Date of Award

Summer 8-1-2007

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Psychology

First Advisor

Brad Brubaker

Second Advisor

Veanne Anderson

Third Advisor

Christopher Gore

Abstract

Unilateral neglect refers to the symptom that patients with brain damage have, when they fail to respond and orient toward stimuli in the one side of space opposite to the damaged hemisphere. Since symptoms of visual neglect are more long lasting and severe in patients with damage in the right hemisphere than left, the right hemisphere has been considered to be involved visuo-spatial processes. When asked to mark the center of a horizontal line, patients with left neglect tended to place the mark too far to the right of the midpoint. A related phenomenon in normal individuals is pseudoneglect, in which subjects place the subj,~ctive middle point slightly to the left of the real midpoint. One prominent interpretation for unilateral neglect and pseudoneglect on line bisection is that the right hemisphere may be asymmetrically more active with respect to the allocation of spatial attention. To examine the presence of pseudoneglect and asymmetrical hemispatial activation, stimulus presentation and unilateral cueing were manipulated to increase [decrease] the activation asymmetry. Participants were instructed to view the pre-bisected lines and to judge which side of the line is longer. Participants were allowed to freely inspect the stimuli for 3 seconds and the motor component was limited to the button pressing. In Experiment 1, pseudoneglect was demonstrated and the effect of stimulus presentation was found with a leftward bias in the left visual field and a rightward bias in the right visual field. In Experiment 2, the interaction between stimulation presentation and unilateral cueing was found with a leftward bias with left cueing in the left visual field and a rightward bias with right cueing in the right visual field. The assumption that the attention may be biased in the direction opposite to the more activated hemisphere was supported. However inconsistent and heterogeneous scan strategies still remain as a confounding factor on performance, because the eye movement was not restricted.

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