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Biomedical subjects

D H Foster

Publications and source records attributed to D H Foster.

At least 91 records · Page 5Linked to original sources
PubMed1980

Variability of visual threshold in multiple sclerosis: effect of background luminance on frequency of seeing.

Visual thresholds were measured at four different background luminance levels in patients with multiple sclerosis (MS) and in control subjects by means of frequency-of-seeing curves. Results were examined by probit analysis and measures of threshold and threshold variability were obtained. Comparison of patient and control groups showed that the patient's threshold was significantly raised only at the highest background luminance level, but that threshold variability was greater at all three non-zero background luminance levels tested. In addition, threshold variability increased with background luminance in the MS patients but not in the control subjects. Possible underlying pathophysiological mechanisms are discussed, and it is suggested that this luminance-dependent variability in visual threshold shown by patients with multiple sclerosis may be due to intermittent conduction block or ephaptic transmission occurring within the demyelinated visual pathway.

Adult↗
PubMed1979

Transformation and relational-structure schemes for visual pattern recognition. Two models tested experimentally with rotated random-dot patterns.

Two models for visual pattern recognition are described; the one based on application of internal compensatory transformations to pattern representations, the other based on encoding of patterns in terms of local features and spatial relations between these local features. These transformations and relational-structure models are each endowed with the same experimentally observed invariance properties, which include independence to pattern translation and pattern jitter, and, depending on the particular versions of the models, independence to pattern reflection and inversion (180 degrees rotation). Each model is tested by comparing the predicted recognition performance with experimentally determined recognition performance using as stimuli random-dot patterns that were variously rotated in the plane. The level of visual recognition of such patterns is known to depend strongly on rotation angle. It is shown that the relational-structure model equipped with an invariance to pattern inversion gives responses which are in close agreement with the experimental data over all pattern rotation angles. In contrast, the transformation model equipped with the same invariances gives poor agreement to the experimental data. Some implications of these results are considered.

Field Dependence-Independence↗