All ETDs from UAB

Advisory Committee Chair

Lei Liu

Advisory Committee Members

Thomas Norton

Harold Bedell

Paul Gamlin

Patti Fuhr

Document Type

Dissertation

Date of Award

2012

Degree Name by School

Doctor of Philosophy (PhD) School of Optometry

Abstract

This study characterized the perceptual and oculomotor adaptation to a simulated central scotoma in normally-sighted subjects and characterized the effects of two different scotoma profiles on the adaptation process. Twelve normally-sighted subjects, 6 for each type of scotoma profile, prac-ticed a search task (finding an "O" target among "C" distracters) for 11 blocks (162 trials per block). Search reaction time (RT) and eye movement data were collected. A head-mounted eye tracker was used to simulate two 10 deg circular central scotomas (CS), one with a sharp change from seeing to unseeing (S-CS) and the other with a gradual transition (G-CS). The half-height diameter of the G-CS was equal to the diameter of S-CS. Search RT was 4.5 times of the foveal value when the subject was first exposed to the simulated central scotoma. Practice resulted in ~250% improve-ment in both groups. The S-CS group took 1-2 fewer blocks to reach half the ini-tial RT value than the G-CS group. Search RT was highly correlated with the number of fixations and least correlated with fixation duration. The initial eye movement scanpath was disorganized, and became more organized with prac-tice. Saccade amplitudes became smaller and saccadic velocities became slower than foveal search values after practice in both groups. At the end of adaptation, subjects were able to consistently use one retinal location near the border of the simulated scotoma, a Preferred Retinal Locus (PRL). The PRL was more concentrated in the S-CS group than the G-CS group. This study demonstrated that normally-sighted subjects could learn to adapt to a simulated scotoma while performing a visual search task. This adap-tation process occurred by making more organized eye movements and by using one retinal location more consistently, a process that bore resemblance to adap-tation observed in central scotoma patients. A scotoma with sharp edge ap-peared to support faster and better adaptation than one with a gradual edge. This difference might be attributable to the difference between the two scotoma profiles in generating salient visual cue about the location and extent of the scotoma to guide eye movements.

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