Separate populations of visually guided saccades in humans: reaction times and amplitudes

Abstract

The saccadic eye movements of 20 naive adults, 7 naive teenagers, 12 naive children, and 4 trained adult subjects were measured using two single target saccade tasks; the gap and the overlap task. In the gap task, the fixation point was switched off before the target occurred; in the overlap task it remained on until the end of each trial. The target position was randomly selected 4 degrees to the left or 4 degrees to the right of the fixation point. The subjects were instructed to look at the target when it appeared, not to react as fast as possible. They were not given any feedback about their performance. The results suggest that, in the gap task, most of the naive subjects exhibit at least two (the teenagers certainly three) clearly separated peaks in the distribution of the saccadic reaction times. The first peak occurs between 100 and 135 ms (express saccades), the second one between 140 and 180 ms (fast regular), and a third peak may follow at about 200 ms (slow regular). Other subjects did not show clear signs of two modes in the range of 100 to 180 ms, and still others did not produce any reaction times below 135 ms. In the overlap task as well three or even more peaks were obtained at about the same positions along the reaction time scale of many, but not all subjects. Group data as well as those of individual subjects were fitted by the superposition of three gaussian functions. Segregating the reaction time data into saccades that over- or undershoot the target indicated that express saccades almost never overshoot. The results are discussed in relation to the different neural processes preceding the initiation of visually-guided saccades.

What are human express saccades?

“…Recently Fischer and colleagues (Fischer et al, 1993) have reported a comprehensive study in which target position was random and RT feedback was not provided (as in Experiment 2 of this paper). Thirty-nine naive subjects (20 adults, 7 teenagers, 12 children) and 4 trained adults were tested in the gap and overlap conditions.…”

Trial type probability modulates the cost of antisaccades

“…Saccade latency was defined as the time interval between target onset and the initiation of a saccadic eye movement. Trials with saccade latency Ͻ100 ms were excluded (0% in this study) because these trials were probably generated not as responses to the visual target (Fischer et al 1993). Trials (0.01%) with saccade latency Ͼ1,000 ms were also excluded in experiment 1.…”

Effects of Risperidone on Procedural Learning in Antipsychotic-Naive First-Episode Schizophrenia

“…The rationale for this classification is threefold. First, sensory-guided (or visually elicited) saccades in no-gap paradigms (old target extinguishes contemporaneously with new target appearance) such as the one used in this study very rarely occur with latencies shorter than 140 ms (Becker, 1989;Fischer et al, 1993). Second, oculomotor studies generally classify saccades with latencies less than 100 ms as predictive because this reflects the minimal time necessary for perceiving a visual stimulus and performing sensorimotor transformations needed to initiate a motor response (Becker, 1989;Wenban-Smith and Findlay, 1991).…”