Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “VISUAL PERCEPTION”

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 289 records · Page 16Linked to original sources
PubMed2001

fMRI activation in a visual-perception task: network of areas detected using the general linear model and independent components analysis.

The Motor-Free Visual Perception Test, revised (MVPT-R), provides a measure of visual perceptual processing. It involves different cognitive elements including visual discrimination, spatial relationships, and mental rotation. We adapted the MVPT-R to an event-related functional MRI (fMRI) environment to investigate the brain regions involved in the interrelation of these cognitive elements. Two complementary analysis methods were employed to characterize the fMRI data: (a) a general linear model SPM approach based upon a model of the time course and a hemodynamic response estimate and (b) independent component analysis (ICA), which does not constrain the specific shape of the time course per se, although we did require it to be at least transiently task-related. Additionally, we implemented ICA in a novel way to create a group average that was compared with the SPM group results. Both methods yielded similar, but not identical, results and detected a network of robustly activated visual, inferior parietal, and frontal eye-field areas as well as thalamus and cerebellum. SPM appeared to be the more sensitive method and has a well-developed theoretical approach to thresholding. The ICA method segregated functional elements into separate maps and identified additional regions with extended activation in response to presented events. The results demonstrate the utility of complementary analyses for fMRI data and suggest that the cerebellum may play a significant role in visual perceptual processing. Additionally, results illustrate functional connectivity between frontal eye fields and prefrontal and parietal regions.

Attention↗
PubMed1977

Studies on visual perception of locomotion.

The problem about visual discrimination between seeing objects in motion and perception of motion of the perceiver (locomotion) was taken up. A flow of vertical motion was presented to limited areas of the far periphery (45 degrees-90 degrees) of the retina simultaneously with optical information about a stationary room over the rest of the retina. The result was that most subjects perceived themselves as sitting in an elevator continuously moving upward or downward. Thus, peripheral motion stimulation over a few percent of the retinal area determines locomotion perception in apparent competition with information about a static state over the rest of the retina. The same type of stimulus presented to the central part of the retina always brought about perception of object motion and a static perceiver. Effects of size and localization of the area stimulated with the motion flow was studied. Theoretical consequences and problems for further experimental analyses are discussed.

Discrimination, Psychological↗
PubMed1978

Young children's knowledge about visual perception: hiding objects from others.

Children of ages 2 1/2, 3, and 3 1/2 years were tested for their understanding of object hiding, believed to reflect an early developmental level of knowledge about visual perception. Even the youngest subjects could nonegocentrically hide an object by placing it on the opposite side of a screen from another person, even though placing it there necessarily left it unhidden from themselves. In contrast, there was a significant increase with age in the ability to achieve the same physical end state by placing the screen between the other person and the object. Most subjects at each age level correctly indicated that the other person could see the object when the experimenter interposed the screen between the child and the object but that the other person could not see the object when she placed the screen between the other person and the object. These and other recent findings indicate that children of this age can be both nonegocentric and skillful at estimating what other people do and do not see under various viewing conditions.

Age Factors↗
PubMed1997

Visual perception modifies goal-directed movement control: supporting evidence from a visual perturbation paradigm.

It is well known that dynamic visual information influences movement control, whereas the role played by background visual information is still largely unknown. Evidence coming mainly from eye movement and manual tracking studies indicates that background visual information modifies motion perception and might influence movement control. The goal of the present study was to test this hypothesis. Subjects had to apply pressure on a strain gauge to displace in a single action a cursor shown on a video display and to immobilize it on a target shown on the same display. In some instances, the visual background against which the cursor moved was unexpectedly perturbed in a direction opposite to (Experiment 1), or in the same direction as (Experiment 2) the cursor controlled by the subject. The results of both experiments indicated that the introduction of a visual perturbation significantly affected aiming accuracy. These results suggest that background visual information is used to evaluate the velocity of the aiming cursor, and that this perceived velocity is fed back to the control system, which uses it for on-line corrections.

Adult↗
PubMed1991

Selective impairment of memory and visual perception in splenial tumours.

The neuropsychological abnormalities found in 9 patients with tumours involving the splenium of the corpus callosum are described. The outstanding features of their cognitive deficits were a severe memory deficit and visual perception impairment in the presence of relatively intact intellect. It is argued that (1) the amnesia is due to damage to the fornix where that structure is closely applied to the splenium and that it is the result of a disconnection between the frontal and temporal lobes, although the possibility that damage to more than one structure, for example, retrosplenial cortex and fornix, cannot be excluded; (2) there is a dual pathway for visual object recognition, one of which passes directly to the dominant hemisphere for semantic analysis and the other via the nondominant hemisphere for prior perceptual analysis. Further, it is postulated that there is a subcortical as well as a callosal route between the hemispheres that is important for visual object recognition.

Aged↗
PubMed1983

The performance of adult males on the Southern California Figure-Ground Visual Perception Test.

The Southern California Sensory Integration Tests have been developed primarily for the evaluation of children with learning disabilities, yet they have potential for the assessment of adult perceptual dysfunction. In this research the Southern California Figure-Ground Visual Perception Test (FGP) was administered to a sample of 100 adult males and validated through correlation with the Embedded Figures Test (EFT). The results of the investigation found a normal distribution of figure-ground scores in addition to a significant correlation with the EFT. The means, standard deviations, and ranges are presented. Further data on relationship of the FGP to age, socioeconomic status, and educational level are presented, as well as a detailed description of the sample. It is concluded that this test is a satisfactory alternative to the EFT in interdisciplinary research by occupational therapists and, as an instrument, it has some important advantages for assessing figure-ground perception in persons with motor impairment or who are under psychotropic medication.

Adult↗
PubMed1999

Understanding the origin of visual percepts elicited by electrical stimulation of the human retina.

BACKGROUND: The success of a retinal prosthesis for patients with outer retinal degeneration (ORD) depends on the ability to electrically stimulate retinal cells other than photoreceptors. Experiments were undertaken in human volunteers to ascertain whether electrical stimulation of cells other than photoreceptors will result in the perception of light. METHODS: In two subjects, two areas of laser damage (argon green and krypton red) were created in an eye scheduled for exenteration due to recurrent cancer near the eye. In the operating room prior to exenteration, under local anesthesia, a hand-held stimulating device was inserted via the pars plana and positioned over the damaged areas and normal retina. Subjects' psychophysical responses to electrical stimulation were recorded. RESULTS: In both subjects, electrical stimulation produced the following perceptions. Normal retina: dark oval (subject 1), dark half-moon (subject 2); krypton red laser-treated retina: small, white light (both subjects); argon green laser treated retina: thin thread (subject 1), thin hook (subject 2). Histologic evaluation of the krypton red-treated retina showed damage confined to the outer retinal layers, while the argon green-treated area evinced damage to both the outer and the inner nuclear layers. CONCLUSION: The perception produced by electrical stimulation was dependent on the retinal cells present. Electrical stimulation of the krypton red-ablated area best simulated the electrically elicited visual perceptions of our blind, ORD patients, suggesting that the site of stimulation in blind patients is the inner retinal neurons.

Aged↗
PubMed1996

Magnetic coil suppression of extrafoveal visual perception using disappearance targets.

We used magnetic brain stimulation with a butterfly coil over the occipital lobes to study extrafoveal visual field effects in six subjects. The visual test pattern was a grid of asterisks around a central fixation point, and the target was the disappearance of one asterisk for a single frame of the video monitor. Using single magnetic pulses at stimulator outputs of 55-95%, we noted robust interference effects at latencies < or = 100 ms, peaking at approximately 50-90 ms. Suppression of visual perception occurred with both transverse and sagittal alignments of the coil. When the coil was moved laterally over either occipital lobe, perception of target disappearance was consistently suppressed in the contralateral visual field. Movement of the coil rostrally produced consistent suppression in the lower and middle field, but preferential suppression of the upper field could not be obtained. This altitudinal asymmetry may be correlated with the anatomy of the occipital lobe in relation to the scalp surface.

Attention↗
PubMed1980

Visual perception of movement patterns during smooth eye tracking.

A visual stimulus moving with constant velocity at a definite angle to the horizontal was presented during a 6.5% horizontal pursuit eye movement. The subjects were asked to report the direction of the stimulus movement under conditions of total darkness and on illuminated structured background. In both cases the subject's reports corresponded to the trajectory of the stimulus image on the retina rather than to the physical movement. In a second experiment the subjects were asked to localize the start and the end point of the stimulus motion on illuminated background. In this case the reports corresponded to the physical trajectory of the stimulus motion on the screen. The influence of the visual task on the perception of movement patterns during eye tracking is discussed.

Adaptation, Ocular↗
PubMedDate not supplied

[The precision parameters of visual perception].

Here we demonstrate that retina resolution is a system parameter, depending not only on the size of receptive fields (RF) of the ganglion cells (GC), but as also on their number and the picture complexity. The curve of visual perception accuracy as a function of these three variables is nonmonotone with pronounced extremum corresponding to the RF size. The system approach allows us to reconsider the accuracy of picture approximation by various retina zones, while its application to the on- and off-subsystems of GC reveals a new function of the lateral geniculate bodies (LGB) which is to processes these afferents. We have deciphered "abnormal" alternation of ipsi- and contralateral projections in the six LGB layers. Neural network simulation demonstrated that LGBs improve the reception accuracy; being transparent for accurate reception they screen out indistinct reception and block its access to the visual cortex. Resumption and refinement of the screened information is related to eye movements and to superior colliculi (SC) assuming that SC inverses LGB function, allocating the map of indistinct pixels (image contours) by processing the on- and off-afferens.

Afferent Pathways↗
PubMed1985

Colour stability and visual perception of dimethacrylate based dental composite resins.

The spectrophotometric method of colour measurement was applied to an investigation of the colour stability of dimethacrylate based composite resins exposed to thermal and photochemical aging. A good correlation was observed between visual perception of colour change and the spectrophotometric colour difference [delta E (FMC-2)] of unexposed and aged specimens, but 50% of the observers considered the colour match of two specimens to be clinically unacceptable when the colour difference exceeded 10.6. Kinetic studies of thermally and photochemically induced colour change showed a sigmoidal dependence of colour change on the logarithm of exposure time. Because the direction and magnitude of the colour change differed for the two procedures, it would appear that different mechanisms are involved.

Acrylic Resins↗
PubMed2000

Reversal-rate dependent differences in the EEG gamma-band during multistable visual perception.

It is an often reported observation in the literature on multistable perception that the reversal rate within a given observation time is subject to a high interindividual variability. Recently, we reported frontal gamma-band enhancement during multistable visual perception. The aim of the present study was to investigate whether changes in the gamma-band correspond to the variability of the reversal rate. Therefore, a total of 25 observers were divided into two subgroups according to their reversal rate during a 400-s observation period of a reversible pattern based on apparent motion. Subjects with more than 40 reversals within the 400-s were defined as high-rate switchers (HRS). Subjects with a reversal rate below 40 switches were defined as low-rate switchers (LRS). EEG was recorded from frontal, central, parietal, and occipital locations of both hemispheres. The results showed significantly higher gamma activity for the HRS in both phase-locked and non-phase-locked oscillations. Both subgroups showed the highest gamma amplitudes at frontal locations. The results support the involvement of attentional top-down processing in figure reversal. It is concluded that the higher gamma activity for the HRS reflects states of higher arousal, alertness and/or attention according to their fast reversal rate.

Adolescent↗
PubMedDate not supplied

Visual processing of configuration-dependent spatial characteristics of shapes and patterns. A model useful in the study of the role of the departure from circularity or dispersion of shapes in human visual perception.

In this work a theoretical model was used in combination with testings on normal subjects to get more insight in the role of the departure from circularity or dispersion of the shapes in visual perception. The model was inspired by the observation that the intensity of the effect of a given level of contrast of a shape usually increases, for the same area, with the shape being better concentrated around a center. The model introduces as a measurable characteristic the degree of concentration or dispersion of a shape with respect to a center. The measure was based on the maximum of the convolution integral of the characteristic function of the shape with the weighting function 1/2 pi r, r being the distance between the point of convolution and the surface element to be integrated. A program for the calculation of the degree of concentration of figures and other related processing operations was developed in Turbo Pascal language on a 486 PC. The program included the possibility to generate various figures and to operate on them various transformations such as strangulation, fragmentation with separation of fragments. The model introduces a center of the figure, the point best surrounded by the whole figure, with a geometric and visual significance, as resulting from the good concordance between its calculated and perceived positioning in different relatively simple shapes. In symmetrical compact figures subjected to a central separation or narrowing two centres appear entering the two resulting nuclear parts; a good concordance between model and perception was again observed in this transition to two centres and their subsequent positions in the two nuclear parts. In accord to model prediction, testings showed a very pronounced dependence of the summation efficiency over a contrasting area on the degree of dispersion of the area. This is reflected in the drastic decrease upon figure dispersion of the intensity with which a given brightness or colour contrast is perceived. Thus, the model gives a better explanation and a more efficient way to approach the great capacity of the visual system to disclose more compact shapes or agglomeration zones in a complex visual scene. This capacity is to a large extent due to the increase in the intensity with which a given contrast is perceived, occurring in these conditions. This intensity, which strongly depends on the degree of concentration or dispersion of the figure, becomes an important additional signal leading to the accentuation of the difference between compact and rarefied shapes. The model based on the degree of concentration determined around a centre, although useful for finding a centre and applicable satisfactorily to many shapes, do not cover well all aspects of shape dispersions. In shapes without a dominant central part the confrontation model-testing showed an important involvement in global perception of all local concentrations, not only central but also peripheral, the later underestimated in our model. The model can be however improved by taking into account also such local concentrations.

Form Perception↗
PubMed1975

[Social behavior, musicality and visual perception in monogloid children (author's transl)].

Forty-nine mongoloid and 48 non-mongol test persons of equivalent age and intelligence were selected and studied with respect to social behavior, speech disorders (observation of behavior), musicality and visual perception. There were significant differences in favor of the mongols with respect to social adaption. Speech disorders of all kinds occurred significantly more frequently in mongol children; stuttering was significantly more frequent in the boys. The mongol group did significantly better in the musicality test; the difference in the rhythmical part was highly significant. The average differences in the capacity for visual discrimination of colors, geometrical forms and the spatial relationship of geometrical forms were not significant.

Adolescent↗
PubMed2004

Moderate alcohol consumption in humans impairs feature binding in visual perception but not across perception and action.

Animal studies suggest a relationship between activation of the cholinergic system and neural synchronization, which again has been suggested to mediate feature binding. We investigated whether suppressing cholinergic activity through moderate alcohol consumption in healthy humans affects behavioral measures of feature binding in visual perception and across perception and action. Indeed, evidence of the binding of shape and color, and of shape and location, of visual objects disappeared after alcohol consumption, whereas bindings between object features and the manual response were unaffected.

Adult↗
PubMed1989

Visual perception of objects: an approach to assessment and intervention.

This paper proposes an alternative to the deficit-specific approach that has been used to guide the visual perceptual assessment and treatment of brain-injured adults. Recent theoretical advances in visual object perception are combined with a cognitive rehabilitation model to provide a framework for occupational therapy assessment and treatment of object-processing dysfunction. Assessment guidelines are presented that emphasize the analysis of residual function by specifying the task conditions that influence visual perception. A case study illustrates clinical application of this approach. Implications for research are discussed.

Aged↗
PubMed1992

[An instrument for projecting visual perception by monofocal and bifocal intraocular lenses].

With the aid of a simple optical system similar to an astronomical telescope, images of spectacle lenses, contact lenses and intraocular lenses can be projected in front of, onto or into the eye. These optical images function like real lenses and enable their performance to be evaluated. In the case of intraocular lenses, visual perception through monofocal or bifocal lenses and teledioptric systems can be reproduced.

Equipment Design↗
PubMed1999

Visual perception of the relative phasing of human limb movements.

Studies of bimanual coordination have found that only two stable relative phases (0 degree and 180 degrees) are produced when a participant rhythmically moves two joints in different limbs at the same frequency. Increasing the frequency of oscillation causes an increase in relative phase variability in both of these phase modes. However, relative phasing at 180 degrees is more variable than relative phasing at 0 degree, and when the frequency of oscillation reaches a critical frequency, a transition to 0 degree occurs. These results have been replicated when 2 people have coordinated their respective limb movements using vision. This inspired us to investigate the visual perception of relative phase. In Experiment 1, recordings of human interlimb oscillations exhibiting different frequencies, mean relative phases, and different amounts of phase variability were used to generate computer displays of spheres oscillating either side to side in a frontoparallel plane or in depth. Participants judged the stability of relative phase. Judgments covaried with phase variability only when the mean phase was 0 degree or 180 degrees. Otherwise, judgments covaried with mean relative phase, even after extensive instruction and demonstration. In Experiment 2, mean relative phase and phase variability were manipulated independently via simulations, and participants were trained to perceive phase variability in testing sessions in which mean phase was held constant. The results of Experiment 1 were replicated. The HKB model was fitted to mean judgment standard deviations.

Adolescent↗