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Results for “Perceptual Distortion”

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PubMed1990

Distorted body image as a risk factor in anorexia nervosa: replication and clarification.

This study replicated the results of an earlier one in which college women showing psychological similarities to anorexics indicated an unrealistically larger body-image relative to controls but only if they were relatively thin. This kind of perceptual enhancement was not found when inanimate objects were rated. The proposal that an enhanced body image plays a dynamic role in motivating food restraint (and may increase the risk of becoming anorexic) was supported by an analysis of dieting strategies.

Adolescent↗
PubMed1979

Menstrual symptoms: a social cognition analysis.

Research on menstrual-related cyclicity often reflects assumptions concerning the generality, severity, and physiological basis of symptoms associated with the menstrual cycle. According to arguments presented in recent articles, these assumptions are not fully justified by the empirical data. In addition, there is evidence that symptom associations may be viewed a reflecting, in part, a set of beliefs. In the present article evidence is reviewed which suggests that symptom associations may originate and be maintained by means of biases in the processing of information about cyclicity. Specifically, the origins of biased beliefs may arise from the connotative meaning of, the salience of, and selectivity in processing the information forming the association. In addition, mechanisms which have been tribute to the maintenance of biased perceptions, once associations have been formed, include distortion, autonomy, and category accessibility of the evidence.

Adolescent↗
PubMed2004

The effects of geometric distortion correction on motion realignment in fMRI.

RATIONALE AND OBJECTIVES: Subject motion is well recognized as a significant impediment to resolution and sensitivity in functional magnetic resonance imaging (fMRI). A parallel confounder to fMRI data quality is geometric image distortion, particularly at high field strengths, due to susceptibility-induced magnetic field inhomogeneity. Consequently, many high-field echo-planar imaging methods incorporate a post-processing distortion correction by acquiring a field map of the sample prior to the fMRI measurement. However, field mapping methods impose a spatial mask on the data, since field information is only obtainable from regions with adequate signal-to-noise ratio (SNR). This masking, when applied to subsequent images in the fMRI time series, can clip the effects of motion, resulting in inaccurate estimation and correction of motion-based changes in the images. MATERIALS AND METHODS: The effects of geometric distortion correction on automated realignment (motion correction) of fMRI data are investigated from data acquired at 4 T. The results of image realignment with and without prior application of distortion correction are compared, using the estimated motion parameters and overall image realignment as metrics. RESULTS: The application of field-map-based distortion correction prior to image realignment reduces the amount of motion detected by a standard motion correction algorithm. Moreover, motion correction applied before distortion correction is shown to result in superior realignment of motion-correction images. CONCLUSION: It is preferable to perform motion realignment prior to correcting for geometric distortion.

Humans↗
PubMed1994

Relationship between in-situ distortion and hearing aid benefit.

In-situ hearing aid distortion is defined as distortion measured in the ear canal with stimulus inputs and hearing aid settings that are similar to those the hearing aid wearer will experience in daily life. This preliminary study examined possible relationships between in-situ distortion and benefit for appropriately fitted contemporary hearing aids. Simulated in-situ distortion was determined for 97 hearing aid fittings, divided among three typical listening environments: living room, classroom lecture, and social event. Measures included intermodulation, harmonic, and transient distortion. Overall results of between- and within-subject analyses of data suggested that there was a significant relationship between distortion and benefit in both reverberant and noisy environments similar to a classroom lecture and a social event, respectively. This outcome was seen despite the fact that distortion was quite low in absolute terms. Analyses also suggested that in-situ harmonic distortion was most closely related to benefit and that the other types of distortion measured did not make additional contributions to benefit prediction. We propose that measurements of in-situ harmonic distortion might be a valuable addition to hearing aid evaluations.

Aged↗
PubMed2000

Modeling the temporal behavior of distortion product otoacoustic emissions.

The temporal behavior of the 2f1-f2 distortion product otoacoustic emission is theoretically investigated for the case in which the lower frequency (f1) primary tone is on continuously, and the higher frequency (f2) one is pulsed on and off [e.g., Talmadge et al., J. Acoust. Soc. Am. 105, 275-292 (1999)]. On physical grounds, this behavior is expected to be characterized by various group delays associated with the propagation of (1) the f2 cochlear primary wave between the cochlear base and the primary distortion product generation region around x2 (the f2 tonotopic place), and (2) the 2f1-f2 cochlear distortion product (DP) waves between the cochlear base, the primary generation region of the distortion product, and the region around the 2f1-f2 tonotopic place where the generated apical moving DP wave is reflected toward the cochlear base [e.g., Talmadge et al., J. Acoust. Soc. Am. 104, 1517-1543 (1998)]. An approximate analytic expression is obtained for this behavior from the analysis of the Fourier integral representation of the auditory peripheral response to the primary stimuli. This expression also approximately describes the transient build-up of the components of different latencies in terms of the damping properties of the cochlear partition. It is shown that considerable caution must be applied in attempting to relate phase derivatives of the distortion product otoacoustic emissions for steady state stimuli and the physical time delays which are associated with the temporal behavior of a distortion product emission in the case of a pulsed primary.

Animals↗
PubMed1983

The cylinder configuration: when is a distortion an illusion?

A figure with one end rounded and the other concluding in an ellipse (the 'cylinder configuration') may appear longer than a rectangle of the same true length. It is proposed that when this configuration is processed as a three-dimensional body, it provides a cue for object orientation which causes the perceptual system to make an adjustment in the direction appropriate for maintaining size constancy. This effect may be considered a normal perceptual adjustment, appropriately applied. When the cylinder configuration is embedded in a context which does not favour its being processed as three-dimensional, a weaker adjustment in length may still occur. It is suggested that this effect, which may properly be classified as an illusion, may arise through direct association of the critical pattern of lines with the process of lengthening produced by the size-constancy mechanisms. Some relations of the present configuration to the Müller-Lyer illusion, and implications for the latter, are also discussed.

Discrimination Learning↗
PubMed1990

Distorted body image in normal college women: possible implications for the development of anorexia nervosa.

College women (N = 100) who averaged about 18 years of age were asked to rate the size of their bodies after looking in a mirror, and these ratings were compared to their actual body sizes. Women whose personality characteristics more closely resembled those proposed as basic to anorexic development in Slade's model were more inclined to overestimate body size, but only if they were relatively thin. A motivational role for body-image overestimation was suggested wherein this distortion serves to maintain dieting behavior even when a thin body is attained.

Adolescent↗
PubMed1991

Systematic distortions of shape from stereopsis.

The effectiveness of disparity information in defining 3-D shape was investigated by means of judgements of the shape of cylindrical continuous curved surfaces presented as random dot stereograms. At a close viewing distance, truly circular cylinders appeared elongated; at an intermediate distance, perception was close to veridical; and, at a far distance, cylinders appeared flattened. Indirect measures of scaling distance were calculated from these data. The results strongly suggest that the observed shape distortions are a consequence of scaling horizontal disparities with an incorrect measure of egocentric distance.

Depth Perception↗
PubMed1998

Repression: a mistaken impression?

How do clinical observations of repression square with experimental evidence suggesting that emotionally arousing memories are especially enduring? This discrepancy can be understood by examining three kinds of memory distortions that give the impression in a clinical context, of repression. Potentially traumatic events such as childhood sexual abuse (CSA) may be subject to ordinary forgetting. Recent research suggests people who fail to understand the sexual nature of CSA report that they remember it less well. In other words, the event occurred and it was forgotten, but not "repressed." In addition, people may be wrong about experiencing a period of forgetting, i.e. the event occurred but was never forgotten. Finally, people may believe that a particular traumatic event occurred and was repressed when, in fact, it did not happen in the first place. Under certain circumstances, some combination of these distortions could lead to situations that are mistakenly interpreted as repression.

Adolescent↗
PubMed1977

Depersonalization and temporal disintegration in acute mental illness.

The authors assessed the relationship between depersonalization (defined by self-estrangement and body image diffusion) and temporal disintegration (impaired goal-directedness and temporal indistinction) in 37 acutely ill hospitalized psychiatric patients. Substantial correlations were found between these two phenomena, confirming previous work. The finding that body image diffusion is positively correlated with temporal disintegration suggests that distortions of personal space accompany distortions of personal time.

Acute Disease↗
PubMed2006

Increasing honest responding on cognitive distortions in child molesters: the bogus pipeline procedure.

Professionals conclude that child molesters (CMs) hold offense-supportive beliefs (or cognitive distortions) from CMs'questionnaire responses. Because questionnaires are easily faked, we asked 32 CMs to complete a cognitive distortion scale under standard conditions (Time 1). A week later (Time 2), the same CMs completed the scale again. This time, approximately one half of CMs were attached to a pseudo lie detector (a bogus pipeline), and the rest completed the scale again under standard conditions (controls). At Time 1, CMs showed low cognitive distortion scores, seeming to indicate that they were faking good. At Time 2, bogus pipeline CMs seemed to believe that the apparatus could detect lies. However, this did not encourage more distorted belief disclosure compared with (a) their own previous scores and (b) controls. Furthermore, the bogus pipeline appeared to reduce cognitive distortion endorsements. The results stand in marked contrast to the common view that most CMs hold distorted beliefs.

Adult↗
PubMed1995

Changes in acoustic distortion during long term electrical stimulation of the guinea pig cochlea: a preliminary study.

In a preliminary study, acoustic distortion was assessed as a measure of cochlear function in both implanted and contralateral ears of electrically stimulated guinea pigs. Prestimulation distortion levels in implanted ears were below those of unimplanted ears and below those previously reported for guinea pigs. This may have been due to the mechanical or irritant effect of the electrode. In both the ipsilateral and contralateral ears or stimulated animals, distortion levels were depressed during the period of electrical stimulation. In addition, the slope of distortion growth as a function of stimulus level was more gradual in stimulated ears and contralateral ears of the same animals for f2 = 6 kHz and 9 kHz, but was unaffected for f2 = 3 kHz. When the distortion could no longer be recorded in the stimulated ear (4 subjects) or contralateral ear (1 subject) the animal was killed and histological evaluation carried out in both ears. Histological changes were restricted mainly to the efferent terminals in those ears where some distortion was still recordable. In one animal where distortion had become unmeasurable immediately prior to death, the outer hair cells were severely damaged and undergoing lysis. In this preliminary study, intersubject and between-test variability in distortion for implanted (ipsilateral) ears indicated that additional controls are necessary to establish the validity of alterations in acoustic distortion to reflect cochlear pathology.

Acoustics↗
PubMed2004

Distortions in the visual perception of shape.

It is known that visual illusions lead to a distorted perception of the length and orientation of lines, but it is not clear how these illusions affect the appreciation of the shape of closed forms. In this study two experiments were performed to characterize distortions in the visual perception of the shape of quadrilaterals and the extent to which these distortions were similar to the distortions of haptically sensed shapes. In the first experiment human subjects were presented with two quadrilaterals side by side on a computer monitor. One was a reference shape; the other was rotated and distorted relative to the first. The subjects used the computer mouse to adjust the corners of the distorted quadrilateral to match the shape of the target quadrilateral. They made consistent errors on this task: the adjusted quadrilateral was about 2% wider and about 2% shorter than the veridical shape. Furthermore, subjects adjusted the inner angles of the quadrilateral to make them closer to 90 degrees . The first type of error was also present in a second experiment in which, in a two-alternative forced-choice paradigm, subjects viewed a reference shape and were asked to indicate which of two transiently presented quadrilaterals was closest to the target shape. The width/height errors and the inner angle errors were comparable to those described previously when subjects felt the outline of a quadrilateral and then drew its reproduction in the absence of vision, suggesting that the distortion occurs in the process of remembering the shape.

Adult↗
PubMed1986

Detection of spatial beats: non-linearity or contrast increment detection?

We measured sensitivity of human observers to the 1 c/deg beat between sinusoidal gratings of 9 and 10 c/deg, at different contrasts of the 2 components. Raising the contrast of one component increases the contrast required in the other component to detect the beat. This is consistent with the hypothesis that the beat is detected because of the local increments in contrast which it produces, but not with the hypothesis that it is detected when a difference-frequency distortion product generated by non-linear transduction of luminance reaches threshold.

Discrimination, Psychological↗
PubMed1982

The influence of transient distortion on reaction time.

Reaction times to acoustic stimuli (250 and 4000 Hz sine waves) varying in rise-decay time (50, 25, 10, 5.0, and 1.0 msec) were obtained from normal hearing listeners (N = 3). Findings indicate that decreasing rise-decay time systematically distorts the shape of the latency-intensity function. Data from the shortest rise-decay condition suggests that transient distortion may affect a relatively small change in signal detectabiliity across a signal intensity range of 75 dB.

Adult↗
PubMed1981

Primary auditory neurons: nonlinear responses altered without changes in sharp tuning.

Two-tone suppression as well as distortion product responses in mammalian auditory neurons were altered by exposure to short, high intensity tones in the frequency region of the suppressing or primary tones. These changes occurred without significant alteration of the single neurons' tuning curves. The findings support the notion that two-tone suppression and distortion product responses are a function of the integrity of cochlear regions remote from the final transduction site.

Acoustic Stimulation↗