Spatial and Temporal Modulation of Visual-Tactile Crossmodal Interactions in Adults with Autism

Background:  

The sensory issues that affect many people with autism spectrum conditions (ASC) may be explained by abnormalities in how information is combined from the separate sensory modalities when creating a unified perception of the environment (Iarroci and McDonald, 2006). Typically, the processing of crossmodal information is spatially and temporally bound: information is more likely to interact if it occurs in the same place and at the same time (Stein and Standford, 2008). However, children with autism have previously been shown to exhibit audio-visual interactions over a range of time double the length of neurotypical (NT) children (Foss-Feig et al,2010; Kwakye et al 2011). 

Objectives:  

The aims of the current study were to:

1. Provide novel insight into visual-tactile interactions in ASC using low-level stimuli, free from social and semantic information.
2. Explore the spatial modulation of crossmodal interactions in ASC.
3. Replicate previous findings of crossmodal interactions over extended temporal asynchronies in ASC.

It was expected that this would provide a more detailed picture of crossmodal interactions in ASC.

Methods:  

Participants were 13 adults with ASC and 13 NT controls matched for age, IQ, handedness and gender. Participants completed an adapted version of the crossmodal congruency task (Spence, 2001). The task involves making speeded discriminations between single or double tactile pulses while presented with distracting visual flashes. Distractors were either congruent (e.g. one pulse- one flash), or incongruent (one pulse- two flashes). A baseline condition was also included in which only tactile information was presented.  Paired sample t-tests were used to compare error rates between the baseline condition and those including visual distractors. The spatial and temporal modulation of crossmodal effects were investigated in two separate experiments. In the spatial version of the task, distractors were presented 0cm, 21cm and 42cm from the hand in ipsilateral positions, and 42cm from the hand in a contralateral position. In the temporal version of the task, distractors were presented near simultaneously (30ms before) or 100ms, 200ms and 400ms after the tactile pulse. 

Results:  

For the spatial version of the task, NT participants only produced an error rate significantly larger than the baseline condition for incongruent distractors presented 0cm from the hand.  ASC participants exhibited this effect in both the 0cm and 21cm conditions.

Temporal version of the task: After correcting for pairwise comparisons, NT participants did not produce a significant effect at any SOA. Contrary to previous research, participants with ASC only exhibited crossmodal effects in the near simultaneous -30ms condition.  

Conclusions:

This is the first work to suggest that crossmodal interactions in ASC occur over greater distances in space than in NT controls.  However, the finding of the typical pattern of temporal modulation in adults with ASC contradicts previous findings in the audio-visual modality in children.  This suggests that there may be a delay in the development of the temporal modulation of crossmodal information processing in ASC.