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J O Limb

Publications and source records attributed to J O Limb.

4 recordsLinked to original sources
PubMed1981

Spatiotemporal characteristics of thresholds adjacent to a luminance edge.

Spatiotemporal incremental and decremental thresholds were measured for a thin vertical line (target) positioned adjacent to a briefly presented vertical edge. A significant difference between the stimuli used here and those used in previous studies is the background level against which the edge was presented. Here the edge was formed by briefly decreasing the luminance of the left side of a light background. This novel condition was compared with the more usual condition in which the edge is formed by briefly increasing the luminance of the right half of a dark background. In a further test the buildup of threshold after an edge was switched on was also measured. When the target was presented on the side of the edge that remained fixed in luminance, a small but reliable threshold change adjacent to the edge was measured. The effect was much larger for measurements made on the side of the edge that changed in luminance; however, the spread was comparable for the two conditions. For the target presented on the light side of the edge, decremental thresholds were much larger than incremental thresholds. This is attributed, at least in part, to the different types of tasks required of the observer. Maximum temporal threshold elevation occurs at or just before (i.e., less than 16 msec) 0 asynchrony between edge and target. The results are interpreted at a qualitative level as supporting a receptive-field type of model in which the edge, at various spatiotemporal locations relative to the target, inhibits or excites activity at the receptive field centered on the target.

Adult↗
PubMed1980

Thresholds at luminance edges under stabilized viewing conditions.

Increment thresholds were measured for a small, briefly presented test line as a function of distance from a high-contrast abrupt luminance edge. The experiments were carried out under both stabilized and unstabilized viewing conditions to determine the role of eye movements in the "edge threshold effect." It was found that the edge threshold effect (i.e., the rise in threshold at the luminance edge) was less pronounced under stabilized conditions. We conclude from this that a significant portion of this effect is mediated by the temporal transients that are brought about by eye movements. Little difference is found between stabilized and unstabilized conditions when the background is briefly presented. Narrow bright bands appear on the bright side of a sharp edge for unstabilized viewing, but disappear under stabilization.

Eye Movements↗