GAP-OVERLAP EFFECTS ON LATENCIES OF SACCADES, VERGENCE AND COMBINED VERGENCE-SACCADES IN HUMANS

We examined the effect of gap-overlap stimuli on the distribution of l atencies for pure saccades, pure vergence and combined saccades and ve rgence in three normal subjects. With the gap stimulus, a distinct pea k of ''express saccades'' occurred, both with and without associated v ergence, but a distinct ''express vergence'' response was not identifi ed, Nevertheless, with the gap stimulus there was a decrease in vergen ce latencies (17 msec), but less so than for saccades (41 msec), In th e combined paradigm the gap effects on saccades and vergence resembled those for each component made alone, In addition, the latencies of th e saccade and vergence components were Linearly correlated with an ave rage slope of 0.5, To explain these results we suggest that there is c ommon signal processing at an early stage of saccade and vergence init iation, which is followed by activity that builds in separate trigger mechanisms that can be influenced by the conditions of fixation.