Abstract
An entire body of vision research has investigated the effects on perception when target stimuli and backgrounds have perceptually similar luminance levels (isoluminance). This literature reports that luminance contrast is specifically carried by oculomotor pathways responsible for stimulus-driven involuntary saccades (magnocellular pathway in particular; Leonard and Luck 2011). The current study investigates how this perceptual mechanism manifests itself in relation to the spatial and temporal properties of saccade planning. By keeping saccade target stimuli isoluminant with the background, we can experimentally remove a significant portion of stimulus-driven, bottom-up information and isolate the goal-directed, top-down signals used for updating the saccade motor plan. Here, we examined the amount of time required to change the initial saccade trajectory to a new target location for several spatial separations (20°, 40°, and 60°) when the stimuli were isoluminant or had luminance contrast with the background. We found across separations and stimuli luminance contrast, saccades that were directed between the two targets occurred when approximately 90 to 150 ms was available to readjust the movement plan. However, the window in which these “intermediate” saccades occurred was narrowed with both increasing target separation and importantly, when using stimuli with a luminance contrast. Suggesting that the removal of stimulus-driven signals in the magnocellular pathway slows the oculomotor system’s ability to update saccade plans.