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At least 181 records · Page 10Linked to original sources
PubMed2003

The time course of abstract visual representation.

Studies in change blindness re-enforce the suggestion that veridical, pictorial representations that survive multiple relocations of gaze are unlikely to be generated in the visual system. However, more abstract information may well be extracted and represented by the visual system. In this paper we study the types of information that are retained and the time courses over which these representations are constructed when participants view complex natural scenes. We find that such information is retained and that the resultant abstract representations encode a range of information. Different types of information are extracted and represented over different time courses. After several seconds of viewing natural scenes, our visual system is able to construct a complex information-rich representation.

Adolescent↗
PubMed2004

Bias to experience approaching motion in a three-dimensional virtual environment.

We used two-frame apparent motion in a three-dimensional virtual environment to test whether observers had biases to experience approaching or receding motion in depth. Observers viewed a tunnel of tiles receding in depth, that moved ambiguously either toward or away from them. We found that observers exhibited biases to experience approaching motion. The strengths of the biases were decreased when stimuli pointed away, but size of the display screen had no effect. Tests with diamond-shaped tiles that varied in the degree of pointing asymmetry resulted in a linear trend in which the bias was strongest for stimuli pointing toward the viewer, and weakest for stimuli pointing away. We show that the overall bias to experience approaching motion is consistent with a computational strategy of matching corresponding features between adjacent foreshortened stimuli in consecutive visual frames. We conclude that there are both adaptational and geometric reasons to favor the experience of approaching motion.

Adaptation, Physiological↗
PubMed2005

Geometric and perceptual effects of the location of the observer vantage point for linear-perspective images.

New geometric analyses are presented of three impressive examples of the effects of location of the vantage point on virtual 3-D spaces conveyed by linear-perspective images. In the 'egocentric-road' effect, the perceived direction of the depicted road is always pointed towards the observer, for any position of the vantage point. It is shown that perspective images of real-observer-aimed roads are characterised by a specific, simple pattern of projected side lines. Given that pattern, the position of the observer, and certain assumptions and perspective arguments, the perceived direction of the virtual road towards the observer can be predicted. In the 'skewed balcony' and the 'collapsing ceiling' effects, the position of the vantage point affects the impression of alignment of the virtual architecture conveyed by large-scale illusionistic paintings and the real architecture surrounding them. It is shown that the dislocation of the vantage point away from the viewing position prescribed by the perspective construction induces a mismatch between the painted vanishing point of elements in the picture and the real vanishing point of corresponding elements of the actual architecture. This mismatch of vanishing points provides visual information that the elements of the two architectures are not mutually parallel.

Art↗
PubMed2004

Stereoscopic matching and the aperture problem.

In order to perceive stereoscopic depth, the visual system must define binocular disparities. Consider an oblique line seen through an aperture formed by flanking occluders. Because the line is perceived behind the aperture, the line must have disparity relative to the aperture. What is the assigned disparity of the line in this aperture problem? To answer this question five observers adjusted the horizontal disparity of a probe until it was perceived at the same depth as the disparate line behind the aperture. The results show that, when both the horizontal and the vertical disparities of the occluders are well-defined, the probe must have the same horizontal disparity as the horizontal separation between the line half-images. However, when the horizontal and vertical disparities of the occluders are ill-defined, the intersections of the line and the occluder borders can determine the matching direction. In the latter case, the matching direction varies with the aperture orientation and there is considerable variability across observers.

Depth Perception↗
PubMed1979

A developmental study of three-dimensional perception in Israeli children.

One hundred thirty-six 5- to 10-year-old Israeli male and female children were given three black and white photographs of a highway, a column of identical tanks, and a row of elephants, and were asked some questions on each one of the photographs in order to elicit responses of three-dimensional perception. The results showed a clear developmental pattern, quite similar to what has been found in other studies. It appears that the procedure used in the present study is an easier and probably more reliable way of assessing perspective responses than the original procedure of Piaget and Inhelder.

Child↗
PubMed1976

Telescopic lenses and driving.

In some states, persons with significantly reduced visual acuity are being licensed to drive while wearing telescopic spectacle lenses (TSL). In order to evaluate possible visual field limitations present with these devices, the peripheral visual fields of a group of normally sighted subjects were measured while they wore TSL. Severely restricted central fields and sizeable ring scotomas were present with all units tested. These result indicate that driving with TSL should be discouraged.

Accidents, Traffic↗
PubMed1984

Horopter shifts due to a magnification change.

Both the equidirection ( nonius ) and the equidistance horopter criteria were used on a group of subjects with and without the application of a 5% overall magnifier before the right eye. For three of six subjects, shifts in the equidirection horopter induced by this afocal lens could not be predicted on the basis of the magnification properties of the lens and the assumption that corresponding points are fixed. Equidistance horopter plots showed reasonably systematic reductions in slope between the predicted and the measured values for all subjects. Irregularities in all data were accounted for by shifts in the vergence angles during the experiment.

Aniseikonia↗
PubMed1986

Vision and refractive status among grade 1 children of the Province of New Brunswick.

A public health program instituted and funded by the Government of the Province of New Brunswick and operated by the Provincial Optometric Association screened 10,464 grade 1 children using a modified clinical technique (MCT). This paper reports the prevalence of refractive and sensory-motor anomalies in large samples of this child population, all of whom were 6 years of age.

Child↗
PubMed2002

Maximum disparity with acuvue bifocal contact lenses with changes in illumination.

PURPOSE: To assess the visual performance of Acuvue bifocal contact lenses at different illumination levels using a stereoscopic parameter, the maximum disparity. We compare the results with those for progressive spectacle lenses. METHODS: We used a modified Wheatstone stereoscope and random-dot stereograms (RDS) as tests. The maximum disparity was measured for each observer at different luminance levels. RESULTS: Maximum disparities did not show statistically significant differences for a wide range of luminance levels with contact lenses. The maximum disparities found when some contact-lens users wore progressive spectacle lenses were similar. CONCLUSIONS: The results show that the Acuvue bifocal lenses offer good performance for a near visual task, in this case the maximum disparity, for changes in illumination and are similar to that with progressive spectacle lenses.

Adult↗
PubMed2002

Treating with spectacle lenses: a novel idea!?

A design approach to low-vision device development-vision multiplexing-was introduced recently. This approach has been applied successfully to the design of novel electronic and optical low-vision aids. This paper discusses the application of the vision-multiplexing concept to spectacle lens design to address issues of low vision and to resolve problems of color discrimination and glare in driving. Because spectacles are considered a fashion accessory as much as they are a vision aid, cosmetic considerations are critical to the design of such aids. Spectacle-borne devices that are not concealed or attractive are unlikely to be used widely. Efforts to combine the functionality of vision multiplexing with improved appearance are illustrated.

Biomedical Engineering↗
PubMed1993

Temporal characteristics of proximally-induced accommodation.

This study sought to determine whether proximally-induced accommodation (PIA) is capable of sustaining an accommodative response over time. Accordingly, the steady-state PIA response was measured during the course of a continuous 5 min stimulus period for targets located at distances of 0.2 or 6 m. The vergence and accommodation loops were opened by subjects (n = 8) monocularly viewing the targets through a 0.5 mm pinhole, while accommodation was assessed using an objective, open-field, infrared optometer. The mean PIA response did not change significantly during the fixation period. This finding suggests that PIA is indeed capable of maintaining a sustained response. This observation is consistent with the constancy of apparent target distance perception during extended fixation of a stationary object of regard under these conditions.

Accommodation, Ocular↗
PubMed1977

Inappropriate constancy scaling as a factor in the Müller-Lyer illusion.

The inappropriate constancy theory of geometrical illusions assumes the existence of implicit depth cues which automatically set constancy scaling. In the present study the phenomenon of cue conflict has been employed to test for latent depth cues in the Müller-Lyer figures. The technique consisted in introducing a stereoscopic disparity between the figures by means of an aniseikonic lens and measuring the perceived depth between the figures. The magnitude of the stereoscopic effect depends on whether the perspective cues augment or inhibit the stereoscopic depth cues. The results were inconsistent with the misapplied constancy theory, but confirmed Pike & Stacey's (1969) observation that the illusion of size may act as a depth cue.

Adult↗