The transient nature of 2nd-order stereopsis

McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue W (H4-14), Montreal, Que., Canada H3A 1A1.
Vision Research (Impact Factor: 1.82). 06/2008; 48(11):1327-34. DOI: 10.1016/j.visres.2008.02.008
Source: PubMed


There are currently two competing dichotomies used to describe how local stereoscopic information is processed by the human visual system. The first is in terms of the type of the spatial filtering operations used to extract relevant image features prior to stereoscopic analysis (i.e. 1st- vs 2nd-order stereo; [Hess, R. F., & Wilcox, L. M. (1994). Linear and non-linear filtering in stereopsis. Vision Research, 34, 2431-2438]). The second is in terms of the temporal properties of the mechanisms used to process stereoscopic information (i.e. sustained vs transient stereo; [Schor, C. M., Edwards, M., & Pope, D. R. (1998). Spatial-frequency and contrast tuning of the transient-stereopsis system. Vision Research, 38(20), 3057-3068]). Here we compare the dynamics of 1st- and 2nd-order stereopsis using several types of stimuli and find a clear dissociation in which 1st-order stimuli exhibit sustained properties while 2nd-order patterns show more transient properties. Our results and analyses unify and simplify two complimentary bodies of work.

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Available from: Laurie M Wilcox, Mar 12, 2014
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    • "This suggests that a second-order mechanism is involved. Behavioral evidence for second-order stereo-depth mechanism has been shown in a number of studies (Zeigler and Hess, 1999; Hess and Wilcox, 2008). Stereoscopic depth perception can even be obtained with dichoptically mixed first- and second-order stimuli (Edwards et al., 2000). "
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    ABSTRACT: When we view nearby objects, we generate appreciably different retinal images in each eye. Despite this, the visual system can combine these different images to generate a unified view that is distinct from the perception generated from either eye alone (stereopsis). However, there are occasions when the images in the two eyes are too disparate to fuse. Instead, they alternate in perceptual dominance, with the image from one eye being completely excluded from awareness (binocular rivalry). It has been thought that binocular rivalry is the default outcome when binocular fusion is not possible. However, other studies have reported that stereopsis and binocular rivalry can coexist. The aim of this study was to address whether a monocular stimulus that is reported to be suppressed from awareness can continue to contribute to the perception of stereoscopic depth. Our results showed that stereoscopic depth perception was still evident when incompatible monocular images differing in spatial frequency, orientation, spatial phase, or direction of motion engage in binocular rivalry. These results demonstrate a range of conditions in which binocular rivalry and stereopsis can coexist.
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    • "Furthermore, like the 2nd-order mechanisms it does not require matching of the interior luminance signals of the half-images—the transient mechanism responds to opposite polarity stimuli in the two eyes (Pope et al., 1999a). Hess and Wilcox (2008) examined the temporal properties of 1st-and 2nd-order stereopsis by measuring stereoscopic thresholds for these stimuli, as a function of exposure duration (Fig. 8). Thresholds for 1st-order stimuli decreased with increasing duration , while the 2nd-order thresholds remained unchanged, or increased over the same range. "
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    ABSTRACT: There is a long history of research into depth percepts from very large disparities, beyond the fusion limit. Such diplopic stimuli have repeatedly been shown to provide reliable depth percepts. A number of researchers have pointed to differences between the processing of small and large disparities, arguing that they are subserved by distinct neural mechanisms. Other studies have pointed to a dichotomy between the processing of 1st- and 2nd-order stimuli. Here we review literature on the full range of disparity processing to determine how well different proposed dichotomies map onto one another, and to identify unresolved issues.
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    ABSTRACT: We recorded the initial disparity vergence responses (DVRs) elicited by 1-D sinusoidal gratings differing in phase at the two eyes by 1/4 wavelength and defined by luminance modulation (LM) or contrast modulation (CM) of dynamic binary noise. Both LM and CM stimuli elicited DVRs, but those to CM had longer latency (on average by ∼20 ms). DVRs showed sigmoidal dependence on depth of modulation, with higher thresholds for CM than for LM. With both LM and CM stimuli, fixing the modulation at one eye well above threshold rendered the DVR hypersensitive to low-level modulation at the other eye (dichoptic facilitation). Disparities defined by LM at one eye and CM at the other generated weak DVRs in the "wrong" direction, consistent with mediation entirely by distortion products associated with the CM stimulus. These (reversed) DVRs could be nulled by adding LM to the CM stimulus (in phase), and the greater the depth of the CM, the greater the added LM required for nulling, exactly as predicted by a simple compressive non-linearity. We conclude that disparities defined by LM and by CM are sensed by independent cortical mechanisms, at least for the purposes of generating short-latency vergence eye movements to disparity steps.
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