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At least 811 records · Page 45Linked to original sources

PubMed2000

Attention-referenced visual representations: evidence from impaired visual localization.

Spatial representations in the visual system were probed in 4 experiments involving A. H., a woman with a developmental deficit in localizing visual stimuli. Previous research (M. McCloskey et al., 1995) has shown that A. H.'s localization errors take the form of reflections across a central vertical or horizontal axis (e.g., a stimulus 30 degrees to her left localized to a position 30 degrees to her right). The present experiments demonstrate that A. H.'s errors vary systematically as a function of where her attention is focused, independent of how her eyes, head, or body are oriented, or what potential reference points are present in the visual field. These results suggest that the normal visual system constructs attention-referenced spatial representations, in which the focus of attention defines the origin of a spatial coordinate system. A more general implication is that some of the brain's spatial representations take the form of coordinate systems.

Adult↗

PubMed2004

Constructing visual representations of natural scenes: the roles of short- and long-term visual memory.

A "follow-the-dot" method was used to investigate the visual memory systems supporting accumulation of object information in natural scenes. Participants fixated a series of objects in each scene, following a dot cue from object to object. Memory for the visual form of a target object was then tested. Object memory was consistently superior for the two most recently fixated objects, a recency advantage indicating a visual short-term memory component to scene representation. In addition, objects examined earlier were remembered at rates well above chance, with no evidence of further forgetting when 10 objects intervened between target examination and test and only modest forgetting with 402 intervening objects. This robust prerecency performance indicates a visual long-term memory component to scene representation.

Cognition↗

PubMed1999

Dissociation of visual, motor and predictive signals in parietal cortex during visual guidance.

The role of the posterior parietal cortex (PPC) in the visual guidance of movements was studied in monkeys trained to use a joystick to guide a spot to a target. Visual and motor influences were dissociated by transiently occluding the spot and by varying the relationship between the direction of joystick and spot movements. We found a strong segregation of function in PPC during visual guidance. Neurons in area MST were selectively modulated by the direction of visible moving stimuli, whereas neurons in area MIP were selectively modulated by the direction of hand movement. In contrast, the selectivity of cells in the lateral intraparietal area (LIP) did not directly depend on either visual input or motor output, but rather seemed to encode a predictive representation of stimulus movement. These predictive signals may be an important link in visuomotor transformations.

Animals↗

PubMed1991

Visual acuity and contrast sensitivity in cataract: summation and inhibition of visual performance.

Patients exhibiting uniocular cataract often report an improvement in vision on closing their cataractous eye. Such qualitative evidence suggests the presence of binocular inhibition--the converse of binocular summation (that is the normal superiority of binocular over monocular vision). To quantify the extent of inhibition in cataract, binocular and monocular visual acuity and contrast sensitivity were measured in 28 patients. Twelve patients showed binocular inhibition for visual acuity whilst 11 showed inhibition for contrast sensitivity measured at four cycles per degree (c.deg-1). Contrast sensitivity for 8 c.deg-1 targets was further recorded in a subset of 14 patients in whom seven showed inhibition. In patients who demonstrated inhibition, the mean decrement in performance for visual acuity was 13%. For contrast sensitivity at 4 and 8 c.deg-1 the mean decrement was 25% and 32% respectively. The clinical significance of these findings is discussed with respect to the assessment of visual function and management of the cataract patient.

Adult↗

PubMed2002

A survey of visual impairment in children attending the Royal Blind School, Edinburgh using the WHO childhood visual impairment database.

PURPOSE: To assess the aetiology and changing patterns of childhood blindness in one school for the blind in the UK and to assess the use of the World Health Organisation Prevention of Blindness (WHO/PBL) methodology and reporting form in a developed country. METHODS: One hundred and seven children in one school for the blind and visually impaired in Edinburgh were examined using the WHO/PBL childhood blindness assessment form. RESULTS: Of the 107 children examined, 87 (81%) were blind or severely visually impaired (corrected visual acuity of <6/60 (20/200) in the better eye). Perinatal related blindness (40%), hereditary disease (26%) and developmental factors (26%) formed the three largest aetiological categories. CONCLUSION: The pattern of childhood blindness seen in this study was similar to reports from other developed countries. The WHO/PBL reporting form allows detailed comparisons between countries and over time. Additional fields for more detailed reporting of cerebral visual impairment and associated handicaps would increase the usefulness of the WHO/PBL form for population-based studies and for use in developed countries.

Adolescent↗

PubMed2001

Visual stimulation-induced phosphorylation of neurofilament-L in the visual cortex of dark-reared rats.

In dark-reared animals, visual exposure is expected to induce drastic changes in both the physiology and anatomy of the cortical neurons, including the rearrangement of their cytoskeletal structures. Phosphorylation of neurofilament-L (NF-L) is probably associated with relatively short-term structural plasticity in vivo, because the assembly and disassembly of the filaments are regulated by phosphorylation of the head domain of NF-L. Thus, by using a series of site- and phosphorylation state-specific antibodies against NF-L, we examined how visual activation induces the phosphorylation of NF-L in the rat brain. We found no specific immunoreactivity for phosphorylated NF-L in the brain of naive rats, whereas one-hour ambient light exposure after dark rearing for ten weeks from birth induced marked phosphorylation of NF-L selectively. Also, the NF-L phosphorylation was found to be localized in the primary and secondary visual cortical areas. These findings suggest that the selective phosphorylation of NF-L plays an important role in the structural plasticity related to the visual experience.

Amino Acid Sequence↗

PubMed1994

Visual motion induces synchronous oscillations in turtle visual cortex.

In mammalian brains, multielectrode recordings during sensory stimulation have revealed oscillations in different cortical areas that are transiently synchronous. These synchronizations have been hypothesized to support integration of sensory information or represent the operation of attentional mechanisms, but their stimulus requirements and prevalence are still unclear. Here I report an analogous synchronization in a reptilian cortex induced by moving visual stimuli. The synchronization, as measured by the coherence function, applies to spindle-like 20-Hz oscillations recorded with multiple electrodes implanted in the dorsal cortex and the dorsal ventricular ridge of the pond turtle. Additionally, widespread increases in coherence are observed in the 1- to 2-Hz band, and widespread decreases in coherence are seen in the 10- and 30- to 45-Hz bands. The 20-Hz oscillations induced by the moving bar or more natural stimuli are nonstationary and can be sustained for seconds. Early reptile studies may have interpreted similar spindles as electroencephalogram correlates of arousal; however, the absence of these spindles during arousing stimuli in the dark suggests a more specific role in visual processing. Thus, visually induced synchronous oscillations are not unique to the mammalian cortex but also occur in the visual area of the primitive three-layered cortex of reptiles.

Animals↗

PubMed2002

From visual function deficiency to handicap: measuring visual handicap in Mali.

BACKGROUND/AIMS: Blindness is a major public health problem in developing countries, even though most could be prevented by relatively simple hygienic and medical interventions. Relatively few patients use the quality health care services available, despite their low cost, due to problems of access or socio-cultural barriers. This health services research project stressed the need for measurement of subjective self-perceived health. The objectives of this study were twofold: a) To translate, adapt and integrate the cultural context found in Mali and validate two instruments for measuring, respectively, perceived vision and quality of life. b) To study the relationship between these variables and visual deficiencies by gender. METHODS: The perceived vision and quality of life questionnaires were based on a translation of the Aravind questionnaire, adapted to Mali. The resulting perceived vision questionnaire comprises 13 questions, grouped according to five subscales (global vision, visual perception, sensory adaptation, visual field and depth perception). Furthermore, the 13 questions on quality of life were grouped into four subscales (personal care, mobility, social life and psychological). For both questionnaires, a global score could be computed. These two questionnaires were administered to a representative sample of 203 subjects with impaired vision, aged over 40, in a rural area in Mali. RESULTS: The acceptability of the questionnaires was good (1% missing data). The convergent validity was adequate for all but one subscale (psychological). The discriminate validity is acceptable for three of the six subscales where measurement can be made (visual perception, personal care, mobility). The Cronbach alpha coefficients indicate good reliability for the global scores. CONCLUSIONS: Analysis of mean results confirms the validity of the International Classification of Disease (ICD) definition of blindness (seeing less than 0.05 results in a steep decrease in quality of life). Moreover, blindness affects the quality of life of women more severely than that of men; this may be related to the availability of social support.

Adult↗

PubMed1977

The relation of auditory, visual, and auditory-visual matching to reading performance of Israeli children.

Six same-different matching tests, both verbal and nonverbal, in three modalities, along with a set of reading tests, were administered to 120 Israeli children in second, third, and fourth grade. The main effect of all S variables, except sex (grade, socioeconomic level, and ability) were significant, as were the test factors of modality (visual, auditory, cross-modal) and form (verbal-nonverbal), but interactions between S and test factors were small. Multiple regression analysis revealed that overall matching test scores accounted for 35% of the variance in reading scores, although the additional contribution of specific subtests was negligible. Performance on the visual-visual tests was virtually perfect. Auditory-auditory matches were more difficult than auditory-visual matches with nonverbal stimuli, while the reverse was true with verbal stimuli.

Auditory Perception↗

PubMed2004

Replacement of the Faces subtest by Visual Reproductions within Wechsler Memory Scale-Third Edition (WMS-III) visual memory indexes: implications for discrepancy analysis.

Within discrepancy analysis differences between scores are examined for abnormality. Although larger differences are generally associated with rising impairment probabilities, the relationship between discrepancy size and abnormality varies across score pairs in relation to the correlation between the contrasted scores in normal subjects. Examinee ability level also affects the size of discrepancies observed normally. Wechsler Memory Scale-Third Edition (WMS-III) visual index scores correlate only modestly with other Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) and WMS-III index scores; consequently, differences between these scores and others have to be very large before they become unusual, especially for subjects of higher intelligence. The substitution of the Faces subtest by Visual Reproductions within visual memory indexes formed by the combination of WMS-III visual subtests (creating immediate recall, delayed recall, and combined immediate and delayed index scores) results in higher correlation coefficients, and a decline in the discrepancy size required to surpass base rate thresholds for probable impairment. This gain appears not to occur at the cost of a diminished sensitivity to diverse pathologies. New WMS-III discrepancy base rate data are supplied to complement those currently available to clinicians.

Face↗

PubMed2007

Human parietal "reach region" primarily encodes intrinsic visual direction, not extrinsic movement direction, in a visual motor dissociation task.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gaze-centered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and event-related functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual-motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world- or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates.

Adult↗

PubMed2006

The effect of colored lenses on the visual evoked response in children with visual stress.

PURPOSE: Some children with visual stress and/or headaches have fewer symptoms when wearing colored lenses. Although subjective reports of improved perception exist, few objective correlates of these effects have been established. METHODS: In a pilot study, 10 children who wore Intuitive Colorimeter lenses, and claimed benefit, and two asymptomatic children were tested. Steady-state potentials were measured in response to low contrast patterns modulating at a frequency of 12 Hz. Four viewing conditions were compared: 1) no lens; 2) Colorimeter lens; 3) lens of complementary color; and 4) spectrally neutral lens with similar photopic transmission. RESULTS: The asymptomatic children showed little or no difference between the lens and no lens conditions. When all the symptomatic children were tested together, a similar result was found. However, when the symptomatic children were divided into two groups depending on their symptoms, an interaction emerged. Children with visual stress but no headaches showed the largest amplitude visual evoked potential response in the no lens condition, whereas those children whose symptoms included severe headaches or migraine showed the largest amplitude visual evoked potential response when wearing their prescribed lens. CONCLUSIONS: The results suggest that it is possible to measure objective correlates of the beneficial subjective perceptual effects of colored lenses, at least in some children who have a history of migraine or severe headaches.

Adolescent↗

PubMed2006

Visual mismatch negativity highlights abnormal preattentive visual processing in Alzheimer's disease.

Mismatch negativity has been found to decline in amplitude with increasing age and also in Alzheimer's disease. It has been suggested that the reduction in amplitude of mismatch negativity in Alzheimer's disease is the result of fatigue rather than a generalized decline in neuronal response. We tested this hypothesis by measuring the effect of time on task on the visual mismatch negativity in both normal aging and in Alzheimer's disease. In older adults, visual mismatch negativity showed a reduction in amplitude, which did not vary with time on task. This argues against fatigue as the cause of visual mismatch negativity amplitude reduction in normal ageing. In Alzheimer's disease, visual mismatch negativity was virtually absent in responses to the first 16 deviant stimuli but present in response to subsequent deviants. This is opposite to the effect predicted by the fatigue hypothesis. It suggests that individuals with Alzheimer's disease are initially refractory to stimulus change.

Adult↗

PubMed2004

Characteristics of attention and visual short-term memory: implications for visual interface design.

Although the human retina can code many object images simultaneously, observers are often aware of only a tiny fraction of this information. These processing limitations of the visual brain have evolved to prioritize particularly relevant features of a scene while ignoring other irrelevant features. However, such selectivity has its drawbacks. In information-rich environments, such as driving a car or landing an aircraft, vision can fail to cope, and accidents can result. Accordingly, much recent research in psychophysics and ergonomics has examined how display characteristics affect our ability to process multiple features of the visual environment simultaneously. The majority of these experiments has found that performance can be optimized by combining several features into one visual 'object'. In contrast, several recent studies from my own laboratory have found the opposite pattern, indicating that information sources can often be more efficiently processed when they belong to separate objects. Indeed, these data suggest that the number of objects has no general effect on our perceptual performance. Instead, I argue for a two-pathway approach to understanding human visual capacities, and suggest that this approach may have important implications for a diverse range of display technologies, including cockpit displays.

Attention↗

PubMed2004

A novel visual analogue scale (VAS) device: an instrument based on the VAS designed to quantify the subjective visual experience.

PURPOSE: To evaluate a novel device intended to facilitate the direct quantification of the subjective visual experience. The design principle is based on that of the visual analogue scale (VAS) technique but obviates the need for subsequent measurement unlike the administration of the conventional paper VAS. METHODS: The visual experience of 134 normally sighted 17-40-year-olds was quantified using (in randomised sequence) a paper VAS and the novel VAS device. A notional 100-point scale was utilised in either case, and the extreme descriptive anchors for both instruments were 'dreadful' and 'perfect'. RESULTS: The degree of clinical agreement between the two alternative VAS techniques was very high. A small bias (mean = +0.7 VAS units: 95% confidence interval 0.3-1.2 units) towards the paper VAS was evident in these data, an outcome of no clinical significance or impediment as regards the substitution of the novel device for the conventional paper-based approach. CONCLUSIONS: The moving of a bead along a wire is shown to be a clinically and statistically reliable alternative procedure to the pen-marking of a conventional paper VAS for the evaluation of the recent subjective visual experience, provided that the same minimum/maximum descriptive anchors are used for either instrument. The instant quantification of the VAS score afforded by the novel technique introduced here broadens the potential clinical application of this technique.

Adolescent↗

PubMed1993

Psychophysical visual function, retinopathy, and glycemic control in insulin-dependent diabetics with normal visual acuity.

We studied relations between psychophysical visual function and grade of retinopathy, glycemic control and clinical background data in 51 insulin-dependent diabetic patients, aged 17-47 years. Three separate qualities of visual function were examined, macular recovery time (nyctometry; 2 min adaptation), contrast sensitivity (Vistech 6000 chart; between 1.5 and 18 cycles per degree (cpd)) and colour vision (Fletcher DS8; protan/deutan and tritan). Only contrast sensitivity of 6 cpd was associated with the grade of retinopathy; reduced function was found in patients with retinopathy compared to those without. No correlations between macular recovery, contrast sensitivity and colour vision were found. None of the visual functions was significantly related to glycemic control, age, duration of diabetes, blood pressure, intraocular pressure, or urinary albumin excretion. Our data suggests that the neurosensory function of contrast sensitivity correlates more sensitively to the grade of diabetic retinopathy than macular recovery and colour vision. Cross-sectional assessments of different psychophysical visual functions seem to be of restricted clinical value as indicators of preceding glycemic control in diabetic patients with no or mild nonproliferative retinopathy.

Adolescent↗

PubMed1983

Very brief visual experience eliminates plasticity in the cat visual cortex.

Rearing cats in the dark extends the critical period for development of visual cortical neurons, which indicates that the experience of visual input is necessary to begin the developmental process. A single brief pulse of visual input (6 hours) during a period of dark-rearing eliminates delayed development in the visual cortex. Light therefore seems to rapidly trigger the developmental process, and once triggered, that process runs to completion in the absence of further input.

Animals↗

PubMed2006

The effect of visual training for patients with visual field defects due to brain damage: a systematic review.

The objective of this review was to evaluate whether systematic visual training leads to (1) a restitution of the visual field (restoration), (2) an increase in the visual search field size or an improvement in scanning strategies (compensation) and (3) a transfer of training-related improvements in activities of daily living such as reading. To retrieve relevant publications, computer-aided searches of databases (Medline, Embase, Cinahl, Cochrane Central Registers of Controlled Trials) and extensive reference tracing and hand searching were performed. Subsequently, all retrieved and blinded studies were scored on methodological quality. 14 studies were included, 2 randomised controlled trials (RCTs) and 12 within-subject repeated-measures designs (RMD). One of the two RCT studies had good quality. The internal validity of the RMD studies varied from poor to good. Five studies reported a significant effect of the vision restoration therapy (VRT), whereas two studies reported no effect using scanning laser ophthalmoscopy or Goldmann perimetry as outcome measure. All authors of the studies on scanning compensatory therapy (SCT) found a significant effect of up to 30 degrees visual search field, a significant increase in reading speed or decrease in reading errors. It is unclear to what extent patients benefit from restoration therapy in relation to a more efficient scanning strategy which enables them to read faster or to avoid obstacles in a better way. No study has given a satisfactory answer. SCT seems to provide a more successful rehabilitation with more simple and user-friendly training techniques. Validated questionnaires provide the most reliable subjective data to assess the transfer of the relevance of training procedures to activities of daily living of the patient. Hence, SCT is recommended until the effect of the VRT is defined.

Brain Diseases↗