Multisensory interactions modulate response of V3A for depth-motion processing
Akitoshi Ogawa, Emiliano Macaluso

Date: 2012-06-20 11:15 AM – 12:45 PM
Last modified: 2012-04-24

Abstract


For the perception of an object moving in depth, stereoscopic signals provide us with an important spatial cue. However, other modalities can also contribute to the motion perception. For example, auditory signals generated by the moving object change according to the approaching/receding direction. Specifically, sound intensity increases/decreases, while sound frequency shifts to higher/lower frequencies (i.e. the Doppler effect). The integration of these unisensory cues may enhance the perception of motion direction by modulating activity within specific brain areas. This fMRI study assessed the interaction between auditory and visual depth-cues on the response of V3A. The task was to discriminate the direction of an auditory target that moved in depth without any azimuth shift. Orthogonally to the volume change, the sound frequency could either rise or fall, yielding to Doppler “matched vs. unmatched” conditions. On two-thirds of the trials, the sound was synchronously coupled with a task-irrelevant visual stimulus moving either forward or backward (i.e. a ball expanding or contracting), thus leading to audio-visual “congruent vs. incongruent” signals of motion. These conditions were presented either in “2D or 3D” viewing. The behavioral data showed the best motion-direction discrimination performance was obtained in Doppler matched and audio-visual congruent condition. In V3A, we found the expected responses to stereoscopic cues and, most importantly, maximal activation was found for 3D trials comprising matched Doppler and congruent audio-visual signals. These results demonstrate that the perception of objects moving in depth entails the integration of multiple unisensory cues. These support that the integration can affect activity in brain regions traditionally considered as unimodal.

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