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Thomas Reppert, PhD
Department of Psychology (Schall Lab)
"Proactive control and performance monitoring of speed-accuracy tradeoff of visual search by supplementary eye field"
Neurophysiological mechanisms of speed-accuracy tradeoff (SAT) have only recently been investigated. Previous studies with macaque monkeys showed that SAT of inefficient visual search was accomplished by modulation of salience map evidence representations in frontal eye field (FEF) and superior colliculus (SC). Targeting errors occurred when salience neurons in the FEF and the SC treated distractors as targets. We extended these findings with a study of 70 supplementary eye field (SEF) neurons during SAT. Two monkeys searched for a form target (T/L) amongst 7 distractors (L/T). At the beginning of each trial, the color of a central fixation cue informed the monkeys as to whether they should emphasize speed (Fast condition) or accuracy (Accurate condition) of responding. Prior to the appearance of the array stimulus, baseline activity of SEF neurons predicted the time of the ensuing response in both Fast (n=28 neurons) and Accurate (n=32) conditions. As the monkeys performed the task, they committed errors in choice (i.e. selection of a distractor) and errors in time (e.g. premature saccade in Accurate condition). After choice errors, monkeys made post-primary saccades. Most of these saccades were corrective (i.e. directed at the foregone target), but a minority were directed either at another distractor or the center of the screen. The latency of the post-primary saccade was greater in the Accurate relative to the Fast condition. Timing errors were more prevalent in the Accurate relative to the Fast condition. SEF neurons signaled the occurrence of both types of error. Out of the population of 70 neurons, some signaled only choice errors or timing errors, whereas some signaled both types of error. These results extend our current understanding of the neural basis of SAT and the role of SEF in proactive control and performance monitoring of behavior.