To advance the understanding of electric hearing, from both a theoretical and practical perspective, the present study employs an engineering approach to examine whether a fundamental stochastic link exists between neural stimulation and perception. Through the use of custom-developed psychophysics software, temporal gap-detection experiments were carried out and compared with simulation results of a theoretical model. The results are informative, and the suggested modeling principles may be a step forward to a clearer understanding of how the hearing system perceives temporal stimuli. To enable the implementation of psycho-electric experiments involving cochlear implants, a software framework was developed for Matlab version 6.5, called the Psychoacoustics Toolbox, which can present stimuli either acoustically or (for interfacing with cochlear implants) using Cochlear Ltd. hardware. This toolbox facilitates easy setup of experiments based on extensible markup language (XML) templates, and allows for both adaptivestaircase procedures and presentation of a fixed set of stimuli to a participant. Multi-track interleaving of stimuli is also supported, as put forward by Jesteadt (1980), to allow for capturing of subjective responses (such as loudness perception). As part of this research, experiments were performed with three subjects, with a total of four cochlear implants. For the temporal gap-detection experiments, the rate of electrical stimulation varied over a range from 100 to 2700 pulses per second; both periodic stimulus sequences and stimuli reflecting a dead-time-modified Poisson process were used. Also, three spatially distinct stimulation sites were used with each implant to allow comparison among basal, central and apical cochlear responses. A biologically plausible psychophysical model (in contrast with a phenomenological one) was developed for predicting temporal gap-detection thresholds in electric hearing. The model was applied to both periodic and Poisson stimuli, but can easily be used with other kinds of stimuli. For comparison with experimental results, model predictions were made over the same range of stimulus rates. As a starting point, the model takes the neural stimuli, runs them through a neural filter, and then draws statistical interspike-interval (ISI) distribution data from the generated spikes. From the ISI statistics, psychometric curves can be calculated using the principles of Green and Swets (1966), from which predictions can be made for threshold measurements based on the percentage-correct mark for the specific experimental setup. With a model in place, simulations were executed to compare the model results with experimental measurements. In addition to the simulations, mathematical equations for the periodic types of stimuli were derived, given that numerical calculations could be made with higher computational e ciency for this kind of stimulus. These equations allowed for an investigation into the implications of varying the values of different neuron-model parameters. Clear similarities were found between the shapes of gap-threshold curves for experimental and modeled data, and qualitative links have been identified between model parameters and features recognized in threshold curves. For periodic stimuli, quantitative predictions of gap thresholds are close to experimental ones, although measured values cover a larger range. The results of experimental measurements using Poisson stimuli are generally somewhat larger than model predictions, although the shapes of the curves show resemblance. A possible explanation is that participants may find decision tasks involving Poisson stimuli, as opposed to periodic stimuli, confusing. Overall, model predictions and experimental results show close correspondence, suggesting Department of Electrical, Electronic and Computer Engineering. University of Pretoria. ii that the principles underlying the model are fundamentally correct. Copyright 2007, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Geldenhuys, TA 2007, Temporal gap detection in electric hearing : modelling and experiments, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-02232012-131459 / > E1091/gm / Dissertation (MEng)--University of Pretoria, 2012. / Electrical, Electronic and Computer Engineering / Unrestricted

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This study examines how Swedish and English adjectives relating to the semantic domain of SADNESS are used and what some of their semantic and syntactic characteristics are. The primary objectives of this study are to determine whether the adjectives in question are used more often attributively or predicatively, whether they are used more frequently along with the semantic role of stimulus or experiencer and whether there are any syntactic, semantic or lexical disparities in how Swedish and English encode the domain of SADNESS. To investigate this, parallel corpus data retrieved from movie and TV subtitles were analyzed in combination with dictionary data. The results showed that predicative usage was more dominant than attributive. While the semantic role of stimulus was more prevalent in the dataset of this study, experiencer-oriented adjectives showed higher prevalence when considering the individual frequencies of each word in the corpus. Notably, the Swedish word tråkig combines the meanings of `sad’ and ‘boring’, illustrating differences in emotion-related concept encoding between the two languages. / Denna studie undersöker hur svenska och engelska adjektiv som relaterar till den semantiska domänen LEDSENHET används och vad några av deras semantiska och syntaktiska egenskaper är. De primära målen med denna studie är att avgöra om adjektiven i fråga används mer ofta attributivt eller predikativt, om de används oftare i samband med den semantiska rollen stimulus eller upplevare och om det finns några syntaktiska, semantiska eller lexikala skillnader i hur svenska och engelska kodar domänen LEDSENHET. För att undersöka detta analyserades parallella korpusdata hämtade från film- och TV-undertexter i kombination med ordboksdata. Resultaten visade att predikativ användning var mer dominerande än attributiv. Medan den semantiska rollen stimulus var mer utbredd i datamaterialet för denna studie visade upplevare-orienterade adjektiv högre prevalens när de individuella frekvenserna för varje ord i korpusen beaktades. Det svenska ordet tråkig kombinerar betydelserna av ‘ledsen’ och ‘(lång)tråkig’ vilket illustrerar skillnader i emotionsrelaterad begreppskodning mellan de två språken.

Online retailing has grown rapidly and nowadays consumers’ needs become more and more demanding. Mass customization satisfies the need of customers for individuality. However, in order for retailers to offer a satisfying shopping experience, they need to take into account their retail environment. In online retailing, atmospherics play a significant role in consumers’ attitudes towards the store. The present study aims to analyze the role of high task-relevant atmospheric cues, thus those atmospherics that are strongly connected with the shopping goal, such as verbal content, display methods and navigation aids. Furthermore, the author will analyze the effect of the above atmospherics on consumers’ response towards the online mass customization environment. In order for the purpose to be fulfilled, semi-structured interviews were conducted in a purposive sample of ten participants. The results were analyzed based on the Stimulus-Organism-Response model. Finally, high task-relevant atmospheric cues are strongly related to the consumers’ final response by provoking either positive or negative emotions. More specifically, verbal content and display methods have a crucial effect on consumers’ end response. On the other hand, navigation aids contribute to a pleasant online experience but they do not affect final consumers; response significantly. Conclusively, the present study aims to be considered as a useful tool for marketing purposes as it can provide knowledge on how consumers behave in a mass customization online environment in the fashion industry. Such knowledge may appear crucial for professionals who want to meet their customers’ needs directly and effectively.

This thesis concerns selective attention in the context of the Stroop task (identify the colour) and Reverse Stroop task (identify the word). When a person is asked to select and identify one dimension of a bidimensional stimulus (e. g. , the word RED printed in green) the typical finding is that the word influences colour identification (i. e. , the Stroop effect) but the colour does not influence word identification (i. e. , no Reverse Stroop effect). A major account of performance in these tasks posits that one dimension interferes with the other only when a translation occurs (e. g. , Roelofs, <i>Psychological Review, 2003</i>; Sugg & McDonald, <i>Journal of Experimental Psychology: Human Perception & Performance, 1994</i>; Virzi & Egeth, <i>Memory & Cognition, 1985</i>). This translation assumption is implicit in virtually all work in the field. The first part of this thesis completely undermines the translation assumption. In a series of four experiments (two unique paradigms), I demonstrate that interference from the colour in a Reverse Stroop task occurs in the absence of a translation. The second part of this thesis contains two additional experiments designed to discriminate between translation effects and response conflict effects. The results of these experiments confirm that a translation was not required because no stimulus conflict effect, the most likely locus of a translation effect, was observed. However, response conflict effects were observed. The third part of this thesis implements a computational model based on the principle that the strength of association (Cohen, Dunbar, & McClelland, <i>Psychological Review, 1990</i>) between a specific stimulus and its response (Logan, </i>Psychological Review, 1988</i>) is important in determining the influence of the irrelevant dimension. This model has no translation mechanism. A final experiment was conducted to test this model; the model accounted for over 98% of the variance in RTs and 92% of the variance in interference and facilitation scores in both the Stroop and Reverse Stroop tasks independent of whether a translation was required.

An Information Theoretic approach is used for studying the effect of noise on various spiking neural systems. Detailed statistical analyses of neural behaviour under the influence of stochasticity are carried out and their results related to other work and also biological neural networks. The neurocomputational capabilities of the neural systems under study are put on an absolute scale. This approach was also used in order to develop an optimisation framework. A proof-of-concept algorithm is designed, based on information theory and the coding fraction, which optimises noise through maximising information throughput. The algorithm is applied with success to a single neuron and then generalised to an entire neural population with various structural characteristics (feedforward, lateral, recurrent connections). It is shown that there are certain positive and persistent phenomena due to noise in spiking neural networks and that these phenomena can be observed even under simplified conditions and therefore exploited. The transition is made from detailed and computationally expensive tools to efficient approximations. These phenomena are shown to be persistent and exploitable under a variety of circumstances. The results of this work provide evidence that noise can be optimised online in both single neurons and neural populations of varying structures.

The present study compared the effects of an errorless stimulus shaping procedure to an errorful fluency based procedure for teaching difficult letter sound discriminations using a counterbalanced multielement experimental design. For 2 participants, letters fsteai were taught using the errorless procedure and letters bpdvou were taught using the errorful procedure. For the other 2 participants the conditions were reversed. All participants had considerably fewer errors and fewer trials to criterion with the errorless than with the errorful procedure. Tests of retention and generalization indicate that the errorful procedure generalized and was retained at a higher frequency than the errorless procedure. For 3 participants preference for the errorless procedure over the errorful procedure was demonstrated; whereas, the fourth participant demonstrated preference for the errorful procedure.

L’hypothèse neurodéveloppementale de la schizophrénie suggère, entre autres, que l’inflammation prénatale sensibilise le cerveau en développement à une atteinte subséquente durant le jeune âge, augmentant le risque de développer la maladie. Pour mieux comprendre la pathophysiologie de la maladie, nous avons développé un modèle à double atteinte basé sur l’activation immunitaire gestationnelle au polyIC (PIC) suivie d’un stress de contention à l’âge juvénile chez la souris. Un effet additif est observé sur le déficit de l’inhibition du réflexe de sursaut par stimulus sonore (IPP), accompagné d’anomalies oxydatives, dopaminergiques et GABAergiques dans le cortex préfrontal (PFC) et le striatum, chez les souris exposées aux deux atteintes dès l’âge juvénile. À notre connaissance, il s’agit du premier modèle à double atteinte démontrant un déficit de l’IPP dès l’âge pubertaire. De plus, l’acide lipoïque, un antioxydant, prévient les déficits d’IPP et les anomalies neurochimiques du PFC, supportant ainsi l’implication du stress oxydatif dans la schizophrénie et suggérant que les déficits d’IPP sont associés à des anomalies du PFC. Ce modèle aidera à étudier de nouvelles alternatives thérapeutiques pour le traitement de la schizophénie, spécialement durant la phase prodromale. Sur un autre ordre d’idée, un taux élevé de mortalité par suicide existe chez les patients schizophrènes et les mécanismes pathophysiologiques de ce phénomène demeurent peu compris. Un deuxième modèle à double atteinte a été développé, présentant des comportements associés au risque suicidaire (agressivité, impulsivité, anxiété et perte d’espoir), via le polyIC prénatal suivi de l’isolement social dès le sevrage des souriceaux. Les deux atteintes interagissent pour induire plusieurs comportements de type schizophrénique et associés au risque suicidaire chez les mâles. Le chlorure de lithium, connu pour ses effets de « prévention du suicide » dans la population générale, améliore les composantes comportementales chez les animaux isolés seulement, alors que la clozapine, l’antipsychotique avec le meilleur effet de « prévention du suicide », prévient les anomalies comportementales principalement dans le modèle à double atteinte. Les effets distincts des deux molécules suggèrent que les souris exposées aux deux atteintes modélisent un phénotype distinct de celui des souris seulement isolées. Comme le diagnostic du risque suicidaire chez les patients schizophrènes demeure un défi pour les psychiatres, notre modèle in vivo aidera à mieux comprendre les mécanismes impliqués dans le comportement suicidaire chez ces patients, favorisant ainsi le développement de nouveaux traitements pour cette population vulnérable.

The experimenter asked if documented equivalence class membership would influence the development of shared discriminative stimulus function established through simple successive discrimination training. In Experiment 1, equivalence classes were established with two sets of 9 stimuli. Common stimulus functions were then trained within or across the equivalence classes. Greater acquisition rates of the simple discriminations with stimuli drawn from within the equivalence classes were observed. In Experiment 2, a third stimulus set was added with which no equivalence relations were explicitly trained. The findings of Experiment 1 were replicated, but the Set 3 results were inconsistent across subjects. The outcomes of the two experiments demonstrate that equivalence classes have an effect on other behavioral relations which requires further investigation.

The present study sought to investigate the combined influences of degree of first-list learning, stimulus order, emphasis, and meaningfulness on the selection strategies of college subjects.