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Biomedical subjects

R Cleary

Publications and source records attributed to R Cleary.

24 records · Page 2Linked to original sources
PubMed1992

Effects of contrast substitutions upon motion detection in spatially random patterns.

We report the effects of contrast changes between frames in a random-square kinematogram. When the contrasts of both frames are too low to permit directional discrimination, increasing the contrast of either the first or the second frame alone makes directional discrimination possible. However, at suprathreshold contrasts for motion detection, increasing the contrast of either the first or the second frame alone makes discrimination more difficult. We conclude that motion detection is a special case of contrast discrimination, in agreement with the Reichardt model of motion detection.

Contrast Sensitivity↗
PubMed1990

Direction discrimination for band-pass filtered random dot kinematograms.

When an array of random dots is displaced, the ability to report the direction of apparent motion is subject to an upper spatial limit (dmax). As the size of the displacement is increased, direction discrimination errors show a monotonic increase that becomes asymptotic at a chance level. We have measured direction discrimination using spatially band-pass filtered random dots. These stimuli do not yield a monotonic increase in errors. Rather, for displacements greater than around 1 cycle of the stimulus centre frequency (Fc), performance oscillates about chance, with displacements of 1 1/4 cycles of Fc yielding systematic errors in perceived direction. We analyse this pattern of performance in terms of the stimulus autocorrelation function and conclude that dmax can be taken as lying on the initial rising portion of the displacement versus error function. Using this definition we find, in line with the results of Chang and Julesz (1985), that dmax scales inversely with Fc. Contrary to the results of Chang and Julesz, we find that this scaling holds beyond 4 c/deg.

Discrimination, Psychological↗
PubMed1990

Masking of low frequency information in short-range apparent motion.

When an array of random dots is displaced, the ability to report the direction of apparent motion is subject to an upper spatial limit (dmax). Using spatially low-pass filtered random dot kinematograms we show that dmax is dependent on the upper cut-off frequency of the stimulus (Fh). The extent of this dependence is critically dependent on the size of the stimulus. Our results suggest a process whereby low spatial frequency motion information is masked by the presence of high spatial frequencies in the same region of the field, analogous to phenomena occurring in the perception of static form (e.g. the Abraham Lincoln effect). The effects of stimulus size on dmax, found for broad-band stimuli by ourselves and others, result from a loss of high frequency sensitivity at increased retinal eccentricities; this loss reduces the masking effect of high frequencies, as stimulus size increases.

Discrimination, Psychological↗
PubMed1990

Contrast dependence of short-range apparent motion.

The apparent motion of band-pass filtered random dot kinematograms was assessed by measurements of two alternative direction discrimination performance. In the case of two-dimensional (isotropically filtered) stimuli, the results were largely independent of contrast: at Michelson contrasts of 5 and 50%, near-perfect direction discrimination was obtainable for a limited range of displacements. However for one-dimensional (grating) stimuli, apparent motion seems to be highly dependent on contrast. At 5% contrast, performance was comparable to that obtained with the two-dimensional stimuli. At 50% contrast the motion percept broke down to a large extent, with consistently poor direction discrimination being obtained. The breakdown of apparent motion is interpreted in terms of a decreased signal-to-noise ratio in the pooled response of motion detectors that are tending to contrast saturation. Here, "noise" refers to the sampling components present in any apparent motion sequence. Evidence relating to the sampling frequency of the motion sequence is presented to support the hypothesis. It is argued that the discrepancy between the results obtained with one- and two-dimensional stimuli support the idea that motion is initially encoded by orientationally tuned mechanisms.

Contrast Sensitivity↗
PubMedDate not supplied

Measuring outcomes in care of the elderly.

This observational study was designed to assess whether routine measurement of outcomes using standard instruments is possible as part of clinical routine in care of the elderly, and to establish if such instruments are responsive to clinical change. Indices of functional status, cognitive function and subjective health status were collected routinely on admission and discharge in 540 inpatients and 340 patients attending a day hospital. Data collection became integrated into clinical routine. Response rates were generally good and yielded acceptably complete data. For inpatients, outcome was reflected by measurement of survival, physical function (Barthel index) and social status, each of these indicators showing significant change between admission and discharge. For day hospital patients, neither these, nor the Nottingham ADL scale, nor a health status indicator proved sufficiently responsive to clinical change to merit recommendation as outcome indicators for routine use in older patients. In ambulatory care in older patients, such as those attending a day hospital, new approaches are needed to measure clinical outcomes.

Activities of Daily Living↗