Thesis (Ph. D.)--State University of New York at Binghamton, Department of Psychology, 2005. / Includes bibliographical references.

Thesis (M.Sc.)--York University, 2004. Graduate Programme in Computer Science. / Typescript. Includes bibliographical references (leaves 144-152). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11814

Thesis (M.S. in psychology)--Washington State University, May 2007. / Includes bibliographical references (p. 19-21).

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 342-357). Also available for download via the World Wide Web; free to University of Oregon users.

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Autism is a neurodevelopmental disorder characterized by difficulties in social interaction, communications and unusual repetitive behaviours. Studies have documented superior performance in autism in visuo-spatial tasks suggesting perceptual differences in this group. This has been suggested to result from enhanced processing of local details and reduced integration of global information. Contour integration tasks are one way of studying visual integration where participants have to detect a contour made of discrete elements (usually Gabor patches) against a background of noise. However, contour integration studies in autism have yielded mixed findings which possibly due to the closed shapes and longer stimulus duration used in these studies. Recently, Jachim et al (2015) compared contour detection using open and closed contours at a shorter duration reported reduced closure in the autistic group. Closed shapes are generally easier to detect than open shapes, termed the closure effect which is thought to result from more involvement of top-down input. Therefore, the main aim of this thesis was to further explore visual integration in autism using contour integration tasks, to understand the reasons for these variations in autism and neurotypicals. We presented six contour integration experiments using open (eg: lines) and closed (eg: square) contours. The first two experiments explored the influence of autistic traits in the general population and attentional feedback on contour integration in neurotypicals using a dual-task which interferes with processes concurrently using attention. The autistic traits showed a weak effect on contour integration, and the dual task produced a non-significant reduction to closure, that requires further exploration with larger participant numbers. The next two experiments investigated the influence of stimulus duration on contour integration in both groups to test the suggestion of slower global processing in autism. Results showed no effect of durations on closure in both groups, and that reduced closure in the autistic group did not resolved with longer durations. The final two experiments explored the relationship between closure and symmetry in both groups; another process that is thought to involve global processing and received input from similar areas that process closure. The control group showed better symmetry detection with closed contour, suggesting closure benefits symmetry detection. Despite comparable performance to the control group with the closed contour, the autistic group showed better thresholds with the open contour leading to lesser benefit of closure in symmetry detection. In summary, we reported possible variations in contour integration in general population. Additionally, results suggested that the autistic group processed contour integration and symmetry using different mechanisms. This converging evidence is suggestive of enhanced perception at low-level processing in autism, in support of Enhanced Perceptual Functioning Theory (EPF).

There are different aims in this thesis. The primary aim is to investigate visual perception in Chinese orthography, from its fundamentally distinct unit, characters, to sentence reading. The first aim of the thesis is to investigate how a single Chinese character is processed in many ways. We have looked into an effect called orthographic satiation/decomposition (Cheng & Wu, 1994). It refers to the feeling of uncertainty about the composition of some characters when staring at a character for too long. Lee (2007) extended Cheng and Wu’s study (1996), and the results have showed that orthographic satiation occurred faster in females than males. We replicated Lee’s study (Experiment 1) (Chapter 3), and have found that: (1) there was no significant difference between male and female and (2) a radical that can stand alone as a single character makes characters in which it occurs resistant to satiation. Following orthographic satiation, in Chapter 4, we explored the preference for eye/hemisphere visual pathways in Chinese characters (Experiment 2 & 3) and words (Experiment 4). In English, researchers have reported a contralateral preference when four-letter words were presented very quickly using a haploscope (Obreg´on & Shillcock, 2012) . It raises the question of whether presenting Chinese characters and words will show similar results considering the complexity and the special characteristics of Chinese orthography. We presented Chinese characters and words to participants using a haploscope. Our results showed that: (1) the contralateral visual pathway was preferred in perceiving right-left structured Chinese characters and two-character words, (2) when a semantic radical is projected to the LH, participants are able to recognise the semantic component better, (3) neighbourhood size (NS) (Tsai, Lee, Lin, Tzeng & Hung, 2006) affects how participants recognise words, and(4) males do better than females recognising characters but not words. After investigating the recognition of Chinese characters and words, we analysed the eye-movements in Chinese and English reading corpora. The processes of reading are intuitively thought to be more complex than perceiving a single character or words. The last studies in the thesis focused on the reading behaviours in Chinese and English. The eye movement differences and similarities between reading Chinese and English were investigated. In Chapter 5, we showed that reading Chinese elicits more divergence of the eyes within a fixation, compared with reading English. We interpreted these data in terms of recent demonstrations that apparent size causes increases in visual sensitivity (Arnold & Schindel, 2010) and engages more cortical resource in V1 (Kersten & Murray, 2010). Our analyses were based on movement within exactly temporally synchronized binocular fixations in the reading of Chinese and English 5000-word multi-line texts, using monocular calibration, with EyeLink-2 technology. When faced with visually complex orthography, the oculomotor system ‘tricks’ the rest of the visual system into ‘zooming in’ on the text. We consolidated the relevant theorizing into the ‘Divergence Affects Reading’ (DOLLAR) Theory. In Chapter 6, we reported that (1) vertical movements within a fixation tend to be smaller than horizontal ones, and (2) vertical movements within a fixation tend to be upwards. We speculated that it is appropriate for the earlier part of the fixation to be associated with visual recognition and for the later part of the fixation to be associated with executive action. The tendency to move upwards also suggested that in real-world reading, the upper part of words/characters were informative. In the last chapter analysing the reading corpus (Chapter 7), we reported corrective saccades after return sweeps. We found that in English, there were more corrective saccades after return sweeps than in Chinese. We interpreted these data in terms of spatial coding (Kennedy & Murray, 1987). In terms of Chinese and English differences, the stimuli that were used in our corpus show that the length for each line was different in English. The length for each line in Chinese was less different. Though the first character of each line was at the same place for two languages, it was more difficult for English subjects to locate the correct place after return sweeps because the length of return sweeps was different. In short, this thesis investigated visual perception in Chinese orthography, in terms of characters, words, and real-world reading. Moreover, we compared the differences and similarities between languages (English and Chinese). Despite the fact that the orthographies of English and Chinese are very different, we still found similar effects (e.g., contralateral preference) between them. This thesis thus has contributed to a better understanding of the differences and similarities between English and Chinese in terms of the orthographies.

Perception is strongly influenced by our expectations, especially under situations of uncertainty. A growing body of work suggests that perception is akin to Bayesian Inference in which expectations can be viewed as ‘prior’ beliefs that are combined via Bayes’ rule with sensory evidence to form the ‘posterior’ beliefs. In this thesis, I aim to answer open questions regarding the nature of expectations in perception, and, in particular, what the limits of complexity and specificity in developing expectations are, and how expectations of different temporal properties develop and interact. First, I conducted a psychophysical experiment to investigate whether human observers are able to implicitly develop distinct expectations using colour as a distinguishing factor. I interleaved moving dot displays of two different colours, either red or green, with different motion direction distributions. Results showed that statistical information can transfer from one group of stimuli to another but observers are also able to learn two distinct priors under specific conditions. In a collaborative work, I implemented an online learning computational model, which showed that subjects’ behaviour was not in disagreement with a near-optimal Bayesian observer, and suggested that observers might prefer simple models which are consistent with the data over complex models. Next, I investigated experimentally whether selective manipulation of rewards can affect an observer’s perceptual performance in a similar manner to manipulating the statistical properties of stimuli. Results showed that manipulation of the reward scheme had similar effects on perception as statistical manipulations in trials where a stimulus was presented but not in the absence of stimulus. Finally, I used a novel visual search task to investigate how expectations of different timescales (from the last few trials to hours to long-term statistics of natural scenes) interact to alter perception. Results suggested that recent exposure to a stimulus resulted in significantly improved detection performance and significantly more visual ‘hallucinations’ but only at positions at which it was more probable that a stimulus would be presented. These studies provide new insights into the approximations that neural systems must make to implement Bayesian inference. Complexity does not seem to necessarily be a prohibitive factor in learning but the system also factors the provided evidence and potential gain in regards to learning complex priors and applying them in distinct contexts. Further, what aspects of the statistics of the stimuli are learned and used, and how selective attention modulates learning can crucially depend on specific task properties such as the timeframe of exposure, complexity, or the observer’s current goals and beliefs about the task.

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

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