Article Figures & Data
Figures
- Figure 1.
Experimental procedures. A, A saccade-countermanding task. Monkeys initiated trials by fixating on a central point. After a variable time, the center of the fixation point was extinguished. A peripheral target was presented simultaneously at one of two possible locations. On no-stop signal trials, monkeys were required to shift gaze to the target, whereupon after 600 ms, a high-pitched auditory feedback tone was delivered, and 600 ms later, fluid reward was provided. On stop-signal trials (∼40% of trials), after the target appeared, the center of the fixation point was reilluminated after a variable stop-signal delay, which instructed the monkey to cancel the saccade in which case the same high-pitched tone was presented after a 1,500 ms hold time, then followed 600 ms later by fluid reward. Stop-signal delay was adjusted such that monkeys successfully canceled the saccade in ∼50% of trials. In the remaining trials, monkeys made noncanceled errors which were followed after 600 ± 0 ms by a low-pitched tone, and no reward was delivered. Monkeys could not initiate trials earlier after errors. B, Countermanding behavior. Top, Cumulative distribution function of response latencies on no-stop (green) and noncanceled (yellow) trials. Response latencies on noncanceled trials were faster than those on no-stop trials. Bottom, Inhibition function plotting the probability of responding across stop-signal delays. C, Goal and nongoal-directed saccades. Monkeys made both leftward (magenta) and rightward (cyan) saccades with similar properties, in response to the target (goal-directed, left) and spontaneously (nongoal-directed, right). Examples are plotted from one representative example session. Goal-directed saccades are shown relative to a central fixation spot and aligned on the target onset. Nongoal-directed saccades are shown relative to the presaccade eye position, aligned on the time a saccadic eye movement was detected within the ITI. D, EEG electrode position. Monkeys were fitted with four EEG electrodes located over the central sulcus (Cz), the medial frontal cortex (FCz), and the frontolateral cortex (F3 and F4). The position of the F3/F4 electrode is estimated to lie over the FEF.
- Figure 2.
A LRP for goal-directed saccades. A, Trial-averaged ERPs from an example session for left (F3) and right (F4) frontolateral electrodes during leftward (orange) and rightward (green) goal-directed saccades. B, A scatterplot illustrating mean EEG amplitudes prior to the saccade at left (F3) and right (F4) frontolateral electrode sites, highlighting lateralization in saccadic activity. C, Heatmaps of normalized activity aligned within an example, representative session. Activity is aligned to saccade onset for left (F3) and right (F4) frontolateral electrodes, for leftward (top) and rightward (bottom) saccades.
- Figure 3.
Ramping of the LRP is modulated by response latency. A, The LRP observed at electrodes F3 and F4, aligned to the target onset (left) and saccade onset (right), for early saccades (red) and late saccades (blue). B, Bar plots comparing mean EEG amplitudes for early and late saccades during the target onset and saccade epochs. Error bars represent standard error of the mean (SEM).
- Figure 4.
Preparatory activity occurs for nongoal-directed saccades. A, Trial-averaged ERPs from an example session for left (F3) and right (F4) frontolateral electrodes during leftward (orange) and rightward (green) nongoal-directed saccades. Shaded areas represent SEM.
- Figure 5.
LRP does not index stopping. A, Trial-averaged ERPs from an example session, during instances of saccade generation (green) and saccade inhibition (red). Data are aligned on the time at which the stop signal appeared (in canceled trials) or would have appeared (on no-stop signal trials). Data are collapsed across both electrodes for the preferred saccade direction. Shaded areas represent SEM. B, Trial-averaged ERPs from an example session, during instances in which a saccade was successfully inhibited (red) or incorrectly generated (yellow) after the presentation of a stop signal. Data are aligned on the time at which the stop signal appeared and is collapsed across both electrodes for the preferred saccade direction. Shaded areas represent SEM.
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