Facilitation of reaction times with GAP paradigm: comparison of manual and saccadic responses

Abstract

Manual and saccadic reaction times (RTs) were measured to peripheral target onsets. Previous researchers reported marked decrement in saccadic latencies when the central fixation mark offset preceded the target onset by a short interval (a gap paradigm). The first experiment ascertained whether a similar RT facilitation would occur with a manual RT task. It was found that, in line with previous studies, a majority of saccades was less than 150 ms when a gap of 200 ms was inserted between the fixation offset and the target onset. These short latency saccades were executed virtually without error. Manual RTs were also facilitated, but the amount of facilitation was modest, and it was bargained for at the expense of increased errors.

To compare these two response modes under the gap paradigm, two additional experiments were conducted. First, to check the possibility that the facilitation of manual RTs was due to the prolonged experience with the gap paradigm, 36 naive subjects were recruited, and their manual RTs were measured under one of two gap durations (100 or 200 ms). Both gap durations were successful in bringing about RT facilitation, suggesting that naive subjects could utilize the gap paradigm to speed up their responses. The gap durations of 100 and 200 ms were equally effective in the facilitation of RTs.

In the final experiment, three subjects were observed in manual and saccadic RT tasks under 13 gap-overlap intervals (— 1000 to + 1000ms, of which a negative sign indicates a delayed fixation mark offset relative to target onset or overlap condition). Both saccadic and manual RTs were shortened in the gap range 100-300 ms, while they were increased under the short (less than 300 ms) overlap condition. These effects were more conspicuous for the saccade. Prolonged fixation mark presentation (overlaps of more than 500 ms) caused delayed response initiations only for the saccade.

Keywords:

• Express saccade
• Anticipation
• Disengagement of attention.