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Results for “SIZE PERCEPTION”

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PubMed2000

Perceptual deficits after lesions of inferotemporal cortex in macaques.

This study used a novel approach to examine a much studied question, the nature of visual deficits caused by lesions of the inferotemporal cortex (IT). Unlike many previous studies of IT lesions, we de-emphasized early, non-specific disruptions of testing caused by the lesions, and instead concentrated on permanent changes in thresholds. This approach produced unexpected results that suggest a re-evaluation of the traditional view of the role of the IT cortex in shape perception and such related visual abilities as perceptual invariances, visual grouping, the visibility of illusory contours and the performance of oddity discriminations. In addition, the measurement of stable, post-lesion hue discrimination thresholds gave us a different perspective on the severity of color vision deficits which result from lesions of the IT cortex. We found that shape distortion thresholds were not permanently elevated by IT lesions and, indeed, showed no greater transitory disruption than did other visual abilities. This result is inconsistent with the common view that IT is critical to shape discriminations. Two other visual abilities that would be expected to be disrupted by IT lesions - the visual grouping of misoriented line segments and shape invariances (failure of irrelevant stimulus changes to disrupt shape distortion thresholds) - were not affected by IT lesions. However, shape discriminations based on illusory contours and some oddity discriminations were severely and permanently affected. Our results also showed that IT lesions caused permanent, moderate to large impairments of color vision, but not color blindness. Bilateral damage to area TEO caused no disruption of performance on any of the abovediscriminations. Our results suggest that the IT cortex in macaques may be critical to the visibility of illusory contours and the performance of some oddity discriminations, that it plays some role in color perception, but that it is not essential for shape, grouping discriminations or perceptual shape invariances.

Animals↗
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↗
PubMed1983

Intelligence and inspection time in normal and mentally retarded subjects.

The present experiments explore the generality of some recent findings relating IQ to a measure known as Inspection Time (IT)--the exposure duration necessary to judge which of two briefly presented straight lines is the longer. In the first study IT and verbal and performance IQ scores were obtained from a large group of normal six- and seven-year-old children. In contrast to some previous suggestions verbal IQ and full-scale IQ did not correlate significantly with IT, and performance IQ showed only a weak correlation with IT (r = -0.29). In the second experiment IT was found to correlate much more highly with performance IQ in a sample of mentally retarded subjects (r = -0.71). Some possible implications of these results for theories of intelligence and of mental retardation are discussed.

Adult↗
PubMed1988

An experimental analysis of factors underlying neglect in line bisection.

The finding that patients with neglect make larger errors when bisecting longer lines could be due to failure to disengage attention from a segment of the line on the ipsilesional side, or to a reduced ability to direct attention and/or action contralaterally. The findings are reported from a patient with left-sided neglect who set the midpoint further away from the right end of lines as their length increased, a finding consistent with the latter interpretation. His errors were significantly related to length and lateral extent of lines presented in left hemispace, but only to length of lines presented in right hemispace.

Aged↗
PubMed1991

The influence of stimulus properties on visual neglect.

Twenty five patients with right cerebral hemisphere damage and neglect participated in a series of bisection experiments. As expected, long lines were bisected to the right of true midpoint. By contrast, large circles and long white paper strips were bisected accurately, or with leftward errors. Small objects were less sensitive to stimulus properties: short lines and paper strips, and small circles, were bisected to the left of true midpoint, and these leftward errors were equally common as rightward errors with long lines. When asked to draw a perpendicular line of the same length as the presented horizontal line, patients overestimated the length of short lines but underestimated that of long lines. Presenting lines in near and far extrapersonal space selectively affected bisection of short lines. The results suggest that two opposing, independent mechanisms determine bisection performance in left neglect.

Aged↗
PubMed1973

Perception.

Explore the source record for details and available documents.

Adaptation, Ocular↗
PubMed2004

Binocular cues and the control of prehension.

The present study was designed to assess the importance of binocular information (i.e. binocular disparity and angle of convergence) in the control of prehension. Previous studies which have addressed this question have typically used the same experimental manipulation: comparing prehensile movements executed either under binocular conditions to those executed when one eye was occluded (monocular). However this may not be the correct comparison as in addition to depriving the subject of binocular depth cues. it also deprives the subject of any visual information in one eye. Therefore we determined the prehensile performance when the subject viewed the target object and scene with either (i) two different views (binocular), (ii) two identical views (bi-ocular), or (iii) one view only (monocular). Overall, the qualitative and quantitative performance in the bi-ocular and monocular control conditions was very similar on all the main measures (and different from the performance in the binocular condition). We conclude that the deficits in performance observed found for 'monocular' reaches should be attributed to the lack of local depth information specified by the binocular cues. In addition we speculate that convergence angle and binocular disparity, although involved in both the pre-movement and movement-execution phases of the reach, the cues may be weighted differently in both phases of a prehension movement depending on the behavioural strategy involved.

Adult↗
PubMed1993

The visibility of symbolic highway signs can be increased among drivers of all ages.

Visibility and comprehension of standard text, standard symbolic, and improved symbolic highway signs were compared among young, middle-aged, and elderly observers. The average distance at which standard symbolic signs could be identified was about two times that of text signs for all three age groups. The visibility distances of the improved symbolic signs, which were designed using an optical blur (i.e., low-pass) approach in order to avoid higher spatial frequencies, exceeded those of both text and standard symbolic signs. Visibility distance was decreased significantly among older drivers on some signs but not others. There were no significant age differences in the comprehension of symbolic signs. Acuity, a good predictor of visibility distance of both text and standard symbolic signs, was only weakly related to the visibility distance of the improved symbolic signs. These findings demonstrate that low-pass symbolic signs have significant advantages in visibility over their test counterparts for all drivers.

Adult↗
PubMed1989

Body image disturbance in anorexia nervosa: beyond body image.

In this paper the literature on body image disturbance in anorexic patients is reviewed. After a decade of experimental investigation of body image in anorexia nervosa, where old and new techniques have been used and where a large number of correlations have been identified, what do we really know? The findings have been conflicting but some regularities exist. It is hypothesized that the conflicting results may be related to the presence of different subgroups among anorexics and different types of body image disturbance. Body size estimation is only one dimension of body image perception. Likewise, body size overestimation is only one aspect of body image perception. Likewise, body size overestimation is only one aspect of body image disturbance. Some, but not all anorexics, overestimate their body size, and those who do, seem to have poor prognosis. Body size overestimation is not confined to anorexics. It is not known whether it is a function of a general perceptual/cognitive disorder, but it does seem to be stable over time. The implications of the presence of other psychiatric conditions in anorexic patients are discussed and suggestions for future research and for practice are made.

Anorexia Nervosa↗
PubMed2001

Runway width effects in the visual approach to landing.

The effect of changes in runway width on the perception of glide-slope has been the subject of extensive investigations. Despite considerable research, an explanation of this effect has been elusive. A mathematical model for glide-slope perception was published recently based on the premise that a desirable goal of perception is to form a perception with minimal uncertainty. One of the qualitative predictions of that model was that changes in the aspect ratio of the runway would affect the perceived glide-slope. In this article, the predictions of the model are quantified and are shown to be in close agreement with experimental results in the literature.

Aerospace Medicine↗
PubMed1975

Note on conservation differences for Indian and white children.

Piagetian tasks for the conservation of length and volume were administered to two groups of 7-and 8-yr.-old Canadian Indian and white children (ns = 35, 33). There was no significant difference across groups for the conservation of length; however, conservation of volume and the ability to conserve both length and volume resulted in a higher proportion of successful performances for the white group.

Child↗
PubMed1976

Influence of pretest waiting time and duration of induction on kinesthetic aftereffect.

The influence of pretest hand-resting time and induction time on kinesthetic aftereffect was determined for 22 males and females. Aftereffect was assessed with the apparatus of Koehler and Dinnerstein (1947). Three separate tests of aftereffect were administered. Each was preceded by either a 10-, 20-, or 30-min. hand-resting period. Significant differences in aftereffect were not found between pretest conditions. Scores were also determined for varying induction times at each pretest condition. Induction periods totaling 90-, 180-, and 300-sec. were used. Aftereffect was significantly less pronounced following 90 than 180 sec. of induction for the 10-and 20-min. pretest conditions but was the same following 90, 180, and 300 sec. of induction for the 30-min. condition. Results indicated that less than 300 sec. of induction could be used regardless of the duration of the pretest period. However, because the internal validity of the 180-sec. score was significantly better than the 90-sec. score, it was concluded that at least 180 sec. of induction were needed.

Female↗
PubMed1977

Mathematical model for assimilation and contrast in perception of extent.

A mathematical model for assimilation and contrast in the perception of extent is presented, and predictions generated from the model are empirically tested. Implications of the model for the Müller-Lyer illusion are dealt with explicitly, and implications of the model for the Delboeuf, Ebbinghaus, and other illusions of extent are discussed in general terms.

Discrimination, Psychological↗