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Biomedical subjects

R F Murray

Publications and source records attributed to R F Murray.

At least 19 recordsLinked to original sources
PubMed2001

Time course of amodal completion revealed by a shape discrimination task.

We measured the extent of amodal completion as a function of stimulus duration over the range of 15-210 msec, for both moving and stationary stimuli. Completion was assessed using a performance-based measure; a shape discrimination task that is easy if the stimulus is amodally completed and difficult if it is not. Specifically, participants judged whether an upright rectangle was longer horizontally or vertically, when the rectangle was unoccluded, occluded at its corners by four negative-contrast squares, or occluded at its corners by four zero-contrast squares. In the zero-contrast condition, amodal completion did not occur because there were no occlusion cues; in the unoccluded condition, the entire figure was present. Thus, comparing performance in the negative-contrast condition to these two extremes provided a quantitative measure of amodal completion. This measure revealed a rapid but measurable time course for amodal completion. Moving and stationary stimuli took the same amount of time to be completed (approximately 75 msec), but moving stimuli had slightly stronger completion at long durations.

Discrimination Learning↗
PubMed2000

Deriving behavioural receptive fields for visually completed contours.

The visual system is constantly faced with the problem of identifying partially occluded objects from incomplete images cast on the retinae. Phenomenologically, the visual system seems to fill in missing information by interpolating illusory and occluded contours at points of occlusion, so that we perceive complete objects. Previous behavioural [1] [2] [3] [4] [5] [6] [7] and physiological [8] [9] [10] [11] [12] studies suggest that the visual system treats illusory and occluded contours like luminance-defined contours in many respects. None of these studies has, however, directly shown that illusory and occluded contours are actually used to perform perceptual tasks. Here, we use a response-classification technique [13] [14] [15] [16] [17] [18] [19] [20] to answer this question directly. This technique provides pictorial representations - 'classification images' - that show which parts of a stimulus observers use to make perceptual decisions, effectively deriving behavioural receptive fields. Here we show that illusory and occluded contours appear in observers' classification images, providing the first direct evidence that observers use perceptually interpolated contours to recognize objects. These results offer a compelling demonstration of how visual processing acts on completed representations, and illustrate a powerful new technique for constraining models of visual completion.

Discrimination, Psychological↗
PubMed1986

Tests of so-called genetic susceptibility.

During the past two decades a number of inherited polymorphic proteins and enzymes have been identified in different ethnic groups. Certain biochemical markers appear to be associated with susceptibility to harmful effects of the environment. This paper reviews the potential for using these markers to determine whether affected persons ought to be excluded from certain jobs or from the environment(s) of specific settings in the workplace. This paper will also attempt to identify the criteria that should be used before it is scientifically and ethically justified to use these markers to "protect" workers and/or persons from harm by not allowing them to work in a specific setting or with specific agents to which they have been deemed to be at special risk for injury.

Disease Susceptibility↗
PubMed1982

Approaches to the evaluation of the genetic counselor.

Regular, formal structured evaluation of the counseling skills of the genetic counselor should be a part of every counseling program. There is no ideal method of evaluation. Each has advantages and disadvantages. A combination of methods, determined by funds and equipment available probably presents the best approach to this problem. Formal studies of the optimum methods of counselor evaluation and the best criteria to be used are needed to provide definitive answers to the problem of how best to evaluate the performance of genetic counselors.

Anemia, Sickle Cell↗
PubMed1980

Special considerations for minority participation in prenatal diagnosis.

Parents who use information from prenatal diagnosis in family planning may be faced with difficult decisions. For a variety of reasons, the communications and decision-making process may be substantially more complex and difficult if the parents are members of a minority group. Unless a number of special considerations are kept in mind when programs of prenatal diagnosis for minorities are developed, such programs may be more harmful than beneficial.

Cultural Deprivation↗
PubMed1976

Psychosocial aspects of genetic counseling.

A competent and effective genetic counselor must recognize and deal with the psychological defense mechanisms which affected persons and parents of affected children use to cope with the strain of genetic disease in the family. Denial, guilt, hostility, grief and mourning and the psychology of defectiveness are all potent emotional factors that must be dispelled or worked through before parents should make reproductive decisions. If the counseling experience is to be satisfactory, the counselor must help parents meet the immediate and long term social needs of affected individuals in addition to their medical needs.

Adult↗
PubMed1975

Linkage studies in Lenz microphthalmia.

Glucose-6-phosphate dehydrogenase (G6PD) phenotype studies were done on a black family with X-linked heredofamilial bilateral microphthalmia (HBM). Three crossovers and three non-crossovers were detected in three informative matings of four generations yielding a recombination value of 0.5. These findings do not provide evidence for linkage between the G6PD and HBM loci, suggesting either that the G6PD and HBM loci are far apart on the X chromosome or that HBM in this family is inherited as an autosomal dominant male sex-limited trait.

Genetic Linkage↗