The production and maintenance of overt attention shifts: A high-density EEG study
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Saccades are a well-studied type of rapid eye-movement that brings the highly innervated foveal portion of the retina onto areas of interest. Saccades occur 3-4 times per second below conscious awareness, but can also be directed voluntarily. Furthermore, as the primary method of visually sampling the world, these eye movements must remain accurate throughout a lifetime of growth, injury and normal neurological decline. Thus saccades represent a model sensorimotor system in which to investigate broad questions of cognitive science such as attention, learning and neuroplasticity. This thesis utilized variations of common saccade tasks, while simultaneously recording high-density EEG and tracking human participants' eyes to evaluate whether known electrophysiological correlates of attention and error monitoring might also be used to investigate the saccadic system.;We first examined a known neural correlate of covert shifting of attention, alpha-band power (∼8-14Hz), utilizing the anti-saccade task in which one must first covertly attend to a peripheral target, before shifting attention in order to saccade to the opposite side. We found the pattern of Alpha power time-locked to saccade onset revealed significantly lateralized topographies in three distinct phases, all within about one second. This pattern closely reflected the temporal dynamics of the anti-saccade task. These results reflect a more rapid dynamic of alpha-band power than previously established, and implicate a shared neural mechanism for directing both covert and overt attention. Furthermore, these rapid shifts of alpha power occur over visual cortices, even when the cues are purely auditory, further clarifying the supra-modal role of alpha oscillatory rhythms in attentional processes.;Our ongoing interaction with the world involves continually evaluating and updating errant behavior to avoid future errors. Since the purpose of rapid eye movements is the realignment of the highly-innervated fovea to areas of interest, avoiding errors, and maintaining the accuracy of overt attention shifts is particularly important. Since saccade parameters have been shown to rapidly adapt in the face of consistent errors, we next considered an electrophysiological marker of error previously identified in response inhibition tasks, the so-called Error-Related Negativity (ERN) during a 'saccade adaptation' task. In saccade adaptation, saccade targets are surreptitiously moved while the eyes are in flight, creating errors upon landing. This visual error causes an automatic correction of subsequent saccades. We hypothesized that medial wall structures in the frontal lobe presumed to generate error signals such as the ERN, would also contribute to the evaluation process thought to underlie more automatic behaviors such as sensorimotor adaptation. We presented a variation of a traditional saccade adaptation paradigm in which a peripheral saccade target is subtly shifted in position while the saccade is in progress in order to produce errors upon saccade landing. Results supported a 'reinforcement learning' model in which error signals result from outcomes that are worse-than-expected, in this case overshooting but not undershooting the target, rather than a more general 'error monitoring theory' which would predict error signals whenever expected and experienced outcomes differed. These results suggest a larger role for the medial frontal cortex (as reflected by the ERN) than previously conceived, and make predictions about mechanisms of rapid motor learning exemplified during saccade adaptation.
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