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 181 records · Page 10Linked to original sources
PubMed2006

Anxiolytic-like properties of the anandamide transport inhibitor AM404.

The endocannabinoids anandamide and 2-arachidonoyglycerol (2-AG) may contribute to the regulation of mood and emotion. In this study, we investigated the impact of the endocannabinoid transport inhibitor AM404 on three rat models of anxiety: elevated plus maze, defensive withdrawal and separation-induced ultrasonic vocalizations. AM404 (1-5 mg kg(-1), intraperitoneal (i.p.)) exerted dose-dependent anxiolytic-like effects in the three models. These behavioral effects were associated with increased levels of anandamide, but not 2-AG, in the prefrontal cortex and were prevented by the CB(1) cannabinoid antagonist rimonabant (SR141716A), suggesting that they were dependent on anandamide-mediated activation of CB(1) cannabinoid receptors. We also evaluated whether AM404 might influence motivation (in the conditioned place preference (CPP) test), sensory reactivity (acoustic startle reflex) and sensorimotor gating (prepulse inhibition (PPI) of the startle reflex). In the CPP test, AM404 (1.25-10 mg kg(-1), i.p.) elicited rewarding effects in rats housed under enriched conditions, but not in rats kept in standard cages. Moreover, AM404 did not alter reactivity to sensory stimuli or cause overt perceptual distortion, as suggested by its lack of effect on startle or PPI of startle. These results support a role of anandamide in the regulation of emotion and point to the anandamide transport system as a potential target for anxiolytic drugs.

Animals↗
PubMed2004

Representation of sound categories in auditory cortical maps.

Functional magnetic resonance imaging (fMRI) was used to investigate the representation of sound categories in human auditory cortex. Experiment 1 investigated the representation of prototypical (good) and nonprototypical (bad) examples of a vowel sound. Listening to prototypical examples of a vowel resulted in less auditory cortical activation than did listening to nonprototypical examples. Experiments 2 and 3 investigated the effects of categorization training and discrimination training with novel nonspeech sounds on auditory cortical representations. The 2 training tasks were shown to have opposite effects on the auditory cortical representation of sounds experienced during training: Discrimination training led to an increase in the amount of activation caused by the training stimuli, whereas categorization training led to decreased activation. These results indicate that the brain efficiently shifts neural resources away from regions of acoustic space where discrimination between sounds is not behaviorally important (e.g., near the center of a sound category) and toward regions where accurate discrimination is needed. The results also provide a straightforward neural account of learned aspects of perceptual distortion near sound categories: Sounds from the center of a category are more difficult to discriminate from each other than sounds near category boundaries because they are represented by fewer cells in the auditory cortical areas.

Acoustic Stimulation↗
PubMed2002

Tinted spectacles and visually sensitive migraine.

A double-masked randomized controlled study with cross-over design compared the effectiveness of precision ophthalmic tints in the prevention of headache in migraine sufferers. Seventeen patients chose the colour of light that optimally reduced perceptual distortion of text and maximized clarity and comfort. They were later given glasses with spectral filters providing optimal colour under conventional white lighting ('optimal' tint) or glasses that provided a slightly different colour ('control' tint). The tints were supplied in random order, each for 6 weeks, separated by an interval of at least 2 weeks with no tints. Headache diaries showed that the frequency of headaches was marginally lower when the 'optimal' tint was worn, compared with the 'control'. The trial extends to adults with migraine, the results of a previous double-masked study demonstrating, in children with reading difficulty, beneficial effects of precision tints in reducing symptom frequency. In the present study, however, the effects are suggestive rather than conclusive.

Adolescent↗
PubMed1999

A review of the management of 323 consecutive patients seen in a specific learning difficulties clinic.

Visual correlates of specific learning difficulties (SpLD) include: binocular instability, low amplitude of accommodation, and Meares-Irlen Syndrome. Meares-Irlen Syndrome describes asthenopia and perceptual distortions which are alleviated by using individually prescribed coloured filters. Data from 323 consecutive patients seen over a 15 month period in an optometric clinic specialising in SpLD are reviewed. Visual symptoms and headaches were common. 48% of patients were given a conventional optometric intervention (spectacles, orthoptic exercises) and 50% were issued with coloured filters, usually for a trial period. 40% of those who were given orthoptic exercises were later issued with coloured overlays. 32% of those who were issued with coloured overlays were ultimately prescribed Precision Tinted lenses. Approximately half the sample were telephoned more than a year after the last clinical appointment. More than 70% of those who were prescribed Precision Tints were still wearing them daily, and results for this intervention compared favourably with data for non-tinted spectacles. The data suggest that many people with SpLD need optometric care and that the optometrist needs to be skilled in orthoptic techniques and cognisant of recent research on coloured filters.

Accommodation, Ocular↗
PubMed1980

Evidence for the role of attentive fields in masking.

A masking task was employed to determine whether predictions derived from the attentive-field postulate of assimilation theory could be verified. The distance between masking and test lines was varied both towards and away from the center of the attentive field. As predicted, masking was greater when the mask was near the center of attention than when it was located at the periphery of the field. A variation of the mathematical formula developed previously to predict visual illusions was employed to fit the individual and group functions found in this study.

Attention↗
PubMed1994

Spatial content and spatial quantisation effects in face recognition.

It has recently become apparent that if face images are degraded by spatial quantisation, or block averaging, there is a nonlinear acceleration of the decline in accuracy of recognition as block size increases. This suggests recognition requires a critical minimum range of object spatial frequencies. Two experiments were performed to clarify the phenomenon. In experiment 1, the speed and accuracy of recognition for six frontoparallel photographs of faces were measured. After familiarisation training sessions, the images were shown for 100 ms with 11, 21, and 42 pixels per face, horizontally measured. Transformations calculated to remove the same range of spatial frequencies were performed by means of quantisation, a Fourier low-pass filter, and Gaussian blurring. Although accuracy declined and speed increased in a significant, nonlinear manner in all cases as the image quality was reduced, it did so at a faster rate for the quantised images. In experiment 2, faces rated as being typical were shown at 9, 12, 23, and 45 pixels per face and with appropriate Fourier low-pass versions. The nonlinear decline was confirmed and it was shown that it could not be attributed to a ceiling effect. A further condition allowed quantised and Fourier low-pass conditions to be compared with an unstructured-noise condition of equal strength to that of the quantised images. These gave comparable, but slightly less impaired, recognition than the quantised images. It can be inferred from these results that the removal of a critical range of at least 8-16 cycles per face of information explains the step decline in recognition seen with quantised images. However, the decline found with quantised images is reinforced by internal masking from pixelisation.

Adult↗
PubMed1995

Panum's limiting case: double fusion, convergence error, or 'da Vinci stereopsis'.

Panum's limiting case--a perceived depth difference between two lines in one eye combined with only one in the other eye--has long been considered weak or reversible. In the last few years this has led to strong promotion of the view that Panum's case is not based on a stereoscopic process involving double fusion, that only one line is fused, with the depth of the other one attributable either to fixation disparity or to occlusion cues. This view is refuted in two ways. First it is shown that when the separation of the two lines, considered as a disparity, is within the range of 'patent stereopsis', depth is perceived with a precision and accuracy indistinguishable from regular stereopsis. The predictions of nonstereoscopic theories concerning the effects of fixation are not borne out at small disparities. Second, very compelling Panum versions of orientation and curvature disparity are introduced, which are difficult to account for except by a process of double fusion. Finally it is shown that at large disparities the depth in Panum's case deviates from prediction more frequently than does regular stereoscopic depth.

Convergence, Ocular↗
PubMed2002

Salvinorin A: a potent naturally occurring nonnitrogenous kappa opioid selective agonist.

Salvia divinorum, whose main active ingredient is the neoclerodane diterpene Salvinorin A, is a hallucinogenic plant in the mint family that has been used in traditional spiritual practices for its psychoactive properties by the Mazatecs of Oaxaca, Mexico. More recently, S. divinorum extracts and Salvinorin A have become more widely used in the U.S. as legal hallucinogens. We discovered that Salvinorin A potently and selectively inhibited (3)H-bremazocine binding to cloned kappa opioid receptors. Salvinorin A had no significant activity against a battery of 50 receptors, transporters, and ion channels and showed a distinctive profile compared with the prototypic hallucinogen lysergic acid diethylamide. Functional studies demonstrated that Salvinorin A is a potent kappa opioid agonist at cloned kappa opioid receptors expressed in human embryonic kidney-293 cells and at native kappa opioid receptors expressed in guinea pig brain. Importantly, Salvinorin A had no actions at the 5-HT(2A) serotonin receptor, the principal molecular target responsible for the actions of classical hallucinogens. Salvinorin A thus represents, to our knowledge, the first naturally occurring nonnitrogenous opioid-receptor subtype-selective agonist. Because Salvinorin A is a psychotomimetic selective for kappa opioid receptors, kappa opioid-selective antagonists may represent novel psychotherapeutic compounds for diseases manifested by perceptual distortions (e.g., schizophrenia, dementia, and bipolar disorders). Additionally, these results suggest that kappa opioid receptors play a prominent role in the modulation of human perception.

Animals↗
PubMed1990

Structure of visual perception.

The response properties of a class of motion detectors (Reichardt detectors) are investigated extensively here. Since the outputs of the detectors, responding to an image undergoing two-dimensional rigid translation, are dependent on both the image velocity and the image intensity distribution, they are nonuniform across the entire image, even though the object is moving rigidly as a whole. To achieve perceptual "oneness" in the rigid motion, we are led to contend that visual perception must take place in a space that is non-Euclidean in nature. We then derive the affine connection and the metric of this perceptual space. The Riemann curvature tensor is identically zero, which means that the perceptual space is intrinsically flat. A geodesic in this space is composed of points of constant image intensity gradient along a certain direction. The deviation of geodesics (which are perceptually "straight") from physically straight lines may offer an explanation to the perceptual distortion of angular relationships such as the Hering illusion.

Animals↗
PubMed1990

Effects of stimulus degradation on letter-matching performance of left and right hemispheric stroke patients.

Performance on a letter-matching task involving conditions of perceptual degradation was tested on 18 Right CVA patients, 18 Left CVA patients and 18 control subjects. Letter stimuli were presented in three conditions: Clear, Line-Masked, and Blurred. Subjects judged whether two letters of a pair were the same in name or different in name. Right CVA patients performed significantly less accurately than did Left CVA patients and control subjects when letters were perceptually degraded with a line mask overlay or by blurring. No significant differences were found between the two patients groups when the letters were presented without perceptual degradation (the Clear condition), but both patient groups were significantly less accurate than control subjects. The results are similar to findings reported in visual half-field studies with neurologically normal subjects and indicate right-hemisphere superiority for the processing of perceptually degraded visual information.

Adult↗
PubMed2002

The link between childhood trauma and later violent offending: the application of attachment theory in a probation setting.

This case-study identifies the links between an insecure-avoidant pattern of attachment organization, unresolved childhood trauma, emotional detachment, substance misuse and violent offending behaviour in adulthood. It demonstrates the way in which attachment theory may be used to explicate offending behaviour and to assess risk in a forensic setting. Further, the model illustrates that the clinical application of attachment theory in brief, time-limited work may enhance the offender's capacity for narrative intelligibility leading to an integration of dissociated thoughts and emotional affect, and to a concomitant cessation of violent behaviour. The process is intersubjective and involves the modification and updating of maladaptive, perceptually distorted cognitive-affective internal working models. This is accomplished by strengthening the offender's capacity for reflective thought, which, in turn, facilitates the organization and integration of error-correcting information.

Alcoholism↗
PubMed1991

Single band amplitude envelope cues as an aid to speechreading.

Amplitude envelopes derived from speech have been shown to facilitate speech-reading to varying degrees, depending on how the envelope signals were extracted and presented and on the amount of training given to the subjects. In this study, three parameters related to envelope extraction and presentation were examined using both easy and difficult sentence materials: (1) the bandwidth and centre frequency of the filtered speech signal used to obtain the envelope; (2) the bandwidth of the envelope signal determined by the lowpass filter cutoff frequency used to "smooth" the envelope fluctuations; and (3) the carrier signal used to convey the envelope cues. Results for normal hearing subjects following a brief visual and auditory-visual familiarization/training period showed that (1) the envelope derived from wideband speech does not provide the greatest benefit to speechreading when compared to envelopes derived from selected octave bands of speech; (2) as the bandwidth centred around the carrier frequency increased from 12.5 to 1600 Hz, auditory-visual (AV) performance obtained with difficult sentence materials improved, especially for envelopes derived from high-frequency speech energy; (3) envelope bandwidths below 25 Hz resulted in AV scores that were sometimes equal to or worse than speechreading alone; (4) for each filtering condition tested, there was at least one bandwidth and carrier condition that produced AV scores that were significantly greater than speechreading alone; (5) low-frequency carriers were better than high-frequency or wideband carriers for envelopes derived from an octave band of speech centred at 500 Hz; and (6) low-frequency carriers were worse than high-frequency or wideband carriers for envelopes derived from an octave band centred at 3150 Hz. These results suggest that amplitude envelope cues can provide a substantial benefit to speechreading for both easy and difficult sentence materials, but that frequency transposition of these signals to regions remote from their "natural" spectral locations may result in reduced performance.

Adult↗
PubMed1995

Cross-over, completion and confabulation in unilateral spatial neglect.

Patients with left-sided neglect generally mis-bisect horizontal lines to the right of mid-position. However, with short lines they frequently cross over and place their marks to the left; a phenomenon not easily explained by current theories of neglect. It is difficult to ascertain whether patients neglect the ipsilateral segment of short lines, perceptually distort these lines, or extend these lines leftward at a representational level. Reading horizontally arrayed letter strings is an alternative task potentially capable of sorting between these hypotheses, providing this task could be demonstrated to be comparable to line bisections. In this study, we exploit the observation that line bisection performance may be described by a power function: psi = K phi beta, in which psi represents the subjective awareness of lines and the objective measurements of these lines. The constant and exponent are empirically derived. We have investigated whether reading task performance also subscribes to power functions. Five patients with left-sided neglect were tested on line bisections and reading tasks with stimuli of varying horizontal lengths. Performance on both tasks could be described by power functions and patients were similarly ordered by severity across both tasks. Since power function analyses established that these tasks were comparable, reading performance on short words provided insight into how patients bisected short lines. Patients reported additional letters to the left end of short words suggesting that cross-over bisections are analogously a consequence of completion or confabulation of short lines beyond their objective left end-point. Although most neglect patients have difficulties forming veridical left-sided representations, this cross-over phenomenon is interpreted as resulting from a lack of inhibition of leftward confabulatory mental representations. Since both bisections and reading tasks are described by a continuous function, it is proposed that similar lack of inhibition must also be present, albeit hidden, when patients confront stimuli with longer lateral extension. Confabulatory phenomena at the left edge of these patients' rightwardly constricted attentional window, may be far more common than hitherto appreciated.

Aged↗
PubMed1998

Transcranial magnetic stimulation in study of the visual pathway.

The authors critically reviewed experiments in which transcranial magnetic stimulation (TMS) and repetitive TMS (rTMS) of the higher visual pathway were used. Topics include basic mechanisms of neural excitation by TMS and their relevance to the visual pathway (excitatory and inhibitory effects), TMS and rTMS of calcarine cortex (suppression, unmasking, and phosphenes), TMS of V5 (suppression), TMS and rTMS of higher level temporoparietooccipital areas (perceptual errors, unmasking, and inattention), the role of frontal lobe output in visual perception, and vocalization of perceived visual stimuli (role of consciousness of linguistic symbols).

Attention↗
PubMed1975

Diurnal variation in depression--is it there?

In this paper we present the results of an investigation designed to measure diurnal variation of mood in a group of unipolar depressives using a sensitive self-assessment inventory and a behavioral measure of the depth of depression. Both measures correlate well with the Hamilton Rating Scale which was designed to quantify depression during a psychiatric interview. Although all patients included in our sample reported that they experienced diurnal variation in mood, this fluctuation was not manifest on behavioral measures and only one patient showed a significant difference on the depressive inventory. Our data indicate that self-report and behavior may not be affected by diurnal variation in eight of these nine depressed patients. One possible explanation is that self-report in depression is subject to perceptual distortion leading to retrospective falsification.

Adult↗
PubMed2002

Posttraumatic, dissociative and grief symptoms in Turkish children exposed to the 1999 earthquakes.

Grief and dissociation after traumatic exposures are among the most important predictors of posttraumatic stress disorder (PTSD). This article introduces the Traumatic Dissociation and Grief Scale (TDGS), a 23-item measure easily administered. The TDGS, the Child PTSD-Reaction Index (CPTSD-RI), and a questionnaire concerning risk factors related to the event (losses, injury, and witnessing death and injuries) were administered to school-aged children who had been directly exposed to the 1999 earthquakes in Turkey and to a nonexposed control group. Factor analysis of the TDGS yielded four factors: perceptual distortions, body-self distortions, irritability, and guilt and anhedonia. A moderate positive correlation was noted between the TDGS and the CPTSD-RI. Different sets of risk factors were associated with the different scale factors. The results suggest that the assessment of psychopathology in children following a disaster requires the complementary evaluation of symptoms of posttrauma, dissociation, and grief.

Age Factors↗
PubMed1982

Asynchronous cortical input and asthenopia.

Abnormal delays in retinal-cortical transmission are typically associated with optic nerve disease. Clinically optic nerve diseases produce visual field abnormalities, decreased visual acuity, and color vision defects. Disease processes causing only interocular differences in retinal-cortical transmission properties are not easily detected. Patients with diseases causing interocular latency differences may complain of visual discomfort and perceptual distortions yet perform normally in standard clinical tests. A simple procedure to minimize differences in interocular latency and provide relief from visual disturbances arising from this abnormality is described.

Asthenopia↗