Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Perceptual Distortion”

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.

At least 523 records · Page 29Linked to original sources
PubMed1996

Explaining impossible phenomena: object permanence beliefs and memory failures in adults.

In three experiments, adult subjects' explanations of the observed nonpermanence of a physical object and their recollections of the order of the events during the experiment were obtained and analysed. The data showed that in order to conserve their strong beliefs in object permanence subjects systematically distorted the real temporal succession of events preceding the phenomenon. The frequency of the distortions depended on the salience of the nonpermanence phenomenon ("disappearance" versus "appearance" of the physical object) and on the time interval between the events whose temporal order was reversed, but not on subjects' nationality (English versus German), gender, type of reproduction (immediate versus delayed), role in the experiment (subject versus observer), and degree of prompting in questioning.

Adolescent↗
PubMed1999

Visual distortions and dissociation.

Visual distortions may be a frightening experience. They are often incorrectly diagnosed and easily dismissed. The causes of visual distortions are poorly understood. The aim of this study was to investigate the link between visual distortions and dissociative experiences in a nonclinical population. A total of 297 nonclinical volunteers completed the Dissociative Experience Scale and answered questions concerning visual distortions. Our study suggests that visual distortions are quite common and that there is a clear link between visual distortions and dissociative phenomena. Literature indicates that this may be caused by disturbances in brain lateralization. Bilateral language capacity may interfere with abilities usually associated with the nondominant hemisphere. Research efforts attempting to shed light on the above matter may benefit our knowledge for dissociative phenomena. An interdisciplinary approach is needed.

Adolescent↗
PubMed1977

Mirror-image response during the first two years of life.

Children aged 1-24 months viewed themselves in planar or distorted mirrors that were either clear or partially occluded. Analysis of videotaped records revealed that interest in viewing one's face did not vary with age among the 1- to 24-month-old subjects. All performed the simple behaviors of observing themselves although the older ones performed more complex (related) behaviors. Neither the flat nor the distorted mirror exposure was preferred suggesting that the infant observes the general configuration of the face for its intrinsic interest. Specific developmental trends were noted in the kind and amount of activity during the 1st 2 years of life culminating in a sequence of behaviors that suggested self-recognition.

Age Factors↗
PubMed1996

To be or not to be at home? A neuropsychological approach to delusion for place.

A woman, LB, while in recovery from a viral encephalitis, exhibited a delusion for place, which led her to insist that she was at home, in spite of compelling evidence to the contrary. Later, she developed a Capgras syndrome, that is, another misidentification syndrome. The patient was given a detailed neuropsychological evaluation to shed light on the mechanisms underlying her delusional misbelief. Two main deficits were in evidence: (1) a severe visual-spatial impairment, giving the patient a distorted perception of her surroundings; and (2) frontal lobe dysfunction, which played a critical role in her impulsive responses and lack of self-awareness. The pathogenesis of delusion for place and persons if discussed in light of these observations.

Awareness↗
PubMed1978

Classification of random forms and distortions presented to the left or right visual field.

Twenty right-handed undergraduate men were taught in free vision to categorize distortions of prototypic random forms and were then tested in a Go/No Go task with lateralized tachistoscopic presentations of previously sorted (old) distortions, new distortions, the prototypes, and unrelated forms. Accuracy of performance on positive items increased in the order New less than Old less than Prototype. More false alarms occurred to unrelated items in the right than in the left visual field, suggesting that the trace systems generated during training had different characteristics in the two hemispheres.

Discrimination Learning↗
PubMedDate not supplied

[Standard parameters of distortion products].

In this study we have analyzed the incidence, range, frequency spectrum and threshold of distortion products in a sample of 232 normal hearing person. 116 younger adults, 58 female ranging in age from 18 to 30 years (mean age 23.1) and 58 males ranging in age from 18 to 32 (mean age 23.7) were included in the study. In all the ears studied, the presence of distortion products in a normal ear were found with regularity in the frequency region between 700 to 6,000 Hz. Higher incidence occurred in younger people and women but was not statistically notable. There is a direct correlation between distortion products amplitude and its primary intensity. Distortion products amplitude increases progressively from low (770 Hz) to high frequencies (6,000 Hz). The amplitude of distortion products and its mean value is higher in women, in all frequencies, except in the 700 to 1,000 Hz region. Input/output function had a mean of 50 dB SPL at 1 kHz, 43.8 at 2 kHz, 38.4 at 4 kHz and 33.5 at 6 kHz.

Acoustic Stimulation↗
PubMed2004

Cochlear delays measured with amplitude-modulated tone-burst-evoked OAEs.

Delay times in the mammalian cochlea, whether from measurement of basilar membrane (BM) vibration or otoacoustic emissions (OAEs) have, to date, been largely based on phase-gradient estimates from steady-state responses. Here we report cochlear delays measured directly in the time domain from OAEs evoked by amplitude-modulated tone-burst (AMTB) stimuli. Measurement using OAEs provides a non-invasive estimate of cochlear delay but is confounded by the complexity of generation of such OAEs. At low to moderate stimulus levels, and provided that the stimulus frequency range does not include a region of the cochlea where there is a large change in effective reflectance, AMTB stimuli evoke an OAE with an envelope shape that is similar to the stimulus and allow a direct calculation of cochlear group delay. Such delays are commensurate with BM estimates of delay, estimates of cochlear delay inferred from neural recordings, and previous OAE measures of delay in the guinea pig. However, a nonlinear distortion mechanism, variation in effective reflectance, and intermodulation distortion products generated by the nonlinear interaction in the cochlea of the carrier and sidebands of the AMTB stimulus, may all contribute to OAEs arising with envelope shapes that are not a scaled representation of the stimulus, confounding the estimation of cochlear group delay.

Acoustic Stimulation↗
PubMed1996

Suppression of human acoustic distortion product: dual origin of 2f1-f2.

In order to explore the origin of acoustic distortion product (DP) in the ear canal, the effect of the level and the frequency of the suppressor tone on the level of the DP was investigated. The results broadly support previous studies in showing that, with increasing suppressor level, the DP level shows an initial relatively stable plateau or gradual decline, followed by a rapid decline. The shape of the human iso-suppression contours derived from these "suppression-rate" curves was found to depend upon the size of the iso-suppression criterion. Low-level suppressor tones close in frequency to 2f1-f2 were effective at suppressing the DP by up to 3 dB in subjects where the distortion frequency fell at a region of strong stimulus frequency re-emission. It is probable that contributions from the DP frequency region, as well as components from the primary frequency region, make up the ear canal measured DP. With a 6-dB iso-suppression criterion, suppressor tones in the primary frequency region suppress DP most effectively.

Acoustics↗
PubMed2004

Memory and emotions for the september 11, 2001, terrorist attacks in patients with Alzheimer's disease, patients with mild cognitive impairment, and healthy older adults.

National traumatic events can produce extremely vivid memories. Using a questionnaire administered during telephone interviews, the authors investigated emotional responses to, and memory for. the September 11, 2001, terrorist attacks in patients with Alzheimer's disease (AD), patients with mild cognitive impairment (MCI), and healthy older adults in the initial weeks following the event and again 3-4 months later. There were several notable findings. First, patients with AD showed less memory than patients with MCI and older adults. Second, patients with AD, but not patients with MCI or older adults, appeared to retain more memory for personal versus factual information. Third, patients with AD and older adults did not differ in the intensity of their reported emotional responses to the attacks, whereas patients with MCI reported relatively less intense emotional responses. Last, distortions of memory for personal information were frequent for all participants but were more common in patients with AD.

Aged↗
PubMed1996

Performance of 3-D digitizing in stereoscopic images.

Experiments were conducted to understand the basic characteristics of pointing to three-dimensional images generated by stereoscopic images. The experimental examination found that it was difficult to point to the correct position of the image and that the depth of the image was underestimated so that the object perceived by the subject was distorted. Subjects who were familiar with viewing 3-D images made less error in position and size perception than did subjects having little experience in viewing 3-D images. These results imply that the performance of 3-D pointing in stereoscopic 3-D images will improve with experience although it is difficult to perform a 3-D pointing precisely.

Adult↗
PubMed2000

Revisiting the perception of upside-down faces.

In two experiments, the effect of orientation on face perception was assessed. Using a scale from 1 (normal) to 7 (bizarre), participants rated normal, unaltered faces and faces in which changes had been made to spatial-relational properties (eyes and mouth inverted or relative position of the eyes and mouth altered) or to component properties (eyes whitened and teeth blackened). For unaltered and component-distortion faces, bizarreness ratings increased linearly as orientation increased from 0 degree to 180 degrees. For spatial-distortion faces, a discontinuity in the function relating orientation and bizarreness was in evidence between 90 degrees and 120 degrees. The results provide support for the view that there is a qualitative difference in the processing of upright and inverted faces due to the disproportionate effect of inversion on the encoding of spatial-relational information.

Adult↗
PubMed2002

Distinguishing prototype-based and exemplar-based processes in dot-pattern category learning.

The authors contrast exemplar-based and prototype-based processes in dot-pattern categorization. In Experiments 1A and 1B, participants provided similarity ratings of dot-distortion pairs that were distortions of the same originating prototype. The results show that comparisons to training exemplars surrounding the prototype create flat typicality gradients within a category and small prototype-enhancement effects, whereas comparisons to a prototype center create steep typicality gradients within a category and large prototype-enhancement effects. Thus, prototype and exemplar theories make different predictions regarding common versions of the dot-distortion task. Experiment 2 tested these different predictions by having participants learn dot-pattern categories. The steep typicality gradients, the large prototype effects, and the superior fit of prototype models suggest that participants refer to-be-categorized items to a representation near the category's center (the prototype), and not to the training exemplars that surround the prototype.

Attention↗
PubMed1976

Dyslexia and specifically distorted drawings of the face - a new subgroup with prosopagnosia-like signs.

Identification of a subgroup (38%) of dyslexics (new syndrome?). These, against controls (5.5%), drew 'neolithic' face configurations analogous to those visually experienced in prosop-agnosia. Essential symptoms of this subgroup are seen as result of specific early ways of processing visual data: lexical shapes (letters, words) and facial features, as if these were concrete entities, not abstract component parts. Thus, with letters, taken as entities, d = q, d = b, N = Z.

Adolescent↗
PubMed1979

Effects of high-frequency cue reduction on the comprehension of distorted speech.

Forty-five subjects with sharply sloping sensorineural high-frequency hearing losses were examined for comprehension with a tape containing sentences that had been time-compressed (250 words/min), interrupted, (50 msec on-50 msec off), and masked with speech-spectrum noise (+2 dB S/N) in that order. All subjects yielded normal speech reception thresholds, and generally normal scores on the Northwestern University Auditory Test No. 6. Distorted-speech testing was completed at 40 dB SL. Subjects with losses at 2 kHz and above were able to comprehend only 50, 65, and 68% of compressed, interrupted, and noise-masked sentences, respectively. In contrast, subjects with losses at 3 kHz and above performed poorer than normal controls by 11.3, 12.5, and 8% points respectively, while subjects within normal hearing sensitivity at 3 kHz performed as well as controls (maximum drop of 4.6 points with noise-masking). The multiplicative hypothesis was upheld in that the performance of subjects with severe high-frequency deficiencies was much poorer than one would predict on the basis of what is known about performance on these tests with either filtering alone or other distortions alone. These subjects, most especially those with severe frequency deficiencies, outperformed by up to 29 percentage points the mean scores of groups of normals given the same test items and distortion conditions, but listening through filtering that simulated the hearing loss of subjects in this study. It was suggested that hypacusics with high-frequency hearing losses can learn to use residual cues efficiently and that it is not altogether permissible to model sensorineural high-frequency losses with normal-hearing subjects using frequency filtering.

Adult↗
PubMed1984

Measurements of the Pulfrich effect over days of exposure.

Mean depth settings and subjective reports appear to confirm previous subjective reports from users of the X-Chrom prescription lens that Pulfrich Effect depth distortions decrease with continued exposure to light intensity disparity. Depth setting variability across Days of exposure indicates a rapid increase in depth judgment errors which persists without decrement across Days. This increased variability, the apparent depth decrements, and color discrimination improvements shed light on the visual processing underlying the Pulfrich Effect and reveal a potentially dangerous illusion.

Adult↗
PubMed1978

Geometric transformations of pictured space.

In general, a picture can represent a specific environment of scene only when the picture is seen from a unique viewing point. The determination of this unique point and of the distortions that occur when the picture is viewed from other points is crucial to all aspects of pictorial perception. To clarify the effects of the point of observation on pictorial space, the present paper discusses how the correct point may be calculated, provides a geometric analysis of the effects of altering the viewing point, and briefly reviews the effects of such alterations on space perception.

Depth Perception↗
PubMed1995

The box alignment illusion: an orientation illusion induced by pictorial depth.

In four experiments, observers attempted to align two sets of oblique edges to parallel. The contexts for these alignments included lines in isolation (2-D control), lines embedded in orthogonal drawings of same-oriented and different-oriented boxes (3-D objects), and each of these viewed against backgrounds depicting strong linear perspective (3-D backgrounds). A consistent distortion was observed in the alignments of different-oriented boxes relative to control lines, indicating that the parallel lines in these stimuli appeared to diverge toward the top of the picture. Furthermore, this box alignment illusion decreased with interstimulus distance, whereas alignment distortions in control lines and same-oriented boxes increased with distance. Viewing the stimuli against 3-D backgrounds produced a dramatic reversal of the illusion, with control lines now appearing to converge more than the boxes. These results suggest that the illusion reflects basic processes involved in pictorial depth perception.

Adult↗
PubMed2004

Spatiotemporal continuity implicated in the binding of features and object identity.

This study continues the work of Anes et al. (in preparation) in which manipulation of features incidental to an object elicited robust effects in a dynamic object recognition paradigm. In the current series, the spatiotemporal continuity of identity and feature presentation is increasingly distorted between experiments in an attempt to disrupt a process Triesman (1996) calls "binding" of an object's identity and features. Across three experiments, increasing disruption of spatiotemporal continuity significantly diminished the effect of features on object identification, evidence that spatiotemporal continuity is, in part, responsible for binding features to an object.

Adult↗