The Gap effect for spatially oriented responses.

The gap effect refers to the finding that a temporal gap between fixation point offset and target onset typically results in shorter saccadic latencies than if the fixation point remains on. Recently, this gap effect was found for aimed hand movements as well as saccadic eye movements, but not for simple keypress responses. In order to examine the hypothesis that the hand gap effect occurs for different types of spatially oriented movements, two experiments were conducted. In the first experiment, subjects produced spatially oriented responses to a peripheral target and the target location was known in advance of the targets presentation. This spatially oriented detection task yielded gap effects for both eye and hand responses. In the second experiment, the duration of the temporal gap was varied between 0-400 ms. The duration of the temporal gap had similar effects on the magnitudes of both the eye and hand gap effects, suggesting that a common mechanism may underlie the gap effect for saccadic and manual pointing movements. Overall, the results of the present experiments confirm the finding of a gap effect for spatially oriented hand movements and suggest that this effect may be related to the functioning of the superior colliculus.