Separating multisensory integration from unspecific warning effects in saccadic reaction time

Adele Diederich, School of Humanities and Social Sciences, International University Bremen

Abstract
Saccadic reaction time (SRT) to a visual target tends to be faster when auditory or tactile non-targets occur in close temporal or spatial proximity even when subjects are instructed to ignore the non-targets. When the non-target appears before the target, it may act as a general alerting or warning cue rather than as a stimulus causing crossmodal integration. The time-window-of-integration (TWIN) model for SRT (Colonius & Diederich, 2004, J Cog Neurosci) distinguishes an early, afferent stage of peripheral parallel processing followed by a compound stage of converging subprocesses. The model is extended here to permit the separation of a - spatially unspecific - warning effect from true multisensory integration. TWIN was tested in a focused attention task with visual target stimuli (LED) and auditory (white noise burst) and tactile (vibration applied to palm) stimuli as non-targets presented ipsi- or contralateral to the target at 23 different stimulus-onset-asynchronies (SOA) over a range of 700 ms. A quantitative fit of the model supports the notion that only a combination of multisensory integration and unspecific warning effects can account for the entire time course of the crossmodal mean SRT responses over SOA values in both ipsi-and contralateral configurations.

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