Perceptual Coherence : Hearing and Seeing

Auditory and Visual Segmentation 409
These timings are consistent with the temporal integration window described
above.
Recanzone (2003) has further demonstrated the auditory capture of temporal
patterns. In the baseline conditions, a standard series of four lights or
four tones was presented at the rate of four elements per second. Then a
comparison series was presented at rates between 3.5 and 4.5 elements per
second, and the participants indicated whether the rate of the second sequence
was faster or slower than the standard. Participants could judge differences
in auditory rate far better than differences in visual rate (i.e., the
difference threshold for auditory rate was smaller).
The interesting conditions involved the simultaneous presentation of the
auditory and visual sequences. In the standard sequences, the auditory and
visual stimuli were always presented synchronously at four elements per
second. In the comparison sequences, the auditory and visual stimuli were
presented at different rates (see figure 9.16). Here, the participants were
told to ignore either the auditory or visual sequence and make their judgments
of rate only on the basis of the other. On those trials in which listeners
were told to attend to the auditory sequence and ignore the visual
sequence, listeners were able to ignore the visual sequence and based their
judgments solely on the rate of the auditory sequence. In contrast, on those
trials in which listeners were told to attend to the visual sequence and ignore
the auditory sequence, they were unable to do so. The rate of the supposedly
ignored auditory sequence determined their judgments of visual
rate. In other words, the timing of the visual lights was perceived to be
equal to that of the supposedly ignored auditory stimuli. The arrows in figure
9.16 depict these two outcomes. There were, however, rate limits; if the
auditory stimuli were presented at twice the rate of the visual stimuli (8/s
versus 4/s) there was no visual capture: Observers were able to accurately
judge the visual rate.
These results confirm previous work demonstrating auditory “driving”
of the perceived visual flashing rate. For example, Shipley (1964) required
participants to adjust the rate of the auditory stimulus so that it appeared
just different than the rate of the visual stimulus. If the rate of the flashing
light was set at 10 Hz, the mismatch was not detected until the auditory rate
decreased to 7 Hz or increased to 22 Hz. Based on these results and those
of Recanzone (2003) described above, it appears that the auditory stimulus
can drive the visual rate from one-half to two times the actual flashing rate
of the visual input.
All of these experiments used nonmeaningful stimuli, so that it is
impossible to determine whether the participants perceived the tones
and lights as coming from a single object or not, or whether the strength
of the illusion depended on the compellingness of the connection between
the auditory and visual inputs. My guess is that auditory driving occurs