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 487 records · Page 27Linked to original sources

PubMed1986

Subfoveal choroidal neovascular membranes in age-related macular degeneration. Visual prognosis in eyes with relatively good initial visual acuity.

We determined the visual prognosis of 94 eyes in 92 patients having age-related macular degeneration, a discrete choroidal neovascular membrane directly under the center of the foveal avascular zone (subfoveal), and an initial visual acuity of 20/100 or better. Of the patients who were reexamined 24 months following their initial presentation, 77% had lost at least four lines of vision and 64% had lost at least six lines. Estimation of visual loss using a conservative assessment procedure showed four-line visual loss in 65% of the patients and six-line loss in 50%. In general, the better the visual acuity at the initial examination, the more likely the patient was to have a smaller choroidal neovascular membrane. These results suggest that it may be reasonable to consider a randomized clinical trial of laser photocoagulation for this group of patients with a relatively poor visual prognosis.

Age Factors↗

PubMed1994

Dependence of visual stabilization of postural sway on the cortical magnification factor of restricted visual fields.

Monocular visual stabilization of fore-aft and lateral body sway was tested posturographically in normal subjects (wearing visual field blinds) as a function of visual field size and location of the visual field on the central or peripheral retina. Body sway applied to a force- measuring platform is less with central (foveal) vision when central and peripheral visual fields have the same area. If, however, the peripheral field size is corrected by the cortical magnification factor of the retina in the primary cortex, body sway is stabilized by the peripheral retina to the same extent. Thus, there is no functional specialization of central and peripheral retina with respect to balance control. Visual stabilization of upright stance is a function of field size and cortical representation of the retina. The central and the peripheral retina have different thresholds to detect motion; this was surprisingly not reflected in measurements of normal fore-aft and lateral body sway.

Adult↗

PubMed1992

Oculo-manual coordination control: ocular and manual tracking of visual targets with delayed visual feedback of the hand motion.

The aim of this study was to examine coordination control in eye and hand tracking of visual targets. We studied eye tracking of a self-moved target, and simultaneous eye and hand tracking of an external visual target moving horizontally on a screen. Predictive features of eye-hand coordination control were studied by introducing a delay (0 to 450 ms) between the Subject's (S's) hand motion and the motion of the hand-driven target on the screen. In self-moved target tracking with artificial delay, the eyes started to move in response to arm movement while the visual target was still motionless, that is before any retinal slip had been produced. The signal likely to trigger smooth pursuit in that condition must be derived from non-visual information. Candidates are efference copy and afferent signals from arm motion. When tracking an external target with the eyes and the hand, in a condition where a delay was introduced in the visual feedback loop of the hand, the Ss anticipated with the arm the movement of the target in order to compensate the delay. After a short tracking period, Ss were able to track with a low lag, or eventually to create a lead between the hand and the target. This was observed if the delay was less than 250-300 ms. For larger delays, the hand lagged the target by 250-300 ms. Ss did not completely compensate the delay and did not, on the average, correct for sudden changes in movement of the target (at the direction reversal of the trajectory). Conversely, in the whole range of studied delays (0-450 ms), the eyes were always in phase with the visual target (except during the first part of the first cycle of the movement, as seen previously). These findings are discussed in relation to a scheme in which both predictive (dynamic nature of the motion) and coordination (eye and hand movement system interactive signals) controls are included.

Adult↗

PubMed1990

Functional compensation in the lateral suprasylvian visual area following bilateral visual cortex damage in kittens.

Previous studies have shown that functional compensation is present in the cat's posteromedial lateral suprasylvian (PMLS) area of cortex after damage to areas 17, 18, and 19 (visual cortex) early in life but not after damage in adults. These studies all have investigated animals with a unilateral visual cortex lesion, whereas all behavioral studies of compensation for early visual cortex damage have investigated animals with a bilateral lesion. In the present experiment, we investigated whether functional compensation also is present in PMLS cortex after a bilateral visual cortex lesion early in life. We recorded from single neurons in the PMLS cortex of adult cats that had received a bilateral lesion of areas 17, 18, and 19 on the day of birth or at 8 weeks of age. We found that PMLS cells in both groups of cats had functional compensation (normal direction selectivity and ocular dominance) similar to that seen after a unilateral lesion at the same ages. These results are consistent with the hypothesis that PMLS cortex is involved in the behavioral compensation seen after early visual cortex damage. In addition, the results indicate that inputs from contralateral visual cortex are not necessary for the development of functional compensation seen in PMLS cortex.

Age Factors↗

PubMed2001

Superior performance for visually guided pointing in the lower visual field.

The superior hemiretina in primates and humans has a greater density of ganglion cells than the inferior hemiretina, suggesting a bias towards processing information in the lower visual field (loVF). In primates, this over-representation of the loVF is also evident at the level of striate and extrastriate cortex. This is particularly true in some of the visual areas constituting the dorsal "action" pathway, such as area V6A. Here we show that visually guided pointing movements with the hand are both faster and more accurate when performed in the loVF when compared to the same movements made in the upper visual field (upVF). This was true despite the fact that the biomechanics of the movements made did not differ across conditions. The loVF advantage for the control of visually guided pointing movements is unlikely to be due to retinal factors and may instead reflect a functional bias for controlling skilled movements in this region of space. Possible neural correlates for this loVF advantage for visually guided pointing are discussed.

Adult↗

PubMed1993

Visual cortex ablations do not prevent extinction of fear-potentiated startle using a visual conditioned stimulus.

Following observations in the literature that sensory cortex ablations prevent extinction of conditioned fear, the present experiments tested the generality of this finding by examining whether visual cortex ablations would prevent extinction of conditioned fear as assessed by fear-potentiated startle using a visual conditioned stimulus. Consistent with previous reports, visual cortex ablations did not prevent the acquisition or expression of fear-potentiated startle to a visual conditioned stimulus. More importantly, visual cortex ablations did not prevent extinction of fear-potentiated startle to a visual conditioned stimulus, nor did they reverse preoperatively established extinction, indicating that sensory cortex is not required for extinction of conditioned fear in all situations.

Animals↗

PubMed1991

Visual imagery and knowledge about the visual appearance of objects in patients with posterior cerebral artery lesions.

The purpose of this study was to explore whether patients with left posterior cerebral artery (PCA) lesions have defective mental visual imagery and to differentiate whether such a deficit stems from a loss of knowledge about the visual appearance of objects or from an inability to create mental visual images out of preserved visual knowledge. Normal controls and patients with either left or right PCA lesions were asked to verify low- and high-imagery sentences and then to verify pictorial representations of the predicates of high-imagery sentences. High-imagery questions concerned either the shape or the color of objects. In addition, perceptual discrimination of shape and color was assessed. Patients with right PCA lesions were impaired on the perceptual discrimination tasks. Left PCA patients did not significantly differ from controls on low-imagery sentences but scored significantly lower on shape and color questions. Their impairment was distinctly more severe with the pictorial than with the verbal versions of shape and color questions. In comparison to patients with occipital left PCA lesions, patients with temporo-occipital left PCA lesions were selectively impaired on verbal and visual color questions. It is concluded that patients with left PCA lesions lack knowledge about shape and color of objects, but that their ability to convert visual knowledge into mental images is preserved.

Analysis of Variance↗

PubMed1993

Laminar expression of m1-, m3- and m4-muscarinic cholinergic receptor genes in the developing rat visual cortex using in situ hybridization histochemistry. Effect of monocular visual deprivation.

The postnatal development of laminar pattern of m1-, m3- and m4-mRNA-muscarinic acetylcholine receptor subtypes in the visual cortex of both normally raised and monocularly deprived rats (one eyelid sutured at the age of 11 days) was studied using in situ hybridization histochemistry and computer-assisted image analysis. From birth until day 15 the level of m1-receptor transcript in layer II/III increases markedly as compared to deeper layers. From day 15 up to day 18 a transient bimodal pattern develops with peaks in layers II/III and VI. Already on day 35 a more homogeneous distribution of m1-receptor mRNA level is detectable persisting until adulthood. In contrast, the m3-receptor mRNA shows already at birth a bimodal distribution with peaks in layers II/III and VI. Further development until adulthood results in transient changes in the ratio of the mRNA levels in these layers. In the adult visual cortex a similar laminar pattern as at birth is observed. From day 1 up to day 10 a relative increase in the mRNA level of the m4-receptor in layers II to IV is observed. From day 10 until day 15 a bimodal distribution of receptor mRNA develops with peaks in layers III and VI which is similar to the adult stage. However, between days 18 and 35 a shift in the laminar receptor mRNA distribution occurs resulting in peaks in layers IV and VI. The labeling of the m5-receptor transcript in rat visual cortex was very weak and did not show any alteration with age. Unilateral eyelid closure from postnatal day 11 resulted in transient changes in the laminar distribution of m3- and m4-receptor mRNA between postnatal days 18 and 25, whereas the development of the laminar pattern of the m1-receptor mRNA was not affected regardless of the length of visual deprivation. The distinct laminar developmental pattern of mRNA muscarinic receptor subtypes in rat visual cortex suggests specific roles of the muscarinic receptor subtypes during the first weeks of postnatal maturation of visual function.

Aging↗

PubMed1993

Differential laminar expression of AMPA receptor genes in the developing rat visual cortex using in situ hybridization histochemistry. Effect of visual deprivation.

The postnatal development of laminar pattern of AMPA receptor mRNA subtypes GluR-A through to GluR-D (flip variants) in the visual cortex of both normally raised and monocularly deprived rats (one eyelid sutured at the age of 11 days) was studied using in situ hybridization histochemistry and computer-assisted image analysis. The AMPA receptors GluR-A through to GluR-D transcripts exhibit a differential laminar expression pattern in the developing rat visual cortex. At birth the levels of GluR-A transcripts are lower by about 50% in each visual cortical layer as compared to the adult values. In contrast, GluR-B to GluR-D mRNAs are expressed in all cases at higher levels at birth than in the adult brain. Unilateral eyelid closure at postnatal day 11 for several periods of time resulted in both transient and permanent changes in the laminar development of GluR-A through to GluR-C transcripts but hardly affected the GluR-D mRNA subtype. The distinct laminar developmental pattern of AMPA receptor mRNAs in rat visual cortex as well as the differential effects of visual deprivation suggest specific roles of AMPA receptor subtypes during the early postnatal maturation of visual function.

Animals↗

PubMed2004

Visual function and subjective perception of visual ability after macular hole surgery.

PURPOSE: To evaluate the functional and anatomical results of macular hole surgery and to explore its effect on patients' Health-Related Quality Of Life (HR-QOL) and to investigate the associations between self-reported HR-QOL and conventional measures of visual function. DESIGN: Case series. METHODS: The National Eye Institute 25-Item Visual Function Questionnaire (VFQ-25) and the 36-Item Short-Form Health Survey (SF-36) were self-administered by 30 patients before and 4 months after macular hole surgery. Preoperative, intraoperative, and postoperative clinical data were collected including visual acuity, contrast sensitivity, and metamorphopsia. Multi-item scales rating different aspects of HR-QOL were compared before and after surgery, and their correlation with traditional methods of outcome evaluation was analyzed. RESULTS: Macular hole closure was achieved in 26 patients (87%). Mean LogMAR visual acuity improved by 6 +/- 10 letters for distance and 7 +/- 12 letters for near. Metamorphopsia was reduced by a mean of 35 +/- 70 squares on Amsler chart, and Pelli-Robson contrast sensitivity decreased by a mean of -0.09 +/- 0.3 log units postoperatively. The VFQ-25 composite score as well as scale scores associated with general vision, near vision, vision-related mental health, and role difficulties were significantly improved (P < .05) after successful closure of macular hole. Conversely out of the eight SF-36 health concepts, limitation in usual role activities because of emotional problems was the only one that significantly improved postoperatively. Both baseline and postoperative best-corrected visual acuity significantly correlated with most of the VFQ subscale scores before and after surgery, respectively. CONCLUSIONS: In this case-series, macular hole surgery appears to have a beneficial effect on patients' subjective perception of visual function. The use of vision-targeted health status questionnaires in conjunction with detailed clinical examination provides a more comprehensive overview of individuals' daily well-being after surgical intervention. Further controlled studies are required to confirm our findings.

Aged↗

PubMed2006

Visualization of the visual cortex in minipigs using fMRI.

Minipigs are widely used to examine physiologic mechanisms under experimental settings. The purpose of our study was to localize the visual cortex of minipigs using visual stimulation in functional magnetic resonance imaging (fMRI). Five male Göttinger minipigs were studied with fMRI during visual stimulation with series of light impulses conducted into the MR cabin via fibre optical wave guides (EPI sequences, block design, 1.5 T clinical routine MR-scanner). Statistics were performed using SPM'99. All minipigs showed activation of the visual cortex due to light stimulation. The activation could be superimposed to T2-weighted structural images with good spatial resolution revealing the exact location of the visual cortex. We were able to localize the visual cortex in minipigs for the first time utilizing fMRI on a routine scanner. However, this may be useful for precise positioning of electrodes or implants or be used as a further uncomplicated non-invasive method in physiologic experiments.

Animals↗

PubMed2006

Achievement of transsaccadic visual stability using presaccadic and postsaccadic visual information.

While saccadic eye movements produce rapid shift of images of objects on the retina, the visual world is perceived as stationary (visual stability), but the precise mechanisms involved in such perception remain unclear. We investigated if visual stimuli existing before and/or after a saccade serve to preserve visual stability. Participants observed a vertical array of light-spots flashing consecutively at the time of horizontal saccades. When total duration of the flashing array was short (38 ms), large distortions of the array were observed. However, as duration increased up to 300 ms, distortion decreased or was completely eliminated. This demonstrated that visual images of a flashing array momentarily perceived before and/or after saccades suppressed illusory distortion of arrays observed when a 38-ms array was used, implying that the same mechanism may be used to achieve transsaccadic visual stability in daily life.

Adult↗

PubMed1997

Detecting high-level and low-level properties in visual images and visual percepts.

In this article we provide further evidence that visual mental imagery and visual perception share modality-specific mechanisms, and we find that representing visual information in a mental image (activating stored information to create a picture-like mental representation) preserves relatively low-level visual detail. Subjects either saw or visualized simple pictures, and evaluated them for the presence or absence of six types of non-accidental properties. These properties varied from very 'low-level' ones, such as T junctions, to very 'high-level' ones, such as global symmetry. The question was whether both sorts of information are equally accessible in percepts and mental images. If mental images are equivalent to descriptions of perceptual units and their organization, as some have argued, then subjects should have greater difficulty accessing low-level properties in a mental image compared to the difficulty they experience when the drawing is visible. The results of two experiments were clearcut: Subjects could evaluate high-level properties more easily than low-level ones, but this difference was the same in imagery and perception. These findings suggest that mental images preserve relatively low-level visual features, and are not simply descriptions of a pattern.

Eidetic Imagery↗

PubMed2003

Visual deprivation effects on the s100beta positive astrocytic population in the developing rat visual cortex: a quantitative study.

After birth, exposure to visual inputs modulates cortical development, inducing numerous changes of all components of the visual cortex. Most of the cortical changes thus induced occur during what is called the critical period. Astrocytes play an important role in the development, maintenance and plasticity of the cortex, as well as in the structure and function of the vascular network. Dark-reared Sprague-Dawley rats and age-matched controls sampled at 14, 21, 28, 35, 42, 49, 56 and 63 days postnatal (dpn) were studied in order to elucidate quantitative differences in the number of positive cells in the striate cortex. The astrocytic population was estimated by immunohistochemistry for S-100beta protein. The same quantification was also performed in a nonsensory area, the retrosplenial granular cortex. S-100beta positive cells had adult morphology in the visual cortex at 14 dpn and their numbers were not significantly different in light-exposed and nonexposed rats up to 35 dpn, and were even higher in dark-reared rats at 21 dpn. However, significant quantitative changes were recorded after the beginning of the critical period. The main finding of the present study was the significantly lower astroglial density estimated in the visual cortex of dark-reared rats over 35 dpn as well as the lack of difference at previous ages. Our results also showed that there were no differences when comparing the measurements from a nonsensory area between both groups. This led us to postulate that the astrocytic population in the visual cortex is downregulated by the lack of visual experience.

Animals↗

PubMed1993

Recovery of a temporally based visual discrimination after visual cortex lesion in the rat.

In Expt. 1, rats were conditioned to emit a shock avoidance response when the pulse rate of a light was increased. Then, after bilateral visual cortex lesions, the rats were given 10, 20, or 40 days recovery before relearning the discrimination. While all rats were able to relearn the discrimination response, lesion rats had a performance deficit after all recovery periods. Expt. 2 compared the effects of postoperative visual pulse rate training to those of auditory pulse rate training on relearning of the photic pulse-rate discrimination 10 days after visual decortication. Recovery of discrimination responding was better after auditory pulse rate training than after visual training. These data suggest that visual cortex lesions in the rat disrupt perceptual or associational functions involving the temporal features of a visual stimulus. In addition, generalization of relational properties during cross-modal training through multimodal CNS structures appears to enhance recovery of behavior after brain insult.

Acoustic Stimulation↗

PubMed1997

Visual receptive fields and movement fields of visuomovement neurons in the monkey premotor cortex obtained during a visually guided reaching task.

Single-neuron activity in the premotor cortex of monkeys was examined while they performed a visually guided reaching task with their eyes fixated. We recorded a total of 177 visually responsive neurons that showed significantly enhanced activity after a presentation of visuospatial cue ('visual response'). Of these neurons, 57% (n = 101) also showed significantly enhanced activity after an onset of the go-signal and before movement ('movement-associated response'). These were designated as 'visuomovement neurons'. The visual response latencies of 81% of the visuomovement neurons were between 60 and 160 ms (median = 100 ms) and the response durations were less than 240 ms in 80% of the neurons. The preferred direction of the visual response (PDV) was toward the contralateral side in 57% and the ipsilateral side in 20% of the neurons. The preferred direction of the movement-associated response (PDM) was toward the contralateral side in 50% of the neurons. In most of the neurons (74/101, 73%), the PDV and the PDM corresponded to approximately the same direction. These results suggest that premotor visuomovement neurons play a role in receiving visuospatial information for visually guided reaching, and commanding reaching movements.

Animals↗

PubMed1998

Decreased glucose transporter densities, rate constants and glucose utilization in visual structures of rat brain during chronic visual deprivation.

The question was investigated whether local changes in glucose transporter densities and transport kinetics can occur when local cerebral glucose utilization (LCGU) is decreased in some brain structures. Unilateral visual deprivation was induced by monocular enucleation in 25 rats. After 1 week, the contralateral structures of the visual system were analyzed for (1) densities of glucose transporters Glut1 and Glut3 (immunoautoradiography), (2) LCGU (2-[14C]deoxyglucose method) and (3) local rate constants (3-O[14C]methylglucose method). The ipsilateral structures served as controls. During chronic visual deprivation Glut1 and Glut3 densities, LCGU and rate constants were significantly decreased in some structures of the visual system and remained unchanged in others. These results indicate a moderate degree of downregulation of glucose transporters, LCGU and rate constants in the visual system during visual deprivation.

Animals↗

PubMed1998

Telencephalic connections of the visual system of the chicken: tracing the interrelation of the efferents of the visual Wulst and the hyperstriatum ventrale.

In the present study the telencephalic connections between the centres of the tectofugal and thalamofugal pathways were investigated with Phaseolus vulgaris leucoagglutinin and biotinylated dextran-amine anterograde tracers in chicken using light and electron microscopy. No direct connection was found between the visual Wulst and the ectostriatum or the telencephalic centres of the tectofugal and thalamofugal pathways. Besides other projections, the visual Wulst emitted fibres also to the middle and lateral parts of the hyperstriatum ventrale. Further experiments revealed that the middle part of the hyperstriatum ventrale projected to the ectostriatum centrale and periphericum and established an indirect connection between the visual Wulst and the ectostriatum. The lateral part of the hyperstriatum ventrale sent a few efferent fibres toward the diencephalon and brainstem, but projected massively to the ectostriatum periphericum, neostriatum intermedium pars laterale, the ventral part of the neostriatum caudale and the archistriatum dorsale. Considering that these areas are structures of the tectofugal circuitry as well, the presence of these connections may result in a more elaborate visual processing. The neostriatum may be an associative visual center and possibly a modulatory area toward the archistriatum intermedium dorsale, by which visual information may mediate, modulate and control the movements.

Animals↗