Saccade latencies in an overlap paradigm when manipulating the stimuli timing, energy and transient changes

Abstract : Previous studies showed that a temporal overlapping of the fixation-target with the saccade-target onset induces a shift of saccade reaction time distributions towards longer values. Here we present a series of experiments probing how an overlap paradigm, combined with the manipulation of stimuli durations, energy and transient changes might modulate saccadic reaction time distributions. We recorded saccadic reaction time in four participants in six experiments in which a saccade-target appeared at a random amplitude after a fixation period. First we parametrically manipulated the duration of the overlap using a range of intervals (from 0 to 200 ms). In a second experiment we probed the interaction of various foreperiod intervals (i.e. the duration of the fixation period prior to saccade-target onset) and overlap using two overlap intervals (20 or 140 ms). In two additional experiments we manipulated either the stimuli sizes or their contrasts in overlap paradigms (20 or 140 ms). Lastly, we introduced a visual transient during the overlap interval via two manipulations (both with a range of SOA): either a distractor ring appeared around the fixation-target, or dynamic random noise replaced the fixation-target. Results show reliable modifications in the latency distributions depending on the overlap interval as well as idiosyncratic differences. Furthermore, all our additional experimental manipulations also affected the latency distributions revealing strong interacting inhibitory processes. We conclude that the effects of overlap intervals may combine with the influence of other stimuli properties to produce strong effects on decision process.