Relationships between manual reaction time and saccade latency in response to visual and auditory stimuli.

Manual reaction time (RT) responses were analyzed from seven human subjects. Responses were recorded using four kinds of target presentations: fixed visual target, moving visual target, fixed auditory target, and moving auditory target. Moving targets (moving in the horizontal plane) were presented at constant intensity and provided only a motion cue. Fixed targets "popped on" at the primary position and provided only an onset cue. RTs for the fixed and moving visual targets were 241.5 ms and 233.1 ms, respectively. The 8.4 ms (3.5%) advantage for the moving visual target over the fixed visual target was statistically significant, p less than 0.05. RT for the moving auditory target varied with target movement amplitude and ranged from 219 ms for 40 degree movements to 268 ms for 5 degree movements. For the fixed auditory target in the sagittal plane, average RT was 182.9 ms. Thus, sound-source motion detection was from 36 to 85 ms slower than sound onset detection, p less than 0.001. The RT results were compared to saccade latency measurements from an earlier study. Both RT and saccade latency showed the same dependency upon target movement amplitude. For small target displacements, saccade latencies for the moving auditory target were longer than for the moving visual target. The longer latencies for the moving auditory target are attributed to the increased processing time required to detect the sound-source motion.