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At least 1,081 records · Page 60Linked to original sources

PubMed2001

Visual jitter: evidence for visual-motion-based compensation of retinal slip due to small eye movements.

When dynamic random noise is replaced by static noise after a period of adaptation, adjacent unadapted regions filled with static noise appear to 'jitter' coherently in random directions for several seconds, actually mirroring the observer's own eye movements of fixation [Murakami, I. & Cavanagh, P. (1998). Nature, 395, 798-801]. The present study aims at psychophysically locating two distinct stages underlying this visual jitter phenomenon: a monocular, adaptable stage that measures local retinal motion and a compensation stage that estimates a baseline motion minimum and subtracts it from motion vectors nearby. The first three experiments revealed that visual jitter has storage, directional selectivity, and spatial frequency selectivity, like the motion after-effect does. These results suggest some overlap in the adaptation mechanisms for the two effects, possibly at or below the level of primary visual cortex. The next two experiments revealed the transfer of the effect across the vertical meridian as well as the existence of a preferred stimulus size that is a linear increasing function of eccentricity, mimicking the RF size of the monkey MT neurons. These results suggest that some extrastriate motion area along the parietal pathway including MT mediates motion-based compensation of retinal slip.

Adaptation, Physiological↗

PubMed2002

Visualization of oxygen transfer across the air-water interface using a fluorescence oxygen visualization method.

Oxygen concentration fields in a water body were visualized by the fluorescence oxygen visualization (FOV) method. Pyrenebutyric acid (PBA) was used as a fluorescent indicator of oxygen, and an intensive charge coupled-device (ICCD) camera as an image detector. Sequential images (over 2000 images) of the oxygen concentration field around the surface water of the tank (1 x 1 x 0.75 m3) were produced during the 3 h experiment. From image processing, the accurate pathway of oxygen-rich, cold water at the water surface was also visualized. The amount of oxygen transferred through the air-water interface during the experiment was measured and the oxygen transfer coefficient (K(L)) was determined as 0.22 m/d, which was much higher than that is expected in molecular diffusion. Results suggest that vertical penetration of cold water was the main pathway of oxygen in the water body in the tank. The average velocity of cold water penetrating downward in water body was also measured from consecutive images and the value was 0.3-0.6 mm/s. The FOV method used in this research should have wide application in experimental fluid mechanics and can also provide a phenomenological description of oxygen transfer under physically realizable natural conditions in lakes and reservoirs.

Environmental Monitoring↗

PubMed1989

Visual conversion disorder: a case analysis of the influence of visual information.

We examined the influence of visual information on a decision task that was administered to an individual with monocular visual conversion disorder. Findings indicated that his performance was influenced by the visual information and by motivation instructions. The findings are discussed in terms of a model of hysterical blindness that recognizes the interplay of cognitive and motivational processes.

Adult↗

PubMed1992

Visual space perception and visually directed action.

The results of two types of experiments are reported. In 1 type, Ss matched depth intervals on the ground plane that appeared equal to frontal intervals at the same distance. The depth intervals had to be made considerably larger than the frontal intervals to appear equal in length, with this physical inequality of equal-appearing intervals increasing with egocentric distance of the intervals (4 m-12 m). In the other type of experiment, Ss viewed targets lying on the ground plane and then, with eyes closed, attempted either to walk directly to their locations or to point continuously toward them while walking along paths that passed off to the side. Performance was quite accurate in both motoric tasks, indicating that the distortion in the mapping from physical to visual space evident in the visual matching task does not manifest itself in the visually open-loop motoric tasks.

Adult↗

PubMed2003

[New possibilities in fracture visualization by means of CT: reconstructions, 3D plannings--difficult joint fractures--modern management--improved visualization and operative planning in joint fractures].

After having been introduced in the seventies computed tomography (CT) has become an important instrument for the diagnosis of difficult joint fractures. With the evolution of the Spiral-CT with multiplanar reformations and three-dimensional (3D-) reconstructions the quality of visualization has been improved considerably. In comparison with conventional radiography the actual CT scanners give a clear image of the fracture configuration and the degree of fragment displacement in joint fractures. Additional information about sub-/luxations of the joint, impaction and comminution is also clearly visualized by the CT. This means a rise in quality of fracture classification and enables a detailed view of the fracture pattern. These findings provide the basis for gratifying treatment regimens and surgical management of the injured joint. By the use of innovative reconstruction methods the CT allows exact visualization of internal fixations/osteosynthesis and secondary angular/rotation or length deformities postoperatively. Furthermore, reconstructed 3D-views enable preoperative computer simulated plannings of internal fixations and of reduction control intraoperatively. In fact, the actual Spiral-CT scanners are nearly equivalent in costs and total radiation dose compared to the performance of special projections of conventional radiographs. Thus, we recommend to enlarge the performance of additional CT diagnostic in difficult joint fractures and special pre- or postoperative cases.

Cost-Benefit Analysis↗

PubMed2006

[Visual improvement of an amblyopic eye in an adult patient after visual loss in the non-amblyopic eye].

BACKGROUND: The sensitive period for a successful amblyopia treatment is limited to the age of 11 to 13 years. HISTORY AND SIGNS: We present a 60-year-old patient with complete visual loss on his dominant eye after retinal arterial occlusion. The fellow eye had a known severe amblyopia with a corrected visual acuity of 0.1. THERAPY AND OUTCOME: After retinoscopy the patient received a full correction for his amblyopic eye and the vision increased to 0.25. After three months follow-up visual acuity was 0.5 for single optotypes. CONCLUSIONS: Even in adulthood a attempt at full correction of an amblyopic eye after loss of vision in the dominant eye should be performed for optimising the quality of life.

Amblyopia↗

PubMed1992

[Evaluating visual function with visual display graphics on the Macintosh II computer].

A collection of programs has been developed on the Macintosh II computer to generate visual tests for an ophthalmological practice. The large number of available colours makes it possible to emulate most of the available tests and also to develop new ones. The system allows testing of the following visual functions: Visual acuity, Stereopsis, Aniseikonia, Phoria, Cyclophoria, Colour Vision and Contrast sensitivity.

Color Perception Tests↗

PubMed1963

THE VISUAL CELLS AND VISUAL PIGMENT OF THE MUDPUPPY, NECTURUS.

Electron microscopy of the visual cells of the mudpuppy Necturus have revealed several new or hitherto neglected features of organization: (a) A system of deeply staining micelles in virtually crystalline array, probably located in the lamellae of the rod outer segments. These particles may contain the visual pigment, porphyropsin. Counts of the micelles, and microspectrophotometric measurements of porphyropsin in the retina and single rods yield the estimate that each lamellar micelle may contain about 50 molecules of porphyropsin. (b) Systems of about 30 cytoplasmic filaments (here called dendrites), continuous with the cytoplasm of the inner segment, and standing like a palisade about the outer segments of the rods and cones. In the rods, one such filament stands in the mouth of each of the approximately 30 deep fissures that carve the outer segment into a radial array of lobules. (c) A system of deeply staining particles in the membranes of the dendrites, and another in the membranes of the pigment epithelial processes. It is suggested that these may have a part in interchanges of material with the outer segments. The ciliary process is found to penetrate more deeply than is commonly supposed into the outer segments of the rods and cones. The edge of each double-membrane disc in rods forms a differentiated rim structure, both around the disc circumference and bordering the fissures. These anatomical arrangements are summarized in Figs. 13 and 14, and the relevant measurements in Table I. The dilution of visual pigment in Necturus rods and cones and a general consideration of their microstructures make it seem unlikely that such typically solid state processes as exciton migration or photoconduction can transport the effects of light far from the site of absorption. Excitation must, therefore, be conveyed to the receptor as a whole by some axial structure. Among axial structures, the plasma membrane is most likely to be the site of nervous excitation. The ciliary process probably plays its main role in the embryogenesis and regeneration of outer segments; and the dendrites and pigment epithelial processes in exchanges of material with the outer segments and perhaps with one another.

Animals↗

PubMed2001

Visual imagery without visual experience: evidence from congenitally totally blind people.

We explored the ability of congenitally totally blind people (who were contrasted with age-, sex- and education matched blindfolded sighted subjects) to perform tasks which are mediated by visual mental imagery in sighted people. In the first (pictorial) task, subjects had to mentally compare the shape of the outline of three named objects and to indicate the odd-one-out. In the second (spatial) task the participants were asked to memorise the position of a target cube in two- and three-dimensional matrices, based on a sequence of spatially based imagery operations. In addition, during half of the trials of both imagery tasks subjects were required to perform a concurrent finger tapping task, to investigate whether the blind subjects would be more dependent on spatial processing. Although blind participants made significantly more errors than sighted participants, they were well able to perform the spatial imagery task as well as the pictorial imagery task. Interference from the concurrent tapping task affected both groups to the same extent. Our results shed new light on the question whether early visual experience is necessary for performance on visual imagery tasks, and strongly suggest that vision and haptics may share common representations.

Adult↗

PubMed2004

Nonlinear visual mapping model for 3-D visual tracking with uncalibrated eye-in-hand robotic system.

A new control scheme for uncalibrated robotic visual tracking problem is proposed that compromises the computational expenses of overall system with offline modeling and online control. A nonlinear visual mapping model for the uncalibrated hand-eye coordination is first proposed with an artificial neural network implementation. An online visual tracking controller is then developed together with a real-time motion planner. To improve the system performance, the control scheme is also integrated with a feedforward controller to compensate unknown object motions. Extensive simulations and experiments demonstrate the effectiveness of the proposed control scheme.

Algorithms↗

PubMedDate not supplied

Pre-school visually impaired children: visual stimulation and micro-computers.

A justification is offered for using micro-computers and specially-designed programs with severely visually impaired pre-school children. It is argued that this technology optimizes the visual environment for the child and provides immediate feedback about the correctness of his responses to the stimuli displayed on the screen. Some of the problems encountered in such use are described, with examples taken from sessions in which teachers are working with children as young as 2 years of age, using teaching/learning sequences designed to promote and exercise visual perception skills. Among the issues addressed are the nature of the language interactions between child and adult, the effects of altering the complexity of the tasks, and the possible value of formal task analysis as a means of enabling the teacher to pinpoint critical stages in the learning process.

Blindness↗

PubMed2001

Visual and non-visual control of landing movements in humans.

1. The role of vision in controlling leg muscle activation in landing from a drop was investigated. Subjects (n = 8) performed 10 drops from four heights (0.2, 0.4, 0.6 and 0.8 m) with and without vision. Drop height was maintained constant throughout each block of trials to allow adaptation. The aim of the study was to assess the extent to which proprioceptive and vestibular information could substitute for the lack of vision in adapting landing movements to different heights. 2. At the final stages of the movement, subjects experienced similar peak centre of body mass (CM) displacements and joint rotations, regardless of the availability of vision. This implies that subjects were able to adapt the control of landing to different heights. The amplitude and timing of electromyographic signals from the leg muscles scaled to drop height in a similar fashion with and without vision. 3. However, variables measured throughout the execution of the movement indicated important differences. Without vision, landings were characterised by 10 % larger ground reaction forces, 10 % smaller knee joint rotations, different time lags between peak joint rotations, and more variable ground reaction forces and times to peak CM displacement. 4. We conclude that non-visual sensory information (a) could not fully compensate for the lack of continuous visual feedback and (b) this non-visual information was used to reorganise the motor output. These results suggest that vision is important for the very accurate timing of muscle activity onset and the kinematics of landing.

Adult↗

PubMedDate not supplied

Near infrared imaging for measuring and visualizing skin hydration. A comparison with visual assessment and electrical methods.

A near infrared (NIR) multispectral imaging method for measuring skin hydration has been applied in a clinical study for estimating skin hydration effects of skin moisturizers and cleansers. The method has been compared to the commercially available, standard electrical methods for evaluating changes in skin hydration based on conductance and capacitance measurements. All of the instrumental methods have been compared to the visual assessment of skin dryness. It has been shown that the NIR imaging method is capable of detecting changes in skin hydration induced by skin moisturizers and cleansers. A large positive hydration change upon treatment by a moisturizing cream was easily detected by all three instrumental methods and by the expert visual assessment of dryness. The imaging technique is rapid, noncontact and noninvasive, and has the additional important advantage of showing the degree of hydration as a function of location, for rapid assessment of change in hydration. There was a clear difference between the instrumental methods when the induced changes were not as great as that from the moisturizing cream. The imaging technique showed more sensitive discrimination between treatments and control, and strong correlation to visual appearance of dryness. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Administration, Topical↗

PubMed1978

Delayed visual evoked potentials with bilateral disease of the posterior visual pathway.

A man of 51 years presented with sudden onset of a confusional state and marked visual deterioration. The computerised transaxial tomogram showed a mass in the corpus callosum which had spread to involve both cerebral hemispheres. The visual evoked potential to pattern stimulus was delayed by about 20 ms. Necropsy confirmed the presence of an astrocytoma of the corpus callosum involving the optic radiation and occipital cortex on both sides. The anterior visual pathway was normal.

Astrocytoma↗

PubMed2003

Virtual reality modelling language: freely available cross-platform visualization technique for 3-D visualization of the inner ear.

This was a study of the use of virtual reality modelling language (VRML) for cross-platform interactive three-dimensional (3-D) visualization of high-resolution magnetic resonance (MR) images of the inner ear in the assessment of cochlear implant candidates. A retrospective case review was made of cochlear implant candidates undergoing pre-operative high-resolution MR studies to determine their suitability for implantation. 3-D visualizations of MR scans of the inner ear structures were created using surface rendering and exported as portable VRML files. Case studies are presented to illustrate different points of interest. VRML reconstructions aided the interpretation of two-dimensional (2-D) source images in a variety of inner ear abnormalities. VRML is an internationally recognized standard for cross-platform 3-D visualization that creates a means of providing the implanting surgeon with a portable 3-D representation of the inner ear, aiding interpretation of the complex cross-sectional anatomy of these structures, and guiding selection of patients for implantation as well as implantation technique. The elucidation of the mechanisms behind inner ear malformations can also be aided by detailed imaging studies of the temporal bone, with VRML reconstructions providing an easily interpreted representation of deformities.

Adolescent↗

PubMed1989

Effects of information conflict and complexity in visual figures on voluntary visual exploration, using structural information theory.

This study was designed to examine the effects of information conflict and complexity on voluntary visual exploration quantitatively. 31 adults viewed each of 16 slides of geometrical figures and places for as long as they wished. The stimuli had two values of information conflict and complexity which had been calculated by means of structural information theory. Free looking times indicated that only when information conflict was low, voluntary visual exploration was positively correlated with complexity. Furthermore, voluntary visual exploration correlated positively with information conflict when complexity was low.

Adult↗

PubMed1996

A visual orientation system for promoting indoor travel in persons with profound developmental disabilities and visual impairment.

A visual orientation system was employed for promoting independent indoor travel for two young adults with profound developmental disabilities and visual impairment. The system was a portable device subjects wore and light sources that marked the routes to the various destinations. Data showed that the system was useful in helping the subjects orient and move independently in their daily environment and in a new (generalization) setting. The visual orientation system is discussed in relation to other systems previously developed.

Adolescent↗

PubMed1997

Test of visual-motor integration:: construct validity in a comparison with the Beery-Buktenica Developmental Test of Visual-Motor Integration.

The 1996 Test of Visual-Motor Integration manual states that an adjusted correlation of .95 was obtained between this test and the Beery-Buktenica Developmental Test of Visual-Motor Integration for 49 children with an average age of 9 years and that the adjusted .95 suggests equivalency of the tests. In the present study, for 103 children whose average age was 9 years, there was a correlation of .33 between the tests. Scores on the Beery-Buktenica test correlated more strongly than the Test of Visual-Motor Integration with both chronological age and academic achievement. Standard scorers for the latter test were high compared to those of the Beery-Buktenica test and the Comprehensive Test of Basic Skills. Interscorer agreement was significantly lower, and more time was required to score the protocols. This study indicates that the 1996 version is not a substitute for the Beery-Buktenica test.

Achievement↗