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Title: Adaptation and contingent after-images
Author: Mahmud, S. H.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1978
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A number of recently discovered contingent after-effects relating to colour orientation and movement were investigated. First the McCollough effect was compared with the classical negative after-image when the two phenomena were evoked under approximately similar conditions. Under the conditions the negative after-image was found to have two phases one of which persisted for relatively long time intervals similar to the McCollough effect. It was then found that the McCollough effect and the negative after-image could be obtained independently of each other following a common adaptation sequence from the same retinal area. In the second series of experiments the McCollough effect was obtained from bars of a single orientation and of equal spatial frequency provided the subject fixated throughout. Under this condition colour after-effects were also obtained with a variety of complex stimulus patterns. It was found that the colour effects are more evident with curved lines concentric to the fovea than with non-concentric or straight lines. The third series of experiments were devoted to the investigation of movement after-effects. These displayed two phaes: (i) an initial phase in which movement was relatively independent of the precise test pattern, (ii) a delayed phase in which movement was only obtained with the pattern employed during adaptation. Movement after-effects were found to transfer interocularly in both phases only when the subjects were tested with the adapting pattern. It was found that transfer only occurred when the test pattern image fell on the area of the retina corresponding to that of the adapted eye. An hypothesis to account for contingent after-effects as arising through adaptation in colour linked opponents systems was tested by measuring the change in saturation of colours observed in the test situation following various types of visual stimulation employed during their retention. The result supports an explanation of both contingent and non-contingent after-effects in terms of a sensory adaptation process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available