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Title: Dynamic and static cues for binocular vision : a systematic comparison
Author: Tidbury, L.
ISNI:       0000 0004 6425 2856
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Background: Patients who are diagnosed as stereo blind, during clinical assessment have reported a compelling, volumetric perception of depth during stereoscopic viewing at the cinema. This effect cannot entirely be explained by the monocular cues present in the cinematic presentation. This lead to the theory that depth from binocular cues may be more apparent when motion is included in the scene. As an object approaches in space is detected through the use of two binocular cues, changing disparity over time, and intraocular velocity difference. These cues have been previously investigated in terms of detecting the presence of motion and discriminating the direction of motion. In this thesis I am to investigate the contribution of stereomotion to the detection of depth. Methods: A four alternate forced choice adaptive staircase presentation paradigm was used to assess the ability of participants to detect which of four random dot patterned stimuli patches appeared closest to them in space. The outcome measure for every experiment was depth detection threshold. The experiments were presented using either linear polarised or dichoptic stereoscopic display methods. The stimulus patches were designed to only define depth through binocular disparity, with care taken to avoid any monocular cues. The target patch was identical to all other stimuli patches other than variations to test the following dynamic characteristics: z-location change, X-location change, changing disparity only, interocular velocity difference change only and changes in pattern. These were all comparable to a static condition, where depth was defined by disparity only. All z-axis (or depth) changes were defined by ‘on-screen’ separations of half images (the images separated to the left and right eyes in turn). A number of control experiments were also included to assess the effect of fusional demand, of spurious temporal correlations, of variations in speed of changes in depth and of cue construction on depth detection thresholds. Results: 410 subjects were assessed, (aged mean (SD) age 21(5) years) across all experiments. In comparison to the static disparity conditions (415”), depth detection thresholds were statistically significantly lower for the stereomotion conditions, with (CDOT 360”) and without (Z-LOCATION CHANGE 310”) pattern change (p < 0.001). The presence of a changing pattern in isolation (p=0.71) (STATIC PATTERN CHANGE 410”) or a horizontal shift (p=0.41) (X-LOCATION CHANGE 420”) did not significantly affect the thresholds. The presence of fusional demand or spurious temporal cues did not cause any statistically significant change in thresholds (P > 0.05). Conclusion: The threshold for detecting depth in stimuli that contain z-motion, is better (lower) than for static stimuli, providing an explanation for the experience of compelling depth at the cinema. As z-motion depth detection thresholds were significantly lower than static thresholds, this suggests motion provides an advantage to extracting depth, above serial static disparity detection alone. The assessment of stereoacuity should include the measurement of depth detection thresholds using changing depth stimuli, in order to fully investigate binocular potential.
Supervisor: Wuerger, S. ; O'Connor, A. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral