Thesis (M.Soc.Sc. Psychology)--University of Waikato, 2006. / Includes bibliographical references (leaves 60-64)

Thesis (Ph. D.)--University of California, San Diego, 2006. / Title from first page of PDF file (viewed December 12, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 112-129).

This thesis investigated the nature of any uniquely social influence of centrally presented, non-informative gaze cues compared to non-social arrow and moving line cues on attention orienting and working memory (WM). Effects were measured using the traditional unilateral paradigm (target information on one side), and a novel bilateral paradigm (target information on both sides). Attention was investigated using a traditional asterisk localisation target task (unilateral) and a novel oddball localisation task (bilateral). WM was measured using a simple array of coloured squares displayed either on one side of the cue (unilateral), or spread evenly over both sides (bilateral). Participants were required to remember all colours and state whether a test colour had been present/absent. Target information was displayed in the valid looked at location, invalid looked away from location, or (WM only) in a no cue shift condition. Across experiments I manipulated the stimulus onset asynchrony (SOA: Attention, 150-1000ms; WM 150ms/500ms). Cue effects on attention and WM differed dependent upon cue type, SOA and unilateral/bilateral presentation. In unilateral attention, valid compared to invalid gaze and arrow cues speeded orienting across all SOAs tested (150ms-1000ms), while motion only reliably oriented attention at early SOAs. For bilateral attention, the pattern for the arrow and moving line cue remained the same, but the gaze cue effect diminished at longer SOAs. In unilateral WM, only the gaze cue influenced WM, facilitating WM for validly cued items (500ms SOA only). This effect was abolished when an opaque barrier occluded the face's ability to 'see' the memoranda, but was partially replicated when the barrier had windows. In bilateral WM, the gaze cue had no effect, instead the arrow (500ms) and line (150ms) enhanced WM. A shared goals hypothesis is presented to address how and in what circumstances eye gaze is utilised as an important social cue.

Depressed and suicidal patients have difficulty in recollecting specific autobiographical events. In response to cue words they tend to generate summarised or general memories instead of specific events. The objectives of this thesis are to explore the mechanisms underlying the production of specific and general autobiographical memories in a non clinical population. The roles of imagery and working memory in the generation of autobiographical memories were investigated. Four experiments examined how manipulating the imageability of the cue affected subsequent retrieval in autobiographical memory. The results show that cues high in imageability facilitated access to specific memories and that visual imageability was the most significant piedictor of memory specificity compared to a range of other perceptual modalities. The effect of an experimental manipulation on retrieval style was examined by instructing participants to retrieve specific events or general events using high or low imageable words to cue memories. The results show that induction. of a generic retrieval style reduced the specificity of images of future events. This models clinical findings with depressed and suicidal patients and suggests that associations between memory retrieval and future imaging share common intermediate pathways. A further experiment suggested that the image ability effects mediating the construction of specific memories may be in part due to the predicability of such retrieval cues. The hypothesis that retrieval of specific autobiographical memories is more effortful compared to the retrieval of general memories was also investigated using a dual task paradigm. Although central executive function has been implicated many times in the monitoring of autobiographical retrieval, no direct assessment of executive capacity during retrieval has been made. The results showed no significant difference in the randomness of a keypressing task when specific or general autobiographical memories were retrieved in response to either high or low imageable cue words. A direct retrieval hypothesis was proposed whereby cues directly accessed specific events in autobiographical memory and the adoption of such a strategy enabled participants to maintain performance on the secondary task.

The inhibitory circuitry of the prefrontal cortex (PFC) is involved in working memory and modulation of brain oscillations. Alterations in this network and especially GABAergic cells that express cholecystokinin (CCK), parvalbumin (PV), or somatostatin (SST) may underlie some of the cognitive deficits observed in schizophrenia. To assess the involvement of CCK+, PV+, and SST+ interneurons in PFC-dependent behaviours, we selectively inactivated these in prelimbic and infralimbic PFC via virus-mediated expression of tetanus toxin light chain (TeLC). We found that functional removal of CCK+ or PV+, but not SST+ neurons leads to specific impairments in working memory, and these represent the main cognitive domains affected in schizophrenia. PV-TeLC and CCK-TeLC mice displayed significant Y-maze alternation index reduction (p < 0.05). Targeting of PV+ prefrontal cells causes anxiety-like phenotype. Moreover, PV+ and SST+, but not CCK+ interneurons, appear to play a role in latent inhibition. Functional removal of CCK+, PV+ and CCK+ cells from PFC does not affect circadian activity and does not cause anhedonia. The involvement of PV-network in generation of neuronal activity and acetylcholine homeostasis was assessed. For neurophysiological recordings, each arm of the Y-maze divided into two equal-sized zones – proximal (close to the central decision point) and distal (far end). Zone entry was event-mapped onto continues local field potential recordings from medial PFC and CA1 region of the hippocampus. PV-TeLC animals displayed significantly lower prefrontal power in the decision zone. This suggests that the PV-TeLC animals are unable to modulate neuronal activity depending on the cognitive demand. Functional removal of prefrontal PV+ interneurons also leads to disturbed acetylcholine homeostasis. These results show that prefrontal GABAergic cells drive different behaviours and control task-relevant neuronal activity in different brain regions engaged with working memory such as hippocampus. Similar signalling anomalies may thus underlie cognitive deficits found in schizophrenia.

Dans l’exercice de leur profession les pilotes doivent fréquemment faire face à des situations soudaines et inattendues, souvent potentiellement dangereuses. Ils sont formés pour les traiter efficacement mais cependant la brièveté du temps disponible avant que la situation ne dégénère, de l’ordre de quelques secondes, au plus la minute, fait que parfois la séquence cognitive perception-diagnostic-décision-action, peut être menée de façon incorrecte sous stress et aboutir à un incident grave ou même à un accident.A partir de l’analyse des comportements cognitifs élémentaires en situation critique dans cinq cas d’incidents et d’accidents, on arrive à déceler des dénominateurs communs aux réactions des pilotes, permettant l’explication des échecs constatés et l’établissement de recommandations. Le rôle primordial sous stress d’une fonction cognitive particulière associée à la mémoire à court terme est mis en lumière.Pour effectuer cette analyse il a été nécessaire de définir une modélisation dynamique du comportement cognitif des pilotes, où le facteur temps est explicité, permettant son étude dans des séquences très brèves de quelques secondes. Cette modélisation peut aussi s’appliquer à d’autres cas que ceux générant des accidents, par exemple à l’étude et à la définition des systèmes nécessitant une interface homme-système.La complexité et la particularité des actions opérationnelles dans des séquences très rapides où elles se combinent, a mené naturellement à effectuer les analyses en utilisant l’expertise de pilotes, suivant une méthode autorisant la validation des hypothèses retenues. / During the exercise of their profession, frequently pilots have to face sudden, unexpected, and often potentially dangerous, situations. They are trained to deal with these effectively, but the very short length of time available before the situation degenerates – in the order of a few seconds, a minute at most – means that the cognitive sequence of perception-diagnosis-decision-action can sometimes be carried out incorrectly due to stress and lead to a serious incident or even to an accident.An analysis of basic cognitive behaviour patterns during a critical situation in five cases of incidents and accidents, reveals common denominators within pilots’ reactions which make it possible to explain the failures observed and establish recommendations. The crucial role under stress played by a specific cognitive function associated with short-term memory is highlighted. In order to carry out this analysis it was necessary to create a dynamic model of the cognitive behaviour of pilots, bringing out the time factor, so as to make it possible to study very short sequences of a few seconds. This model can also be applied to cases other than those generating accidents, for instance to the studying and defining of systems requiring human-machine interface.The complexity and specificity of operational actions when combined into very rapid sequences led naturally to carrying out analyses making use of pilots’ expertise, according to a method which enabled validation of the hypotheses employed.

The activity of neurons in the prefrontal cortex (PFC) may underlie working memory processes in the brain. Both the performance of working memory tasks and the activity of PFC neurons are modulated by dopamine. The goal of the present thesis was to gain insight into the neural basis of working memory by studying the PFC, and the DA system in the PFC, from both a behavioral and cellular perspective. The functional contribution of the PFC to working memory processes in the rat was assessed in Chapter 2 of the present thesis using memory-based foraging tasks on an 8-arm radial maze. The results of these studies indicated that lidocaine-induced inactivations of the PFC selectively disrupted the ability to use mnemonic information to guide foraging, but not the ability to acquire or retain such information. The ability to use mnemonic information to guide foraging was also disrupted by microinjection of a D1 but not D2 receptor antagonist into the PFC. Chapters 3-5 investigated how PFC neurons process synaptic inputs to their dendrites to produce spike output. The intrinsic membrane properties and synaptic responses at the soma and dendrites of deep layer PFC pyramidal neurons were recorded using sharp intracellular or whole-cell patch-clamp techniques in a brain-slice preparation. Different passive and active membrane properties of the soma and dendrites of PFC neurons were observed. The distal dendrites of PFC neurons responded most effectively to strong, highly coincident synaptic inputs. Ca²⁺currents near the soma both amplified the effects of these inputs and modulated the spike output pattern. Spike output at the soma was also controlled by the interplay of slowly-inactivating Na⁺ and K⁺ currents. Chapter 6 investigated the modulation of PFC neurons by DA. DA or a D1 but not D2 receptor agonist increased the evoked firing of PFC neurons via a D1- mediated modulation of slowly-inactivating Na⁺ and K⁺ currents. Concurrently, D1 receptor activation reduced burst firing in PFC neurons, due to a attenuation of Ca²⁺ currents. D1 receptor activation also increased both GABA[sub A] IPSPs and NMDA EPSPs. The final chapter of this thesis integrated these data into a cellular model of PFC function and its modulation by DA. It is proposed that DA may tune PFC neurons such that they respond selectively to strong synchronized inputs from other cortical areas. In the presence of DA, working memory processes mediated by the PFC may be influenced selectively by stimuli of behavioral significance. / Arts, Faculty of / Psychology, Department of / Graduate

0 / SPK / specialcollections@tulane.edu

This dissertation is based on the papers written by Platen and Rebolledo (1996), and Platen (1999). The papers focuses on modeling the short term interest rate by optimizing relative entropy of two probability measures Q and P. The derivation of the model is done by applying the three principles of market clearing, exclusion of arbitrage and minimization of increase of arbitrage information on a simple financial market model. The last principle is equivalent to minimization of the distance between the risk neutral and the real world probability measures. We test the model on historical data from two countries, United States and South Africa from different time frames. The results are then compared to the findings of Platen (1999). / Dissertation (MSc)--University of Pretoria, 2012. / Mathematics and Applied Mathematics / unrestricted

The delayed matching‐to‐sample (DMTS) procedure involves the insertion of a delay between the offset of a sample stimulus and the onset of an array of comparison stimuli; one of which is designated as the “correct” match for the sample on each trial. The procedure has served as the base preparation in which the effects of environmental variables on short‐term remembering and is, in many ways, responsible for a refined understanding of the phenomenon. Despite its utility, however, there are a few problems with the DMTS procedure – first, the procedure doesn’t adjust for individual differences and second, the conventional dependent measure, percent of correct trials, is not as sensitive as one might like. The titrating-delay matching to sample (TDMTS) procedure is a variant of the DMTS procedure in which the delays between sample and comparison are adjusted as a function of the subject’s performance. Stable measures of adjusted delay are not only sensitive measures of the performance of interest but they are also automatically tuned to differences across individuals. The study reported here continues our efforts to understand the dynamics of the TDMTS procedure so that it can be used to ask important questions related to short‐term remembering.