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PubMedDate not supplied

Modelling biological depth perception in binocular vision: the local disparity estimation.

This paper presents an approach to solving the correspondence problem in binocular vision and to computing the local horizontal disparity map using a biologically inspired algorithm. A computer application was developed as a tool for implementing, developing, and testing computational models for stereopsis, and also as a framework for integrating the disparity map with other perspective clues. Two models for stereopsis have been implemented. One of them is biologically inspired (it models the behaviour of simple and complex cells from the striate cortex) and the other is the 'classical' model of David Marr and Tomaso Poggio, implemented in order to have a comparison term for the simulation results. The paper details the results obtained on random-dot stereograms and on pairs of real images.

Algorithms↗
PubMed1989

Spatial properties of disparity pooling in human stereo vision.

The spatial limits of disparity averaging were investigated using Julesz random dot stereograms with two different depth planes. Such stimuli could be perceived as two separate surfaces, one of which was seen through the transparent veil of the other, but under some conditions the depth of information provided by the two surfaces was pooled and the resulting surface was seen at the average of the local disparities. Two types of model are considered for disparity averaging. In the first, disparity averaging occurs as a consequence of attraction/repulsion effects in the disparity domain or as an interpolation process working on a dense depth map of the image. In the second, disparity averaging is seen as a consequence of monocular spatial filtering of the left and right eye images prior to binocular combination.

Depth Perception↗
PubMed1973

Steroscopic vision: cortical limitations and a disparity scaling effect.

The spatial limitations of stereoscopic vision were studied by using vertical line stimuli containing sinusoidal disparity variations such that different parts of the line appeared at different depths. Stimuli with a finer grain than about 3 cycles per degree did not elicit depth perception, even though the sinusoidal curvature was clearly visible monocularly. At low spatial frequencies of curvature, stereoacuity was limited to the same extent as the monocular sensitivity. The limiting disparity for Panum's fusional region and the upper depth limit are subject to a scaling effect in proportion to stimulus dimensions. The disparity scaling can be characterized by a fixed maximum angular difference between the parts of the stereoscopic half-images.

Depth Perception↗
PubMed2003

Comparison of the time courses of concomitant and nonconcomitant vertical phoria adaptation.

Vertical phoria adaptation was measured before, during, and after 1 h of training with either a prism or magnifying lens. With the prism (concomitant adaptation) a single vertical disparity was presented at primary position. With the magnifier (nonconcomitant adaptation) two vertical disparities of opposite sign were presented along the vertical meridian. Following adaptation, binocular vision was prevented with an eye patch, and vertical phorias were measured periodically along the primary vertical meridian over the course of 8 h. Despite individual variation, adaptation followed approximately exponential time courses. The average time constants for the decay of concomitant and nonconcomitant adaptation were 31 and 83 min, respectively. There was no consistent relationship between the rates of acquisition and decay nor was there a strong relationship between the gains of the adaptive responses and the rates of decay although there was a general trend for the gains of the nonconcomitant responses to be higher and the rate of decay slower than the concomitant responses. The results support the notion that concomitant and nonconcomitant phoria adaptation involve different mechanisms but not the contention that adaptation to prisms is easier or more robust than adaptation to lenses.

Adaptation, Physiological↗
PubMed2002

Combining sensory information: mandatory fusion within, but not between, senses.

Humans use multiple sources of sensory information to estimate environmental properties. For example, the eyes and hands both provide relevant information about an object's shape. The eyes estimate shape using binocular disparity, perspective projection, etc. The hands supply haptic shape information by means of tactile and proprioceptive cues. Combining information across cues can improve estimation of object properties but may come at a cost: loss of single-cue information. We report that single-cue information is indeed lost when cues from within the same sensory modality (disparity and texture gradients in vision) are combined, but not when different modalities (vision and haptics) are combined.

Cues↗
PubMed1996

Monocular dot-density cues in random-dot stereograms.

In the original random-dot stereograms (RDSs) invented by Julesz, binocular disparity could only take on values that were integral multiples of dot width. The other common method for constructing RDSs (the projection method) relaxes this restriction. However, the projection method can introduce dot-density cues into the monocular images. When polar projection is employed, density variation is introduced as an expression of perspective cues; when parallel projection is employed, there are no perspective cues, but density variation is nonetheless introduced whenever disparity varies as a function of horizontal position. de Vries, Kappers, and Koenderink [(1994) Vision Research, 34, 2409-2423] proposed to minimize the density cues by selecting half of the random dots from a uniform random distribution in the right-eye image, projecting them onto the cyclopean surface, and then projecting them back to the left eye image and vice versa. In this paper the precise nature of the density cues introduced by the projection method, and by de Vries et al.'s modification of that method, are derived. It is also shown that the projection method and its modification have very similar density cues near the medial sagittal plane when polar projection is employed, and that they have identical density cues over the entire random-dot field when parallel projection is employed.

Cues↗