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Biomedical subjects

S Heywood

Publications and source records attributed to S Heywood.

At least 19 recordsLinked to original sources
PubMed1996

Vocim--a system for measuring the larynx endoscopically.

Examination of the larynx with a flexible endoscope has been a standard procedure for over 20 years. Although excellent images have been obtained there has not been a method for achieving any objective measurements and there are clearly both research and clinical applications for this. The reason for this is firstly because of the inherent distortion of the lens and secondly because of an absence of a reliable method of assessing the relative position of the endoscope within the larynx. This paper illustrates the theory of how these problems have been overcome and describes the equipment used in the clinical situation. The first clinical trial of the Vocim system is detailed, demonstrating an error of only 4%.

Computers↗
PubMed1993

Orientation acuity for sine-wave gratings with random variation of spatial frequency.

Orientation discrimination thresholds were estimated for sine-wave grating stimuli using a two-alternative forced-choice procedure on the two principal, and the two main oblique axes. The two discriminanda within any trial were subject to independent random variation of their spatial frequency. The variation of spatial frequency was defined by a Gaussian probability density function. Thresholds were obtained for five different depths of frequency variation within the range 0.0-1.0 octave. We find that orientation acuity on any of the axes tested is unaffected by variation in the spatial frequency of the targets. The data support the hypothesis that orientation and spatial frequency are independent and orthogonal neural codes.

Discrimination, Psychological↗
PubMed1981

Detection of displacement during saccades: spatial and functional differences allied to preprogramming.

An experimental group of subjects was required to make two saccades to a series of defined points; during the first, either the target for the second, or a point irrelevant to the second, was displaced A control group saw identical displays and displacements but made only one saccade; for them, all displaced points were irrelevant to the saccade. No differences in detection between the groups were found for an irrelevant point, but for the target point clearly lower detection rates and higher rates of misattribution occurred in the experimental group. Displacements of the point next to the target were also harder to detect for the experimental group but were less likely to be misattributed. These results can be interpreted as a perceptual stabilisation of the target for a second saccade (its adoption as a frame of reference) even during a prior saccade, and they are compatible with the preprogramming of the second saccade.

Eye Movements↗
PubMed1979

Hans Gertz revisited: the different effects of invisibility and darkness on pursuit eye movements.

Subjects were required to track their self-moved hands with smooth eye movements in total darkness. The effect of holding transparent and opaque screens between the eyes and the hand upon pursuit eye movements was examined. Opaque screens produced a significant decrement in pursuit when the eye was moving in a direction in which it was generally less efficient at making smooth eye movements.

Darkness↗
PubMed1977

Expanding angles? Systematic distortions of space involving angular figures.

Using simple, single angular figures, including figures containing only one line, we have shown systematic misestimations of distance defined by these figures. These misestimations are not related to the absolute distance per se, but are related both to the size of the angle defining the distance, and to the part of the angle defining it. Some implications of these findings are discussed.

Adolescent↗