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Title: Adaptation processes in relation to contingent colour after-effects
Author: Jones, R.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1983
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The adaptation processes involved in the production of contingent colour after-effects, non-contingent after-effects and sensory motor effects were investigated. The main difference between the McCollough effect and the classical negative after-image is one of fixation. While many simple sensory after-effects require fixation, it is not necessary to fixate to observe the McCollough effect. In the first series of experiments, the necessity for fixation in the adapting process was investigated with the McCollough effect. The possibility of spatial frequency analysis being involved in the production of the McCollough effect was examined by adapting subjects to patterns in which no regular spatial frequency element was present. As an alternative explanation, the presence of individual fixation tendencies was investigated by controlling subjects fixations and giving a more generalized type of adaptation. The tendency of individuals to fixate on a particular feature of a grating was confirmed when there was found to be a higher probability that a subject would fixate on an edge of a bar rather than the centre of a bar. In the course of these experiments, it was found necessary to take into account two stages of adaptation. Using an induction method similar to that utilized with the McCollough effect, the classical negative after-effect was shown to have two stages, an initial short term effect and a long term effect with a retention time comparable to that experienced with the McCullough effect. It was demonstrated that the short term and long term effects observed were not due to the presence of two separate McCollough effects by tearing for the after-effects using a variety of test patterns in which the presence of bars and edges was gradually omitted. In this way, any feature which could lead to McCollough-type effects was eliminated. The final experimental investigations examined the presence of two phases of adaptation in other forms of non-contingent after-effect and in the McCollough effect. Separate short and long term adaptational effects were produced with the movement after-effect and in relation to adaptive mechanisms when adapting to a displaced visual field where motor systems are involved. A separate long term and short term effect was not obtained with the McCollough effect under any experimental conditions. It is proposed that this could be due to the contingency between colour and orientation interfering with the short term adaptation mechanism. Arising from these studies, a theory to account for the long term retention of the McCollough effect was proposed in terms of sensory adaptation. Contingent colour after-effects are considered in relation to general properties of the eye.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available