SEARCH · PubMed Health

Results for “visualization”

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 271 records · Page 15Linked to original sources

PubMed1988

Effects of lateral displacement of the visual field on the development of visual-motor abilities in cats.

In this study, we test the flexibility of the cat's visual system by examining the visual-motor effects of both moderate and extreme lateral displacement of the visual field. While being reared with masks that provided either 0, 15, or 30 diopters lateral displacement of the visual field, 23 kittens received 3 tests of visual-motor abilities: a visual cliff task, a visual guiding task, and a five-alley choice task. No significant differences were found among the 0, 15, or 30 diopter displacement groups for any of the 3 tasks for either the total number of days to reach criterion performance, for the development of performance over time during the early days of testing, or for the development over time to criterion performance. After reaching criterion, kittens readapted to transposed conditions of displacement. The group changed 30 diopters did significantly worse than the group changed 15 diopters, both in error scores and in time to criterion performance. The present results with kittens are compared to those of other investigators and suggestions are made for future research.

Aging↗

PubMed1998

Spatial and temporal differentiation of fMRI BOLD response in primary visual cortex of human brain during sustained visual simulation.

The blood oxygenation level dependent (BOLD) response during sustained visual stimulation has been studied by several groups using fMRI with controversial conclusions. This issue was investigated for the human brain at high (4 Tesla) magnetic field strength using a flashing goggle at 8 Hz. The results demonstrate that the overall BOLD response in the primary visual cortex has an initial overshoot after the onset of visual stimulation and an undershoot after the termination of visual stimulation. A significant and positive BOLD response, however, remains constant between the initial and terminal transient responses. The temporal BOLD responses in the primary visual cortex were spatially dependent. The regions identified as draining veins in images displayed proportionately larger initial and terminal transient responses, whereas regions devoid of such vessels and associated mainly with parenchyma exhibited a more time-independent BOLD response. These results reveal that the BOLD effect and, presumably, the uncoupling between cerebral blood flow and cerebral metabolic rate of oxygen consumption, are maintained in the primary visual cortex during sustained visual stimulation, and the temporal characteristics of the BOLD effect are spatially dependent.

Humans↗

PubMed1992

Does work with visual display units impair visual activities after work?

It is well established that visual display unit (VDU) operators complain of visual fatigue and visual stress during after-work hours. The present study was divided into two parts. In the first part, standard eye examinations were performed on a group of VDU workers (n = 32) and a control group (n = 15); those subjects who were found to have correct vision (n = 16 and 13, respectively) participated in the second part. The eye examinations revealed that on the average, the VDU workers suffered more than twice as many visual impairments as the controls. In those with correct vision, the near point of accommodation was measured at the beginning of the workday at the start of the week, and at the end of the workday, four days later. In the VDU group, the decrease in accommodation was uniformally distributed between zero and 1.0 diopter, whereas among the non-VDU workers, 77% of the decrease was between zero and 0.25 diopter. The dynamic range of accommodation in the VDU workers on the second examination was smaller than on the first. We conclude that some of the visual stress and visual fatigue that developed at work hindered visual activities after work.

Accommodation, Ocular↗

PubMed1991

Impairment of visual perception and visual short term memory scanning by transcranial magnetic stimulation of occipital cortex.

Transcranial magnetic stimulation (TMS) of occipital cortex was performed using a magneto-electric stimulator with a maximum output of 2 Tesla in 24 normal volunteers. The identification of trigrams, presented for 14 ms in horizontal or vertical arrays was significantly impaired when the visual stimulus preceded the occipital magnetic shock by 40 to 120 ms. The extent of impairment was related to TMS intensity. The latency of perceptual impairment was shorter for more intense TMS. No perceptual impairment was obtained by "sham" stimulation when TMS shocks were applied to the upper cervical region rather than the occipital region to rule out unspecific startle reactions affecting attention possibly responsible for the observed reduction in performance. Occipital TMS did not evoke systematic eye movements except for blink responses at latencies beyond 40 ms which were too late to interfere with visual input. Depending on the required serial order of readout of the trigram perceptual impairment was more marked for the second and third part of the trigram. This demonstrates that TMS interferes with the internal serial processing of visual input. To elucidate this further, TMS was used in a Sternberg short term visual memory scanning task. TMS caused a marked decrease in memory scanning rates whereas visual stimulus encoding and storage remained unaffected when tested at various TMS delays. TMS appears to be a useful method to study processes of visual perception and short term memory handling in the occipital cortex. Advantages over classical visual masking techniques especially regarding topical localisation are discussed.

Adult↗

PubMed1991

Visual detectability gradients: effect of high-speed visual experience.

The detectability of a target pattern presented briefly with a number of similar nontarget patterns varies as a function of the spatial location of the target. Previous work attributes these detectability gradients to a visual search process--a non-eye movement serial scan--that examines a decaying neural representation of the image. (Heron, 1957; Efron, Yund, & Nichols, 1987, 1990a,b,c; Yund, Efron, & Nichols, 1990a,b,c). The results reported in the companion paper (Ostrosky-Solis, Efron, & Yund, 1991) indicated that literacy did not affect overall performance levels but did influence scanning behavior: "...reading, or learning to read, caused the scanning mechanisms of literate subjects to adopt more consistent scan paths, from subject to subject, than they would have adopted without this reading experience." The purpose of the present experiment was to determine the effect on this scanning mechanism, if any, of an entirely different type of visual experience--the high-speed visual processing required of tennis players. Unlike reading which requires the linguistic interpretation of a highly structured visual input, tennis skill requires rapid target detection and tracking in three-dimensional visual space as well as large scale visual-motor coordination. As in the previous experiments, subjects were required to detect a vertical stripe pattern among a number of similar non-target patterns. The experiment was performed on a group of 52 tennis players and on an age- and sex-matched group of 52 non-tennis players. The overall accuracy of target detection was greater among the tennis players than among the non-tennis players and, of more interest, there was a significant difference in the detectability gradients. The detection advantage of the tennis group seemed to reach its maximum in the first half of the scan and then to deteriorate as the scan proceeded. These results indicate that visual experience other than reading can affect the habitual activity of the scanning mechanism.

Adult↗

PubMed1988

A critical period of the development of beta-adrenergic receptor binding in the visual system of rat during visual deprivation.

The density of [3H]dihydroalprenolol binding to beta-adrenergic receptors in the visual structures (visual cortex, superior colliculus and lateral geniculate nucleus) of rats raised under a normal 12 hr light-dark cycle was compared to those of rats visually deprived at different postnatal ages. Unilateral eyelid suture from postnatal days 10 or 16 to 3 months resulted in an increased [3H]dihydroalprenolol bilateral binding in the lateral geniculate nucleus compared to control animals. Monocular deprivation from postnatal days 25, 40, 60 and 90 had no effect on the density of [3H]dihydroalprenolol binding. After re-opening of the eyelid, which was sutured on postnatal day 10, at postnatal day 25 no changes in beta-adrenergic receptor binding in the lateral geniculate nucleus of the adult animal could be detected. After re-opening of the sutured eyelid on day 90, followed by examination of the adrenoceptor density 4 weeks later, the [3H]dihydroalprenolol binding in both lateral geniculate nuclei remained elevated as was also found in corresponding regions of monocular deprived animals. Binocular visual deprivation from postnatal day 10 until the age of 3 months had no effect on [3H]dihydroalprenolol binding in the visual centres in comparison to corresponding control animals. The data suggest that there exists a critical period for the ontogenetic development of beta-adrenergic receptors binding in the visual system of rats during which permanent alterations of receptor binding can be induced by monocular but not binocular visual deprivation.

Aging↗

PubMed2003

Effect of lesion size, visual acuity, and lesion composition on visual acuity change with and without verteporfin therapy for choroidal neovascularization secondary to age-related macular degeneration: TAP and VIP report no. 1.

PURPOSE: To determine whether differences in baseline lesion size and visual acuity might explain differing results found in three different lesion compositions (predominantly classic, minimally classic, and occult with no classic) among three placebo-controlled, randomized clinical trials evaluating photodynamic therapy with verteporfin (Visudyne, Novartis AG), also termed verteporfin therapy, in patients with subfoveal choroidal neovascularization (CNV) due to age-related macular degeneration (AMD). METHODS: Exploratory analyses were conducted in patients with predominantly classic or minimally classic lesions at enrollment in the Treatment of AMD with Photodynamic Therapy (TAP) Investigation and in AMD patients with occult with no classic CNV in the Verteporfin In Photodynamic Therapy (VIP) Trial. Baseline characteristics of patients among these three lesion compositions were compared. In addition, multiple linear regression modeling was used to explore the effect of baseline lesion size, visual acuity, and lesion composition on mean change in visual acuity from baseline to 24 months. RESULTS: At baseline, the mean size of predominantly classic lesions (3.4 disk areas) was smaller than that of minimally classic (4.7 disk areas) and occult with no classic lesions (4.3 disk areas). In the multiple linear regression model of individual lesion compositions, there was a significant treatment-by-lesion-size interaction for minimally classic and occult with no classic lesions, but not for predominantly classic lesions. Interaction between treatment and baseline visual acuity was not significant for any lesion composition. Small verteporfin-treated lesions lost less vision than large verteporfin-treated lesions in each lesion composition. In the multiple linear regression model that included all lesion compositions, lesion size was a more significant predictive factor for the magnitude of treatment benefit than either lesion composition or visual acuity. Smaller (4.0 disk areas or less) minimally classic and occult with no classic lesions had similar visual acuity outcomes to those observed in predominantly classic lesions. CONCLUSIONS: Based on exploratory analyses, lesion size in the TAP Investigation and VIP Trial was an important predictor of the magnitude of treatment benefit with verteporfin therapy in occult with no classic and minimally classic lesion compositions. In patients with AMD, treating smaller rather than larger neovascular lesions, regardless of lesion composition, likely will result in a better level of visual acuity.

Aged↗

PubMed2000

Visual field progression in patients with initially unilateral visual field loss from chronic open-angle glaucoma.

PURPOSE: To investigate visual field progression in patients with initially unilateral glaucomatous visual field loss, and to determine risk factors for progression. DESIGN: Retrospective observational case series. PARTICIPANTS: Forty-eight consecutive patients with primary open-angle glaucoma, pseudoexfoliative glaucoma, or pigmentary glaucoma, seen over an 18-month period, who initially had unilateral visual field loss as defined by use of modified Anderson criteria. Patients were followed with standard Humphrey perimetry for a minimum of 2 years. METHODS: Progression was defined by use of modified Anderson criteria, and Advanced Glaucoma Intervention Study (AGIS) and Collaborative Initial Glaucoma Treatment Study scores. MAIN OUTCOME MEASURE: Visual field progression. RESULTS: Three patients (6.2%) had fellow eye progression over a mean follow-up of 76 months and duration of disease of 8.7 years. Fellow eye progression correlated with progression of the first-affected eye (P = 0.044). Ten patients (21%) had progression of the first-affected eye; these eyes had a larger initial cup/disc ratio compared with stable eyes (P = 0.041). Increasing initial AGIS score was associated with progression (P: = 0.003). Kaplan-Meier survival analysis estimated the risk of progression at 5 years to be 25% in first-affected eyes and 7.2% in fellow eyes. CONCLUSIONS: In this population, the risk of fellow eye progression in patients with initially unilateral visual field loss from open-angle glaucoma is low. Progression is higher in eyes with visual field loss at initial testing, and the risk of progression increases as the level of initial visual field loss increases.

Adult↗

PubMed2001

Visual discrimination learning in the water maze: a novel test for visual acuity.

Learning about space, the environment and specific objects comprising three-dimensional arrangements requires processing of visual information. As learning and memory experiments in mammals rely heavily on normal processing of visual cues, drug-induced disruption of acquisition learning or memory formation necessitates the important control for visual acuity. A popular task used frequently for rats is the Morris water maze. However, previously used visual tasks in the water maze only control for gross visual disturbances. Here we describe a new training procedure enabling visual acuity to be tested in the water maze. Animals were trained to discriminate between two cue cards containing a pattern of vertical black and white stripes. Cards were presented in two adjacent quadrants separated by a barrier with the escape platform located in front of the smaller stripes (1 cm wide). Once 80% correct responses were attained, the wider cue card (normally 5 cm wide stripes) was randomly changed to gratings of 1,2,3,4,5, and 10 cm width. Animals learned the discrimination with acuity of 1.5 c/deg. A detailed analysis of the swim patterns further suggests that, independent of the grating used, animals make a choice immediately after release and swim along the walls towards the cue. In a further acuity test taken a few weeks later when animals were given saline infusions, performance was better than in the first test suggesting an effect of learning. This novel test may prove useful in determining subtle drug-induced deficits in visual acuity that may contribute to disruption of spatial performance in the water maze.

Animals↗

PubMed1997

Prognostic value of visual evoked potentials (VEP) in infants with visual inattentiveness.

Visual evoked potentials elicited by strobe flash (fVEPs) were recorded in 56 infants (3 months to 15 months of age) with visual inattentiveness but without prechiasmal problems. Their visual status was reexamined one or more years later when 41 children were found to be visually competent (Group NB) and 15 were blind (Group B). We also evaluated a group of 32 age-matched children who had no visual symptoms (Group C). It was found that well organized VEP waveforms over one or both hemispheres (Types U and S), or those with a characteristic negative shift (Type N) suggest favorable prognosis. Integrated voltage of the VEP correlated well with long-term prognosis for visual recovery. The vertex VEP also (had) provided some predictions for visual prognosis. Overall results indicate good prognosis if related to sufficient voltage and complexity of the VEP components.

Blindness↗

PubMed1999

Increased activity in human visual cortex during directed attention in the absence of visual stimulation.

When subjects direct attention to a particular location in a visual scene, responses in the visual cortex to stimuli presented at that location are enhanced, and the suppressive influences of nearby distractors are reduced. What is the top-down signal that modulates the response to an attended versus an unattended stimulus? Here, we demonstrate increased activity related to attention in the absence of visual stimulation in extrastriate cortex when subjects covertly directed attention to a peripheral location expecting the onset of visual stimuli. Frontal and parietal areas showed a stronger signal increase during this expectation than did visual areas. The increased activity in visual cortex in the absence of visual stimulation may reflect a top-down bias of neural signals in favor of the attended location, which derives from a fronto-parietal network.

Attention↗

PubMed2001

Visual contrast sensitivity in deaf versus hearing populations: exploring the perceptual consequences of auditory deprivation and experience with a visual language.

Early deafness in humans provides a unique opportunity to examine the perceptual consequences of altered sensory experience. In particular, visual perception in the deaf may be altered as a result of their auditory deprivation and/or because the deaf rely heavily upon a visual language (American Sign Language, or ASL, in the US). Recently, we found that deaf, but not hearing, subjects exhibit a right visual field/left hemisphere advantage on a low-level direction of motion task, a finding that has been attributed to the deaf's experience with ASL [Psychol. Sci. 10 (1999) 256; Brain Res. 405 (1987) 268]. In order to determine whether this visual field asymmetry generalizes to other low-level visual functions, in this study we measured contrast sensitivity in deaf and hearing subjects to moving stimuli over a range of speeds (0.125-64 degrees /s). We hypothesized that if ASL use drives differences between hearing and deaf subjects, such differences may occur over a restricted range of speeds most commonly found in ASL. In addition, we tested a third group, hearing native signers who learned ASL early from their deaf parents, to further assess whether potential differences between groups results from ASL use. These experiments reveal no overall differences in contrast sensitivity, nor differences in visual field asymmetries, across subject groups at any speed tested. Thus, differences previously observed between deaf and hearing subjects for discriminating the direction of moving stimuli do not generalize to contrast sensitivity for moving stimuli, a result that has implications for the neural level at which plastic changes occur in the visual system of deaf subjects.

Adult↗

PubMed1998

Periventricular leukomalacia causes visual impairment in preterm children. A study on the aetiologies of visual impairment in a population-based group of preterm children born 1989-95 in the county of Värmland, Sweden.

PURPOSE: To determine the causes of visual impairment in a population-based group of visually impaired preterm children. METHODS: Ophthalmological examination and magnetic resonance imaging or computed tomography of the brain were performed in all visually impaired preterm children born 1989-95 in Värmland. RESULTS: Ten of 18 children had periventricular leukomalacia affecting the optic radiation, six had other lesions or malformations in the posterior visual pathways/cortex, but no child had visually impairing retinopathy of prematurity. CONCLUSION: We conclude that cerebral lesions or malformations are common causes of the visual functional deficit in visually impaired children born preterm. Brain damage should be suspected in a prematurely born child who presents with either of the signs: fixation difficulties, strabismus or nystagmus.

Adult↗

PubMed1999

Auditory activation of cortical visual areas in cats after early visual deprivation.

Auditory activation of the primary visual cortex (area 17) and two extrastriate visual cortical areas - the anterolateral lateral suprasylvian area (ALLS) and anteromedial lateral suprasylvian area (AMLS), was investigated in visually impaired cats. Impairment was accomplished shortly after birth by bilateral eyelid suturing (binocularly deprived cats, BD) or bilateral enucleation (binocularly enucleated cats, BE). In BE cats, the optic nerve and chiasm were entirely degenerated. No cortical atrophy or cytoarchitectural malformation was noticed in either BD or BE cats. In both normal and impaired cats we found auditory-responsive cells in the ALLS and AMLS, areas that are considered strictly visual. The most remarkable finding was an increase in the relative number of these auditory cells in the BD and BE cats, which was more prominent in the latter. Some auditory-responsive cells were also found in area 17 of BE cats. On the basis of formal calculation, it is tempting to suggest that the increase in relative number of auditory cells in these areas reflects the transformation of all the visual cells in the ALLS of BD and BE cats into auditory cells. In BE cats, all bimodal cells and an appreciable percentage of non-responsive cells also had transformed to auditory cells. In the AMLS of BD cats, it is primarily the bimodal cells that become auditory cells, whereas in BE cats all the visual and bimodal cells as well as non-responsive cells undergo this transformation. This assumption, however, is one possible interpretation of our results but not the only one. Other modes of neuronal plasticity that might yield similar results in the visually deprived cats can not be ruled out.

Acoustic Stimulation↗

PubMed1994

The contribution of motion, the visual frame, and visual polarity to sensations of body tilt.

Three types of visual information contribute to the sense of self orientation with respect to gravity: visual polarity of objects with a distinct top and bottom, the principal vertical and horizontal lines of the visual environment, and visual motion. Three visual displays were designed to investigate the contribution of each visual feature to illusory self tilt: a large sphere lined with dots, a cubic room lined with dots, and a furnished room with floor and ceiling. In experiment 1 the dotted room and the furnished room were tilted to various angles about the roll axis of the erect subject who set a visual line and an unseen rod to the apparent vertical. In the dotted room, settings were made either with respect to the nearest surface to the horizontal or with respect to the nearest diagonal of the room. In the furnished room, settings were made with respect to the nearest horizontal wall but not with respect to diagonals. In experiment 2 each of the three displays was rotated at constant velocity and subjects' responses were classified into four categories: illusory self tilt at a constant angle, alternating self tilt with the body becoming erect each time a surface became horizontal, continuous head-over-heels self rotation, and a feeling that the body was supine. Almost all responses were of constant tilt in the sphere. Constant and alternating tilt were the most common responses in the dotted room. In the furnished room 60% of subjects experienced full head-over-heels self rotation.

Attention↗

PubMed1998

The effects of visual discomfort and pattern structure on visual search.

Unpleasant somatic and perceptual side effects can be induced when viewing striped repetitive patterns, such as a square wave or a page of text. This sensitivity is greater in participants with higher scores on a scale of visual discomfort. In three experiments the effect that this sensitivity has on performance efficiency in a reading-like visual search task was investigated. In experiments 1 and 2, the 'global' structure of the patterns was manipulated to produce a square-wave, a checkerboard, and a plaid pattern. It was found that the group that suffered severe visual discomfort took significantly longer than other groups to perform the task, with interference greatest with presentation of the square-wave-like pattern. This supports the prediction of greatest distraction of visual attention from the local target elements with presentation of the pattern structure inducing greatest visual discomfort. In experiment 3, the internal pattern components were manipulated and task difficulty reduced. A no-interference and two interference patterns, one with a global characteristic only and the second made up of distracting line elements, containing global and local components were used. The global pattern structure produced interference effects on the visual-search task. All groups performed with the same speed and accuracy on the task involving the no-interference pattern, a finding attributed to reduced task difficulty. McConkie and Zola's model of visual attention was used to explain these results.

Asthenopia↗

PubMed1986

Infarcts of both inferior parietal lobules with impairment of visually guided eye movements, peripheral visual inattention and optic ataxia.

Clinicopathological correlations are reported in a case with bilateral isolated infarcts in the posterior part of the parietal lobes, due to nonbacterial thrombotic endocarditis accompanying pancreatic adenocarcinoma. The initial left-sided infarct induced right visual neglect, impairment of right-beating optokinetic nystagmus (OKN), optic ataxia, Gerstmann's syndrome and apraxia. After the right-sided infarct, which occurred six weeks later, bilateral visuo-oculomotor disturbances were observed, including peripheral visual inattention, disorder of visually guided saccades, severe impairment of foveal smooth pursuit and OKN slow phase. The lesion on the left involved the upper part of the angular gyrus and a part of the adjacent superior parietal lobule (SPL). That on the right involved the supramarginal gyrus and extended posteriorly into the superoanterior extremity of the angular gyrus, into both margins of the adjacent intraparietal sulcus and into a small part of the SPL. As the oculomotor deficits and the peripheral visual inattention were bilateral after the second infarct, they probably resulted from the lesion of homologous areas in both cerebral hemispheres. The zone damaged in common included a small part of the SPL, the superoanterior extremity of the angular gyrus, and the adjacent intraparietal sulcus and a small portion of the subcortical white matter. This restricted cerebral zone could therefore, in man, be implicated both in the control of all visually guided eye movements and in visual attention. It is further suggested that two corticofugal pathways are implicated in visually guided saccades, the first arising from the frontal eye fields and projecting directly onto the premotor structures in the brainstem, the second arising from the posterior parietal cortex (probably mainly the intraparietal sulcus adjacent to the angular gyrus) and including a relay in the superior colliculus before reaching the premotor structures. Lastly, the findings support the hypothesis that optic ataxia results from interruption of direct and/or crossed occipitofrontal pathways coursing in the deep white matter of the parietal lobe.

Ataxia↗

PubMed2001

Development of cytochrome oxidase blobs in visual cortex of normal and visually deprived cats.

Cytochrome oxidase (CO) blobs are central to our understanding of the columnar organization and parallel pathways in primate and cat visual cortex. In primates, development of blobs and their relationship with other columnar features of the visual cortex begins pre-natally, before visual experience. In kittens, the supragranular layers differentiate post-natally, after eye opening, raising the possibility that visual experience may influence the development of blobs in cat V1. We have examined the development of blobs in unfolded and flattened sections through the visual cortex of normally reared, dark-reared, monocularly deprived and binocularly deprived kittens. Blobs were found in superficial layers of V1 of normally reared kittens as early as 2 weeks of age, although at this age the overall CO staining in V1 was lighter than in V2. By 6 weeks of age the blobs were adult-like. A patchy pattern of CO staining was also found in V2 of young kittens but not in adults. Visual experience was not necessary for expression of the blobs and monocularly deprived kittens had well developed blobs, indicating that strong Y cell drive is not necessary for the development of blobs in cat V1. CO blobs appear in kitten V1 very early in post-natal development and their expression is independent of visual experience, suggesting that they may be an intrinsic feature of V1 organization.

Age Factors↗