Psychology ETDs

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The effects of transcranial direct current stimulation (tDCS) on global and local feature processing and cued attentional switch were tested. Anodal and cathodal tDCS were applied to the left posterior parietal cortex while subjects completed a global/local compound feature task. The task required subjects to attend to either the global or local features of compound stimuli while ignoring the features of the irrelevant level. Subjects were cued to frequently shift attention between the global and local features. The processing of global and local features was unaffected by parietal tDCS but attentional shifts were compromised. Anodal tDCS degraded the ability of subjects to shift attention from local to global features, and cathodal stimulation degraded performance on all cued global/local shifts. Electrophysiological activity was monitored while subjects performed the global/local task. Event-related and oscillatory changes were observed immediately following cathodal stimulation. Cathodal stimulation increased early-latency (P1) responses to global/local switch cues. Cathodal tDCS also reversed the pattern of late-latency (P3) responses to global and local cues. P3 responses to global cues were greater than local cue responses when compared to a sham condition. These changes were accompanied by altered 30 to 50 Hz (beta) oscillatory activity over the left parietal cortical stimulation site. Cathodal stimulation decreased left hemisphere beta activity in response to global cues, and differences in beta activity between global and local responses were greater and in the opposite direction than responses following sham. No significant electrophysiological changes were detected following anodal stimulation. These results support the role of left parietal cortex in cued global/local attentional shifts and represent the first successful modulation of global/local switching using exogenous brain stimulation. Changes in event-related and oscillatory activity reveal possible electrophysiological mechanisms mediating the behavioral effects of tDCS on attentional switch.

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First Committee Member (Chair)

Delaney, Harold

Second Committee Member

Yeo, Ronald




Attention--Physiological aspects, Brain--Electric properties, Brain stimulation, Electrophysiology.

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