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PubMed1986

A spatial property of the retino-cortical mapping.

Striate cortex topography derives from a stretching of retinal space along the optic axis. At the retina, relative distances are preserved in a mapping of retinal space onto a spherical surface in the environment. At the cortex, relative distances along visual meridia in the cortical map are preserved in a mapping of striate cortex onto an environmental conic surface whose base is in the plane of the eye. This eco-cortical relationship can be considered a reference frame through which spatial relationships at the cortex might provide information about the environment. The present analysis provides an explanation of changes in cortical magnification with visual eccentricity in the primate and a detailed three-dimensional model of striate topography for the macaque monkey. In man, a conic environmental surface is shown to be uniformly resolvable along meridia in the visual field. Finally, the implications of this analysis of the structural properties of the retino-striate pathway and visual resolution are considered in relation to depth and distance perception.

Brain Mapping↗
PubMed1989

The effect of accommodative hysteresis on apparent distance.

The influence of accommodative hysteresis on monocular distance perception was examined in 18 visually normal young adults. Tonic accommodation and apparent distance were measured immediately before and after a 10 minute period of sustained focus at either the accommodative nearpoint or farpoint. Separate sessions were used for the two sustained focus conditions. On each session, apparent distance was assessed for both a highly effective and a non-effective accommodative target viewed at a constant optical distance of 3D. Sustained focus at the nearpoint resulted in a significant increase in the apparent distance of the highly effective accommodative target, as well as in tonic accommodation. Sustained focus at the farpoint yielded a slight decrease in tonic accommodation, but no significant alteration in the apparent distance of the highly effective accommodative target. No tendency for change in the apparent distance of the non-effective accommodative target was observed under either the nearpoint or farpoint condition. The results suggest that accommodative distance information is linked to the level of monocular blur-driven accommodative innervation necessary for clarity of focus.

Accommodation, Ocular↗
PubMed1991

Systematic distortions of shape from stereopsis.

The effectiveness of disparity information in defining 3-D shape was investigated by means of judgements of the shape of cylindrical continuous curved surfaces presented as random dot stereograms. At a close viewing distance, truly circular cylinders appeared elongated; at an intermediate distance, perception was close to veridical; and, at a far distance, cylinders appeared flattened. Indirect measures of scaling distance were calculated from these data. The results strongly suggest that the observed shape distortions are a consequence of scaling horizontal disparities with an incorrect measure of egocentric distance.

Depth Perception↗
PubMed1979

Absolute and relative cues for the auditory perception of egocentric distance.

Three experiments were performed to examine the reverberation cue to egocentric auditory distance and to determine the extent to which such a cue could provide 'absolute', as contrasted with 'relative', information about distance. In experiment 1 independent groups of blindfolded observers (200 altogether) were presented with broadband noise from a speaker at one of five different distances (0.55 to 8 m) in a normal hard-walled room. Half of each group of observers were presented with the sound at 0 deg azimuth, followed (after a delay) by the identical sound at 90 deg azimuth. The order of presentation was reversed for the remaining observers. Perceived distance varied significantly as a function of the physical distance to the speaker, even for the first presentations. The change in the binaural information between the 0 deg and 90 deg presentations did not significantly modify the results. For both orientations, near distances were overestimated and far distances were underestimated. Experiment 2 and 3 were designed to evaluate how much prior auditory exposure to the laboratory environment was necessary. A 200 Hz square-wave signal was presented from one of three distances (1, 2, or 6 m) to observers who had either minimal room information or an exposure which included talking within the room. Perceived distance varied significantly with physical distance regardless to exposure condition.

Acoustic Stimulation↗
PubMed1991

Pictorial and motion-based information for depth perception.

When computer-generated objects approached the viewpoint in midair, a large far object appeared to be nearer than a small near object and appeared to hit the viewpoint before the small object, which was specified by time-to-contact information to arrive sooner. These judgements were consistent with relative size and occurred even when motion-based information was potentially above threshold. The effects of relative size persisted with higher resolution animated films of approaching objects, were weakened by ground-intercept information, and were not as robust with laterally translating objects. Although it is often asserted that the kinds of information that have traditionally been called static depth cues are superseded by motion-based depth information, this article attempts to show that the reverse also can occur in distance perception, as has been shown in form perception.

Adult↗
PubMed1985

Auditory-visual perception of changing distance by human infants.

2 studies examined 5-month-old infants' sensitivity to auditory-visual specification of distance and direction of movement. In 1 experiment, infants were presented successively with 2 filmed events--1 of an automobile approaching, and the other of the same automobile driving away. A soundtrack that increased or decreased in amplitude was played along with each film, either in a match or mismatch condition. Infants did not show differential looking patterns related to the match or mismatch of auditory and visual information. In a second experiment, infants were tested using a paired preference technique. The films were shown side-by-side along with a single soundtrack appropriate to 1 of them. Looking time was monitored as before. These infants demonstrated visual preferences for the sound-matched films, evidently detecting the relationship between auditory and visual information when this procedure was used.

Auditory Perception↗
PubMed1990

Stereopsis, cyclotorsional "noise" and the apparent vertical.

In principle, stereopsis can be used to evaluate the subjective vertical in a sagittal plane, but temporal variation in cyclotorsion should degrade that ability. Video recordings of eye orientation during steady fixation were used to evaluate long-term instability in cyclotorsion. Torsion was measured simultaneously in each eye at 1-sec intervals during about 30 sequential fixations (5-sec duration) on the same target. For each eye separately, the standard deviation of torsion around its mean value averaged about 18 min arc. Some of this variation was conjugate, but the variability in torsional difference between the eyes averaged 17 min arc. Most of this second-to-second variation arose between fixations (average SD = 15 min arc). Such low-frequency, inter-fixational variation in torsional difference between the eyes must produce spurious horizontal disparities in the upper and lower visual fields, and should thereby limit the precision with which the vertical horopter can be evaluated. All subjects exceeded those theoretical limits on precision, however, in performance tests requiring that two vertically separated targets be adjusted to apparent equidistance--but only when permitted to shift fixation back and forth between the upper and lower targets. That latter result provides a challenge to current understanding of stereopsis.

Adolescent↗
PubMed1989

Perception of three-dimensional structure from optic flow without locally smooth velocity.

A common assumption in several analyses of optic flow is that the velocity field must be locally smooth in order to recover relative depth and the structure of surfaces in the environment. This study investigated the appropriateness of this constraint to human perception. In the first experiment, subjects were asked to identify the number of planes present in a display simulating one, two, three, four, or five overlapping, transparent planes. Subjects were able to detect the presence of up to three planes accurately for both horizontal and depth translations. In the second experiment, subjects' judgments of the depth separation of two transparent, overlapping planes increased with the simulated separation. In Experiment 3, subjects were able to determine accurately the sign of depth for two overlapping, transparent surfaces. These results suggest that a smoothness constraint is not required for the analysis of optic flow by human observers. Alternative approaches to the analysis of optic flow are discussed.

Acceleration↗
PubMed1991

Apparent size as a function of vertical gaze direction: new tests of an old hypothesis.

The hypothesis was tested that the decline of apparent size with elevated gaze results from a latent tendency of the eyes to diverge and thus increased vergence effort. Through the use of a method of category estimation, the decline of apparent size on elevation or depression of gaze was found not to be different between subjects with larger or smaller changes of dark vergence and thus vergence effort. In a 2nd experiment, vergence effort was varied by varying gaze elevation and the angle of convergence. With vergence effort constant, apparent size was dependent on the angle of convergence rather than being constant. It is concluded that apparent size does not depend on vergence effort and that the effect of gaze elevation on apparent size cannot be attributed to its concomitant effect on dark vergence.

Adolescent↗
PubMed1992

Stereokinetic effect and its relation to the kinetic depth effect.

The stereokinetic effect (SKE) has been defined and studied by nested circular patterns rotating on a turntable. Circles must appear not to rotate as they revolve, which in turn results in their appearing to translate relative to one another. A powerful illusion of object depth results even though the individual circles do not undergo an appropriate foreshortening consistent with their apparent changes in slant. It is suggested and tested that the SKE is based on the changing positions between the nested contours despite the absence of any change within each contour, whereas the kinetic depth effect (KDE) entails both kinds of change. It follows that a turntable method of presentation is not necessary, and between-contour transformations can be simulated by computer animation. Displays consisting of simple translations were shown to evoke robust depth impressions as were patterns consisting of contours of varying shapes. Comparisons of the depth, compellingness, and rigidity of matched SKE and KDE displays are reported. The SKE is taken to be paradigmatic for how the visual system perceives depth when observing small object rotations that occur in everyday situations.

Depth Perception↗
PubMed1977

Stereopsis in toads.

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Accommodation, Ocular↗