Abstract
When stereoscopic images are presented alternately to the two eyes, stereopsis occurs at F ≥ 1 Hz full-cycle frequencies for very simple stimuli, and F ≥ 3 Hz full-cycle frequencies for random-dot stereograms (eg Ludwig I, Pieper W, Lachnit H, 2007 “Temporal integration of monocular images separated in time: stereopsis, stereoacuity, and binocular luster” Perception & Psychophysics 69 92–102). Using twenty different stereograms presented through liquid crystal shutters, we studied the transition to stereopsis with fifteen subjects. The onset of stereopsis was observed during a stepwise increase of the alternation frequency, and its disappearance was observed during a stepwise decrease in frequency. The lowest F values (around 2.5 Hz) were observed with stimuli involving two to four simple disjoint elements (circles, arcs, rectangles). Higher F values were needed for stimuli containing slanted elements or curved surfaces (about 1 Hz increment), overlapping elements at two different depths (about 2.5 Hz increment), or camouflaged overlapping surfaces (> 7 Hz increment). A textured cylindrical surface with a horizontal axis appeared easier to interpret (5.7 Hz) than a pair of slanted segments separated in depth but forming a cross in projection (8 Hz). Training effects were minimal, and F usually increased as disparities were reduced. The hierarchy of difficulties revealed in the study may shed light on various problems that the brain needs to solve during stereoscopic interpretation. During the construction of the three-dimensional percept, the loss of information due to natural decay of the stimuli traces must be compensated by refreshes of visual input. In the discussion an attempt is made to link our results with recent advances in the comprehension of visual scene memory.
Highlights
1.1 Origin of the work In clinical ophthalmology a classical treatment for reeducating patients with a lazy eye uses pairs of images that can be fused
A subject may perceive a flickering image which seems intermediate between the left and right images or he or she may experience a form of unstable stereopsis: the stereogram is interpreted in three dimensions, but the relative locations of parts of the image are alternately those of the left image and those of the right image, giving an apparent rocking motion effect
The measurements we report here relate to this transition to or from stable stereopsis
Summary
1.1 Origin of the work In clinical ophthalmology a classical treatment for reeducating patients with a lazy (amblyopic) eye uses pairs of images that can be fused. The idea is to present the images in alternation to the two eyes, with a specialized apparatus called a synoptophore. At a 2 Hz alternation frequency, each image is presented for 250 ms, and the patient with a lazy eye perceives two images in alternation, rather than a single stable or blinking image. Up to 4 Hz the patient usually perceives two alternating images. 4 Hz the lazy eye’s image is perceived with a lag, and at around 6–7 Hz this image completely disappears (SR; data not shown). The patient becomes able to perceive the two images at increasingly high alternation frequencies, until he or she hopefully succeeds in fusing the two images
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