Latency dependence of colour-based target vs nontarget discrimination by the saccadic system.

First saccade responses to sudden presentations of a target/nontarget stimulus consisting of green and red spots of light have been investigated. This paradigm, which avoids certain ambiguities present in earlier experiments with identical double stimuli, leads to remarkably similar conclusions. We found, again, that the saccadic system had short-latency compromising responses (averaging response mode) when the stimulus pair had a modest direction difference (delta phi). When delta phi was enlarged, first saccades were either directed near the green or the red spot (bistable response mode). In a second series of experiments different instructions, emphasizing either speed or accuracy of response, have been given to investigate the relation between saccade accuracy and latency. It appears that, independent of instruction, there is a fixed relation between saccade metrics and latency. The only way to avoid errors, such as averaging responses, is to delay the saccade. Hypothetical mechanisms underlying this relation are discussed against recent neurophysiological studies.