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At least 235 records · Page 13Linked to original sources
PubMed1992

Occlusion as a depth cue in the Wheatstone-Panum limiting case.

We examined the hypothesis (Ono & Wade, 1985) that occlusion of far stimuli by a near one on the same visual line can operate as a depth cue in stereograms containing different numbers of targets in the two eyes. By controlling eye positions, we created conditions in which the visual system could interpret the retinal images as originating from stimuli on the visual axis of one eye and also created other conditions in which the origin of the retinal images was ambiguous. In Experiment 1, we presented two lines to one eye and a single line to the other eye. When the image of the line on the temporal side of the line pair on one retina fused with the image of the single line on the other retina, the nonfused line appeared farther away more often than it did when the image on the nasal side fused. In Experiment 2, we used two differently shaped stimuli. In the condition in which the nonfused stimulus represented an object being occluded, it appeared farther away more often than in the four conditions in which it did not. In Experiment 3, we extended the idea to three different objects. When the middle of the three images fused with the single image, the nonfused stimulus appeared farther when it could be interpreted as being occluded than when it could not. In the condition in which the most temporal image fused with the single image, the nonfused stimuli appeared farther than in the condition in which the most nasal one fused. The results supported the hypothesis that occlusion plays a role in depth perception in the Wheatstone-Panum limiting case.

Adult↗
PubMed1991

Adaptation to form distortion of a familiar shape.

Adaptation to the shape distortion produced by an arrangement of cylindrical lenses was demonstrated. Adaptation was produced by exposing subjects to a series of photographs of faces, which appeared horizontally stretched when seen through the lens arrangement. A 16-min adaptation procedure caused a change when the width of a test face was gradually varied and the subject indicated that it looked normal. An alteration in the perceived shape of a test face and an ellipse was also demonstrated when subjects gave estimates of the height and width of these test objects. These studies provide evidence for the operation of memory representations as the veridical cue in process assimilation.

Adaptation, Ocular↗
PubMed1991

Movement and focused attention: a failure to replicate.

Our original goal was to explore the nature of the grouping-by-movement phenomenon reported by Driver and Baylis (1989). In their studies, distractors that moved in common with a centrally located target had a larger influence on focused-attention performance than did more proximate but stationary distractors. These results seemed particularly important since they suggested, contrary to the predictions of space-based models of attention, that attention could be allocated to noncontiguous regions of the visual field. Their results also suggested mandatory processing of stimuli with common motion. Unfortunately, we were unable to replicate this grouping-by-movement effect. In the conditions of Experiment 1 in which we replicated Driver and Baylis's methodology, stationary distractors produced a larger response-compatibility effect than did the more distant distractors that moved in common with the target. In Experiment 2, we redundantly coded the centrally located target and the far distractors with common movement and color. However, the results were identical to those obtained in Experiment 1. The stationary near distractors that appeared in a different color from the target and the far distractors produced the largest response-compatibility effect. In a final experiment, we attempted to compensate for the reduced acuity of the moving distractors by adjusting their size by a cortical magnification factor. However, even with this manipulation, we found a larger response-compatibility effect for the stationary near distractors than for the moving distant distractors. Our results suggest that subjects are capable of selectively processing a target item that moves in common with distractors.

Adolescent↗
PubMed1989

The vista paradox: a natural visual illusion.

Suppose an observer views a distant object through a window in the far wall of a room or corridor--a visual scene constituting a vista. If the observer moves toward the window, then the distant object will shrink in apparent size and appear farther away. These effects are paradoxical, because the distant object appears smaller as its visual angle increases. The vista paradox occurs under many other real-world conditions, such as viewing a distant object while moving out of the mouth of a valley, or driving across a topographic crest. In the present study, framing effects and the equidistance tendency are considered as possible factors. However, an explanation based on the dynamic relationship between the visual angle of the framing portion of a vista and the visual angle of a distant object appears more promising.

Adult↗
PubMed1992

Active regulation of altitude as a function of optical texture.

Two empirical studies are reported that examine active regulation of altitude as a function of the type of ground texture. Three ground textures were examined: lines perpendicular to the direction of motion, lines parallel to the direction of motion, and the combination (i.e., square or checkerboard texture). Although subjects only controlled altitude, disturbances were introduced on three axes: vertical, lateral, and fore-aft. The results show a clear advantage for texture parallel to the direction of motion. However, in considering these results in the context of previous research on altitude control, the argument is made that there is no compelling evidence that suggests either parallel (splay) or perpendicular (density) texture is privileged with regard to altitude control. Rather, the most effective display for altitude control will be the one that best isolates the optical activity associated with changing altitude from the optical activity arising from other sources of disturbance (such as forward locomotion). Such a display will make it easier for the observer to distinguish and respond specifically to the disturbances of altitude.

Adult↗
PubMed1999

Is the anisotropy of perceived 3-D shape invariant across scale?

A number of studies have resulted in the finding of a 3-D perceptual anisotropy, whereby spatial intervals oriented in depth are perceived to be smaller than physically equal intervals in the frontoparallel plane. In this experiment, we examined whether this anisotropy is scale invariant. The stimuli were L shapes created by two rods placed flat on a level grassy field, with one rod defining a frontoparallel interval, and the other, a depth interval. Observers monocularly and binocularly viewed L shapes at two scales such that they were projectively equivalent under monocular viewing. Observers judged the aspect ratio (depth/width) of each shape. Judged aspect ratio indicated a perceptual anisotropy that was invariant with scale for monocular viewing, but not for binocular viewing. When perspective is kept constant, monocular viewing results in perceptual anisotropy that is invariant across these two scales and presumably across still larger scales. This scale invariance indicates that the perception of shape under these conditions is determined independently of the perception of size.

Adult↗
PubMed2001

Development of a procedure to determine odour emissions from animal farming for regulatory purposes in Flanders.

The purpose of the project described in this paper was to develop a procedure to determine odour emissions at existing and new intensive animal farming houses. The procedure should be scientifically valid and preferably applicable on a large scale at reasonable costs. In this project odour emissions were measured during one year at the same farm. Measurements included 20 olfactometric sampling days and 50 sniffing measurements, all spread over one year. For each olfactometric sampling day, samples were taken in duplicate for the different pig categories. The olfactometric analysis resulted in the determination of odour emission factors for growing/fattening pigs, weaned piglets, dry sows and farrowing sows. The influence of external parameters (ventilation rate, inside temperature, outside temperature, pen dirtiness, number of pigs and their weight) was examined. Good correlation between the odour emission and an external parameter could only be found for the ventilation rate (r = 0.98) and outside temperature (r = 0.87). The sniffing measurements resulted in maximal odour perception distances and odour emissions calculated with short and long term dispersion models. No significant influence of the outside temperature (season) could be found here. The results of the olfactometric and sniffing measurements will be presented, including a combination of both techniques to determine the odour emission of an agricultural construction.

Agriculture↗
PubMed1975

Tests of the psychological meaning of the power law.

The purpose of this study was to establish a theoretical framework for Stevens' empirically derived power law. Three models were proposed to explain the power law. They respectively outline how sensory, stimulus, and response variables determine the judgmental behavior in a psychophysical task. A correlational study on individual differences in exponents was carried out to test the predictions derived from each model. The use of four different sensory continua and four scaling procedures provided the experimental means of manipulating the sensory, stimulus, and response variables in the scaling situation. The results showed that response variables are important determinants of judgmental behavior in psychophysical scaling. These findings suggest that subjects' responses to stimulus intensities in a scaling task are largely cognitive.

Adolescent↗
PubMedDate not supplied

[Attention and executive processes in neuropsychological rehabilitation of the visuospatial processes].

INTRODUCTION AND OBJECTIVE: Cognitive deficits following lesions in parieto occipital areas tend to cause, among others, visuospatial and visuoperceptive alterations. The aim of this article is to examine the influence of others possible deficit over its rehabilitation. DEVELOPMENT: We discuss several patients who present visuospatial impairment after different brain injuries, not only those affecting the areas typically involved in these deficits, such as parieto occipital cortex. Rehabilitation was conducted on an individual basis in the brain injury unit of Beata Maria Ana hospital. Neuropsychological evaluation showed some difficulties not previously described together with these deficits, related to attention, working memory and executive functions, as well as topographic disorientation, lack of visuospatial coordination, distances perception disorders and difficulty to mentally rotate objects. The rehabilitation was AIMed not only at restoration but also compensation of visuospatial deficits, successfully achieved after treatment: patients were capable of returning to their daily activities, including their jobs. CONCLUSION: In patients with visuospatial deficits, a compressive neuropsychological evaluation seem to be essential to define the influence of the other cognitive domains over the rehabilitation of visuospatial problems. In particular, the reinforcement of processes related to attention control and executive functions could very important, give their contribution to the learning of compensatory strategies and assuming that those functions pay key role in the organization and supervision demanded for perceptual skills.

Adult↗
PubMed1988

Infants' sensitivity to boundary flow information for depth at an edge.

We investigated infants' sensitivity to a recently discovered kinetic depth cue, boundary flow. 5-month-old infants viewed computer-generated displays in which the relation between the motion of a boundary, indicating an edge, and 2 regions of dots on either side of the boundary, indicating surfaces, provided the only information specifying the order of the 2 surfaces in depth. Infants showed a significant reaching preference for the apparently nearer region of the display. Since previous research has demonstrated that infants reach more frequently for the nearer of 2 surfaces, this result indicates that 5-month-old infants are sensitive to boundary flow information for depth at an edge.

Attention↗