PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Visual Perception”

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 1,387 records · Page 77Linked to original sources
PubMed1993

Visual and statistical assessment of spatial clustering in mapped data.

Maps have seen increasing use to examine regional variation in health, but there has been little research on the visual perception of spatial patterns in mapped data. Theories of graphical perception suggest that the interpretation of maps is complex relative to other types of graphical material. This paper describes an experiment in which observers assessed a series of maps with respect to their amount of clustering. Maps with various types of spatial pattern were visually distinguishable; comparisons between variants of the same map, however, using different shading and plotting symbols indicated that the method of data representation also had a strong effect on visual perception. There was some evidence for a learning effect in complex maps. The relationship between the visual assessments and a statistical measure of spatial autocorrelation was significant but imperfect.

Cluster Analysis↗
PubMed2005

The neuropsychology of variant CJD: a comparative study with inherited and sporadic forms of prion disease.

OBJECTIVE: To assess cognitive function in variant Creutzfeldt-Jakob disease (vCJD). We describe the neuropsychological profiles of 10 cases and compare these data with cross sectional data obtained from patients with histologically confirmed sporadic CJD and cases with inherited prion disease with confirmed mutations in the prion protein gene. METHODS: Patients referred to the Specialist Cognitive Disorders Clinic at the National Hospital for Neurology and Neurosurgery and the National Prion Clinic at St Mary's Hospital, London for further investigation of suspected CJD were recruited into the study. The neuropsychological test battery evaluated general intelligence, visual and verbal memory, nominal skills, literacy skills, visual perception and visuospatial functions, and visuospatial and executive function. RESULTS: The results indicate that moderate to severe cognitive decline is a characteristic feature of vCJD. Specifically, verbal and visual memory impairments and executive dysfunction were pervasive in all disease groups. Nominal skills were impaired in variant and sporadic CJD, significantly so when compared with the inherited prion disease group. Perceptual impairment was less frequent in the vCJD group than in the sporadic and inherited groups. CONCLUSION: This study confirms the occurrence of generalised cognitive decline in patients with vCJD. Although decline in cognitive function ultimately affects all domains, there is a suggestion that some components of visual perception may be spared in vCJD. The results also suggest that nominal function may be preserved in some cases with inherited prion disease.

Adult↗
PubMed2004

Ophthalmic impairment at 7 years of age in children born very preterm.

AIMS: To determine the prevalence of ophthalmic impairments in very preterm compared with term infants, the relation between impairments and cerebral ultrasound appearances and retinopathy, and the correlation with visual perception and motor and cognitive measures. SUBJECTS: 279 children at 7 years of age born before 32 weeks gestation within Liverpool during 1991-92 and attending mainstream schools, and 210 term controls. METHODS: Visual acuity was assessed by Snellen chart, and strabismus by the cover test. Stereopsis was determined using the TNO random dot test, and contrast sensitivity using the Cambridge low contrast gratings. Visual and motor abilities were assessed using the Developmental test of motor integration (VMI) and the Movement ABC. Intelligence was measured with the Wechsler intelligence scale for children UK. Perinatal cranial ultrasound and retinopathy data were extracted from clinical records. RESULTS: Children born preterm were significantly more likely to wear glasses, to have poor visual acuity, reduced stereopsis, and strabismus than term controls, but they showed no significant decrease in contrast sensitivity. Ophthalmic impairments were significantly related to poorer scores on the VMI, Movement ABC, and Wechsler IQ tests, but were not significantly related to neonatal cranial ultrasound appearances. Stage 3 retinopathy was related to poorer subsequent acuity. CONCLUSIONS: Children born very preterm and without major neurodevelopmental sequelae have an increased prevalence of ophthalmic impairments at primary school age which are associated with visual perceptional, motor, and cognitive defects. The cause may be a generalised abnormality of cortical development rather than perinatally acquired focal lesions of the brain.

Case-Control Studies↗
PubMed1991

[Modification of refraction and visual noise perception by suction cup oculocompression].

In 17 ocularly healthy persons the IOP was artificially raised by suction cup oculopression (negative pressure: 65 mmHg [8.67 kPa]) from initially 15.5 +/- 2.2 mmHg (2.07 +/- 0.29 kPa) to 25.2 +/- 4.0 mm Hg (3.36 +/- 0.53 kPa) (mean +/- SD). Continuing the initial refractive correction, visual acuity (Landolt's rings) decreased from initially 1.06 +/- 0.13 to 0.39 +/- 0.22 (P less than 0.001* [*t-test, paired ties each]). A new optical refraction with suction cup in position significantly raised the visual acuity to 0.64 +/- 0.24 (P less than 0.002*). The suction cup itself induced astigmatism of 2.15 +/- 1.46 dpt (Canon Auto-Refractometer RK-1), which significantly differed from the initial astigmatism (0.32 +/- 0.23 dpt) (P less than 0.001*). The minus cylinder axis initially showed no preferential position. During artificial IOP elevation it shifted to 90 degrees...125 degrees (referred to the right eye) and thus ran about perpendicular to the meridian the suction cup was positioned on the eyeball. Effects of such refractive changes on differential light threshold and VEP amplitude are demonstrated. The results presented allow critical interpretation of previous IOP tolerance tests. The influence of suction cup oculopression on the perception of the white-noise field is shown in some glaucoma patients: the speed of the white-noise campimetry allows the increase in field defects during artificial IOP elevation to be followed up directly.

Adult↗
PubMed1985

An evaluation of perceptual retraining.

A group of head injury and stroke patients with impairment of visual perception were randomly allocated to receive either perceptual retraining or conventional occupational therapy. No significant differences were found between the groups, either before or after 4 weeks of treatment, on measures of visual perception or on activities of daily living scale.

Activities of Daily Living↗
PubMed2003

Is neural filling-in necessary to explain the perceptual completion of motion and depth information?

Retinal activity is the first stage of visual perception. Retinal sampling is non-uniform and not continuous, yet visual experience is not characterized by holes and discontinuities in the world. How does the brain achieve this perceptual completion? Fifty years ago, it was suggested that visual perception involves a two-stage process of (i) edge detection followed by (ii) neural filling-in of surface properties. We examine whether this general hypothesis can account for the specific example of perceptual completion of a small target surrounded by dynamic dots (an 'artificial scotoma'), a phenomenon argued to provide insight into the mechanisms responsible for perception. We degrade the target's borders using first blur and then depth continuity, and find that border degradation does not influence time to target disappearance. This indicates that important information for the continuity of target perception is conveyed at a coarse spatial scale. We suggest that target disappearance could result from adaptation that is not specific to borders, and question the need to hypothesize an active filling-in process to explain this phenomenon.

Depth Perception↗
PubMed1997

Visual motion perception after brain damage: II. Deficits in form-from-motion perception.

We investigated form-from-motion perception (FFM perception) in a sample of 39 patients with acquired brain damage. Pronounced FFM deficits were found in two patients (FM1 and FM2) with biparietal lesions. Both patients were able to identify the relevant figure, when it was not embedded in obstructive texture. Moreover, they could localize the figures in the FFM condition, although they could not reliably identify them. The two patients had normal motion coherence thresholds. Their performance in a static figure-ground task did not differ from that of other patients. These findings imply that the FFM deficits are not caused by impairment of basic visual motion or form perception but are the consequence of damage to a parietal brain structure involved in the combined analysis of visual motion and form information. The nature and functional role of this brain structure as well as the implications of our results for models of FFM perception are discussed.

Adult↗
PubMed2005

Tunable retina encoders for retina implants: why and how.

Current research towards retina implants for partial restoration of vision in blind humans with retinal degenerative dysfunctions focuses on implant and stimulation experiments and technologies. In contrast, our approach takes the availability of an epiretinal multi-electrode neural interface for granted and studies the conditions for successful joint information processing of both retinal prosthesis and brain. Our proposed learning retina encoder (RE) includes information processing modules to simulate the complex mapping operation of parts of the 5-layered neural retina and to provide an iterative, perception-based dialog between RE and human subject. Alternative information processing technologies in the learning RE are being described, which allow an individual optimization of the RE mapping operation by means of iterative tuning with learning algorithms in a dialog between implant wearing subject and RE. The primate visual system is modeled by a retina module (RM) composed of spatio-temporal (ST) filters and a central visual system module (VM). RM performs a mapping 1 of an optical pattern P1 in the physical domain onto a retinal output vector R1(t) in a neural domain, whereas VM performs a mapping 2 of R1(t) in a neural domain onto a visual percept P2 in the perceptual domain. Retinal ganglion cell properties represent non-invertible ST filters in RE, which generate ambiguous output signals. VM generates visual percepts only if the corresponding R1(t) is properly encoded, contains sufficient information, and can be disambiguated. Based on the learning RE and the proposed visual system model, a novel retina encoder (RE*) is proposed, which considers both ambiguity removal and miniature eye movements during fixation. Our simulation results suggest that VM requires miniature eye movements under control of the visual system to retrieve unambiguous patterns P2 corresponding to P1. For retina implant applications, RE* can be tuned to generate optimal ganglion cell codes for epiretinal stimulation.

Action Potentials↗
PubMed1979

[Certain patterns in the formation of optical illusions].

A structural dynamic analysis of productive disorders in visual perception was attempted on the basis of psychological study of 344 patients. These disorders were studied according to the increasing degree of inadequacy (anisomorphia) of pathological images in respect to real stimula. Considering the differences of such phenomena according to the degree of discrepancy of their perceptive characteristics with the traits of real objects, some successively complicated pathological images were examined, including traditional false recognition, illusions and hallucinations, as well as interlapping intermediate structures. Some pathogenetical mechanisms in the formations of visual illusions are suggested. Clinico-psychopathological parallels are made between disorders of visual perception and disease entities.

Dementia↗
PubMed2002

Monocular vision leads to a dissociation between grip force and grip aperture scaling during reach-to-grasp movements.

It has been argued that visual perception and the visual control of action depend upon functionally distinct and anatomically separable brain systems. Electrophysiological evidence indicates that binocular vision may be particularly important for the visuomotor processing within the posterior parietal cortex, and neuropsychological and psychophysical studies confirm that binocular vision is crucial for the accurate planning and control of prehension movements. An unresolved issue concerns the consequences for visuomotor processing of removing binocular vision. By one account, monocular viewing leads to reliance upon pictorial visual cues to calibrate grasping and results in disruption to normal size-constancy mechanisms. This proposal is based on the finding that maximum grip apertures are reduced with monocular vision. By a second account, monocular viewing results in the loss of binocular visual cues and leads to strategic changes in visuomotor processing by way of altered safety margins. This proposal is based on the finding that maximum grip apertures are increased with monocular vision. We measured both grip aperture and grip force during prehension movements executed with binocular and monocular viewing. We demonstrate that each of the above accounts may be correct and can be observed within the same task. Specifically, we show that, while grip apertures increase with monocular vision, consistent with altered visuomotor safety margins, maximum grip force is nevertheless reduced, consistent with a misperception of object size. These results are related to differences in visual processing required for calibrating grip aperture and grip force during reaching.

Adaptation, Physiological↗
PubMed2003

Comparison of fMRI activation at 3 and 1.5 T during perceptual, cognitive, and affective processing.

Previous studies comparing fMRI data acquired at 1.5 T and higher field strengths have focused on examining signal increases in the visual and motor cortices. No information is, however, available on the relative gain, or the comparability of data, obtained at higher field strengths for other brain regions such as the prefrontal and other association cortices. In the present study, we investigated fMRI activation at 1.5 and 3 T during visual perception, visuospatial working memory, and affect-processing tasks. A 23% increase in striate and extrastriate activation volume was observed at 3 T compared with that for 1.5 T during the visual perception task. During the working memory task significant increases in activation volume were observed in frontal and parietal association cortices as well as subcortical structures, including the caudate, globus pallidus, putamen, and thalamus. Increases in working memory-related activation volume of 82, 73, 83, and 36% were observed in the left frontal, right frontal, left parietal, and right parietal lobes, respectively, for 3 T compared with 1.5 T. These increases were characterized by increased activation at 3 T in several prefrontal and parietal cortex regions that showed activation at 1.5 T. More importantly, at 3 T, activation was detected in several regions, such as the ventral aspects of the inferior frontal gyrus, orbitofrontal gyrus, and lingual gyrus, which did not show significant activation at 1.5 T. No difference in height or extent of activation was detected between the two scanners in the amygdala during affect processing. Signal dropout in the amygdala from susceptibility artifact was greater at 3 T, with a 12% dropout at 3 T compared with a 9% dropout at 1.5 T. The spatial smoothness of T2* images was greater at 3 T by less than 1 mm, suggesting that the greater extent of activation at 3 T beyond these spatial scales was not due primarily to increased intrinsic spatial correlations at 3 T. Rather, the increase in percentage of voxels activated reflects increased sensitivity for detection of brain activation at higher field strength. In summary, our findings suggest that functional imaging of prefrontal and other association cortices can benefit significantly from higher magnetic field strength.

Adolescent↗
PubMed2003

Retinal slip during active head motion and stimulus motion.

Gaze control in various conditions is important, since retinal slip deteriorates the perception of 3-D shape of visual stimuli. Several studies have shown that visual perception of 3-D shape is better for actively moving observers than for passive observers watching a moving object. However, it is not clear to what extent the improved percept of 3-D shape for active observers has to be attributed to corollary discharges to higher visual centers or whether the improved percept might be due to improved gaze stabilization during active head movements. The aim of this study was to measure binocular eye movements and to make a quantitative comparison of retinal slip for subjects instructed to fixate a visual stimulus in an active condition (subject makes an active head movement, object is stationary) and in a passive condition (the stimulus moves, the subject is stationary) for various movement frequencies, viewing distances, and stimulus diameters. Retinal slip remains below the "acuity threshold" of about 4 deg/s in active conditions, except for the highest frequency tested in this study (1.5 Hz) for nearby targets (0.25 cm). Retinal slip exceeds this threshold for most passive conditions. These results suggest that the enhanced performance in the visual perception of 3-D shape during active head movements can, at least partly, be explained by better fixation by actively moving observers.

Adult↗
PubMed2002

The effects of a confectionery snack on attention in young boys.

The relationship between consumption of a confectionery snack after an overnight fast and cognitive function was examined using a variety of cognitive tasks, including spatial memory, verbal memory, attention, visual perception and short-term memory, in a sample of 21 boys, ages 9-12 years. Performance on the vigilance attention task was significantly improved when the participants consumed a confectionery snack compared to consumption of a noncalorie snack. Participants had significantly higher hit rates and significantly lower miss rates after the confectionery snack. In addition, false alarm rates increased as a function of time for the placebo condition and decreased for the confectionery condition. Thus, the confectionery snack enhanced ability to stay on task for an extended period of time, enabling the children to more accurately identify target information, as well as correctly reject nontarget information. Analysis of the types of errors made also revealed that when the children were in the confectionery condition they were less likely to make more glaring errors. No significant differences were found in tests of digit span, verbal memory, spatial memory or visual perception.

Attention↗
PubMed2001

Non-veridical visual motion perception immediately after saccades.

It is widely assumed that combining the eye movement vector with the motion vector of the retinal image is both sufficient and necessary for recovering the direction and speed of visual motion. Here, we report that execution of a saccadic (rapid) eye movement in the dark systematically biased subsequent perceptual judgment of the direction of visual motion in the direction opposite to the saccade. This non-veridical motion perception reached a maximum immediately after saccade offset and then decayed in approximately equal to 100 ms. These results suggest that the oculomotor signal interacts with central mechanisms related to motion and possibly form perception, as well as spatial vision, as documented with mislocalization of visual objects at the time of saccades.

Adult↗
PubMed1989

Perception time and reaction time.

Two experiments were performed in order to examine the possible contribution of visual perception time in motor response time under conditions of pursuit eye movements. Subjects had to follow with their eyes a light spot moving horizontally along a reference scale at a constant velocity of 14 degrees/s. Stimuli (the disappearance of the moving spot) were presented randomly at distances of 11.3, 17.7 and 24.2 angular degrees from the onset of motion. In Experiment 1 subjects had to report verbally the scale division at which the stimuli were presented. In Experiment 2 subjects had to press a button as quickly as possible after stimulus presentation. No relationship between visual perception time and motor reaction time was found.

Adult↗
PubMed1977

Micropsia and testicular retractions.

Five episodes of micropsia, which were precipitated by oedipal masturbatory fantasies, are described in the analysis of an adult male. Traumatic visual events and testicular retractions during the oedipal and latency years predisposed the ego functions concerned with visual perception to later involvement in conflict. The micropsia itself is seen as defending against castration anxiety by means of a series of unconscious fantasies of denial. These fantasies cause a regression to an earlier mode of visual perception (and to micropsia) characteristic of latency. The defensive modifications of the functions of the ego itself seen in micropsia are closely allied to those seen in the dèjá vu experience and in depersonalization.

Adult↗
PubMed1978

Eye movements, scanpaths, and dyslexia.

The oculomotor performance of 25 dyslexic and 19 normal children was evaluated to determine whether or not dyslexia involves deficits in oculomotor function or visual perception. When the children were required to follow a meaningless target or to solve pictorial tasks, the two age-matched groups could not be differentiated. When they were required to read selections commensurate with their measured reading level, the dyslexic children were markedly different on a number of parameters. It appears that the dyslexic's difficulty lies beyond visual perception, perhaps in the language area itself. The dyslexic's characteristic deficit seems to involve the integration of visual input into the language-acquisition function.

Adolescent↗