Influence of stimulus eccentricity and direction on characteristics of pro- and antisaccades in non-human primates

The ability to inhibit reflexes in favor of goal-oriented behaviors is crit ical for optimal exploration and interaction with our environment. The anti saccade task can be used to investigate the ability of subjects to suppress a reflexive saccade (prosaccade) to a suddenly appearing visual stimulus a nd instead generate a voluntary saccade (antisaccade) to its mirror locatio n. To understand the neural mechanisms required to perform this task, our l ab has developed a non-human primate model. Two monkeys were trained on a t ask with randomly interleaved pro- and antisaccade trials, with the color o f the central fixation point (FP) instructing the monkey to either make a p rosaccade (red FP) or an antisaccade (green FP). In half of the trials, the FP disappeared 200 ms before stimulus presentation (gap condition) and in the remaining trials, the FP remained visible (overlap condition) during st imulus presentation. The effect of stimulus eccentricity and direction was examined by presenting the stimulus at one of eight different radial direct ions (0-360 degrees) and five eccentricities (2, 4, 8, 10, and 16 degrees). Antisaccades had longer saccadic reaction times (SRTs), more dysmetria, an d lower peak velocities than prosaccades. Direction errors in the antisacca de task were more prevalent in the gap condition. The difference in mean SR T between correct pro- and antisaccades, the anti-effect, was greater in th e overlap condition. The difference in mean SRT between the overlap and the gap condition, the gap effect, was larger for antisaccades than for prosac cades. The manipulation of stimulus eccentricity and direction influenced S RT and the proportion of direction errors. These results are comparable to human studies, supporting the use of this animal model for investigating th e neural mechanisms subserving the generation of antisaccades.