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Masahiro Ishii, Ian P. Howard; Threshold for detection of a continuous change in relative depth. Journal of Vision 2004;4(8):462. doi: 10.1167/4.8.462.
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We measured the threshold for detection of a continuous change in the relative depth of two spots as they approached and receded from the observer. Two white dots separated 56 mm vertically were presented on each of two flat-screen monitors at a distance of 50 cm. The two images were combined in a mirror stereoscope to create one pair of dots centred in the median plane with the upper dot 25 mm further away than the lower dot. The horizontal disparity of the two images was modulated sinusoidally to simulate forward-backward motion of the two dots in depth between 40 cm and 100 cm at a velocity of 30, 60, or 120 cm/s. Information about the distance of the two spots was provided by changing vergence and by changes in angular subtense. The depth separation of the dots did not appear to change when it was held constant as the dots moved in depth, even though the relative disparity changed considerably. Observers therefore scaled relative depth by absolute depth. We measured the threshold for detection of a change in the depth separation of the two dots as they moved as a pair back and forth. The threshold increased in proportion to the velocity of forward-backward motion.
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