A Direct Measurement of Auditory-Visual Temporal Integration

Philip Jaekl, Psychology, York University

Abstract
The perceived time of occurrence of a visual stimulus may be shifted
towards an auditory stimulus that follows within 200ms: the so-called
'temporal ventriloquism' effect. However, this effect has only been
demonstrated indirectly. Here we measure the perceived time shift
directly by presenting subjects with sequences of three stimuli that
could each be either lights (an LED switching on) or sounds (a 5ms
burst of white noise) and asking them to indicate which of the two
intervening intervals was shortest. The two intervals totaled
either 600 or 125ms. The onset of the central member of the trio
within the flanking stimuli was varied using the method of constant.
stimuli. A psychometric function was obtained from which the
perceived temporal midpoint of the sequence was deduced. When the
total was 600ms, shifts in the perceived midpoint were consistent
with the shorter neural processing time of sounds relative to lights.
For the shorter intervals, when the central stimulus occurred within
100ms of the flanking stimuli, there were additional shifts in which
the perceived timing of a visual stimulus shifted by 15-30ms towards
a later auditory stimulus. These results show quantitative evidence
for auditory-visual temporal integration.

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