SEARCH · PubMed Health

Results for “Perceptual Distortion”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1980

Message valence, familiarity, sex, and personality effects on the perceptual distortion of height.

The perceptual distortion of height was examined in a group of American male and female college student volunteers (n = 139). A message which announced either good or bad news was delivered by a familiar or unfamiliar person who was either male or female. After hearing the message, the students were asked to estimate the height of the communicator. Additionally, the variables of self-esteem and independence of judgment were measured. Results indicated that familiarity with the message source (p less than .0025) as well as sex of the communicator (p less than .024) were predictors of the perceptual distortion of height, but message valence was not. Neither self-esteem nor independence of judgment was functionally related to the proclivity to distort the heights of the communicators.

Affect↗

PubMed2006

Systematic perceptual distortion of 3D slant by disconjugate eye movements.

When an observer pursues an object moving away from him or her, both eyes rotate in the opposite direction, and this type of disconjugate eye movement can generate eye movement-induced disparities in the case of dynamic objects that are present around the pursuit object. Such disparities are not usually generated by conjugate eye movement. The aim of this study was to determine whether eye movement-induced disparities could be calibrated with eye position information. Observers were requested to judge the slant of an object defined by the spatiotemporal pattern of occlusion during disconjugate eye movement. Interestingly, the observers' perception of the slant of the target object was systematically distorted, although the perceptual distortion decreased somewhat in the presence of a salient reference around the target. This suggests that eye movement-induced disparities are not calibrated properly with eye position information.

Eye Movements↗

PubMed2000

Multiple perceptual distortions and their modulation in leftsided visual neglect.

There is an ongoing debate concerning the perception and neural representation of space in neglect. Four experiments are here reported designed to further investigate the nature of perceptual distortions and their modifiability in patients with neglect. In Experiment 1 it was found that neglect patients, in contrast to left- or right-hemisphere lesioned control patients and normal subjects, show similar distortions of perceived visual space when judging the extension of horizontal distances (space distortion) as compared to the horizontal size of objects (size distortion). Similar deficits were present in most neglect patients in a newly developed space bisection task. These results attest that neglect patients have perceptual distortions related to within-object (size) and between-object (distance) spatial processing in their horizontal plane. Objects were oversized by 33% and distances by 19% horizontally in neglect patients, whereas all control groups showed nearly veridical spatial coding (deviations<5%). In Experiment 2 the modifiability of these distortions was tested by the use of slow visual background motion. Leftward, coherent background motion transiently restored normal horizontal size and distance coding in neglect patients, whereas rightward motion aggravated the deficit significantly in the distance task, but not in the size task. None of the other subject groups showed any influence of background motion on spatial judgments. Experiment 3 evaluated possible effects of simultaneous vs successive stimulus presentation in perceptual distortions, thus modulating attentional factors. Neglect patients performed significantly better - although not normal - with a successive presentation of the spatial stimuli (2 s, 10 s delay) as compared to the simultaneous condition in the size judgment task, but not in the distance task. In contrast, this manipulation had no effects in any of the control groups. Experiment 4 reports more detailed results of subject J.S., a neglect patient with a right mediotemporal lesion, who showed a marked horizontal size distortion, but normal horizontal distance judgments. Despite some fluctuation in J.S.'s size judgments he showed a significant overestimation of horizontal object size by +22% to +40% across several test blocks and testing sessions. Thus, performance fluctuations due to attentional or other reasons cannot fully account for J.S.'s dissociation in size vs distance judgments. He thus shows that the visual coding of horizontal spatial extension within an object can be dissociated from that of the spatial extension between objects along the horizontal plane. Finally, performance in the three spatial tasks (used in Experiment 1) was found to correlate significantly with three typical tests of spatial neglect (line bisection, cancellation, copying, r=0.42-0.77), thereby indicating a significant relationship to the neglect syndrome.Together, the results of the four experiments are interpreted in support of multiple spatial-perceptual distortions in visual neglect, which are influenced by visual motion and attention. Perceptual distortions relating to objects and space between objects are present in most neglect patients, but may dissociate, as in case J.S. It is argued that these might reflect the existence of several, partially overlapping and diverging neural maps for the representation of different spatial attributes in the horizontal plane. Furthermore, it is hypothesized that these perceptual distortions constitute an important element of the spatial-perceptual deficits encountered in the syndrome, contribute to its severity, but are not the key deficit of the disorder.

Aged↗

PubMed1976

The Honi phenomenon revisited: factors underlying the resistance to perceptual distortion of one's partner.

An individual being viewed in an Ames room usually appears considerably altered in physical size to an observer. However, some married persons perceive less size distortion of their spouses than a stranger. This instance of selective perceptual distortion, known as the Honi phenomenon, could perhaps reflect differential familiarity and/or emotional involvement toward these stimulus persons. Using heterosexual couples as subjects, we investigated familiarity (i.e., length of the relationship), type of relationship (i.e., dating, engaged, or married), and positive cathexis (i.e., love, liking, and trust of one's partner) as possible mediators of this effect and also explored the impact of some judgemental variations. Neither familiarity nor type of relationship influenced relative perceptual distortion of partner versus stranger. Rather, selective perceptual distortion was directly related to the strength of positive cathexis, principally among females. Only women high in positive cathexis exhibited the Honi phenomenon and perceived a stranger as being more distorted than their partners. In contrast, size judgements by men were affected only by the sequence in which stimulus persons were observed. Implications and interpretations of these findings are discussed.

Awareness↗

PubMedDate not supplied

Cognitive and perceptual distortions in borderline personality disorder and schizotypal personality disorder in a vignette sample.

Clinical vignettes of patients with borderline personality disorder (BPD) and schizotypal personality disorder (STPD) were evaluated and rated for evidence of cognitive and perceptual distortions. The differences in the distortions of each group were then compared. The findings show that while STPD patients have significantly more cognitive and perceptual distortions than borderlines, there is an abundance of such distortions in the borderline group. The borderline group may differ, moreover, in that their cognitive and perceptual distortions were found to be significantly more object-related than those of the schizotypal group.

Borderline Personality Disorder↗

PubMed1985

Developmental differences in depression: cognitive-perceptual distortion in adolescent versus adult female depressives.

This study was undertaken to determine differential cognitive-perceptual distortion in depression for adolescent versus adult females. Twenty-five female adolescent and twenty-five female adult psychiatric inpatients served as subjects. Each had received a primary diagnosis of neurotic or reactive depression and had completed the Beck Depression Inventory within five days of hospitalization. Results indicated significant similarities between the groups in anger at self and sense of failure. These may serve as unifying themes for adolescent and adult depressives. Results also indicated significant differences between the two groups. Adult female depressives demonstrated an internalized, ruminative focus to their depressive cognitions. Adolescent female depressives demonstrated an externalized focus to their depressive cognitions. Adults demonstrated a preoccupation with their own view of themselves and perceived themselves as a failure in their own eyes. Adolescents demonstrated a preoccupation with how others view them and perceived themselves as a failure in the eyes of others. These results are discussed in terms of developmental, theoretical, and treatment issues for adolescent versus adult depressives generally. Depression may exacerbate cognitive-perceptual distortions already existing within the adolescent population. In treatment, group psychotherapy may prove particularly efficacious for adolescent depressives.

Adjustment Disorders↗

PubMed1992

Preliminary observations concerning treatment of visual discomfort and associated perceptual distortion.

A system for therapeutic precision tinting is described. Some individuals who are subject to perceptual distortion of text no longer perceive the distortion when the text has a particular colour. A simple colorimeter enables an observer to illuminate text with light of a particular chromaticity, varying first CIE 1976 hue angle (huv), then saturation (suv), and then luminance, to obtain a setting that maximizes visual comfort and reduces any perceptual distortion. The colorimeter setting is then matched by a combination of tinted trial lenses. The combination uses only two dyes at a time from a selection of seven, unless a dark lens is required, when a third neutral (grey) dye is added. The subject observes both text and a normal scene when wearing tinted trial lenses. A variety of trial lenses are compared including those that match the colorimeter setting and others with similar hue angle. Spectacle lenses are then tinted so as to have a spectral transmission identical to that of the chosen combination of trial lenses. Certain patients with reading disorders, eye-strain, headaches or photosensitivity epilepsy report benefit when wearing spectacles tinted according to the above techniques. The physiological basis for the therapeutic effects is uncertain, but may involve a selective impairment of luminance or colour-difference channels.

Adolescent↗

PubMedDate not supplied

Artificial scotoma-induced perceptual distortions are orientation dependent and short lived.

Conditioning human observers with an "artificial scotoma"-a small retinal area deprived of patterned stimulation within a larger area of dynamically textured noise-results in contractions and expansions of perceived space that are thought to reflect receptive-field changes among cells in the primary visual cortex (Kapadia et al., 1994). Here we show that one-dimensional counter-phase flickering grating patterns are also potent stimuli for producing artificial scotomata capable of altering three-element bisection ability analogous to those results reported earlier. Moreover, we found that the magnitude of the induced spatial distortions depends critically on the relative orientations of peri-scotomatous and test-stimulus spatial contrast. In addition, the perceptual distortions are found to be relatively short lived, decaying within 660 ms. The results support the hypothesis that artificial scotoma-induced perceptual distortions are generated by dynamic alteration of connection efficacy within a network linking cortical areas of similar orientation specificity, consistent with established anatomical and physiological results.

Humans↗

PubMed1989

Perceptual distortions and hallucinations reported during the course of sleep deprivation.

Subjects worked 30 to 45 min. of each hour for either 48 (n = 2) or 72 hr. (n = 8) without sleep. The frequency of reported visual task-related perceptual distortions and hallucinations showed both a linear increasing component and a strong circadian component. Perceptual distortions were most frequent in the late night-early morning hours (0400) and least frequent in the late afternoon-early evening hours (1600-2000).

Adolescent↗

PubMed1999

Residual perceptual distortion in 'recovered' hemispatial neglect.

In most neglect patients, line bisection errors become smaller on repeated tests over the months following the lesion. We have tried to determine in two typical patients whether this is because of a real reduction in the perceptual distortions that appear to underlie line bisection errors in neglect, or whether it reflects a learned behavioural strategy to counteract those perceptual biases. We tested the patients on two occasions (2 and 12 months post-stroke), on line bisection and also on the 'Landmark' task. The data indicated that at the first testing session both patients showed strong 'perceptual' neglect, making large rightward errors in the standard bisection task and uniformly leftward pointing in the Landmark task. On the second occasion, as expected, both patients showed a marked recovery when tested with the line bisection task, making only very small errors. In contrast, their landmark performance was still markedly biased in the same direction as before. These findings suggest that despite their apparent recovery on the bisection task, both patients still experience some form of perceptual distortion of horizontal lines. It is suggested that the Landmark task may provide a sensitive means for identifying real recovery of the underlying perceptual deficit.

Adaptation, Psychological↗

PubMed1994

Perceptual distortion contributes to the curvature of human reaching movements.

Unconstrained point-to-point human arm movements are generally gently curved, a fact which has been used to assess the validity of models of trajectory formation. In this study we examined the relationship between curvature perception and movement curvature for planar sagittal and transverse arm movements. We found a significant correlation (P < 0.0001, n = 16) between the curvature perceived as straight and the curvature of actual arm movements. We suggest that subjects try to make straight-line movements, but that actual movements are curved because visual perceptual distortion makes the movements appear to be straighter than they really are. We conclude that perceptual distortion of curvature contributes to the curvature seen in human point-to-point arm movements and that this must be taken into account in the assessment of models of trajectory formation.

Arm↗

PubMed1992

Pregenital fixation and perceptual distortions to conflict-laden material.

Three standard questionnaire measures of oral and anal fixation were administered to 142 students. On the basis of their scores 26 students were selected and shown tachistoscopic exposures of pictures designed to activate oral or anal conflicts. Five subjects in each group had extremely high scores on the corresponding measure of fixation, five had extremely low scores, and 16 had intermediate scores. It was hypothesised that individuals who were fixated at one or other of the psychosexual stages would show stereotyped perceptual distortions to repeated dim exposures of the corresponding picture. Highly fixated subjects showed significantly more deviant responses than did subjects who showed low levels of fixation at the same stage. A form of Q-factor analysis indicated that subjects who were fixated at the oral sadistic or anal stages showed different patterns of perceptual distortions to the anal picture than those who were not fixated. These results were interpreted as supporting the link between defenses against anal eroticism and the anal character.

Adult↗

PubMed1989

Food cues and perceptual distortion of the female body: implications for food avoidance in the early dynamics of anorexia nervosa.

The present studies concerned a perceptual mechanism that could partially explain the anorexic's severe eating restraint despite continuing hunger. If a woman values a thin body, unrealistic perception of food's fattening effects should increase the aversiveness of ingesting food and foster restraint in eating. The first study considered the perceived thinness/fatness of women's bodies without and with food cues present. College women who (1) shared the stress-generating personality characteristics of anorexics (AP); and (2) judged models as fatter after food cues were introduced (enhancers) reported more stress than AP non-enhancers; no effect of enhancement upon stress was observed in controls. This moderator effect was replicated in a second study. Thus, women with the personality characteristics and high stress that put them at-risk for anorexia also displayed the perceptual distortion involved in the proposed mechanism. Self-ratings verified the same perceptual mechanism in the high-stress AP woman's perception of her own body.

Adolescent↗

PubMed1996

Gratings that induce perceptual distortions mask superimposed targets.

Masking is known to depend upon the relationship between the spatial-frequency content of target and mask. This relationship has been held constant in three experiments in order to investigate the separate contribution of the spatial parameters of the mask, in this case a grating with square-wave luminance profile. Thresholds for the detection of a probe target were highest when the background grating upon which the probe was superimposed had a spatial frequency of about 4 cycles deg-1 (experiment 1) and a duty cycle of 50% (experiment 3). In experiment 2, the thresholds were strongly affected by the size of the background grating even though the size of the target was small in proportion to the grating and remained constant. The increase in threshold was linearly related to the area of visual cortex to which the grating projected. The spatial parameters of gratings that maximise masking are therefore the same as those that have been shown to be optimal for the induction of perceptual distortions, suggesting a possible physiological mechanism for both the masking and the distortions.

Adult↗

PubMed1992

Colorimeter for the intuitive manipulation of hue and saturation and its role in the study of perceptual distortion.

A simple optical method for mixing coloured light is described. The observer has intuitive and approximately independent control over hue and saturation at constant brightness. The method facilitates colour matching by unpracticed observers. It allows children with reading difficulties to select a colour that reduces perceptual distortion of text. The chromaticity coordinates of this colour vary from one observer to another but can be very specific. Complementary colours can exacerbate the distortions and induce pain. For the majority of children reporting beneficial perceptual effects, the u' coordinate is less than 0.25.

Adolescent↗

PubMed1987

Post-trial hormonal treatment effects: memory modulation or perceptual distortion?

An extensive literature has developed in recent years demonstrating that a variety of peripheral-acting hormonal and pharmacological treatments, administered in post-trial learning paradigms, can substantially influence memory. Careful analysis of the effects of such treatments in passive avoidance paradigms has provided evidence for an interaction between these treatments and the hormonal and physiological events triggered by the noxious stimulation used to induce passive avoidance behavior. The argument developed in this paper is that such post-trial manipulations distort the relationship between the intensity of the noxious stimulus and its physiological sequelae. Considered in this light, changes in passive avoidance behavior appear to represent perceptual distortions rather than memory effects, per se. That is, rather than interfering or enhancing memory processes, peripheral hormonal treatments may simply produce distortions in the perceived intensity of the noxious stimulus.

Animals↗

PubMed1982

Modelling perceptual distortion: amplitude and phase transmission in the human visual system.

In this paper we consider the complementary properties of image amplitude and phase components and their role in normal and amblyopic vision. Specific two-dimensional filtered images are included to demonstrate the possible perceptual distortions due to both amplitude and phase disturbances. Finally, the relationships between amplitude and phase filters are discussed with reference to the types of receptive field distributions expected to underly the normal and abnormal cases.

Amblyopia↗

PubMed2006

JPEG2000 encoding with perceptual distortion control.

In this paper, a new encoding approach is proposed to control the JPEG2000 encoding in order to reach a desired perceptual quality. The new method is based on a vision model that incorporates various masking effects of human visual perception and a perceptual distortion metric that takes spatial and spectral summation of individual quantization errors into account. Compared with the conventional rate-based distortion minimization JPEG2000 encoding, the new method provides a way to generate consistent quality images at a lower bit rate.

Algorithms↗