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Accueil du site > Séminaires LNC > séminaires à venir (upcoming seminars)

Manuel Vidal (Institut de Neurosciences de la Timone)

When did I hear that flash ? Timing audiovisual events : from perception to (re)action

When processing audiovisual events, unimodal signals are transmitted and processed at different speeds, reaching the brain areas for sensory integration at different moments. In order to perceive synchronicity, these signals must be realigned in time. I will describe two recent projects related to this temporal integration flexibility, going from perception to motor control. In the first project I manipulated the audiovisual offset between events to quantify reciprocal sensory attractions in the temporal dimension. Flashes were perceptually shifted toward beeps in an asymmetrical fashion, revealing a stronger attraction of visual events by future auditory events than past. Conversely, beeps were never shifted in time by flashes. Although audition dominates for timing, when breaking the modality appropriateness vision can take over as well, showing that the natural preference is not hardwired. In the second project we explored how irrelevant signals near target onset modulate motor reaction time. Subjects had to perform quick saccades towards targets appearing left/right with short beeps delivered centrally (SOA from –240ms to +240ms). Synchronous beeps speeded-up saccades suggesting an increased alertness. Early beeps reduced further latencies while late beeps increased them, compatible with the audiovisual interactions found earlier. Replacing the beeps with short background luminosity decreases resulted in slower saccades just before and after visual synchrony much as in forward and backward masking. The absence of modulation with this visual signal shows that the initial effect was not related to priming but rather to low-level audiovisual integration. Replacing ocular with manual responses (left/right press) resulted in a regular increase of reaction times reaching the no beep baseline for an SOA of +240ms. The modulation observed with this slower motor system (350ms) was compatible with the much faster saccades (150ms). In conclusion, sounds falling within the temporal binding window of visual events modulate motor reactivity (ocular or manual), even if non-informative about the target direction or timing.