Abstract
Neurophysiological recordings indicate that sensory latencies are shorter for auditory than for visual signals. Whether this processing advantage for sounds causes them to be perceived earlier has been studied using synchrony and temporal order tasks with a click and a flash, but results have been inconsistent across both tasks and individuals. Some or all of the inconsistency may result from temporal attraction and repulsion effects (e.g. temporal ventriloquism) of a click and flash presented close in time. We probed relative perceptual latency in two tasks for which auditory-visual interactions should be smaller or absent. METHODS. In the first, a flash-lag task, participants reported the location of a moving object at the time of a click or a flash. Relative perceptual latency was inferred from the difference in reported positions between the click and the flash conditions. The second task was to judge which of two intervals was longer. A click and a flash were used to bound the intervals, which were several hundreds of milliseconds long to avoid auditory-visual interactions or sensory integration. A shorter perceptual latency for clicks should yield a longer perceived duration for click-flash than for flash-click intervals. RESULTS. Across several individuals, the apparent perceptual latency difference for the flash and the click was inconsistent between our duration and flash-lag tasks, as well as for order and synchrony judgments. CONCLUSION. The absence of a consistent perceptual correlate of neural latency differences is apparently not due solely to sensory interactions between the click and the flash. The temporally extended nature of responses may play a role. Although physically brief, a click and a flash yield sustained neural responses with separate onset and offset transients. Differences in the use of these responses in different tasks and across individuals may result in the large variability in perceptual latencies observed.
Supported by an Australian Research Council Discovery Project to AH.