SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Although no relationship was found between the actual height of 69 young adolescent males and their self-esteem, positive and significant relationships were found between their own, peers', and teacher's perceptions of their height and self-esteem. These results are discussed with reference to the relationship between body morphology, behavior, and personality.
Subjects wielded occluded rods, with or without attached masses, and reported the distances reachable with their distal tips. Experiments 1-3 compared wielding about the wrist, the elbow, and the shoulder. Experiments 4 and 5 compared free wielding, using the whole arm, with wielding only about the wrist. The two comparisons, respectively, were of spatial and temporal variations in the rod's rotational inertia. Perceived extent was found to be constant in both comparisons. This constancy was tied to the inertia tensor Iij defined about a point that remains a fixed distance from the object during wielding--an invariant of the spatially and temporally dependent patterning of mechanical energy impressed upon the tissues of the body. Discussion focused on the reciprocal action and perception capabilities of multisegmented limbs, the tensorial relations in the neurobiology of dynamic touch, and the strategy of understanding perceptual constancy through invariants.
A monkey was trained to discriminate between a shrinking and expanding test figure presented after steady fixation of the center of a rotating spiral. Differential shifts in the animal's perception of size constancy were found for clockwise and counter-clockwise rotation of the spiral. The magnitude of the aftereffect was within the range found in human subjects.
One hundred seventy-two undergraduate women responded to twelve sets of stimuli consisting of a constant jacket silhouette varying proportionally in components of lapel, yoke, and pocket details. Using a 9-point scale in Likert format, the subjects were asked to respond to questions comparing the jacket stimuli of each set in terms of same/different, unattractive/attractive, unwearable/wearable, unfashionable/fashionable, not acceptable/acceptable, and dislike/like. This jacket was varied in its component parts to correspond to proportions currently available in Petite and Misses size apparel. Analysis indicated that subjects detected differences in proportions of garment details within the context of a petite jacket silhouette and preferred proportions adjusted to the smaller size.
For 30 undergraduates, brief exposures were shown to increase the apparent length of a line. This enhancement of length diminished as duration of exposure increased, creating an illusion of line length that resembles the Broca-Sulzer brightness anomaly.
BACKGROUND: Evidence suggests that individuals with autism may not attend to contextual information (conceptual or perceptual) when processing stimuli (Frith 1989; Shah & Frith, 1983). METHOD: We investigated the role of prior knowledge and perspective cues when judging the shape of a slanted circle in individuals with and without autism. Individuals adjusted a shape on a computer screen to appear the same as a slanted circle. RESULTS: Participants in all groups (autistic, moderate learning difficulties, children aged 9 years and adults) exaggerated circularity. Strikingly, however, individuals with autism were unique in exaggerating circularity significantly far less when perspective cues surrounding the slanted circle were eliminated. Prior knowledge that the shape was a slanted circle provoked a strong exaggeration effect in participants without autism, but not in those with autism. CONCLUSIONS: Perhaps classifying the stimulus as a 'circle' was sufficient to provoke a strong exaggeration effect in those without (but not with) autism. In this domain, we show that perception in autism may be less influenced by prior knowledge, and therefore less 'top-down'.
In the first experiment we showed that difficult length discriminations can be facilitated by imagining a visual context frame that serves to emphasize small length differences between pairs of horizontal and vertical lines. This facilitative effect of imagery cannot be attributed to response-bias or expectancy effects because we have separated the object to be imagined from the objects to be discriminated. In the second experiment we showed that real context facilitates the line-length discrimination in much the same way as imagined context does. The results from these experiments suggest that (a) functional interactions can occur between imagery and perception at feature-processing levels of the visual system, and (b) there is a functional equivalence between the imagination and perception of helpful context. Results of a third experiment suggest that although imagery and perception may be functionally equivalent at the levels of visual processing where parts of patterns are combined, they are not functionally equivalent at the lower levels of simple detection.
The literature reports that focused attention alters perceived length of lines. Some tests of this attentional effect require that subjects compare line lengths. This note shows that conceptual confusions inherent in this comparison make the tests invalid.
The study tested the effect of the left and right hemisphere lesions on the susceptibility to visual illusions. Twenty-five patients with left hemisphere damage, 22 patients with right hemisphere damage and 23 control subjects inspected series of figures producing four different illusions: Ponzo, Ehrenstein-Orbison, Poggendorff and Zoellner. Series of stimuli configurations were constructed so that different degrees of distortion opposite to the illusory effect were introduced in each pattern. The amount of distortion was increased in steps so that at a certain point of the series the patterns produced percepts opposite to the illusory ones. That point indicated the strength of the illusion. Stimuli of a given series were presented to each subject 5 times in random order and subject's judgements of illusions were collected. The illusion strength was established using the Spearman distribution method for determining psychophysical thresholds. The results showed that the left and right hemisphere lesions either did not affect the subject's susceptibility to illusions (in Ponzo and Poggendorff) or their effects were similar, i.e. they reduced the strength of the perceived illusions (in Ehrenstein-Orbison and Zoellner). Our data contradict the hypothesis of hemisphere differences in the perception of visual illusions and support the view that those phenomena are multiple-caused.
Subjects judged change and proportion when viewing graphs in two experiments. Change was judged more quickly and accurately with line and bar graphs than with pie charts or tiered bar graphs, and this difference was larger when the rate of change was smaller. Without a graduated scale, proportion was judged more quickly and accurately with pie charts and divided bar graphs than with line or bar graphs. Perception is direct when it requires simpler or fewer mental operations; we propose that perception of change is direct with line and bar graphs, whereas perception of proportion is direct with pie charts and divided bar graphs. The results are also consistent with the proximity compatibility principle. Suggestions for improving the design of graphical displays are given.
In six experiments, we used the Müller-Lyer illusion to investigate factors in the integration of touch, movement, and spatial cues in haptic shape perception, and in the similarity with the visual illusion. Latencies provided evidence against the hypothesis that scanning times explain the haptic illusion. Distinctive fin effects supported the hypothesis that cue distinctiveness contributes to the illusion, but showed also that it depends on modality-specific conditions, and is not the main factor. Allocentric cues from scanning an external frame (EF) did not reduce the haptic illusion. Scanning elicited downward movements and more negative errors for horizontal convergent figures and more positive errors for vertical divergent figures, suggesting a modality-specific movement effect. But the Müller-Lyer illusion was highly significant for both vertical and horizontal figures. By contrast, instructions to use body-centered reference and to ignore the fins reduced the haptic illusion for vertical figures in touch from 12.60% to 1.7%. In vision, without explicit egocentric reference, instructions to ignore fins did not reduce the illusion to near floor level, though external cues were present. But the visual illusion was reduced to the same level as in touch with instructions that included the use of body-centered cues. The new evidence shows that the same instructions reduced the Müller-Lyer illusion almost to zero in both vision and touch. It suggests that the similarity of the illusions is not fortuitous. The results on touch supported the hypothesis that body-centered spatial reference is involved in integrating inputs from touch and movement for accurate haptic shape perception. The finding that explicit egocentric reference had the same effect on vision suggests that it may be a common factor in the integration of disparate inputs from multisensory sources.
Damage to the occipital cortex in children can result in many complex disorders of cognitive visual function. A series of clinical questions, developed from the specific problems of a cohort of children with cortical visual impairment, was asked of the parents of 200 children with no history of cerebral pathology, aged 5 to 12 years. One hundred and ninety-two parents gave reliable consistent responses. The results show a progressive improvement in performance with age, culminating in few 11- and 12-year olds having frequent problems, apart from 8% having frequent difficulty with orientation in new surroundings and 2% having problems with simultaneous perception tasks. The parents of 52 children (aged 5 to 17 years) with shunted hydrocephalus were then asked the same set of questions. Evidence of cognitive visual problems was identified in 27 of these children of whom 16 manifested multiple difficulties. The disabilities identified by our study comprised problems with: shape recognition, simultaneous perception, perception of movement, colour perception, orientation, object recognition, and face recognition. The range, nature, and combinations of these disorders are presented in this paper.
The perception of the size and shape of one's body (body image) is a fundamental aspect of how we experience ourselves. We studied the neural correlates underlying perceived changes in the relative size of body parts by using a perceptual illusion in which participants felt that their waist was shrinking. We scanned the brains of the participants using functional magnetic resonance imaging. We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking. These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex. Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.
The current paper reviews the methods used for assessing body image in anorexia nervosa and bulimia nervosa. A major concern in the assessment of body image in the area of eating disorders has been the apparent failure to recognize the complexity of the body image construct. The development of a range of standardized measures of body image has been an important advancement in recent years; however, it would be premature to assume that any of these methods assesses body image in its entirety. Rather, each provides an operational index of one aspect of this multidimensional construct. The relationship between different dimensions of body image and their respective operational measures remains a potentially valuable area for investigation. Few studies have employed multiple measurement techniques and it is recommended that future investigations incorporate convergent measures which tap perceptual, affective and cognitive elements of the broad body image construct. Factors such as reliability and validity of the different measures of body image must be considered in planning studies with eating disorder patients. Reliability is particularly important because it sets an upper limit on validity. Most studies may be criticized for not addressing the validity of measures employed. Concurrent, convergent, discriminant and predictive validity should be demonstrated for existing as well as new methods. The issue of construct validity which remains a more general concern in the area of body image applies to the investigation of eating disorders. There is the danger that 'body image disturbances' become reified based upon group differences on a particular operational measure. Therefore, conclusions must be cautious even when inferences are drawn from measures which appear to have 'face validity'. The literature on body image in eating disorders has expanded rapidly during the past several years. Generally, it has confirmed the clinical impression that these patients display serious distortions in the feelings, attitudes and perceptions related to their bodies. Hopefully, future research will clarify the mechanisms of action of these body image disturbances and provide insights which will lead to improved treatment.
Maintaining vertical divergence of about 2 diopters for 6, 8, or 10 min was shown to yield an induced vertical phoria (IVP). IVP increased with the duration of the inducing period and decayed with time in the dark, though not completely. Decay of IVP decreased with duration of induction period and increased as a result of maintaining the normal fusional response for 30 s. Vertical eye movements in the dark, however, were ineffective in reducing IVP. Some evidence also was provided for eye-specific errors in the perception of elevation of a visible target that were appropriate to the direction of the induced phoria. It was proposed that IVP may be modulated by resetting the output of the system used to induce the original effect.
To study some aspects of the relationship between body schema and lateralization, 44 female subjects between 19 and 39 yr. of age were measured using a test of accuracy of perception for the right and left halves of the body. Analysis gave three different groups: subjects with larger indexes of deviation on the left (56%), those with larger indexes of deviation on the right (31%), and others with no difference between right and left halves (11%).
The modulation of repetition effects by the lag between first and second presentations of a visual object during a speeded semantic judgment task was examined using both scalp event-related potentials (ERPs) and event-related functional magnetic resonance imaging (efMRI). Four levels of lag were used within a single session, from zero to one, to tens of intervening stimuli, and which allowed partial separation of the effects of interference from the effects of time. Reaction times (RTs) showed that the magnitude of repetition priming decreased as lag increased. The ERP data showed two distinct effects of repetition, one between 150 and 300 ms post stimulus and another between 400 and 600 ms. The magnitude of both effects, particularly the earlier one, decreased as lag increased. The fMRI data showed a decrease in the haemodynamic response associated with repetition in several inferior occipitotemporal regions, the magnitude of which also typically decreased as lag increased. In general, and contrary to expectations, lag appeared to have mainly quantitative effects on the three types of dependent variable: there was little evidence for qualitative differences in the neural correlates of repetition effects at different lags.
It has been argued that visual perception and the visual control of action depend upon functionally distinct and anatomically separable brain systems. Electrophysiological evidence indicates that binocular vision may be particularly important for the visuomotor processing within the posterior parietal cortex, and neuropsychological and psychophysical studies confirm that binocular vision is crucial for the accurate planning and control of prehension movements. An unresolved issue concerns the consequences for visuomotor processing of removing binocular vision. By one account, monocular viewing leads to reliance upon pictorial visual cues to calibrate grasping and results in disruption to normal size-constancy mechanisms. This proposal is based on the finding that maximum grip apertures are reduced with monocular vision. By a second account, monocular viewing results in the loss of binocular visual cues and leads to strategic changes in visuomotor processing by way of altered safety margins. This proposal is based on the finding that maximum grip apertures are increased with monocular vision. We measured both grip aperture and grip force during prehension movements executed with binocular and monocular viewing. We demonstrate that each of the above accounts may be correct and can be observed within the same task. Specifically, we show that, while grip apertures increase with monocular vision, consistent with altered visuomotor safety margins, maximum grip force is nevertheless reduced, consistent with a misperception of object size. These results are related to differences in visual processing required for calibrating grip aperture and grip force during reaching.