Purpose: Temporal integration of stimuli of different sensory modalities plays a crucial role in multisensory processing. Previous studies using temporal-order judgment determining the point of subjective simultaneity (PSS) with multisensory cues yielded conflicting results about modality-specific delays. While it is known that the relative stimulus intensities of stimuli from different sensory modalities affect their perceived temporal order, we have hypothesized that some of these discrepancies might be explained by a previously overlooked confounding factor, namely the duration of the multisensory stimulus.
Methods: We have studied the influence of both factors on the PSS in a spatial-audiovisual temporal-order task using the method of constant stimuli and participants were asked which onset of an event appeared first ("left" or "right").
Results: In addition to confirming previous results on the role of stimulus intensity, we report that varying the temporal duration of an AV stimulus pair stimulus also affected the perceived temporal order of the auditory and visual stimulus components. While individual PSS values varied from negative to positive values across participants, we found a systematic shift of PSS values towards an attractor value with increasing stimulus duration.
Conclusion: This effect was manifest in a shift of a subject's individual PSS value with increasing stimulus duration towards an attractor value that was valid for the entire population. This dependence is indicative of a mechanism which stabilizes perceived stimulus asynchronies and might serve as a mechanism which exploits stimulus duration to compensate individually present attentional imbalances between sensory modalities. Thus, increasing stimulus duration, at least in the range tested, might facilitate crossmodal binding processes. Moreover, we provide evidence that the duration effect helps resolving conflicting results in previous studies on audiovisual temporal-order judgment.