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published_or_final_version / abstract / Psychology / Doctoral / Doctor of Philosophy

Previous bilingual studies showed reduced hemispheric asymmetry in visual tasks such as face perception in bilinguals compared with monolinguals, which suggested that hemispheric asymmetry in visual tasks could be modulated by experience in reading one or two languages. Here I examined whether differences in hemispheric asymmetry in visual tasks can also be observed in bilinguals who have different language backgrounds. I compared the behavior of three language groups: (1) English monolinguals, who acquire only one alphabetic language, (2) European-English bilinguals, who know two alphabetic languages, and (3) Chinese-English bilinguals, who master an alphabetic language and a logographic language; in three tachistoscopic tasks: (1) English word sequential matching task, (2) Intact-altered face judgment task, and (3) face sequential matching task. The results showed that European-English bilinguals had a stronger right visual field (RVF)/ left hemispheric (LH) advantage in the English word sequential matching task than English monolinguals and Chinese-English bilinguals, suggesting that different language learning experiences can influence how visual words are processed in the brain. However, the results showed no group difference between the left visual field (LVF)/ right hemisphere (RH) advantage in the intact-altered face judgment task and the face sequential matching task. These results suggested a modulation of language experience on visual word processing but not on face processing. In addition, I showed that the hemispheric asymmetry in visual word processing could be accounted for by a computational model that implements a theory of hemispheric asymmetry in perception (i.e. the Double Filtering by Frequency theory, Ivry & Robertson, 1998); the modeling data suggested that this lateralization difference in visual word processing may be due to both the difference in participants’ vocabulary size and the difference in word-to-sound mapping between alphabetic and logographic languages. / published_or_final_version / Psychology / Master / Master of Philosophy

A variety of measures are enlisted in an explanation of some longstanding perceptual phenomena associated with an assortment of visual patterns. In following the proximity principle of Gestalt psychology, these are commonly based upon a statistical treatment applied to one or another of a hierarchy of distance measures. Following from this, some problems of visual perception are tackled in terms of an active perceiving mechanism, which generates transformations in the realization of object invariance in space and over time. This generative transformational approach is also employed in an account of perception of various patterns and visual illusions. Although a range of proximity measures is involved throughout, the nearest neighbour metric is staple. For perception of unstructured visual arrays, the contribution of distance mechanisms, particularly nearest neighbours, is shown to be important. For structured arrays, the contribution of distance mechanisms along with transformations is important. Information about relative positions of image elements permits the selection of transformations that reveal structure. With respect to such information, however, the proximity principle is taken to its limits. / Thesis (Ph.D.)--School of Psychology, 2006.

While various studies have related susceptibility to the Mueller-Lyer illusion to mental health, to developmental maturity, and to self-differentiation, there have been no studies in which susceptibility to the illusion has been related to a wide spectrum of self-concept dimensions. It is one of the purposes of the present study to analyze susceptibility to the Mueller-Lyer illusion as a function of errors in self-perception. To the extent that an individual suffers conflicts with regard to his self-concept, in any of its significant dimensions, it is expected that he will suffer a greater susceptibility to the illusion.

Accurate perception and control of self-motion is vital for human survival. Most animals rely on vision for navigating through complex environments. In this thesis, I investigated how vision influence perception and guide self-motion from two aspects: (1) what visual information humans pick up from the environment to form their perception and guide their self-motion; (2) how the degeneration of the basal ganglia and cerebellum, the two largest subcortical nuclei connecting the visual and motor areas of the brain, affect the controller’s performance. Study 1 examined the condition under which optic-flow information beyond velocity field helps heading perception. I systematically varied the amount of information in velocity field through manipulations of field of view (FOV). The amount of optic-flow information beyond velocity field was manipulated by two types of displays. I found heading bias increased with the reduction of FOV only when optic-flow information beyond velocity field was not available. Study 2 investigated whether the information investigated in Study 1 is sufficient and necessary for active control of heading. I used the similar display simulations as study 1 with the exception that the vehicle orientation was perturbed pseudo-randomly. Participants used a joystick, under both velocity and acceleration control dynamics, to continuously rotate the vehicle orientation back to its heading direction. The results showed that participants’ accurate performance under condition that only provided velocity field information was further improved when optic-flow information beyond velocity field was available. Study 3 examined the relative contributions of three visual cues (i.e., heading from optic flow, bearing, and splay angle) for lane-keeping control. Observers controlled the car’s lateral movement to stay in the center of the lane while facing two random perturbations affecting the use of bearing or splay angle information. I found that performance improved with enriched flow information. In the presence of splay angles, participants ignored bearing angle information. Study 4 investigated the roles of the basal ganglia and cerebellum in motor control task using brain-damaged patients. Participant’s task was to use the joystick to keep a blob in the center of the display while the horizontal position of the blob was perturbed pseudo-randomly. This task is not a self-motion task but mimics real-world lane-keeping control. Both the Parkinson’s disease patients and cerebellar patients showed impaired motor control performance in comparison with the healthy controls. In conclusion, the visual information used for motor control in general depends on the task. For traveling along a curved path, the velocity field contains sufficient information for heading perception and heading control. Optic-flow information beyond velocity field improves heading perception when the velocity field does not contain sufficient information. It also helps heading control when available. For lane-keeping control, adding optic flow information improves participants’ performance. Splay angle information plays a more important role than does bearing angle information. The visual information used for motor control changes when certain brain areas are damaged. Parkinson’s disease patients and cerebellar patients show the inability to process visual input effectively for online motor control. / published_or_final_version / Psychology / Doctoral / Doctor of Philosophy

Doctorat en sciences psychologiques / info:eu-repo/semantics/nonPublished