Experience of perceptual distortion as a source of anxiety.
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Anxiety↗
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Perceptual distortion of body image in adolescent girls: distortion of body image in adolescence.
Body image estimations in 86 normal-weight adolescent girls showed (a) a tendency to overestimate body width and underestimate body length and (b) an association between the younger ages and the extent of overestimation of body width. In particular there is a sharp drop in overestimation between ages 10 and 11 and thereafter a more gradual and non-significant decline. These age-specific normative data are useful in assessing body image distortions in a variety of medical and psychiatric disorders.
Adolescent↗
Perceptual distortion of intrapersonal and near-personal space sensed by proprioception.
It is known that the illusory displacement of a vibrated limb can be transferred to a nonvibrated contacted limb. The purpose of this study was to quantify and compare the transferred illusory displacements occurring in the intrapersonal and near-personal space. In two tasks, 8 male and 8 female blindfolded subjects estimated (1) the height of the left elbow and (2) the height of an external object located at the same height as the left elbow, by the proprioception of the right arm which was Subject to illusory displacement. If the internal representation of the left elbow in one's body schema could provide precise information of its static position independently of the proprioception of the right arm, the perceived displacement of the right arm might be smaller when influenced by proprioceptive information from the static left arm, than when in contrast instead with an object which is not a body part. There was no difference in the estimation of illusory displacement between male and female subjects and between right and left arms. No significant difference was observed between transferred displacements of the left elbow and the object. This means that the perception of limb position sensed by the proprioception of another limb can be distorted as easily as the perception of location of an external object. This suggests that the internal representation of static limb position is not enough to provide the correct information of current limb position in the absence of vision.
Adult↗
Global hemianaesthesia: a parietal perceptual distortion suggesting non-organic illness.
In two patients, lesions in the non-dominant parietal lobe were associated with global anaesthesia to all sensory modalities affecting the opposite half of the body. A striking inconsistency existed between the complaints of limb anaesthesia and the grossly preserved motor and postural control of the involved limb. The gross discrepancy between complaint and functional ability prompted early consideration of a "non-organic" diagnosis. It is suggested that this unusual sensory deficit may be due to distorted perception of somatosensory stimuli, representing another disorder of body schema associated with parietal lobe lesions. The diagnosis of non-organic illness may then be avoided by focusing on a search for parietal disease.
Adolescent↗
Perceptual distortions of speed at low luminance: evidence inconsistent with a Bayesian account of speed encoding.
Our perception of speed has been shown to be distorted under a number of viewing conditions. Recently the well-known reduction of perceived speed at low contrast has led to Bayesian models of speed perception that account for these distortions with a slow speed 'prior'. To test the predictive, rather than the descriptive, power of the Bayesian approach we have investigated perceived speed at low luminance. Our results indicate that, for the mesopic and photopic range (0.13-30 cd m(-2)) the perceived speed of lower luminance patterns is virtually unaffected at low speeds (<4 deg s(-1)) but is over-estimated at higher speeds (>4 deg s(-1)). We show here that the results can be accounted for by an extension to a simple ratio model of speed encoding [Hammett, S. T., Champion, R. A., Morland, A. & Thompson, P. G. (2005). A ratio model of perceived speed in the human visual system. Proceedings of Royal Society B, 262, 2351-2356.] that takes account of known changes in neural responses as a function of luminance, contrast and temporal frequency. The results are not consistent with current Bayesian approaches to modelling speed encoding that postulate a slow speed prior.
Bayes Theorem↗
Subjective perceptual distortions and visual dysfunction in children with autism.
Case reports and sensory inventories suggest that autism involves sensory processing anomalies. Behavioral tests indicate impaired motion and normal form perception in autism. The present study used first-person accounts to investigate perceptual anomalies and related subjective to psychophysical measures. Nine high-functioning children with autism and nine typically-developing children were given a questionnaire to assess the frequency of sensory anomalies, as well as psychophysical tests of visual perception. Results indicated that children with autism experience increased perceptual anomalies, deficits in trajectory discrimination consistent with dysfunction in the cortical dorsal pathway or in cerebellar midsagittal vermis, and high spatial frequency contrast impairments consistent with dysfunctional parvocellular processing. Subjective visual hypersensitivity was significantly related to greater deficits across vision tests.
Adolescent↗
Perceptual distortions by mentally retarded and normal children in response to failure information.
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Child↗
A Newtonian model of perceptual distortion in visuo-spatial neglect.
We propose a simple mathematical model that describes how unilateral brain damage distorts the representation of length in two-dimensional space. The model was tested on eighteen normal adults and six patients with left visuo-spatial neglect after right hemisphere lesion. The subjects bisected lines at eight orientations from vertical to horizontal and the displacement of their transections from true centre was expressed as a function of inclination. Although accuracy differed considerably from patient to patient, sinusoidal functions of the predicted form were found in all cases. The pattern of distortion is an exaggeration of one subtype of normal performance, and is fully consistent with the hypothesis that the cerebral hemispheres have antagonistic attentional biases.
Aged↗
Perceptual distortions of the human body image produced by local anaesthesia, pain and cutaneous stimulation.
1. Knowledge of the size and orientation of the hand is essential if it is to be moved accurately in space. We used two psychophysical methods to determine whether the perceived size of a body part changes when its sensory input is changed: first, the selection of scaled drawings which matched the apparent size of a body part, and second, a motor task in which the subject drew the body part to depict its perceived size. 2. Complete anaesthesia of the thumb (with a digital nerve block) significantly increased its perceived size by 60-70% when assessed with both psychophysical methods. During this anaesthesia, the perceived size of the adjacent index finger or digits on the contralateral side was unaltered. However, the size of the unanaesthetized lips increased (by approximately 50%). 3. Marked sensory loss for the lips (produced by topical anaesthetics) significantly increased their perceived size when assessed with both methods of measurement. There was a small increase in apparent size of the thumb. 4. To determine whether changes in perceived size could also be produced by an elevation of peripheral inputs, innocuous electrical stimulation of the digital nerves and also painful cooling of the digit were used. Both procedures produced small but significant increases in perceived size of the stimulated part. 5. The results highlight lability in the perceived size of parts of the body and how this affects motor output. The data may reveal perceptual consequences of acute changes in central somatosensory maps, changes which are known to occur with deafferentation.
Adult↗
Perceptual distortions in the neural representation of visual space.
The visual mechanism by which human observers determine the separation between objects has long been of interest. This study examines the extent to which separation in visual space can be misperceived in foveal and extrafoveal vision. Foveally, vertical separations were consistently overestimated relative to horizontal separations, a result which is consistent with the well-documented horizontal-vertical illusion (HVI). Extrafoveally, much larger misrepresentations of visual space were perceived. In addition, separations tangential to fixation were consistently perceived as being greater than separations in a radial direction. These marked misperceptions of visual space which occur in extrafoveal vision take the form of a radial/tangential anisotropy combined with an overestimation of vertical distance. The results have important implications for meridional anisotropies which have previously been documented in a number of visual performance tasks.
Adult↗
Perceptual distortion of face deletion by local anaesthesia of the human lips and teeth.
As visual guidance of facial movements is impossible, accurate movements for speech and mastication require an established body image that is formed via the information from mechanoreceptors in the skin, mucosa, periodontium, and proprioceptors in the facial and masticatory muscles and in the jaw joints. In this study we aimed to investigate how the acute deafferentation of lips and teeth alters the established image of lips, teeth and the thumb. We used a psychophysical method to determine whether the perceived sizes of the upper lip and front teeth change when the sensory input from the lips and front teeth is fully blocked. We also examined the perceived size of the thumb to test for acute interactions between the thumb and facial structures. Local anaesthetic blocking of upper lip and upper front teeth significantly increased the perceived size of the upper lip by as much as 100% (range 21-100%) in ten out of eleven subjects tested (overall mean 52%; p=0.001). The perceived size of the upper teeth also significantly increased by as much as 155% (range 30-155%) in eight of the eleven subjects during anaesthesia (overall mean 41%; p=0.035). When the region of anaesthesia was increased and both upper and lower teeth and lips were anaesthetised, the perceived size of the upper lip again increased, by 53% (p=0.040), but the change in perceived size of the upper front teeth (18%) was not significant (p=0.206). In both studies there was no change in perceived size of the thumb. The results illustrate the labile central interaction between sensory inputs and the importance of feedback from peripheral afferents in generating the subjective facial image. The timing, level, and area of anaesthesia may be important modifiers of these interactions.
Adolescent↗
Perceptual distortion around homonymous scotomas is not restricted to defects located in the right hemifield.
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Adult↗
On the perceptual distortion of data: early intervention programs are effective in overcoming environmental deprivation.
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Age Factors↗
Fearful distortions.
Clinical observations suggesting that perceptual distortions can take place during episodes of fear are described, and two hypotheses are set out: (1) perceptual distortions occur during episodes of fear, and (2) such distortions decline after reduction of the pertinent fear. An experiment in which fearful subjects were asked to report their perceptions of a feared object during episodes of fear, and then again after fear-reduction, was carried out. Snake-phobic and spider-phobic subjects showed evidence of some distortions in the activity of the pertinent fear object, but no distortions of size. After the reduction of the relevant fear, the subjects reported significant declines in the activity of the pertinent animal. The two hypotheses received partial support.
Adult↗
Convergent and divergent effects of neck proprioceptive and visual motion stimulation on visual space processing in neglect.
Visual motion stimulation as well as neck muscle vibration are known to effectively modulate the subjective body orientation in spatial neglect. However, so far only motion stimulation has been demonstrated to substantially influence size and space distortion in neglect patients. The present study aimed to compare the two stimulation methods with respect to their potentially differential impact on subjective body orientation and on space and size distortion, in five neglect patients showing perceptual distortions. We found comparable beneficial effects during left motion stimulation and left neck vibration for the subjective straight ahead. Additionally, left motion stimulation significantly ameliorated the leftward overextension in size matching, line bisection and distance estimation in all five patients. In contrast, during neck vibration only two patients showed an improvement for line bisection and size estimation and none did so for distance estimation. Since these two patients differed from the others as they had either no visual field defects or a major visual field sparing, we suggest--based on recent anatomical and neuropsychological findings--that neck vibration only tends to improve pure neglect-related visuo-perceptual distortions whereas motion stimulation can additionally improve perceptual distortions in neglect associated with hemianopia.
Adult↗
Social aspects of body image: perception of normalcy of weight and affect of college undergraduates.
Two aspects of body image, perception of normalcy of weight and affect, were studied by means of a paper-and-pencil test with 62 male and 117 female undergraduates. The relationship of the social characteristics of sex, age, race, and actual body weight (underweight, normal weight, overweight) to body-image distortion was investigated. Individuals who were underweight or overweight were more likely to perceptually distort their weight-related appearance than were normal weight respondents. Among those who misperceived their weight-related appearance, both underweight and overweight persons tended to normalize their appearance. Among those who misperceived their weight-related appearance, sex was also related to the type of perceptual distortion experienced. Females tended to perceive themselves as appearing heavier, whereas males tended to perveive themselves as appearing lighter, than they actually were. There was no relationship between perceptual distortion of body weight and body affect. Age, race, and actual body weight were related to affect. Affect was more negative among young respondents than older respondents. White individuals had poorer affect scores than non-whites. Overweight respondents also had more negative affect scores than other respondents.
Adolescent↗
Ocular scanning and perceptual size distortion in hemispatial neglect: effects of prism adaptation and sequential stimulus presentation.
When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite.
Adaptation, Physiological↗
The perception of distances and spatial relationships in natural outdoor environments.
The ability of observers to perceive distances and spatial relationships in outdoor environments was investigated in two experiments. In experiment 1, the observers adjusted triangular configurations to appear equilateral, while in experiment 2, they adjusted the depth of triangles to match their base width. The results of both experiments revealed that there are large individual differences in how observers perceive distances in outdoor settings. The observers' judgments were greatly affected by the particular task they were asked to perform. The observers who had shown no evidence of perceptual distortions in experiment 1 (with binocular vision) demonstrated large perceptual distortions in experiment 2 when the task was changed to match distances in depth to frontal distances perpendicular to the observers' line of sight. Considered as a whole, the results indicate that there is no single relationship between physical and perceived space that is consistent with observers' judgments of distances in ordinary outdoor contexts.
Humans↗