Biomedical subjects

W F Alkhateeb

Publications and source records attributed to W F Alkhateeb.

2 recordsLinked to original sources

PubMed1990

Effects of stimulus complexity on simple spatial discriminations.

We have extended previous measurements on the detection of a target, differentiated in orientation or magnification from a number of identical reference elements. In these new experiments, we have used more than one class of reference element from which the target must be discriminated. For example, in the case of orientation discrimination, the reference elements are of two classes, which differ from each other in orientation, but are otherwise identical. Representatives of the two classes are present in equal numbers, and the target to be detected is presented at an orientation angle different from that of either class of reference element. Data for discrimination of target magnification or orientation are given for simple geometric elements, namely lines, squares and triangles. In nearly all cases, the characteristic time required for 50% probability of target detection, T1/2, is greater with two classes of reference elements than with a single class. In nearly all cases, T1/2 values for the mixed reference elements increase with the number of reference elements, N, corresponding to discrimination by serial processing. This remains the case even when detection is parallel (T1/2 independent of N) for either class of reference element used separately. We discuss the properties of the spatial discrimination mechanisms which give rise to these responses.

Depth Perception↗

PubMed1990

Spatial, colour and contrast response characteristics of mechanisms which mediate discrimination of pattern orientation and magnification.

We have measured response times for the detection of a single target presented against a set of reference elements which are characterised by combinations of four different stimulus parameters; colour, contrast polarity, magnification and orientation. The aim of the experiments was to determine the response characteristics of visual mechanisms which mediate target detection through the discrimination of orientation and magnification. In the first experiments, we determined sensitivity to differences in colour and contrast polarity, and show that the mechanisms responsible for the discrimination of orientation and of magnification are both selective in their responses to colour and to contrast polarity. There are, nonetheless, residual interactions between patterns of different contrast polarities and between those of different colour, and in the latter case, weak interactions persist under equiluminance conditions. In a second set of experiments, we examined the interactions between orientation and magnification. We conclude that the responses of visual mechanisms which mediate target detection through discrimination of orientation are markedly dependent on stimulus magnification whereas those which mediate detection through discrimination of magnification are, in contrast, relatively insensitive to stimulus orientation.

Adult↗