Conclusions: These results suggest that simple audiovisual integration is intact in autism. The group difference at longer auditory separations is likely to reflect differences in cognitive strategy or response bias rather than perception, although further experiments must be done to rule out perceptual differences completely. Our results are consistent with previous unimodal studies demonstrating normal or enhanced perception for simple but not complex stimuli (Bertone et al., 2005).