It is well established that anticipation of the arrival of an expected stimulus is accompanied by rich ongoing oscillatory neurodynamics, which span and link large areas of cortex. An intriguing possibility is that these dynamic interactions may convey knowledge that is embodied by large-scale neurocognitive networks from higher level regions of multi-model cortex to lower level primary sensory areas. In the current study, using autoregressive spectral analysis, we establish that during the anticipatory phase of a visual discrimination task there are rich patterns of coherent interaction between various levels of the ventral visual hierarchy across the frequency spectrum of 8 - 90 Hz. Using spectral Granger causality we determined that a subset of these interactions carry beta frequency (14 - 30 Hz) top-down influences from higher level visual regions V4 and TEO to primary visual cortex. We investigated the functional significance of these top-down interactions by correlating the magnitude of the anticipatory signals with the amplitude of the visual evoked potential that was elicited by stimulus processing. We found that in one third of the extrastriate-striate pairs, tested in three monkeys, the amplitude of the visual evoked response is well predicted by the magnitude of pre-stimulus coherent top-down anticipatory influences. To investigate the dynamics of the coherent and topdown Granger causal interactions, we analyzed the relationship between coherence and top-down Granger causality with stimulus onset asynchrony. This analysis revealed that in an abundance of cases the magnitudes of the coherent interactions and top-down directional influences scaled with the length of time that had elapsed before stimulus onset. / Together these results reveal a complex network of coherent and top-down directional interactions that predict the amplitude of early components of the visual evoked potential in primary visual cortex and vary in strength on the basis of the length of the stimulus onset. / by Craig G. Richter. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

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This research consisted of three individual studies, examining intra- and inter-modal haptic and visual processing in able learners and reading disabled children spanning the elementary school grades. / Performance was measured in terms of: accuracy scores, haptic exploration scores, and exploration times. Higher scores were obtained on the intra-modal visual condition than on any of the conditions involving a haptic component. Increasing the exploration times for haptic stimuli did not significantly improve performance on tasks involving a haptic component. / Performance scores of poor readers were depressed on all tasks, suggesting a general deficit in sensory processing rather than an inter-sensory processing deficit. Poor readers further employed less sophisticated haptic exploration strategies than able readers, suggesting use of less efficient task strategies.

This thesis explores the visual functions of the right anterior temporal cortex of the human brain. In Part 1, 92 patients with unilateral temporal- or frontal-lobe excisions and 35 normal control subjects were tested under two experimental conditions (global, local) of a reaction-time task, employing hierarchically structured letters or designs as stimuli. In both versions, the right temporal-lobe group was less affected than other groups by interference from the global aspect of the stimulus. These findings support the hypothesis that the right temporal lobe contributes to global visual processing. In Part 2, the ability to learn a cue-system for discriminating between two targets against a background of visually similar items was examined in 107 patients with unilateral temporal- or frontal-lobe excisions and 37 control subjects, using three versions of a visual-cue learning task. With letters and nonsense syllables, all groups took longer to complete the task when the background information was changed after three learning trials. With abstract designs, only patients with right temporal-lobe lesions failed to show this interference effect after three learning trials, but did so after six. Hence, it is argued that the right temporal lobe plays a role in visual pattern-discrimination learning.

Changes in memory and the nature of the mnemonic trace are a source of never-ending interest, as well as of physiological importance, to the investigator. To date, no satisfactory solution has been provided as to exactly what occurs within the trace itself when increasing errors of memory are manifested with the passage of time. Traditionally there have been two opposing theories - one, supported by G. E. Müller, which maintains that forgetting consists principally of an increasing indefiniteness of the trace, and the other, originated by Wulf, who concluded, from studies pursued under Koffka’s direction, that the trace tends, not towards vagueness, but towards “better figures”. That is, in certain instances, such as in the perception of an irregular figure, the unstable organization of forces within the trace itself will tend towards equilibrium overriding the influence of external events upon it. (Wulf himself distinguished three sources of error, “normalizing”, “emphasizing” and “autonomous changes”, but Koffka later reduced these to two, namely “external influence” and “spontaneous change”). Not only this, the tendency towards stability which is manifested in increased symmetry, tendency to close a gap, sharpening, etc., will be progressive in time. [...]

Title page, abstract and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1274742 / Thesis (Ph.D.) -- University of Adelaide, School of Psychology, 2007

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This research proposed to determine, in the context of preliminary data analysis, whether one can generate more--and more complex--"insights" (meaningful or possibly relevant relationships suggested by the data) by looking at a graphic (multiple bar chart) representation--as opposed to numeric table--of a large, multivariate quantitative dataset (twenty variables with twenty four observations each), displayed and manipulated h interactively in a personal computer-based system. If the more complex observations made possible by graphic representations can be explored in more detail--with further help from statistical and mathematical techniques-then the probability of achieving truly novel and useful solutions can be increased. The major issue involved is not how to communicate more effectively information to a large audience; it is rather what would stimulate deeper, sharper, and more expeditious analysis of a problem. An experiment--of a "posttest only control group" design--was conducted, with eighty Subjects. Half of those Subjects were randomly assigned to a treatment group (graphic representation of a quantitative dataset) and the other half, to a control group (multivariate representation of same dataset). Individual experimental sessions took approximately two hours, with an interactive tutorial--designed to give both groups the same level of basic skills for handling the computer program--followed by sixty minutes (maximum) for problem analysis. The null hypothesis was there would be no differences between the scores of Subjects looking at a graphic versus a numeric representation of data for each of four classes of "insight" generation: 1 "Insights" ignoring complexity levels 2 Multiple-field "insights", exclusive of single-field "insights" 3 Multiple "field-group" (such as age groups) "insights" 4 Number of different complexity levels A methodology was developed for objective scoring of the raw data (written notes with requested observations and inferences). Observations were eliminated on the basis of repetition, incompleteness, and lack of validation from underlying dataset. The differences between "insights" produced by the "graphic" and “numeric" groups were statistically significant. The major differences corresponded to the higher levels of "insight" complexity-—those observations relative to a large number of problem variables or to the whole dataset. The "graphic“ group produced a significantly larger number of such observations. / Ph. D. / incomplete_metadata