Auditory flutter changes the perceived speed of visual motion

Pascal Mamassian, CNRS & Université Paris Descartes

Abstract
Several cross-modal studies show an interaction when two modalities provide converging evidence for a given attribute, for instance an estimate of spatial location from audio-visual cues in the ventriloquist effect. Two modalities can also interact on a dimension different from that of the percept. We present here studies where the temporal frequency of an auditory signal interacts with that of a visual display, thereby leading to a change in perceived speed of the visual stimulus.

Visual stimuli were drifting Gabors where motion was produced by shifting the carrier's phase by 45deg at a rate of 7.5Hz. These visual displays were presented simultaneously with auditory stimuli consisting of amplitude modulated noise that fluttered at a rate 10% above or below that of the visual stimuli. Observers had to decide whether these test stimuli appeared to move faster or slower than stimuli whose auditory and visual temporal frequencies were identical.

The rate of the periodic auditory stimulus influenced the perceived speed of the visual display: slow auditory rate slowed down the perceived speed, and fast rate accelerated it. These results suggest that the integration between auditory and visual temporal signals occurs before the estimation of speed.

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