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Vincent A. Nguyen, Ian P. Howard, Robert S. Allison; The contribution of image blur to depth perception. Journal of Vision 2004;4(8):461. doi: 10.1167/4.8.461.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: An object nearer or further than the fixation point produces a blurred image. The magnitude and direction (sign) of image blur guides accommodation but it could also provide information about relative depth. We examined the contributions of active accommodation and stationary image blur to the precision of monocular judgments of relative depth. Methods: The test stimulus consisted of two vertical sharp edges presented to the right eye. The right edge was set at each of eleven distances, in front or behind the fixed left edge. The lateral distance between the edges was jittered about a mean value of 4 mm to minimise parallactic depth cue. Subjects prefixated coplanar edges at the fixed edge's distance. The test was presented replacing the fixation stimulus. In one condition, the test remained until the subject responded. In a second condition, the test appeared for only 0.2 sec, too short a period for accommodation. Subjects made forced-choice judgements of the depth order of the edges. Depth acuity thresholds were obtained by the method of constant stimuli. Results: The proportion of correct responses was plotted against the depth between the two edges. For long exposures, mean depth acuity (80% correct responses) was 4 cm at a viewing distance of 37 cm. The threshold was higher in the short-duration condition. Conclusion: Monocular depth acuity from image blur was better than previously reported. Reasonably precise relative depth judgments were obtained by actively focussing between stimuli at different distances. Judgments were less precise when based on instantaneous blur.
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