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Biomedical subjects

A Blake

Publications and source records attributed to A Blake.

At least 19 recordsLinked to original sources
PubMed1995

Two-dimensional constraints on three-dimensional structure from motion tasks.

Can humans recover metric structure from motion sequences or, as has been claimed by Todd and Bressan [(1990) Perception & Psychophysics, 48, 419-430], are they limited to recovering only relief structure? Two experiments were carried out to investigate this question. In a metric-structure task, the angular thresholds for discriminating two rotating bi-planar structures were approximately 91 deg. By contrast, in a relief-structure task, the angular thresholds for discriminating a planar from a non-planar structure, both undergoing simple rotational motion, were only approximately 11 deg. A computational model is proposed to examine the image motion sensitivity required to perform discriminations of both three-dimensional metric and relief structure from motion. When the experimental data were re-plotted in terms of this two-dimensional sensitivity, the thresholds were found to be the same for both tasks. This finding is related to the model's revelation that recovering metric structure from motion is inherently more noise-sensitive than is recovering relief structure from motion. The conclusion is that the differences in angular thresholds reflect the differing nature of the two tasks. There is no evidence that the visual processes themselves are preferentially sensitive to non-metric over metric structure from motion.

Depth Perception↗
PubMed1995

Adherence of bacteria to intraocular lenses: a prospective study.

AIMS: The study was designed to investigate the bacterial flora of the operating field during routine cataract surgery and the source of intraocular lens contamination during the surgery. METHODS: The normal flora of the external eye and fornices of 17 patients undergoing selective cataract surgery was determined preoperatively. Swabs taken from the eyelid surface and lashes showed coagulase negative staphylococci (CNS) in 90%, Propionibacterium acnes in 62%, Corynebacterium sp in 18%, and Peptostreptococcus in 3% of the patients. The lower fornices of 70% had CNS, 47% P acnes, 6% Staphylococcus aureus, 6% Corynebacterium sp, and 6% Candida. RESULTS: A sterile PMMA intraocular lens was touched on the upper bulbar conjunctiva immediately before the surgery. Eighty two per cent of lenses grew CNS, 18% P acnes, 18% Bacillus sp, 12% S aureus, and 6% Corynebacterium sp. A second sterile PMMA intraocular lens was left on the drape and near the eye during surgery. Forty seven per cent of these cultured CNS, 12% Corynebacterium sp, and 6% Bacillus sp. A high count of bacteria in the operating field, especially CNS and P acnes can contribute to postoperative inflammation and endophthalmitis. CONCLUSION: Special measures are needed before and during the surgery to reduce the chance of intraocular inoculation of these bacteria. Use of proper culture media and techniques are necessary to identify these organisms, especially anaerobes, in postoperative inflammation.

Adult↗
PubMed1993

Shape from texture: ideal observers and human psychophysics.

We describe an ideal observer model for estimating "shape from texture" which is derived from the principles of statistical information. For a given family of surface shapes, measures of statistical information can be computed for two different texture cues--density and orientation of texels. These measures can be used to predict lower bounds on the variance of shape judgements of "ideal" and human observers. They can also predict optimal weights for cue integration for the inference of shape from texture. These weights are directly proportional to the information carried by each cue. The ideal observer model therefore predicts that the variance of subjects' responses in a psychophysical shape judgement task should reflect the statistical importance of individual texture cues. Our results show that human performance in shape judgements for a one-parameter family of parabolic cylinders is often better than what an ideal observer achieves using a density cue alone. Therefore other information, for example the compression cue, must be used by human observers. For the first time, such results have been obtained without recourse to the unnatural cue conflict paradigms used in previous experiments. The model makes further predictions for the perception of planar slanted surfaces in the case of wide field of view.

Form Perception↗
PubMed1992

Factors associated with adherence to breast cancer screening among working women.

This study identified sociodemographic, knowledge, attitude, and social influence correlates of obtaining mammograms among employed women age 40 and over. Telephone interviews were conducted with 798 women who worked at 39 different work sites. Eighty-four percent of respondents had ever had a mammogram, and 72% had had one at the recommended interval for their age group. The only personal characteristic that was associated with past mammography use was having a co-worker, friend, or relative with a history of breast cancer. Logistic regression analyses indicated that a doctor's advice to have a mammogram, knowledge of screening guidelines, knowing someone with breast cancer, and the beliefs that mammography is effective and that mammography is necessary in the absence of symptoms were associated independently with past use of mammography. Three factors contributed independently to explaining adherence to mammography guidelines: younger age, knowledge of guidelines for one's own age group, and the belief that breast cancer is curable. The findings suggest that emphasizing the recommended guidelines, the need for and benefits of mammography in educational programs, and offering low-cost or free mammography at the workplace, can further increase appropriate utilization among working women.

Age Factors↗
PubMed1991

Shape from specularities: computation and psychophysics.

Images of artificial and natural scenes typically contain many 'specularities' generated by mirror-like reflection from glossy surfaces. Until fairly recently computational models of visual processes have tended to regard specularities as obscuring underlying scene structure. Mathematical modelling shows that, on the contrary, they are rich in local geometric information. Recent psychophysical findings support the notion that the brain can apply that information. Our results concern the inference of 3D structure from 2D shaded images of glossy surfaces. Stereoscopically viewed highlights or 'specularities' are found to serve as cues for 3D local surface-geometry.

Cues↗
PubMed1991

Fused rhabdomeres (fur) in Drosophila: an eye mutation that alters rhabdomere morphology and retinal function.

In the Drosophila compound eye, the photoreceptor cells are organized in highly precise units, the ommatidia. In each photoreceptor cell, the primary photopigment, opsin, is contained in the rhabdomere, an ordered array of densely packed microvilli. A genetic and phenotypic analysis of a new X-linked. P element-induced mutation, fur, (fused rhabdomeres) is presented. Light and electron microscope studies show that mutations at the fur locus result in the fusion of the adjacent rhabdomeres in the developing eye and the fusion takes place during the pupal stage of eye development. Electrophysiological experiments indicate that the fur mutant photoreceptors have reduced sensitivity to light and lack a PDA (prolonged depolarizing afterpotential), a response characteristic of normal photoreceptor cells. Recombination and deficiency mapping localize fur to the proximal region of the X chromosome. Reversion analysis indicates the fur mutant is the result of a P element insertion. These studies suggest that the fur locus encodes a gene that has specific roles in rhabdomere morphogenesis and retinal function.

Animals↗
PubMed1990

Consumption of olive oil, butter, and vegetable oils and coronary heart disease risk factors. The Research Group ATS-RF2 of the Italian National Research Council.

The cross-sectional association between consumption of various fats (eg, butter, olive oil, and vegetable oil) and risk factors for coronary heart disease was analyzed in a sample of 4903 Italian men and women 20 to 59 years of age. The intake of fats was ascertained by an interviewer-administered questionnaire. Increased consumption of butter was associated with significantly higher blood pressure and serum cholesterol and glucose levels for men; in women only the association with glucose reached statistical significance. In both sexes consumption of olive oil and vegetable oil was inversely associated with serum cholesterol and glucose levels and systolic blood pressure. These findings were adjusted for confounding effects of other risk factors for cardiovascular disease. These cross-sectional findings from a large population sample suggest that consumption of butter may detrimentally affect coronary risk factors, while polyunsaturated and monounsaturated fats may be associated with a lower coronary risk profile.

Adult↗
PubMed1990

Does the brain know the physics of specular reflection?

Images of artificial and natural scenes typically contain many highlights generated by mirror-like reflection from glossy surfaces. Until recently, computational models of visual processes have tended to regard highlights as obscuring the structure of the underlying scene. The truth is that, on the contrary, highlights are rich in local geometric information. Here we report that the three-dimensional appearance of a highlight on a computer-simulated stereoscopic curved surface affects observers' judgment of surface gloss. We also show that the 3-D appearance of a highlight affects the perception of surface curvature--that is, it can force an ambiguous convex-concave figure to change state. We thus conclude that human visual analysis seems to employ a physical model of the interaction of light with curved surfaces, a model firmly based on ray optics and differential geometry.

Brain↗
PubMed1990

Diet and coronary heart disease risk factors in a population with varied intake. The Research Group ATS-RF2 of The Italian National Research Council.

The relationship between consumption of foods high in saturated fats and cholesterol and a number of coronary heart disease risk factors (blood pressure, serum glucose, serum cholesterol, and triglycerides) was analyzed in a large sample (4,917) of Italian men and women, ages 20-59 years. The dietary habits of the participants were ascertained with a food frequency questionnaire. Intake of atherogenic foods (foods high in cholesterol and saturated fats) was evaluated for each participant. In both sexes, systolic blood pressure, serum glucose, and serum cholesterol increased with higher consumption of atherogenic foods. These findings were independent of any possible confounding effect of age, adiposity, alcohol intake, and cigarette smoking. The present article confirms previous findings that consumption of foods high in saturated fats and cholesterol is associated with an increased risk for atherosclerosis.

Adult↗