Target Selection for Saccadic Eye Movements: Prelude Activity in the Superior Colliculus During a Direction-Discrimination Task

Abstract

We investigated the role of the superior colliculus (SC) in saccade target selection while macaque monkeys performed a direction-discrimination task. The monkeys selected one of two possible saccade targets based on the direction of motion in a stochastic random-dot display; the difficulty of the task was varied by adjusting the strength of the motion signal in the display. One of the two saccade targets was positioned within the movement field of the SC neuron under study while the other target was positioned well outside the movement field. Approximately 30% of the neurons in the intermediate and deep layers of the SC discharged target-specific preludes of activity that "predicted" target choices well before execution of the saccadic eye movement. Across the population of neurons, the strength of the motion signal in the display influenced the intensity of this "predictive" prelude activity: SC activity signaled the impending saccade more reliably when the motion signal was strong than when it was weak. The dependence of neural activity on motion strength could not be explained by small variations in the metrics of the saccadic eye movements. Predictive activity was particularly strong in a subpopulation of neurons with directional visual responses that we have described previously. For a subset of SC neurons, therefore, prelude activity reflects the difficulty of the direction discrimination in addition to the target of the impending saccade. These results are consistent with the notion that a restricted network of SC neurons plays a role in the process of saccade target selection.

Preparing to Move Increases the Sensitivity of Superior Colliculus Neurons

“…Based on these results, we propose that these neurons, rather than the visual phasic, visual tonic, or saccade-related burst (not reported here), are part of the circuitry involved in identifying saccade goals. This conclusion is consistent with recent reports in a target selection task showing that buildup neurons and not burst neurons are modulated by target probability Wurtz, 1997, 1998) and that visual motor neurons with prominent visual responses discriminate the presence of a target in the RF independent of when the saccade occurs (Horwitz and Newsome, 2001;McPeek and Keller, 2002).…”

Prefrontal Cortex Deactivation in Macaques Alters Activity in the Superior Colliculus and Impairs Voluntary Control of Saccades

“…1996; Ignashchenkova et al, 2004), target selection (Horwitz and Newsome, 2001;McPeek and Keller, 2002), and choice (Thevarajah et al, 2009).…”

Inactivation and stimulation of the frontal pursuit area change pursuit metrics without affecting pursuit target selection

“…To address this problem, we used a second method based on signal detection theory that involved comparing eye velocity on trials where the correct target moved to the left vs. to the right (Green and Swets 1966). We constructed receiver-operating characteristic (ROC) curves at each millisecond based on the distribution of eye velocities and calculated 95% confidence intervals for the ROC area by performing a bootstrap permutation analysis (Britten et al 1996;Horwitz and Newsome 2001). We then identified pursuit latency as the millisecond at which the ROC area crossed the 95% confidence intervals and then remained above it for 100 ms.…”