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dc.contributor.authorSchmidt, William Carl.en_US
dc.date.accessioned2014-10-21T12:33:54Z
dc.date.available2014-10-21T12:33:54Z
dc.date.issued1999en_US
dc.identifier.otherAAINQ49290en_US
dc.identifier.urihttp://hdl.handle.net/10222/55672
dc.descriptionSeveral theories have been put forward to explain an illusory impression of motion within a figure that appears all at once (similar to the expansion of the figure over time). This illusion has recently been referred to as "Illusory Line Motion" (ILK because it was found to strongly occur within a line probe presented beside a priming object. Gradient theories suggest that the source of the illusion is an asynchrony of signals arriving a motion detection system across space and time. On the gradient account, this asynchrony is introduced by a spatial gradient inherent in the visual system or created as the result of the visual system's response to prior stimulation.en_US
dc.descriptionGradient theories have been challenged by low and high-level explanations of the phenomenon. High-level explanations of the illusion postulate that the motion is the result of transformational processes that attempt to link successive views of objects in the world and fill-in object transformations that were most likely to have occurred from one view to the next. Low-level explanations hypothesize that the illusion is an artifact of the neural machinery that is used to segment the visual scene.en_US
dc.descriptionThis thesis examines the adequacy of alternative explanations through phenomenal demonstrations that have been put forward as counterexamples to the gradient hypothesis. In Experiments 1 and 2, contrary to claims of a high-level theory, it is demonstrated that ILM and classical apparent motion differ with respect to their spatial and temporal characteristics. In Experiments 3, 4 and 5 it is demonstrated that contrary to previous results, ILM is sensitive to, and can be influenced by, voluntary attention. This suggests that the representation underlying the illusion can be modulated by top-down visual processes, though it is found that such contributions are less than from stimulus-driven factors. In Experiment 6 the empirical examination of a high-level theory's claim that ILM occurs after amodal completion was not supported in a paradigm that had been reported to produce results incompatible with gradient theory predictions. In Experiment 7, a low-level neural model explanation that was incompatible with gradient theory predictions was shown to be incorrect when empirically tested. It was argued that the model has too many degrees of freedom to be a useful tool. In Experiment 8, a paradigm taken by others to demonstrate that the illusion is not produced by a gradient of signals arriving at a motion detection system, is shown not to wan-ant this conclusion because even real signals arriving over space and time were found to be masked in this paradigm. The results of Experiment 9 supported a motion system integration source for the effect derived in the aforementioned paradigm. To answer high-level theories that propose that ILM does not involve the motion processing system, Experiment 10 was used to reveal that ILM can be found to interact with the classic motion aftereffect, suggesting that both of these effects influence a common level of motion processing. A final experiment demonstrated that as a stimulus becomes more identifiable, processes other than the simple gradient dictate perception.en_US
dc.descriptionAfter a discussion of the arguments put forward by the various hypotheses in light of existing empirical evidence, it was concluded that none of the other theories are as easy to apply or as comprehensive in detailing the phenomenal effects of ILM as are gradient theories.en_US
dc.descriptionThesis (Ph.D.)--Dalhousie University (Canada), 1999.en_US
dc.languageengen_US
dc.publisherDalhousie Universityen_US
dc.publisheren_US
dc.subjectPsychology, Experimental.en_US
dc.titleIn defense of gradient theories of illusory line motion.en_US
dc.typetexten_US
dc.contributor.degreePh.D.en_US
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