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At least 595 records · Page 33Linked to original sources
PubMed2003

Computer aided vertebral visualization and analysis: a methodology using the sand rat, a small animal model of disc degeneration.

BACKGROUND: The purpose of this study is to present an automated system that analyzes digitized x-ray images of small animal spines identifying the effects of disc degeneration. The age-related disc and spine degeneration that occurs in the sand rat (Psammomys obesus) has previously been documented radiologically; selected representative radiographs with age-related changes were used here to develop computer-assisted vertebral visualization/analysis techniques. Techniques presented here have the potential to produce quantitative algorithms that create more accurate and informative measurements in a time efficient manner. METHODS: Signal and image processing techniques were applied to digitized spine x-ray images the spine was segmented, and orientation and curvature determined. The image was segmented based on orientation changes of the spine; edge detection was performed to define vertebral boundaries. Once vertebrae were identified, a number of measures were introduced and calculated to retrieve information on the vertebral separation/orientation and sclerosis. RESULTS: A method is described which produces computer-generated quantitative measurements of vertebrae and disc spaces. Six sand rat spine radiographs illustrate applications of this technique. Results showed that this method can successfully automate calculation and analysis of vertebral length, vertebral spacing, vertebral angle, and can score sclerosis. Techniques also provide quantitative means to explore the relation between age and vertebral shape. CONCLUSIONS: This method provides a computationally efficient system to analyze spinal changes during aging. Techniques can be used to automate the quantitative processing of vertebral radiographic images and may be applicable to human and other animal radiologic models of the aging/degenerating spine.

Aging↗
PubMed2000

A lesion analysis of visual orienting performance in children with cerebral vascular injury.

Anterior brain insults during development have been shown to result in visual orienting deficits; however, the type of orienting deficit has varied across studies. Performance on an orienting task was examined in relation to the location and volume of injury on magnetic resonance exams in 15 children with cerebral infarction and 32 control children. Contralateral lesions including the parietal lobe were associated with larger validity effects, suggesting difficulties disengaging attention. A similar trend was found for the middle-frontal gyrus. Basal ganglia injury contralateral to a given hemifield was associated with less facilitation of attention. Lesion volume in each hemisphere did not show a significant relation with contralateral validity effects. The data suggest that variability in the type of visual orienting deficits shown in prior studies of children with anterior brain insults may be related in part to the specific location of lesions within the frontal lobe.

Adolescent↗
PubMed2004

Marketing drugs, marketing health care relationships: a content analysis of visual cues in direct-to-consumer prescription drug advertising.

Proponents and opponents of direct-to-consumer advertising (DTCA) of prescription drugs argue that it promotes greater participation in health care by consumers with significant implications for public health and health care outcomes. This article (a). proposes a social cognitive theoretical framework to explain DTCA's effects, and (b). reports the first in a series of studies on DTCA's observational learning functions that may influence consumer behavior and the physician-patient relationship. This investigation addresses visual features of print DTCA. Results focus on the prevalence and nature of models featured in the ads and how visual cues may offer identity and relational motivators while reinforcing the value of prescription drug treatments. Further, DTCA may market disenfranchising images that increase disparity in health care information and access, despite their argued educational function.

Advertising↗
PubMed1985

Analysis of visual modulation sensitivity. II. Peripheral retina and the role of photoreceptor dimensions.

Temporal-frequency characteristics were measured as a function of retinal location, with test-field size scaled to provide equivalent sensitivity at each eccentricity. The results showed that the temporal-frequency limits increased uniformly by about a factor of 2 between the fovea and 45 degrees eccentricity, corresponding to a decrease in the response-time constant from 70 to 35 msec. These data were compared with the change in inner- and outer-segment diameters of the cones across the same retinal range. The data conform to the hypothesis that visual time constant varies inversely with cone outer-segment diameter. A second hypothesis that visual sensitivity increases in proportion to come outer-segment length in the central fovea was also supported.

Flicker Fusion↗
PubMed1990

Analysis of visual modulation sensitivity. IV. Validity of the Ferry-Porter law.

The maximum flicker frequency was determined over a 5+6-log-unit range of retinal illuminance for a stimulus configuration designed to isolate the linear response from long-wavelength (R) cones. For a particular retinal location, the data conformed to the Ferry-Porter law and departed significantly from the predictions of the diffusion equation. The slope of the function was an invariant characteristic and was unaffected by stimulus intensity or area, modulation waveform, or modulation amplitude. However, the slope varied substantially with retinal locus, increasing by more than a factor of 2 between the foveola and 35 degrees eccentricity. This increase shows that the time constant of the linear, unadapted visual response decreases with increasing eccentricity. The difference between foveola and periphery remained at high spatial frequencies, implying that it was not attributable to lateral inhibitory effects.

Algorithms↗
PubMed1992

Analysis of visual modulation sensitivity. V. Faster visual response for G- than for R-cone pathway?

To determine the linear, unadapted responses of the cone pathways, we have measured the critical fusion frequency (CFF) for green (555-nm) and red (642-nm) flicker as a function of retinal illuminance. Both functions obeyed the Ferry-Porter law (CFF proportional to log illuminance) to high accuracy over a > or = 5-log-unit range. In both foveola and periphery the CFF/illuminance functions were significantly steeper for green light than for red light. The peripheral 555-nm function had an average slope 1.26 times the average slope of the 642-nm function. An additive model of flicker detection could not account for the observed differences in slope. A threshold independence model, in which detection is based on the most sensitive mechanism, accurately fits the data. Whichever model is assumed, the presence of different slopes for the two wavelength flicker conditions strongly implies that the R- and G-cone pathways have different temporal properties. The occurrence of steeper CFF/illuminance slopes in response to green light implies that the linear (near-CFF) response of the G-cone pathways in inherently faster than that of the R-cone pathways at both retinal loci. These differences in R- and G-cone-mediated temporal properties complicate the fundamental concept of luminance and invalidate it for precise application over the full illuminance range.

Color Perception↗
PubMed2005

Forward genetic analysis of visual behavior in zebrafish.

The visual system converts the distribution and wavelengths of photons entering the eye into patterns of neuronal activity, which then drive motor and endocrine behavioral responses. The gene products important for visual processing by a living and behaving vertebrate animal have not been identified in an unbiased fashion. Likewise, the genes that affect development of the nervous system to shape visual function later in life are largely unknown. Here we have set out to close this gap in our understanding by using a forward genetic approach in zebrafish. Moving stimuli evoke two innate reflexes in zebrafish larvae, the optomotor and the optokinetic response, providing two rapid and quantitative tests to assess visual function in wild-type (WT) and mutant animals. These behavioral assays were used in a high-throughput screen, encompassing over half a million fish. In almost 2,000 F2 families mutagenized with ethylnitrosourea, we discovered 53 recessive mutations in 41 genes. These new mutations have generated a broad spectrum of phenotypes, which vary in specificity and severity, but can be placed into only a handful of classes. Developmental phenotypes include complete absence or abnormal morphogenesis of photoreceptors, and deficits in ganglion cell differentiation or axon targeting. Other mutations evidently leave neuronal circuits intact, but disrupt phototransduction, light adaptation, or behavior-specific responses. Almost all of the mutants are morphologically indistinguishable from WT, and many survive to adulthood. Genetic linkage mapping and initial molecular analyses show that our approach was effective in identifying genes with functions specific to the visual system. This collection of zebrafish behavioral mutants provides a novel resource for the study of normal vision and its genetic disorders.

Animals↗
PubMed2003

Analysis of visual evoked potentials and background electroencephalographic activity in young and elderly subjects.

OBJECTIVE: New techniques developed in this laboratory to overcome the loss of information involved in conventional evoked potential averaging are applied here to visual evoked potential (VEP) in young and elderly normal subjects. METHODS: The techniques are based on statistical descriptions of the times and amplitudes of the electroencephalographic deflections recorded before (background) and after (evoked) a series of pattern reversal visual stimuli. RESULTS: The elderly had a higher rate of background deflections at all electrode sites, but lower amplitudes at the occipital electrodes. The elderly had a lower rate of deflections during the period of evoked activity compared with the background period. The young had a higher degree of response deflection time locking and amplitude. The mean amplitude of the deflections recorded during the period of evoked activity was significantly greater in amplitude than the background deflections and greater than the amplitudes of the conventionally averaged VEP derived from the same data. Thus the lower amplitude VEPs seen in the elderly are due to their poor time locking and reduced amplification. Only 79% of the stimulus trials contributed deflections to the P1 response component in both young and elderly subjects and 63% to the N1. In young subjects, several of the new response parameters showed the presence of evoked response components that were not apparent in the conventionally averaged VEP derived from the same data. CONCLUSIONS: The novel methods presented here provide a great deal of additional information that is unavailable when analyzing data using only conventional evoked potential averaging.

Adolescent↗
PubMedDate not supplied

[Comparative analysis of visual function and the quality of life index with eyeglasses or a progressive contact lens].

PURPOSE: To compare the visual function and the answers to a questionnaire of quality of life of patients wearing a progressive contact lens or eyeglasses. METHODS: The Focus Progressive contact lens had been fitted in 35 patients with far visual acuity with progressive-addition eyeglasses equal to zero (log MAR) and near J1 (Jaeger). The far and near visual acuities and the measurement of contrast sensitivity were compared when the patients were wearing the eyeglasses or the contact lens and the patients' results of the scores of the quality of life questionnaire (NEI VFQ-25) were analyzed statistically considering the type of ametropy and the age. RESULTS: The far and near visual acuities and the contrast sensitivity measurement were worse with the contact lens than with eyeglasses. The answers to the questionnaire did not differ when were comparing the same patients wearing eyeglasses or contact lens, no matter the type of ametropy. The myopic and the hyperopic subgroups had worse answers to the quality of life questionnaire when corrected with the contact lens than with eyeglasses, both with age equal to or less than their median. CONCLUSIONS: The visual function was worse with the contact lens. The type of ametropy did not influence the answers to the quality of life questionnaire considering the optical correction, but age did.

Adult↗
PubMed1979

Relative locations among moving spots and visual vector analysis.

How the direction of apparent movement changed with the relative locations among spots was quantitatively measured by the method proposed by Hochberg and Fallon. From the vector-extraction model (proposed by Johansson) expanded as, "The vector to be subtracted depends on the relative location." and the directions of apparent movement, the vector to be subtracted was calculated at each relative location. Consequently data showed (i) the region in which the directions of spots in motion are affected by the frame is finite, and (ii) the degree of the influence is not iniform in the region but is rapidly reduced as spots go away from the frame.

Distance Perception↗
PubMed1979

Analysis of visual and auditory rhythmic perception abilities of piano majors.

7 male and 15 female college level piano majors representing three categories of majors served as subjects. Piano instructors were asked to rate subjects' sight-reading ability on a scale from 0 to 10, where 0 indicated minimum sight-reading ability and 10 professional sighting. Subjects were exposed to 30 pairs of rhythmic stimuli from the rhythm subtest, Seashore Measures of Musical Talents, to determine whether the second pattern was the same or different from the first. The visual test was reproduced by a 7.5-v bayonet lamp and socket. These flashes were near exact replications of the original source with little or no detectable latency. Aural and visual presentations were significantly different and favorable for aural medium. A significant correlation of .60 was found between ratings of sight-reading and grade point average.

Adolescent↗