Contributions of attentional and inhibitory functioning to saccadic decisions

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Project Summary Saccades are a fundamental behavior that enables functional vision by frequently changing which input receives foveal processing. Fixations are the moments in time between saccades during which new input is processed, and the destination of the next saccade is also programmed. Therefore, the decision to produce a saccade is complex and depends on the interaction of numerous systems. Saccadic behavior differs widely across a range of clinical states, and differences emerge in infancy. A large literature has investigated the dynamics of saccadic decisions through computational modeling and neurophysiological data. However, relatively less is known about individual differences within the typical population. The objective of this proposal is to identify underlying mechanisms that explain individual differences in fixation duration tendency, and to investigate how they affect downstream attentional selection. In Aim 1, independent measures of attentional and inhibitory functioning will be compared against individual fixation duration variability. Psychophysical thresholding will determine sensitivity to peripheral targets at a range of eccentricities while fixation is maintained. Thus, individual differences in ability to detect task-relevant peripheral information, critical for planning a saccade, will be measured. Inhibitory function will be estimated as stop-signal reaction time (SSRT) obtained from a saccadic countermanding task. Inhibition plays an important role in slowing accumulation to prevent motor units from reaching threshold quickly. Previous results show that individuals with longer initial fixations make larger amplitude saccades and may land closer to a target. Therefore, enhanced peripheral detection abilities are hypothesized to cooccur with longer fixation duration tendencies. Alternatively or in addition, individual inhibitory function is hypothesized to prevent fast saccades and extend fixation durations. Aim 2 will investigate how individual tendency for short fixation durations affects the choice of saccade destination. This aim uses more complex search displays than Aim 1, with strong competition from salient distractors. A novel hypothesis is proposed about the relationship between individual differences in SSRT and oculomotor capture: individuals with longer SSRT will produce more fast saccades to salient distractors. Finally, Aim 3 will use novel methodology to investigate individual differences in fixation duration known to occur during extended viewing of natural scenes. A dynamic useful field of view (UFOV) task will use gaze-contingent probe presentation at precise eccentricities to measure individual sensitivity to peripheral information during free-viewing. This measure of peripheral processing will more directly mirror conditions present during natural vision, and these measures of attentional breadth are predicted to relate to individual differences in fixation behavior during free-viewing of natural scenes. The long-term goal is to bridge a gap between theories from computational models of neurophysiological data and human saccadic behavior. Understanding the etiology of oculomotor behavior can help target treatments for disorders and shed light on how individual variability might alter visual information acquisition and environmental interactions.