Closer in time when farther in space--spatial factors in audiovisual temporal integration

Abstract

We investigated the effect of visual eccentricity and spatial alignment on judgments of audiovisual synchrony. Sequences of flashes at 4, 6, and 8 Hz were presented centrally, or at horizontal eccentricities of 6 degrees or 18 degrees. Concurrent sequences of clicks were presented at the same rate as the flashes, or at higher or lower rates. Subjects judged whether the flash rate was the same as (synchronous with), faster than, or slower than the click rate. With the 4- and 6-Hz flash rates, subjects' judgments of audiovisual synchrony increased with increasing eccentricity, but only when the click rate was more rapid than the flash rate. This effect remained even when the size of the peripheral visual stimuli was adjusted to compensate for cortical magnification, and was not significantly influenced by the spatial proximity of the auditory and visual signals. However, it was absent when the auditory and visual stimuli were presented serially rather than concurrently. With the 8-Hz flash rate, synchrony judgments were prevalent irrespective of eccentricity. When two serially presented flash rates were compared, visual-visual matching judgments increased with eccentricity at flash rates of 6 Hz and higher, but decreased at flash rates below 6 Hz. Finally, when two concurrent flash rates were compared, visual-visual synchrony judgments increased with eccentricity at all flash-rate combinations. Together, these results suggest that while perceptual uncertainty can play a role in synchrony judgments at rates of 6 Hz and higher, below 6 Hz eccentricity produces a widening of the window of apparent audiovisual temporal synchrony which perceptual uncertainty cannot explain.