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At least 109 records · Page 6Linked to original sources
PubMed1998

Vision for perception and vision for action in the primate brain.

Visual systems first evolved not to enable animals to see, but to provide distal sensory control of their movements. Vision as 'sight' is a relative newcomer to the evolutionary landscape, but its emergence has enabled animals to carry out complex cognitive operations on perceptual representations of the world. The two streams of visual processing that have been identified in the primate cerebral cortex are a reflection of these two functions of vision. The dorsal 'action' stream projecting from primary visual cortex to the posterior parietal cortex provides flexible control of more ancient subcortical visuomotor modules for the production of motor acts. The ventral 'perceptual' stream projecting from the primary visual cortex to the temporal lobe provides the rich and detailed representation of the world required for cognitive operations. Both streams process information about the structure of objects and about their spatial locations--and both are subject to the modulatory influences of attention. Each stream, however, uses visual information in different ways. Transformations carried out in the ventral stream permit the formation of perceptual representations that embody the enduring characteristics of objects and their relations; those carried out in the dorsal stream which utilize moment-to-moment information about objects within egocentric frames of reference, mediate the control of skilled actions. Both streams work together in the production of goal-directed behaviour.

Animals↗
PubMed2001

Links between vision and somatosensation. Vision can improve the felt position of the unseen hand.

During reaching movements, sensory signals must be transformed into appropriate motor commands. Anatomical, electrophysiological, and neuropsychological evidence suggest that there is no single, supramodal map of space that is used to guide reaching. Instead, movements appear to be planned and controlled within multiple coordinate systems, each one attached to a different body part. Recent neuropsychological investigations demonstrating that somatosensory impairments can be ameliorated by visual cues, and visual impairments by proprioceptive cues, have been interpreted as evidence that arm-centered representations may exist in humans. A critical difference between the findings obtained in the monkey and in humans, however, is that in the latter case, vision of the limb appears be critical for visual somatosensory binding. Here, we report a case study of a patient (C.T.) recovering from unilateral somatosensory impairment, including tactile extinction, who executed reaches toward visually defined or proprioceptively defined locations. We demonstrate that when the target location of a reach was defined proprioceptively, by passively positioning our patient's impaired hand beneath the table surface, vision of the workspace immediately adjacent to the unseen hand dramatically increased the endpoint accuracy of her reaching movements, even though such cues could not possibly signal the position of the target directly.

Aged↗
PubMed2000

From vision to reality: how to actualize the vision of discharging patients from a hospital, with an increased focus on prevention.

Experiences in creating dialogue possibilities to stimulate interdisciplinary and intersectoral collaboration in hospital discharge and prevention are presented. Time is often a major constraint that persuades decision-makers to avoid using qualitative methodologies in research and development. Quick results are demanded of today's health-care system, not allowing ideas to be implemented or visions owned by professionals. Action-orientated research is used and recommended, despite its time-demanding methodology. A multidisciplinary management team and the authors, over a 2-year period, worked with the development and implementation of 'Preventive Discharge' in a Danish hospital clinic. The empirical starting point, developmental processes, piloting and implementation of the project are described. Earlier research from a literature review on discharge is referenced. The results show that while there are many barriers to dialogue between professions and between organizational levels, it is possible to frame such opportunities and improve interdisciplinary and intersectoral collaboration for health. External supervision may be an effective tool for stimulating dialogue. The testing phase afforded a valuable lesson when pilot-site collaborators, initially not involved in the development of the process tools, reformulated the project to suit their cultural climate while maintaining the project's original aims. Finally, a discussion is presented on actualizing the vision for 'Preventive Discharge'.

Aged↗
PubMed1999

Relationship between ventral stream for object vision and dorsal stream for spatial vision: an fMRI + ERP study.

Recent imaging studies indicated the existence of two visual pathways in humans: a ventral stream for object and form vision and a dorsal stream for spatial and motion vision. The present study was motivated by a stimulating question: Supposing shape and motion are processed separately in the two pathways, how do the respective cortical areas respond to the stimuli of "forms defined by motion"? fMRI and ERP recordings were combined in order to measure the spatiotemporal activation pattern in the two pathways responding to forms defined by motion, which were produced solely by coherent movement of random dots against a background of dynamic or static random dots. The fMRI data indicated that the stimuli of forms defined by motion indeed activated both dorsal MT/V5 and ventral GTi/GF. Furthermore, the RV curves resulting from fMRI-seeded dipole modeling indicated that each pair of dipoles located at MT/V5 or GTi/GF reached the same best-fit point; a single pair of free dipoles located near the fMRI foci of MT/V5 and GTi/GF could be identified at the corresponding best-fit point; and the source waveforms resulting from fixed dipole modeling also showed simultaneous activation of MT/V5 and GTi/GF dipoles in the time interval around the best-fit point. The present results, therefore, suggest that MT/V5 and GTi/GF appear to be activated in parallel and simultaneously responding to forms defined by motion. Such findings raise interesting issues about the hierarchical organization and the functional specialization in the two pathways.

Adult↗
PubMed1994

[Effect of diffractive multi-focal lenses on contrast vision, glare sensitivity and color vision].

BACKGROUND: Due to theoretical considerations an increase in the depth of field of the diffractive IOL may be combined with a reduction in contrast sensitivity, glare sensitivity and colour perception. PATIENTS AND METHODS: A comparative analysis of both eyes was performed in ten patients with a diffractive multifocal IOL (3M 815LE) in one eye and a monofocal IOL in the other eye. Contrast sensitivity was examined by computer generated sine wave gratings of 6 different spatial frequencies; visual acuity with glare and glare sensitivity were determined under 7 different levels of field luminance; colour vision was examined using the Farnsworth-Munsell-100-Hue-test. RESULTS: Contrast sensitivity of the diffractive lens was reduced for intermediate spatial frequencies, but not for low and high frequencies. Visual acuity with glare was only reduced at maximum field luminance; no differences were found in glare sensitivity and colour perception between monofocal and multifocal. CONCLUSION: Altogether, the diffractive lens did not show a dramatic reduction in the examined visual functions compared with the monofocal IOL.

Aged↗
PubMedDate not supplied

Low vision rehabilitation: visual acuity measurement in the low vision range.

1. To predict function and prescribe low vision aids, accurate measurements are needed. The routine measurement range can be extended by moving test charts normally used at 20 ft to a closer distance; 1 m is recommended, which gains a factor of 6. 2. Some practitioners recommend testing all reading at a standard distance, but they differ in the distances they recommend. Using a variable distance and recording the distance with every measurement allows for patients' preferred distances. 3. If the distance and letter size are properly recorded, the same visual acuity score should be calculated for all distances. Inches and J numbers, the most prevalent measurements, make visual acuity calculations impossible, but by adopting metric measurements, calculations are far easier.

Distance Perception↗
PubMed1982

Residual vision in the low vision patient--some concepts.

The ability to function with residual sight--visual ability--varies widely among individuals with low vision. The theoretical nature of visual ability, however, is poorly understood. Various components of visual ability are defined in an attempt to advance the understanding of this subject.

Blindness↗
PubMed1976

[Evidence for reduced colour vision in carriers of congenital colour vision deficiencies (author's transl)].

The ability to recognize small spots of coloured light in parafoveal regions of the retina was investigated in women heterozygous for protanopia (2 subjects), deuteranopia (2 subjects), or deuteranomaly (1 subject) and in 3 normal subjects. The homozygous colour normals had excellent discrimination up to 8 degrees excentricity, whereas in heterozygous carriers of congenital colour vision deficiencies the ability to differentiate colours varied from point to point within the retina. The results may be explained by assuming the existence of alternating patches of trichromatic and dichromatic cell populations with the retina of the heterozygous carriers.

Color Perception↗
PubMed2005

Why is second-order vision less efficient than first-order vision?

Research has shown that the sensitivity to second-order modulations of carrier contrast is lower than that to first-order luminance modulations stimuli. We sought to compare the efficiency of processing first- and second-order information. Employing a phase-discrimination paradigm we found that when humans were given sufficient a priori information of signal parameters they detected both luminance and contrast modulations of 0.6 and 2c/deg by a phase-sensitive algorithm. The overall detection efficiency for second-order patterns, however, was lower that that for first-order stimuli. To study the factors which limit the efficiency of first- and second-order vision, we measured detection performance for luminance and contrast modulations of 0.6 and 2c/deg embedded in Gaussian noise. The results showed that the detection of second-order patterns had lower sampling efficiency and higher additive internal noise as compared to the detection of first-order stimuli. Classification images for detecting contrast modulations of 2c/deg resembled the side-band component of the contrast modulations which suggests that human observers may detect contrast modulations of a sinusoidal carrier using first-order luminance channels. The lower sensitivity of the mechanism detecting second-order patterns might be due to higher levels of additive internal noise and lower sampling efficiency than those of the mechanism analysing first-order patterns.

Contrast Sensitivity↗
PubMed1992

["Glare vision". I. Physiological principles of vision change with increased test field luminance].

Clinical tests of visual acuity are an important measure of visual function. However visual acuity is usually determined only in narrow range of luminance levels between 160 and 320 cd/m2; therefore losses of visual acuity in other ranges of light intensity can not be detected. In a distance of 80 cm from the patients eyes, Landolt rings of varying sizes were presented on a small test field whose light intensity can be varied between 0.1 and 30,000 cd/m2. Thereby an acuity-luminance-function can be obtained. We studied such functions under different conditions of exposure time both with constant and with increasing luminance of the test field. We found that persons with normal vision can increase their visual acuity with increasing test field luminance up to a range of 5000 cd/m2. The maximum values of visual acuity under optimal lightening conditions lie (varying with age) between 2.2 and 0.9. Under pathological conditions visual acuity falls at high luminances accompanied by sensations of glare. Tests of glare sensitivity as a function of exposure time showed 4 sec to be a critical time of exposure since after 4 sec normal persons just reach their maximum visual acuity at high luminances. The underlying physiological mechanisms lead us to suppose that patients with neuronal light adaptation disturbances display a greater visual loss as a result of decreased time of exposure than those with disturbances in the ocular media. Visual acuity as well as the capacity to increase the patients visual acuity under optimal conditions of lighting were both found to be strongly age-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Clinical study of low vision. Part I: Refraction and the aided distance vision.

Eighty three cases of low vision patients (144 eyes) were examined with distant visual aids. The average visual acuity of the 144 eyes before refraction was approximately 0.07, while the counterpart afterwards was about 0.1 (p less than 0.01). With the 4x monocular focusable aid, acuity improved in 142 eyes out of the 144 eyes. The combined use of clip-on distance aid and the spectacle reading aid was observed to be especially suitable for partially sighted students. The mean MEF of 142 eyes was 0.9435 +/- 0.2068. The paired T-test between the difference of actual magnification and theoretical magnification was not significant at the 5% level. The factors contributing to the variance of MEF were discussed.

Adolescent↗
PubMed1978

Central representation of colour vision deduced from studies on a subject with a central colour vision defect.

M.W.'s grossly defective responses to red light stimuli are caused by an abnormality of central vision which is highly specific in its action. The abnormal activity does not affect stereoscopic function and only partially modifies the parametric characteristics of the contrast threshold elevation effect. These experimental observations lend support to the concept of parallel processing of different attributes of the visual stimulus, possibly by different cortical areas. We suggest that understanding of central visual processes could be facilitated by further studies on subjects with malfunction of the visual cortex.

Adult↗
PubMedDate not supplied

[The relationship between work and vision in a preventive medicine context: the initial guidelines for a correct ergonomic ophthalmological approach proposed by the Italian Group for the Study of the Relationship between Work and Vision (G.I.L.V.). II. The method].

In view of the numerous problems concerning the relationship between work and vision, the Italian Group for the Study of Work/Vision Relationships has developed a document that sets out initial guidelines for environmental monitoring and health surveillance in ergophthalmology. Particular emphasis is given to fact-finding inspections and collection of subjective assessments that will enable the occupational health physician to identify any adverse factors in the working environment and assess the visual effort of the operators. The importance of cooperation between occupational health physicians and ophthalmologists in the various phases of ergophthalmological assessment is stressed. An analytical list is provided of the parameters that the ophthalmologist should measure during eye examination as well as the appropriate assessments that the occupational health physician should perform if an ophthalmological specialist is not available. Suggestions for periodic controls on the basis of visual effort and ophthalmological status are made. It is the task of the occupational health physician to establish the fitness or otherwise of the patients for the job, and for this the Group is preparing further documents.

Environmental Monitoring↗
PubMed1985

Characteristics and low vision corrections in Stargardt's disease. Educational and vocational achievements enhanced by low vision corrections.

One hundred and sixteen patients with Stargardt's disease demonstrated the most useful optical aids that enabled them to obtain an education and employment. The most useful optical aid for distance was the 8X monocular focusable telescope. For near, high-add bifocals, tri-focals, half-eye binocular spectacle magnifiers, paperweight-type magnifiers and hand magnifiers were most useful. Optical aids were prescribed for 102 patients with a success rate of 96%. The progression of visual loss is generally gradual and symmetrical terminating within ten years after onset and not becoming worse than 20/800 (6/240). Academic success seems to be related more to intellectual ability than degree of visual impairment. Highly trained and educated individuals with Stargardt's disease were able to find employment and perform duties usually associated with normal vision.

Adolescent↗