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Results for “SIZE PERCEPTION”

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PubMed1988

Multicompetent health professionals: needs, combinations, and curriculum development.

Goals of this study included the investigation of the need for multicompetent health practitioners, the relationship between hospital size and perception of this need, and feasible combinations of professions and skills from the employer's perspective. Surveys of health professions alumni and hospital administrators revealed a perception of need for multicompetency regardless of hospital size or profession. Hospital administrators identified medical technology/radiology technology; nursing/respiratory therapy; and physical therapy/occupational therapy as the three combinations with the greatest potential for benefit; these related well to alumni perceptions of a need for added skills in other professions. This article also suggests a general approach to multicompetency curriculum development.

Allied Health Personnel↗
PubMed2005

Center-surround inhibition and facilitation as a function of size and contrast at multiple levels of visual motion processing.

Visual context often plays a crucial role in visual processing. In the domain of visual motion processing, the response to a stimulus presented to a neuron's classical receptive field can be modulated by presenting stimuli to its surround. The nature of these center-surround interactions is often inhibitory; the neural response decreases when the same direction of motion is presented to center and surround. Here we use binocular rivalry as a tool to study center-surround interactions. We show that magnitude of surround suppression varies as a function of luminance contrast and surround width. Increasing the size of surround motion increased surround suppression at high contrast. Furthermore, large, high-contrast surrounds facilitated opposite-direction motion in the center. For stimuli presented at low contrast, surround suppression peaked at a smaller surround width. In addition, we provide evidence that surround inhibition occurs at multiple levels of visual processing: Surround inhibition in motion processing is likely to originate from both monocular and binocular processing stages.

Contrast Sensitivity↗
PubMed1996

Visual search for size is influenced by a background texture gradient.

Research on the perception of texture gradients has relied heavily on the subjective reports of observers engaged in free-viewing. We asked whether these findings generalized to speeded performance. Experiment 1 showed that an important aspect of subjective perception--size-constancy scaling with perceived distance--also predicted the speed of pop-out visual search for cylinders viewed against a texture gradient. Experiment 2 showed that this finding could not be attributed to the local contrast between search items and the background texture. Experiment 3 assessed the relative contributions of 2 separable dimensions of texture gradients--perspective (radial spreading) and compression (foreshortening)--finding them to be independent in the more rapid search conditions (long target shorter distractors) but combined in the influence in the slower conditions (short target longer distractors).

Adolescent↗
PubMed1996

Cyclopean motion perception produced by oscillations of size, disparity and location.

UNLABELLED: For cyclopean and monocularly-visible targets we measured psychophysical thresholds for perceptions produced by the following three stimuli: oscillations of disparity (DO), oscillations of size (SO) and oscillatory motion within the frontoparallel plane (FPO). RESULTS: thresholds for motion in depth perception produced by DO were similar for cyclopean and non-cyclopean targets over the entire 0.25-8 Hz frequency range investigated. Thresholds for perceiving motion in depth produced by SO were considerably (up to 2.5 times) higher for cyclopean targets than for monocularly-visible targets, as were thresholds for perceiving size oscillations. For both cyclopean and monocularly-visible target the perception of motion in depth could be canceled by pitting DO vs SO. Thresholds for perceiving FPO were similar to DO thresholds for the monocularly-visible target, but for the cyclopean targets FPO thresholds rose more steeply than DO thresholds for oscillation frequencies above 1 Hz. CONCLUSIONS: (1) for our subjects, the effective binocular stimulus for motion in depth perception is a rate of change of disparity; an interocular velocity difference is significant only to the extent that it produces a rate of change of disparity. (2) The sensations of motion in depth produced by DO and SO are qualitatively identical. (3) Neural signals produced by DO and SO converge onto a single neural mechanism that signals motion in depth.

Adaptation, Ocular↗
PubMed1980

Human aging and spatial vision.

The ability to see spatial structures of a wide range of sizes was measured for two groups of observers (mean ages, 18 and 73 years). All observers had good visual acuity. Although older and younger observers did not differ in ability to see targets with fine structure (high spatial frequencies), older observers were only one-third as sensitive to targets with coarse structure (low spatial frequencies) as were younger observers or to changes in criterion. Older observers were also less able than younger observers to see moving targets. The reduced sensitivity of the older observers may adversely affect routine perceptual activities, such as face recognition and visually guided postural behavior, that depend upon low spatial frequencies.

Adult↗
PubMed1982

The dependence of the induced effect on orientation and a hypothesis concerning disparity computations in general.

The induced size effect is an apparent rotation about a vertical axis that results from binocularly viewing a target in which one half-image is vertically magnified. A previous paper (Arditi et al., 1981, Vision Res. 21, 755-764) described a theory of this effect in terms of horizontal disparities that exist between vertically magnified images of oblique features and their unmagnified counterparts. The present studies test two aspects of that theory: the requirement of oblique features in stimuli eliciting the induced effect, and the assumption that binocular associations (inputs to disparity computations) are made across horizontal meridians. The former aspect was confirmed in a stereo discrimination experiment in which the direction of rotation (tilt) for crossed line patterns of varying orientation was judged, for a fixed vertical magnification of one half-image. The latter aspect was rejected on the basis of the results of that experiment, and of two experiments in which observers matched the apparent tilt of the lines with a horizontal adjustment line which could be stereoscopically rotated in depth. The data and some associated demonstrations suggest that stereoacuity and apparent depth of oblique lines vertically magnified in one half-image are determined by the horizontal separation between binocular points which are nearest in a fixed binocular coordinate map, rather than by purely horizontal point-matchings. This "nearest neighbor hypothesis" seems to be operative in classic measures of stereoacuity as well as in the induced effect.

Eye Movements↗
PubMed2003

Body image of adolescents in a multi-ethnic Caribbean population.

OBJECTIVE: To examine the perceptions of body size among adolescents in Trinidad and to determine whether there were ethnic differences. DESIGN: Cross-sectional survey. SETTING: Secondary schools in Trinidad. SUBJECTS: A stratified random sample of 1139 adolescents, aged 14-17 y. MEASUREMENTS: Silhouettes of different body sizes were used to determine perceptions of body size, while weights and heights were measured to determine actual body size. RESULTS: A total of 1090 students (96% response rate) participated, comprising 578 (53%) females. The main ethnic groups were South Asian (49%), African (25%) and persons of mixed ethnicity (23%). The calculated body mass index (BMI) indicated that 14% were thin, 73% normal and 13% overweight; however there was a preponderance of thinness among South Asian males (28%). Whereas 68% of students correctly identified their body size, South Asian males were also more likely to overestimate their body size than the other adolescents, ie they were thinner than they thought. Overall, 64% of the sample was satisfied with their current size, but thin South Asians were more likely to be satisfied with their size than other thin adolescents (P=0.04), while overweight Africans were more likely to be satisfied than other overweight persons (P=0.03). The majority of the sample associated the normal body size with good health, but the majority also associated the overweight and obese silhouettes with wealth. In addition, 40% of them associated the male overweight and obese silhouettes with happiness. CONCLUSION: Although the prevalence of overweight/obesity was not high, the perception of the Trinidadian adolescent that obesity was associated with wealth, and to a lesser extent happiness, and the satisfaction of the overweight African females with their size, were all causes for concern.

Adolescent↗
PubMed2006

Spatial relational learning in rufous hummingbirds (Selasphorus rufus).

There is increasing evidence that animals can learn abstract spatial relationships, and successfully transfer this knowledge to novel situations. In this study, rufous hummingbirds (Selasphorus rufus) were trained to feed from either the lower or the higher of two flowers. When presented with a test pair of flowers, one of which was at a novel height, they chose the flower in the appropriate spatial position rather than the flower at the correct height. This response may also have been influenced by a preference for taller flowers as acquisition of the task during experimental training occurred more readily when the reward flower was the taller of the pair. Thus, it appears that although learning abstract relationships may be a general phenomenon across contexts, and perhaps across species, the ease with which they are learned and the context in which they are subsequently used may not be the same.

Animals↗
PubMed1993

Interaction of stereo, texture and outline cues in the shape perception of three-dimensional ridges.

We report five psychophysical experiments that employed a cue conflict paradigm to investigate integration by the human visual system of surface shape information from stereo, texture and outline cues. The experiments used convex parabolic and triangular three-dimensional ridge stimuli, with amplitudes (base to peak) in the range 3-9 cm, viewed from 57 cm. The observers' task was to judge ridge amplitude using a scale of two-dimensional drawings of ridge profiles. Cue integration was studied using both vertically and horizontally oriented ridges and both real ridges and stereograms of ridges. The main findings were: (a) stereo strongly dominated all horizontal ridge stereograms; (b) texture and outline cues strongly dominated low (3-6 cm) but not high (9 cm) amplitude vertical ridge stereograms; (c) stereo strongly dominated all real ridge stimuli. These results are evidence against explanations of the vertical/horizontal stereo anisotropy which propose that it derives from stereo mechanisms being tuned only to disparity cues with non-zero second-order spatial derivatives or to disparity discontinuities. They also show that radically different results can be obtained when stereo mechanisms are explored using stereograms and real surfaces and possible reasons for this are discussed.

Adult↗
PubMed1994

Spatial vision in the honeybee: the use of different cues in different tasks.

Much of the knowledge available on sensory performances in insects has been obtained from training experiments in honeybees. The present article reviews results of several behavioural studies on spatial vision in the bee. When considered jointly, they demonstrate the large amount of flexibility in the bee's visually guided behaviour. The visual cue that is used in a task depends on the experimental situation, e.g. the bee learns that particular cue that would most reliably guide it to its goal.

Animals↗