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PubMed2000

Vision as temporal trace.

Most current models of human and animal vision assume that the processes of vision involve 2D (or even 3D) internal representations of the external world--an iconic representation. Within these models, recognition involves some form of lineal, areal or volumetric comparison of these internal representations (either learned or innate) with current sensory inputs. However, this view has recently come under criticism. In this paper, a neural model of vision is explored in which this iconic world view is replaced by a temporally ordered trace of (essentially) local features. The model employs hierarchical, recurrently linked, self-organizing topological maps.

Animals↗
PubMed2005

Simulation of artificial vision, III: do the spatial or temporal characteristics of stimulus pixelization really matter?

PURPOSE: In preceding studies, simulations of artificial vision were used to determine the basic parameters for visual prostheses to restore useful reading abilities. These simulations were based on a simplified procedure to reduce stimuli information content by preprocessing images with a block-averaging algorithm (square pixelization). In the present study, how such a simplified algorithm affects reading performance was examined. METHODS: Five to six volunteers with normal vision were asked to read full pages of text with a 10 degrees x 7 degrees viewing window stabilized in central vision. In a first experiment, reading performance with off-line and real-time square pixelizations was compared at different resolutions. In a second experiment, off-line square pixelization was compared with off-line Gaussian pixelization with various degrees of overlap. In a third experiment, real-time square pixelization was compared with real-time Gaussian pixelization. RESULTS: Results from the first experiment showed that real-time square pixelization required approximately 30% less information (pixels) than its off-line counterpart. Results from the second experiment, using off-line processing, revealed a restricted range of Gaussian widths for which performances were equivalent or significantly better than that obtained with square pixelization. The third experiment demonstrated, however, that reading performances were similar in both real-time pixelization conditions. CONCLUSIONS: This study reveals that real-time stimulus pixelization favors reading performance. Performance gains were moderate, however, and did not allow for a significant (e.g., twofold) reduction of the minimum resolution (400-500 pixels) needed to achieve useful reading abilities.

Adult↗
PubMed2006

Development of a questionnaire to assess vision problems under low luminance in age-related maculopathy.

PURPOSE: To develop a questionnaire for assessing self-reported visual problems under low luminance and at night for use in studies on age-related maculopathy (ARM). METHODS: The questionnaire was developed in three steps: (1) Content for questionnaire items was identified through focus groups of older adults with ARM and those exhibiting normal retinal aging. The topic for discussion was "vision at night and under low lighting." Discussion was audiotaped, transcribed, and subjected to content analysis to identify problem categories expressed by patients. (2) This content was used to develop a preliminary questionnaire administered by telephone to persons with ARM or normal retinal aging. Principal-components analysis identified groups of items that formed the questionnaire's subscales that were evaluated for internal consistency, and an item-reduction strategy was implemented to generate a briefer questionnaire. (3) Psychometric properties of the shortened Low-Luminance Questionnaire (LLQ) were determined, including construct validity, criterion validity, and test-retest reliability. RESULTS: The 32-item LLQ has six subscales (driving, extreme lighting, mobility, emotional distress, general dim lighting, and peripheral vision), all with good internal consistency (Cronbach alpha > or = 0.82). Scores on LLQ subscales correlated moderately with nearly all National Eye Institute Visual Function Questionnaire (NEI VFQ)-25 subscales and decreased in value (indicating more disability) for patients with increasing ARM disease severity. Whereas rod-mediated parameters of dark adaptation were significantly associated with LLQ subscale scores (r = 0.19-0.43, all P < 0.03), cone-mediated parameters were not. Test-retest reliability ranged from 0.74 to 0.88 for all subscales (P < 0.0001), except for peripheral vision (0.46; P = 0.0003), which also exhibited a ceiling effect in almost half of the respondents. CONCLUSIONS: The 32-item LLQ, derived from the content of focus group comments by persons with ARM, has good construct validity, subscale scores related to rod-mediated visual function, and good test-retest reliability for five of six subscales. The LLQ may ultimately be useful in patient-centered evaluation of the outcome of interventions to prevent ARM or to arrest progression of early disease.

Aged↗
PubMed2006

The Impact of Vision Impairment Questionnaire: an evaluation of its measurement properties using Rasch analysis.

PURPOSE: To explore the psychometric properties of the Impact of Vision Impairment scale (IVI) by using Rasch analysis. METHODS: Three hundred fourteen first-time referrals to low-vision clinics completed the 32-item IVI. The data were Rasch-analyzed with a partial credit model using RUMM2020 software (RUMM Laboratory, Perth, WA, Australia). The overall fit of the model, response scale, individual item fit, differential item functioning, unidimensionality, and person-separation reliability were assessed. RESULTS: Initially, 26 items displayed disordered thresholds. However, collapsing the response scale to three categories (4 items) and four categories (28 items) produced ordered response thresholds for all items. Four items with high proportions of missing responses, poor spread, high skewness, and deviation between observed and expected model curves were then removed. This adjustment produced overall fit to the Rasch model (item-trait interaction chi(2) = 118.3; P = 0.32). The final mean (SD) person and item fit residuals ere 0.06 (0.85) and -0.20 (1.45), respectively. The person-separation reliability was 0.9, indicating that the scale was able to discriminate between several different groups of participants. The revised scale was well targeted to the participants, with similar mean locations for items (0.00) and persons (0.16). A significant difference between participants of mild, moderate, and severe visual impairment (ANOVA; P 0.001) supported the criterion validity of the Rasch-scaled IVI. CONCLUSIONS: The results provide support for the measurement properties of the Rasch-scaled 28-item version of the IVI and of its potential for assessing outcomes of low-vision rehabilitation. A raw score-to-Rasch person measure conversion is supplied.

Adult↗
PubMed2006

Preschool vision screening in pediatric practices.

A national sample of pediatricians was surveyed to evaluate preschool vision screening practices (response rate 55%, 377 of 690 eligible respondents). The rate of acuity screening for 3-year-old children was low (35%), but increased for 4- (73%) and 5-year-old children (66%). Few used photoscreening or autorefraction (8%). Common barriers were that screening is too time-consuming and children are uncooperative. Half reported that there should be separate reimbursement for vision screening. Financial incentives may be important for ensuring the delivery of preschool vision screening, as well as adoption of emerging screening technologies if such devices are shown to be effective.

Attitude of Health Personnel↗
PubMed1995

Evaluation of vision screening practices of Illinois pediatricians.

A survey of vision screening practices of American Academy of Pediatrics physicians in Illinois is described. The response rate was 42%. Sixty percent of physicians tested visual acuity of children 5 years and older, and half of this group tested children 2 to 4 years old. The most common reasons for not testing visual acuity were inadequate time (42%), children too young (18%), or screening done at school (18%). The majority (88%) refer to an ophthalmologist after a single vision screening failure, while about half perform the cover-uncover test on infants and children. The results suggest many Illinois pediatricians do not perform vision screening of preschool children, though screening does occur at other sites.

Child↗
PubMed2004

Handedness and macular vision: laterality of motor control underpins both.

This article pursues the corollaries of the anatomy of handedness recently discovered. Specifically, it addresses the issues concerning central vision as it relates to the command center and the circuitry of the saccades. It presents data that support the directionality of callosal traffic in motor and sensory realms even further. Evidence is presented that denotes a relationship between the anatomy sustaining movement control and that responsible for the part of the vision handled by the maculae. The evidence shows bypassing of the callosum by fibers serving the central vision. This aspect has ramifications for surgical approach to the third ventricle by callosotomy, relaxing the earlier prohibitions advocated in approaching the third ventricle via splenectomy.

Brain Mapping↗
PubMed2004

Spatial vision in the echinoid genus Echinometra.

Although eyes are generally considered necessary for image resolution, a diffuse photoreceptive system with directional sensitivity may also have this ability. Two species of the echinoid genus Echinometra were tested for spatial vision by examining their ability to locate and move towards targets of different sizes. The echinoids were significantly oriented (P<0.0001) towards a target with an angular width of 33 degrees (0.3 sr) but were not oriented to targets with angular widths of 26 degrees and 16 degrees . This ability is probably due to the blocking of off-angle light by the spines, which have approximately the correct spacing for the observed resolution. Spatial vision is advantageous for echinoids of this genus because they leave and return to small dark shelters. This first demonstration of spatial vision in an echinoderm sheds further light on the complex optical structures and photobehaviors found in this phylum.

Animals↗
PubMed2006

The role of the lateral line and vision on body kinematics and hydrodynamic preference of rainbow trout in turbulent flow.

The ability to detect water flow using the hair cells of the lateral line system is a unique feature found in anamniotic aquatic vertebrates. Fishes use their lateral line to locate prey, escape from predators and form cohesive schooling patterns. Despite the prevalence of complex flows in nature, almost nothing is known about the function of the lateral line and its relationship to other sensory modalities for freely swimming fishes in turbulent flows. Past studies indicate that under certain conditions the lateral line is not needed to swim steadily in uniform flow. This paper examines how the lateral line and vision affect body kinematics and hydrodynamic habitat selection of rainbow trout (Oncorhynchus mykiss) exposed to vortices generated behind a cylinder. Trout Kármán gaiting (i.e. exploiting vortices to hold station in a vortex street) with a pharmacologically blocked lateral line display altered kinematics; body wavelength and wave speed increase compared to control animals. When visual cues are withheld by performing experiments in the dark, almost all Kármán gait kinematics measured for fish with and without a functional lateral line are the same. The lateral line, rather than vision, plays a larger role in affecting body kinematics when trout hold station in a vortex street. Trout show a preference to Kármán gait in the light but not in the dark, which may be attributed to physiological state rather than hydrodynamic or sensorimotor reasons. In the dark, trout both with and without a functional lateral line hold station near the downstream suction region of the cylinder wake (i.e. entraining) and avoid the vortex street. Vision therefore plays a larger role in the preference to associate with a turbulent vortex street. Trout in the light with a blocked lateral line show individual variation in their preference to Kármán gait or entrain. In the dark, entraining trout with an intact lateral line will alternate between right and left sides of the cylinder throughout the experiment, showing an ability to explore their environment. By contrast, when the lateral line is blocked these fish display a strong fidelity to one side of the cylinder and are not inclined to explore other regions of the flow tank. Both entraining and Kármán gaiting probably represent energetically favorable strategies for holding station relative to the earth frame of reference in fast flows. The ability to decipher how organisms collect and process sensory input from their environment has great potential in revealing the mechanistic basis of how locomotor behaviors are produced as well as how habitat selection is modulated.

Animals↗
PubMed2004

Consumption of caroltenoid-rich foods and central vision loss:a matched case-controlled study in Kansas.

The purpose of this study was to explore the association between consumption of carotenoid-rich foods and risk of central vision loss in 168 rural elders. Food consumption was estimated using a food frequency questionnaire. Median servings per week were used as the cut points for consumption levels. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by using discordant pairs. High consumption of corn bread indicated significant association with central vision loss (OR 0.4; 95% CI 0.2, 0.9). Insignificant inverse associations were observed for seven other foods and the summary index of all selected foods. Prospective studies are needed to further evaluate the potential protective influence of carotenoid-rich foods on central vision loss among older adults.

Aged↗
PubMed2000

Jean Théophile Desaguliers (1683-1744) and eighteenth century vision research.

The emergence of psychology as an empirical discipline was influenced to a great extent by experimental investigations of visual phenomena, particularly in the nineteenth century. Less attention has been paid to experimental enquiries conducted in the eighteenth century, especially those of Jean Théophile Desagliers (1683-1744). He was an ardent advocate of Newtonian optics, on which he lectured and gave demonstrations. His research on colour and binocularity is outlined, together with those of other students of vision in that century. Experiments on visual vertigo conducted at the end of the century are also described. In 1716 Desaguliers reported a method of binocular combination that became widely employed in other studies of binocular vision, namely, placing an aperture in such a position that two more distant, adjacent objects were in the optical axes of each eye. Under these circumstances red and green patches of silk did not mix after the manner of combining prismatic lights, but engaged in rivalry. Desaguliers also investigated size perception and showed that apparent size was determined by apparent distance rather than physical distance. Moreover, he did not base his conclusions on his own observation but on those of 'any unprejudic'd Person'. Thus, both stimulus control and the use of the unbiased observer were employed in eighteenth century experimental studies of vision.

England↗
PubMed1987

Cortical magnification and peripheral vision.

In a generalized form, the cortical magnification theory of peripheral vision predicts that the thresholds of any visual stimuli are similar across the whole visual field if the cortical stimulus representations calculated by means of the cortical magnification factor are similar independently of eccentricity. Failures of the theory in spatial vision were analyzed, and the theory was tested with five visual acuity tasks and two hyperacuity tasks. Almost all increases in thresholds with eccentricity were explained by the theory in five of these tasks, which included the two-dot vernier hyperacuity test, the measurement of visual acuities with gratings, the Snellen E test, and two acuity tests that required either separation between dots or discrimination between two mirror-symmetric forms. The two-dot vernier thresholds could be explained as a special case of orientation discrimination, and orientation discrimination at different eccentricities was in agreement with the cortical magnification theory. The increase of thresholds in peripheral vision was larger than predicted by the theory in the Landolt visual acuity and bisection hyperacuity tests, possibly because of retinal undersampling.

Humans↗
PubMed1987

Contrast discrimination in peripheral vision.

Contrast discrimination provides a psychophysical method for studying contrast coding in vision. Our purpose was to compare properties of contrast discrimination in central and peripheral vision. We used forced-choice procedures to measure contrast-increment thresholds as a function of pedestal contrast. Our stimuli were 2-cycle/deg Gaussian-windowed sine-wave grating patches. They were centered at retinal loci ranging from 10 degrees nasal to 20 degrees temporal on the horizontal meridian. At each eccentricity, curves relating increment threshold to pedestal contrast had the same shape. When increment thresholds and pedestal contrasts were both normalized by the contrast thresholds at the retinal eccentricity in question, the curves became superimposed and fell along the same dipper-shaped contrast-discrimination function. We conclude that, after scaling by the local contrast sensitivity, properties of contrast discrimination are qualitatively and quantitatively similar from 0 degree to 20 degrees on the retina. These findings suggest that mechanisms of contrast coding are similar in central and peripheral vision.

Discrimination, Psychological↗
PubMed2006

[Development of a low vision aid device].

PURPOSE: To develop the design of a near low vision aid that has esthetic and functional qualities intending to give its user a better life quality. METHODS: To verify low vision people's main needs concerning the current devices for near distance; to identify possible design interventions to make a project that fulfills their main needs. RESULTS: A prototype having a reading stand tied to the end of a magnifier that moves horizontally and vertically permitting the horizontal reading of a text line was developed. CONCLUSIONS: The developed device fulfills low vision people's visual and handling needs for near distance, contributing to the easiness to read and write.

Equipment Design↗
PubMedDate not supplied

Improving nighttime mobility in persons with night blindness caused by retinitis pigmentosa: A comparison of two low-vision mobility devices.

This study compared the effectiveness of the ITT Night Vision Viewer with the Wide Angle Mobility Lamp (WAML) as low-vision mobility devices for people experiencing night blindness due to retinitis pigmentosa (RP). Both engineering bench testing and functional evaluations were used in the assessments. Engineering evaluations were conducted for (1) consistency of the manufacturer's specifications, (2) ergonomic characteristics, (3) modifications of devices, and (4) pedestrian safety issues. Twenty-seven patients with RP conducted rehabilitation evaluations with each device that included both clinical and functional tests. Both devices improved nighttime travel for people with night blindness as compared with nighttime travel with no device. Overall, the WAML provided better travel efficiency-equivalent to that measured in daytime. Recommendations have been developed on ergonomic factors for both devices. Although some participants preferred the ITT Night Vision Viewer, overall most participants performed better with the WAML.

Adult↗
PubMed1999

Measurement of the validity of a preschool vision screening program.

OBJECTIVES: The validity (sensitivity and specificity) of a preschool vision screening program was measured over a 3-year period to determine how well strabismus and significant refractive errors could be detected. METHODS: Public health nurses were trained to administer tests of visual acuity, stereoacuity, and ocular alignment. Failure on any test, visual acuity of 6/9 or less, stereoacuity of less than 100 seconds of arc, or an apparent misalignment of the eyes resulted in referral to an eye care practitioner. An age-matched control was also referred. Analysis of practitioner reports used predefined study-based criteria for ocular abnormalities. RESULTS: More than 1100 children were screened each year. The annually calculated prevalence of vision problems ranged between 10.5% and 13.8%. The estimated sensitivity varied from 60.4% to 70.9% (specificity, 69.6% to 79.9%). The yield indicated that a very high percentage of children with vision problems were identified for the first time. CONCLUSIONS: The validity of this screening is comparable to that of other school screenings. The limitations are predictable. Consideration should be given to replacing visual acuity tests with a rapid, objective measure of refractive error and ocular alignment.

Age Factors↗
PubMedDate not supplied

Abnormal color vision and reliable self-monitoring of blood glucose.

Color vision was assessed in 103 insulin-dependent diabetic patients using the Farnsworth-Münsell 100-Hue Test. All showed color vision impairment. Thirty-four had true dyschromatopsia while 22 suffered from tritanopia or other axial defects. We evaluated how accurately diabetic patients could monitor their own blood glucose by asking them to read a series of 30 precalibrated BM Test Glycemic Strips (Chemstrip, Boehringer, Mannheim, West Germany) without a meter. Patients with axial defects performed least well regardless of 100-Hue scores. Reading accuracy of patients with no axial defects was strongly correlated to 100-Hue scores, although patients having dyschromatopsia were consistently hesitant about their readings. Our results suggest that self-monitoring of blood glucose without a meter is indicated only after color vision has been examined by the 100-Hue Test. Self-monitoring should be voided with patients suffering from axial defects or having unsatisfactory 100-Hue scores.

Adult↗
PubMed1983

Effects of passive physical exercise on peripheral vision in muscular dystrophic children.

To investigate the effects of passive exercise of the extremities on peripheral vision of muscular dystrophic children aged 9 to 13 yr. these subjects were either not exercised (control days) for a 6-min. period or were exercised (experimental days) for a 6-min. period after a 5-min. rest. Peripheral vision was recorded after each condition. Analysis of variance with repeated measures on the exercise and no exercise conditions was computed for each measure. 6 min. of passive exercise significantly increased peripheral vision. It was assumed that exercise increased blood flow through the lungs allowing for greater oxygen diffusion in the brain and other facilitory responses which increased effective cerebral activity. Curriculum revisions for such children indicate the importance of activity in facilitating subsequent learning.

Adolescent↗