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At least 865 records · Page 48Linked to original sources
PubMed1989

A physiological correlate of the Pulfrich effect in cortical neurons of the cat.

When a swinging pendulum is viewed with a light-attenuating filter before one eye, the pendulum bob is perceived to move in an elliptical path in depth. It is believed that the filter causes this illusion, the Pulfrich effect, by delaying processing of the image in the filtered eye relative to that of the unfiltered eye. We sought a physiological correlate of this effect by studying binocular integration in cortical neurons of cats while they viewed moving stimuli. Special attention was focused on single unit disparity tuning because it is widely believed that depth perception is related to the responses of disparity selective neurons in visual cortex. We found that placing a filter before one of the cat's eyes produced a temporal delay in the cortical response. The temporal delay was always associated with a shift in the neuron's spatial disparity tuning. The observed temporal delays and disparity shifts are comparable with the magnitude of the Pulfrich effect in humans.

Action Potentials↗
PubMed1990

Psychophysical measurement of the blur on the retina due to optical aberrations of the eye.

The blur on the retina in the horizontal meridian due to monochromatic and chromatic aberrations has been measured using a novel psychophysical technique. Longitudinal chromatic aberration gives the dominant blur for pupil sizes of 4-5 mm, followed by monochromatic aberrations, and blur due to optical transverse chromatic aberration. In some eyes, coma was present as a result of a displacement of the axis of symmetry from the centre of the pupil, but in three eyes, coma was present without spherical aberration. The technique also allows a measurement of the effective pupil centre relative to the geometric centre and a partial analysis of the relative positions of the reference axes of the eye.

Adolescent↗
PubMed1993

The effect of interactions between one-dimensional component gratings on two-dimensional motion perception.

Ferrera and Wilson [(1990) Vision Research, 30, 273-287] reported veridical perception of the direction of motion of Type I plaids, whose component gratings span the resultant direction, but marked misperception of the direction of motion of Type II plaids, whose component gratings both lie on one side of the resultant direction. Because they failed to find any effect of component direction (angular) separation on this misperception, Ferrera and Wilson concluded that the misperception was not due to perceptual repulsion of component directions. We report that component direction repulsion does occur, that plaid direction misperception is tuned to component separation, with larger repulsions for smaller angles. It is concluded that there is no fundamental difference in direction coding for Type I and Type II plaids, and that Ferrera and Wilson failed to find a direction separation effect because the range of separations they used was insufficiently broad to detect the slope of the angular function.

Humans↗
PubMed1994

The spatial properties of binocular suppression zone.

Spatial properties of binocular suppression zones were studied with one-dimensional difference of Gaussian (DOG) patterns. Two parallel DOG patterns were presented in one eye and a single DOG, perpendicular to the double DOG, was presented to the other eye. When viewed together, the probability of seeing the portion of the single DOG in between of the double DOG depended on the separation of the double DOG stimulus. Threshold separations for detecting an intermediate segment of the single DOG pattern (binocular suppression zones) were measured as a function of spatial frequency, contrast and orientation of the stimuli. The diameter of suppression zone decreased proportionally with increasing peak spatial frequency of the DOG patterns. The vertical dimension of the suppression zone was larger than the horizontal dimension at low spatial frequencies but the inverse tended to occur at high spatial frequencies. Diameter of the suppression zone increased rapidly with increasing contrast of the stimuli when the contrast was lower than 20-30% but asymptoted at higher contrasts.

Contrast Sensitivity↗
PubMed1990

Typicality effects in artificial categories: is there a hemisphere difference?

In category classification tasks, typicality effects are usually found: accuracy and reaction time depend upon distance from a prototype. In this study, subjects learned either verbal or nonverbal dot pattern categories, followed by a lateralized classification task. Comparable typicality effects were found in both reaction time and accuracy across visual fields for both verbal and nonverbal categories. Both hemispheres appeared to use a similarity-to-prototype matching strategy in classification. This indicates that merely having a verbal label does not differentiate classification in the two hemispheres.

Adult↗
PubMed1991

Device for quantifying tactile neglect in stroke patients.

Perceptual problems such as tactile neglect are important features of stroke and strong predictors of a poor outcome. Although new methods of treatment have been described, documentation of the effects of such treatment is inadequate, mainly because satisfactory methods of quantifying tactile neglect are unavailable. We describe a device for quantifying neglect based upon the principle of the Bender test which uses double or simultaneous bilateral stimulation to determine neglect. The device, which is computer driven to ensure uniformity of test protocols, determines the cutaneous perceptual threshold to controlled-current electrical stimulation using surface electrodes. The effect of rival contralateral stimulation on the perceptual thresholds on the affected side of the patient's body is a quantitative measure of tactile neglect. The device was evaluated in normal young and neurologically normal elderly subjects and in stroke patients with clinical evidence of tactile neglect. It was shown to distinguish reliably between normal subjects and those who had tactile neglect. The device will be suitable for use in trials of treatments for tactile neglect and in tracking the natural history of this symptom.

Adult↗
PubMed1990

Discerning the latent structure of hypothetical psychosis proneness through admixture analysis.

The application of psychometric procedures to a normal population sample to detect individuals with increased liability for schizophrenia is a useful methodological adjunct to the traditional genetic high-risk strategy. A necessary and reasonable step in the process of establishing the utility of a viable psychometric index of schizotypy is the formal investigation of the latent structure of psychometric values. The present study used admixture analysis to examine the distribution of scores on the Perceptual Aberration Scale (PAS), an objective measure of hypothetical psychosis-proneness, in a randomly ascertained sample of 18-year-old university students (n = 707). We applied parametric methods that assumed normally distributed component distributions; viewed in this context, our results are hypothesis-generating and not definitive confirmation of specific hypotheses. Within our methodological framework, the results provide strong evidence for the commingling of normal distributions, even after allowing for unequal variances across components and after removing skewness. The overall distribution of power-transformed data is consistent with the existence of three qualitatively distinct classes of PAS responders. We discuss our results in light of Meehl's model of schizotaxia, a "mixed model" of inheritance of liability to schizophrenia, and we review the methodological implications of our findings for future research.

Adolescent↗
PubMed1991

Confirming schizotypic personality configurations in hypothetically psychosis-prone university students.

The personality features of hypothetically psychosis-prone (or schizotypic) subjects were examined. Schizotypic (n = 32) and control (n = 44) subjects were identified within a pool of 726 randomly ascertained nonclinical university students who had completed the Perceptual Aberration Scale (PAS) during a large-scale screening study. Approximately 4-6 months after the initial screening, the schizotypic and control subjects completed the Minnesota Multiphasic Personality Inventory (MMPI). Schizotypic subjects as a group displayed an average MMPI profile consistent with schizotypic personality features, whereas the control subjects did not. Moreover, multivariate profile analysis revealed that the schizotypic group MMPI profile differed significantly in shape from the control group profile. Finally, schizophrenia-related MMPI high-point codes were five times as prevalent among the PAS-identified schizotypic subjects as among the controls. The results suggest that the PAS identifies individuals who show schizotypic personality MMPI configurations and may carry a latent vulnerability for schizophrenia or, more broadly, psychosis.

Adult↗
PubMed1996

The effects of visual cortex lesions on the perception of rotated shapes.

Monkeys with inferior temporal cortex lesions cannot discriminate between different shapes (e.g., + vs. O) but can discriminate between shapes that differ only in orientation (e.g., 6 vs 9). Lesions of the parietal cortex, on the other hand, impair the discrimination of rotated shapes but spare the ability to discriminate between different shapes. A similar dissociation is found between some visual agnosics who can match but not identify rotated views of objects and other patients who can identify and discriminate objects only if the view is conventional; any change in orientation disrupts performance. In this paper we argue that two mechanisms may be available for the perception of rotated shapes. Which mechanism is used depends on the degree of rotation. It is suggested that the different effects of parietal and temporal lesions reflect the relative contributions of the two areas to the task and disrupt different stages of the two strategies used. A framework for the cortical processing of rotated shapes in the non-human primate is presented.

Agnosia↗
PubMed1994

Impaired perception of moving objects after minor injuries to the eye and midface: the Pulfrich phenomenon.

Delayed conduction along one optic nerve can result in an incorrect appreciation of moving objects. The temporal mismatch between the two different pathways results in altered perception of the vector of a moving target and is known as 'the Pulfrich phenomenon'. This is a well-recognised handicap in patients with multiple sclerosis, but has not previously been reported as a consequence of injury. All 187 patients who presented during 1991 with reduced visual acuity as a result of midfacial injuries were examined with a pendulum. Six had the defect and five of these had symptoms. In each case the patients were disturbed by car travel, because they perceived oncoming traffic moving in a hyperbolic curve towards them. These patients have been examined in detail and given a tinted lens for the normal eye to eliminate the illusion by delaying the input from the normal side to equal that on the damaged side. We recommend that this phenomenon is sought in all patients with mid-facial injuries or with later evidence of mild traumatic optic neuropathy, particularly if they are disturbed by car travel.

Automobiles↗
PubMed1990

Psychology of time awareness.

Mind transforms the continuance of physical space-time into moments (the absolute Now) and blends these moments into an apparent continuity through an overlapping of unfolding capsules. The flow of psychological time is an illusion based on the rapid replacement of these capsules. Each mind computes the measure of time passing and duration from the decay of the surface present in relation to a core of past events. As each new surface is generated, that surface, the rim of the immediate past, recedes in the wake of rising contents. This recession, an uncovering of phases latent in the original traversal, exposes layers in the past forming the content of the immediate past moment. The surge of the microgeny to a surface that dissolves the instant it appears, the priority of the Self in the unfolding sequence, the feeling of agency, create a Self in a state of becoming, a Self that travels in time like the crest of a wave, always in pursuit of a future just beyond the grasp of the present.

Arousal↗
PubMed1990

Pathological gambling treated with cognitive behavior therapy: a case report.

A novel approach to the cognitive behavioral treatment of pathological gambling is described. The approach is based on the hypothesis that biased information may form the basis of the rules governing gambling behavior. The treatment focused on modifying assumptions and beliefs underlying the gambling behavior of a 47-year-old male with a 26-year gambling history. Based on a 6-month follow-up, the intervention successfully reduced the frequency of the client's gambling behavior from 10 times per month in the 3 years prior to treatment to three total times in the 6-month follow-up period.

Alcoholism↗
PubMed1983

Neural correlates of cubic difference tones in the medial geniculate body of the cat.

Single unit responses to the cubic difference tone CDT (2f1 - f2 = CF) and the difference tone DT (f2 - f1 = CF) were studied in the medial geniculate body (MGB) of the cat. Out of 66 units tested with CDT stimuli and having characteristic frequencies (CF) below 10 kHz, 77% gave a response to the two-tone combination stimulus. The component tones when presented alone evoked no responses, or in some cases a response pattern that was different from the one observed for the combination tone. The CDT response pattern was always similar to that seen for a pure tone at the CF. The threshold of response for the CDT was 10-70 dB higher than for a pure tone stimulus at the CF. The few units which were phase-locked could be synchronised with the CF, CDT, or DT, depending on the particular stimulus conditions. The index of synchrony was in many cases found to be higher for CDT responses than for a pure tone at CF.

Animals↗
PubMedDate not supplied

Alice in Wonderland syndrome as a presenting symptom of EBV infection.

Four Chinese patients (2 boys, 2 girls), ages 4-9 years, who had episodes of perception error of body schema and objects are reported. The metamorphopsia, which had been named Alice in Wonderland syndrome, is the major presentation. All of them were proved to have acute Epstein-Barr virus infection, as documented by positive heterophil antibody test and/or positive IgM antibody to Epstein-Barr virus capsid antigen. The duration of the perception disorder ranged from 1 week to 3 months. We believe that any young child presenting with Alice in Wonderland syndrome should undergo examination for Epstein-Barr virus infection; complete recovery from the disorder can be expected.

Antibodies, Viral↗
PubMed2005

Catching and matching bars with different orientations.

The hypothesis that perception enslaves action is examined by assessing whether systematic distortions in perceptual judgments are reflected by inaccuracies in catching. In the first experiment, participants had to align manually the orientation of a reference bar placed at different distances in the frontoparallel plane. In the second experiment participants had to catch differently orientated moving bars, which became invisible at different distances from the interception point. In the matching experiment, systematic errors in the alignment of orientation were found in particular for oblique orientations, the magnitude of which increased with increasing distance of the reference bar. The inaccuracies in the final hand orientation during the catching task, however, did not mirror this pattern of deviations. The findings are interpreted to be more consistent with recent views that vision for perception (i.e., matching) and vision for action (i.e., catching) are dissociated than with the view that perception enslaves action.

Adult↗
PubMed2006

Assessing the influence of schematic drawings of body parts on tactile discrimination performance using the crossmodal congruency task.

Seeing one's own body (either directly or indirectly) can influence visuotactile crossmodal interactions. Recently, it has been shown that even viewing a simple line drawing of a hand can also modulate such crossmodal interactions, as if the picture of the hand somehow corresponds to (or primes) the participants' own hand. Alternatively, however, it could be argued that the modulatory effects of viewing the picture of a hand on visuotactile interactions might simply be attributed to cognitive processes such as the semantic referral to the relevant body part or to the orientation cues provided by the hand picture instead. In the present study, we evaluated these various different interpretations of the hand picture effect. Participants made speeded discrimination responses to the location of brief vibrotactile targets presented to either the tip or base of their forefinger, while trying to ignore simultaneously-presented visual distractors presented to either side of central fixation. We compared the modulatory effect of the picture of a hand with that seen when the visual distractors were presented next to words describing the tip and base of the forefinger (Experiment 1), or were superimposed over arrows which provided another kind of directional cue (Experiment 2). Tactile discrimination performance was modulated in the hand picture condition, but not in the word or arrow conditions. These results therefore suggest that visuotactile interactions are specifically modulated by the image of the hand rather than by cognitive cues such as simply semantic referral to the relevant body sites and/or any visual orientation cues provided by the picture of a hand.

Adult↗
PubMed2005

Role of the visuomotor system in on-line attenuation of a premovement illusory bias in grip aperture.

In this investigation participants formulated a grip aperture (GA) consistent with the size of an object embedded within a Muller-Lyer (ML) figure prior to initiating visually guided grasping movements. The accuracy of the grasping response was emphasized to determine whether or not the visuomotor system might resolve the premovement bias in GA very early in the response, as predicted by the perception/action model (PAM: ), or more gradually as the action unfolds over time, as predicted by the planning/control model (PCM: ). Grasping time (GT) was normalized and GA was measured at 11 time points: a premovement GA and ten time points beginning at 10% of GT and ending at 100% of GT. Not surprisingly, premovement GA was influenced in a direction consistent with the perceptual effects of the ML figure (cf. ). Interestingly, however, the bias in GA was not attenuated during the response, that is, a reliable illusory effect was observed for upwards of 90% of GT. Only at 100% of GT did we find resolution of the illusory effect. Based on these results, it is proposed that shaping GA in advance of response execution leads to a feedforward mode of grasping control in which the spatiotemporal characteristics of GA are controlled via an offline and context-dependent planning mechanism (i.e., the ventral visual pathway).

Bias↗