Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references (p.32-34).

Thesis (M.Sc.)--York University, 1999. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 95-104). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ56183

Thesis (M. Phil.)--University of Hong Kong, 1986.

Previous investigations have suggested that visual memory may involve short-term (STVM) and long-term (LTVM) components. Evidence for this comes from the functional differences between visual memory tested after short, unfilled retention intervals (STVM conditions), and performance measured after any interpolated task with a high mental load (LTVM conditions). The suggestion is that stimulus information is maintained over short, unfilled intervals by visualization, an active, voluntary control process utilizing central resources. Under LTVM conditions interference prevents active maintenance, and the item must be memorized. The aim of this thesis was to provide further evidence on the functional distinction, and the nature of the underlying processes. A number of experiments were conducted using novel matrix patterns as stimulus materials, and on-line control to allow precise manipulation of timing and other display parameters. The dissociation of STVM and LTVM was reflected in several results: STVM and LTVM (a) have different requirements for display time (b) differ in the consistency of performance over trials (c) they involve different coding processes at acquisition and (d) they show quite different relations between accuracy of performance and mean response time. In contrast to this, varying the exposure of a recognition test probe did not dissociate STVM and LTVM performance, and the provision of feedback and retrieval cues durin recall had no clearly interpretable effect. Visualization is a limited capacity process, insofar as it is restricted to one item or presentation at a time, and can maintain information up to a certain level of complexity. Visualized descriptions are constructed rapidly from short display times, and have general application to this class of novel visual patterns. With other evidence, this suggests that visualization is based on low-level 'figural' descriptions, specifying stimuli as a spatial arrangement of shapes formed by groupings of the pattern elements. LTVM performance increases slowly and irregularly with display time and there is a wide variation in performance over trials. Higher-level, 'semantic' descriptions contribute to memorization, and these cannot be applied rapidly and consistently to randomly generated abstract patterns. The results have widespread implications for theories of visual memory. Single-process theories which deny any distinction between short- and long-term memory are ruled out by the data. Other models which (a) consider STVM as an 'activated' part of LTVM or (b) claim the dichotomy arises from simple distinctions in coding or storage or retrieval do not give a complete account of the results. The 'modal' model is also rejected since prolonged visualization of an item after stimulus offset does not lead to an increase in LTVM. To account for this latter finding, it is proposed that visualization and: the elaborate encoding processes required for memorization compete for-central processing resources.

published_or_final_version / Psychology / Master / Master of Philosophy

Flanked objects are difficult to identify using peripheral vision. This is visual crowding. Crowding is the perceptual bottleneck for reading (Pelli et al., 2007) and object recognition (Pelli & Tillman, 2008). Theories for crowding had been suggested, but the underlying neural mechanism remained unclear. Some perceptual manipulations had been shown to break crowding, hinting the cortical locus of crowding. In the first part of the current study, we ask whether illusory contour formation survives crowding of illusion inducers. We measured the contrast thresholds for discriminating the rotation angle of a target Kanizsa inducer with and without flankers. When the other three Kanizsa inducers were rotated to misalign with the target, we observed strong crowding indicated through contrast threshold elevation. Interestingly, however, subjects were able to judge the shape (thin vs. fat) of the illusory Kanizsa square even when the individual inducers were flanked. Internal representation of the percept in the inducer-aligned condition was further studied through the classification image technique. Classification images indicated that illusory contours were formed and used in the perceptual decision task in both the non-flanked and flanked conditions. These findings suggest that crowding happens after illusory contour formation. In the second part, we ask if Chinese character orientation affects crowding. Fifty commonly used traditional Chinese characters were selected as stimuli. We measured the contrast threshold for identifying upright and inverted target surrounded by either upright or inverted flankers. At 5? eccentricity, we observed an interaction effect between target and flanker orientation on crowding: upright flankers produced a stronger crowding effect than inverted flankers for inverted but not upright target. Follow-up experiments showed that the observation was not due to a rise of detection sensitivity for upright flankers or a change of spatial extent between upright and inverted target. Yet, adding an enclosure to flankers eliminated the flanker orientation effect, suggesting that the flanker orientation effect may be attributed to the facilitation of texture perception in the periphery. At 10? eccentricity, upright target was generally more immune from crowding, further supporting that crowding takes place after Chinese character orientation has been coded. From previous fMRI studies, we know that lateral occipital complex (LOC) is the cortical site that first responds to Kanizsa?s illusory contours (Murray et al., 2002) and the fusiform gyrus is sensitive to the inversion of Chinese character (Kao, Chen, & Chen, 2009). Taken together with our findings, we infer that crowding happens at or after the two cortical locations. / published_or_final_version / Psychology / Master / Master of Philosophy

Perceptual grouping plays an indispensable role on attention distribution. An example of this interaction is the impaired visual search performance when the target overlaps with a task-irrelevant salient distractor organized to a snake-like configuration by collinear bars, and when the collinear distractor is long enough (Jingling & Tseng, 2013). This phenomenon is puzzling because it is opposite to our understanding of attention capture which predicts search facilitation instead of impairment. As an attempt to fully understand the interaction between perceptual grouping and attention, the current research probed the possible neural stage of this collinear search impairment effect. In Study 1, the distractor column of the search display was split into two eyes: one eye saw a distractor with varied length (= 1, 5, or 9 bars) while the other eye saw the rest of the distractor column. When both eyes were properly fused, observers saw a search display containing a 9-bar distractor. Observers were asked to identify the orientation of a target gap that could be overlapping or non-overlapping with the distractor. It was found that search impairment was dominated by monocular collinear distractor length. In Study 2, a 9-bar distractor was shown to one eye of observers and strong flashing color patches were shown to the other eye (Continuous Flash Suppression) such that part of the distractor was suppressed from observers’ awareness. It was found that invisible collinear distractor parts enhanced search impairment, suggesting awareness of the distractor is not necessary for the effect. Results from both studies converge to suggest that the effect of collinear grouping on attention is likely to be at early visual sites like V1 where monocular information but not awareness is processed. It highlights the need to incorporate perceptual grouping into current salience-based attention models. / published_or_final_version / Psychology / Master / Master of Philosophy

Information pick-up from peripheral vision is thought to play an important role in dynamic decision-making; however, this has not been verified empirically. This thesis reports a series of experiments that used a gaze-contingent manipulation of video footage to examine the role of central and peripheral vision in expert decision-making in the dynamic sport of basketball. In Experiment 1, opaque (black) occlusion was selectively applied to the central and/or peripheral vision of skilled and novice basketball players using a real-time gaze-contingent display. The skilled players made better decisions irrespective of whether they were using central vision, peripheral vision, or the full visual field. However, the opaque occlusion in this task could have concurrently impaired both information pick-up and the guidance of subsequent eye movements. In Experiment 2, occlusion was achieved via visual blur rather than black opaque occlusion in an effort to constrain information pick-up while permitting the guidance of normal visual search. The results again showed that skilled players had consistently higher response accuracy irrespective of the area of visual field they used or the level of blur applied. However, as the expert advantage remained strongly robust even under highly impaired viewing conditions, the question arose as to whether the response slide itself may have contained information that could support expert decision-making performance. Experiment 3 confirmed this suspicion and in Experiment 4 a suitable response mode that contained no inherent information was identified and validated. Experiment 5 adopted this revised response mode to essentially replicate Experiment 2 while also introducing further combinations of central and peripheral blur. Experiment 5 confirmed that skilled players demonstrate higher decision-making accuracy irrespective of the area of the visual field they rely on. Even low levels of blur, despite not influencing decision-making performance, were found to alter the pattern of eye movements used. This suggests that performance is maintained despite measurable changes in gaze. Remarkably, the decision-making performance of the novice participants improved when certain levels of blur were applied to the peripheral visual field. As a consequence, Experiment 6 examined whether the decision-making skill of inexperienced players could be enhanced through training when viewing with gaze-contingent blur. It was found that perceptual training with clear central + blurred peripheral vision led to better performance than equivalent training with normal (full-field) vision or with blurred central + clear peripheral vision. The improvements in performance were independent of changes in visual search strategy, suggesting that alterations in attentional allocation may have been responsible for the training effect. Collectively, the results of the experimental series lead to the conclusion that the ability to interpret information is the critical limiting factor to skilled decision-making rather than the location of the information within the visual field or the pattern of visual search. The findings provide a basis for the development of methodological guidelines for the use of gaze-contingent displays in dynamic tasks and lead to enhanced approaches in the investigation and training of decision-making skill. / published_or_final_version / Human Performance / Doctoral / Doctor of Philosophy

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Against a plethora of visual input, visual attention filters and selects relevant information and disengages from irrelevant items. One possible mechanism to enable disengagement is reflected in inhibition of return (IOR), the finding that previously visited locations are responded to slower than locations that have not been investigated before. In line with the proposal that IOR reflects a mechanism to facilitate visual search, evidence suggests that IOR is coded in space-based (“spatiotopic”) coordinates, despite the largely retina-based (“retinotopic”) coding scheme of the visual system. For IOR to efficiently facilitate visual search it should be coded solely in spatiotopic coordinates, but recent investigations show retinotopic IOR effects alongside spatiotopic IOR. The putative function of IOR has also been challenged by the observation that the eyes return to previously visited locations more frequently than would be predicted based on chance. The presented program of research examines the factors that influence whether, and how, IOR is implemented in a way that would facilitate visual search. Firstly, it was examined whether it is an efferent signal about an upcoming eye movement or a more general prediction-based mechanism that maintains IOR in spatiotopic coordinates across eye movements. IOR was observed in both retinotopic and spatiotopic coordinates across eye movements, but was observed in a weakened form and only in location-based coordinates when objects, instead of the eyes, were moved. These results suggest that efferent signals about upcoming eye movements contribute to updating and maintaining IOR tags in useful locations when the eyes move. Secondly, the relative strength and robustness of retinotopic and spatiotopic IOR were examined; the relative frequency of cue-target pairings in retinotopic and spatiotopic references frames had no significant effect on the presence of retinotopic IOR, whereas practice with the experimental task strengthened spatiotopic IOR III and eliminated retinotopic IOR. Thirdly, spatiotopic IOR was observed to be more robust than retinotopic IOR for both saccadic and manual responses. Fourthly, for responses to targets appearing in the brief interval before the eye movement (< 150ms), IOR was observed in the future retinotopic location of the target, suggesting that IOR was remapped predictively. Finally, it was demonstrated that IOR is reduced for intermediate locations along pre-planned sequences of saccades. Taken together the findings of the presented series of research suggest that IOR is updated into spatiotopic coordinates across eye movements. Spatiotopic IOR involves the efferent signal of the eye movement and is updated predictively before the saccade, extending the notion that predictive remapping updates attentional pointers to updating of inhibitory effects. Retinotopic IOR was consistently weaker than spatiotopic IOR across all experiments, and was eliminated with practice, consistent with retinotopic IOR being an undesirable, but avoidable, consequence of inhibiting locations while moving the eyes. Finally, the reduction of IOR for intermediate locations along preplanned saccade sequences is consistent with the idea that the degree to which a location was attended can determine how inhibited that location subsequently becomes. It also could explain why refixations are commonly observed in free visual search, which would typically contain many such pre-planned sequences. Taken together, the findings are additional evidence that IOR reflects a mechanism that facilitates visual search under the conditions in which search normally occurs, that is, across overt eye movements and sequences of eye movements.