Multisensory integration of velocity information

Salvador Soto-Faraco

Abstract
Information about the motion of objects is extracted by multiple sensory modalities and integrated during perception. Several studies have demonstrated strong multisensory interactions in motion direction, but much less is known about other motion parameters such as speed. Here, we used a 2IFC psychophysical procedure to find the velocity at which a moving sound combined with a moving visual grating had to be presented in order to be subjectively equivalent to a standard sound moving at 30º/sec. Information about visual speed of motion is derived from the integration of Spatial and Temporal Frequency (SF and TF) characteristics, two features that are coded by separate populations of neurons up to V1 and MT/V5. In this study, we assessed the effects of Temporal and Spatial Frequency variations independently. We found a strong influence of visual speed on the perceived speed of sounds. Yet, none of the separable components of visual speed (Temporal or Spatial frequency) exerted a considerable effect individually. Therefore, it seems that the integration of auditory and visual information about motion occurs only after the unimodal visual integrative processes leading to speed perception have been completed.

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