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V. Subramanian, N. Fogt; The relationship between disparity vergence detection limits and stereoscopic detection limits . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4321.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It has been speculated that disparity vergence eye movements and stereopsis are sub–served by the same binocular neurons in the visual cortex. An indirect method to test this hypothesis is to compare the disparity limits for driving vergence eye movements with the disparity limits for accurate qualitative stereopsis. The purpose of this experiment was to measure disparity vergence detection limits and to compare those values to fusion limits and to previously published stereoscopic disparity detection limits. Methods:2 experiments were performed. In experiment 1, 8 subjects participated. Subjects viewed a small letter "E" at 1m. Loose prisms ranging from 3.4 to 21.5 prism diopters (PD) were slid in front of the right eye to produce a disparity. In each successive trial, the prism was increased in 2.5PD steps. After prism insertion, the subjects were to attempt to quickly fuse the diplopic images. All of the base–in prism trials were performed prior to the base–out trials. There was a rest period between prism directions. Binocular eye movements were recorded with a video tracker. In experiment 2, 2 subjects participated. Risley prisms were used to introduce equal amounts of prism to the two eyes as subjects viewed a small vertical line of letters at 50cm. The prism values ranged from 3.4 to 24.1PD, and in each trial these prism values were increased in 2PD steps. Base–in trials were alternated with base–out trials. Subjects closed the eyes between trials, and then opened them to see the diplopic images. The subjects were to attempt to fuse the diplopic images rapidly and to report whether fusion occurred. Binocular eye movements were recorded using an infrared tracker. Results: To determine the disparity vergence detection limits, the eye movement records were examined for evidence of disparity vergence in the appropriate direction for each trial. For the two experiments, 9 values for base–in detection limits were obtained and 7 values for base–out detection limits were obtained. The mean disparity vergence detection limit was 15.1±5.8PD for base–in and 13.2±4.0PD for base–out. In experiment 2, the mean difference between the disparity vergence detection limits and the fusional limit was 2.0 ± 2.8PD. Conclusions:The mean disparity vergence detection limits closely matched the disparity limits for accurate qualitative stereopsis of 15.8PD. This suggests that vergence eye movements and stereopsis are driven by the same set of cortical neurons. The fusional vergence limits matched the disparity vergence detection limits, implying that fusion of an object must be possible in order for its stereoscopic depth to be perceived.
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