Unconfounding the role of retinal eccentricity and stimulus separation for diplopia thresholds

Aaron Sothmann (2010). Unconfounding the role of retinal eccentricity and stimulus separation for diplopia thresholds Honours Thesis, School of Psychology, The University of Queensland.

       
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Author Aaron Sothmann
Thesis Title Unconfounding the role of retinal eccentricity and stimulus separation for diplopia thresholds
School, Centre or Institute School of Psychology
Institution The University of Queensland
Publication date 2010
Thesis type Honours Thesis
Supervisor Grove, Philip
Total pages 57
Abstract/Summary Humans have two laterally separated front facing eyes which move together. Consequently, the images of objects at different distance from the observer project onto different positions in each retina. These slight differences in the two eyes’ images are called disparities. When disparities are relatively small, single vision and depth are perceived. When disparities are large, double vision is experienced. Diplopia threshold refers to the largest positional difference between the two images projected to the retina for which a single fused image can be seen. There is universal agreement that the diplopia threshold increases as stimuli are moved into more peripheral positions. However, this increase may be partly attributable to the increasing separation between the fixation stimulus and the test stimulus. In order to avoid confounding the role of separation and eccentricity, stimuli were presented on the circumference of a circle centred on the fixation point at various separations. This allowed stimulus separation to be varied while eccentricity was held constant. This was adapted from Levi and Klein (1990, 1992) and Levi, Klein and Yap (1988) who used a similar procedure for the measurement of spatial acuity. The results obtained suggest that both retinal eccentricity and stimulus separation are important when determining diplopia thresholds. When the test stimulus and reference stimulus were presented in close proximity in the visual field, diplopia thresholds were smaller than when their separation was larger. As the angular separation between the stimuli increased, there was no difference between the diplopia thresholds. This finding suggests that when the stimuli are in close proximity, stimulus separation is the critical limiting factor for the diplopia threshold. As the angular separation between the stimuli becomes larger, it appears that the diplopia threshold increases as a function of eccentricity.

 
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