Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 89-93).

Thesis (M.S.)--University of Wisconsin--Madison, 1971. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 41-44). Also available on the Internet.

Thesis (M. Sc.)--University of Hong Kong, 2005.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

This thesis examines the effects of secondary tasks and click trains upon temporal judgement in the context of a Pacemaker-Gate-Counter (PGC) model. All the timing experiments reported employ a paradigm in which subjects are first trained to reliably reproduce a 2.5 s target interval, and are then required to perform time production with a concurrent secondary task. Previous research with digit memory loads has shown that varying memory load had no impact upon concurrent time production (Fortin & Breton, 1995; Fortin & Masse, 1999). Here, it is shown that increasing pitch memory load lengthens time production, but that this is not the case for a colour memory task, or a timbre memory task. The effect obtained with pitch is replicated, and it is demonstrated that the effect is directly due to the processing requirements of retaining pitch information. Furthermore, the pitch effect is not due to a difference in attentional requirements between retaining pitch and retaining digits. Finally, it is shown that the lengthening of time production also occurs when a concurrent duration memory load is increased. In confirmation of previous research (e.g. Fortin, Rousseau, Bourque, & Kirouac 1993), it is shown that when memory-search is performed concurrently with time production, increasing the number of items to be searched causes a lengthening of time production. A novel finding is that the increase in mean time produced is not accompanied by an increase in standard deviation. Furthermore, it is shown that the shortening of mean time production caused by concurrent click trains does not interact with the increase caused by concurrent memory search, and is accompanied by a reduction in standard deviation. These findings are taken to support the separation made in the PGC model between the Pacemaker and Gate components. Overall, the data presented in this thesis provide a number of constraints upon future theorising within the framework of the PGC model and other similar models.

Tese (doutorado)—Universidade de Brasília, Instituto de Ciências Biológicas, Programa de Pós-Graduação em Biologia Animal, 2008. / Submitted by Jaqueline Oliveira (jaqueoliveiram@gmail.com) on 2008-11-06T18:15:15Z No. of bitstreams: 2 TESE_2008_DenisePradoAlvarenga_anexos.pdf: 4956925 bytes, checksum: 0ea693ab71cf1ad447c9a5c50bccb7f8 (MD5) TESE_2008_DenisePradoAlvarenga.pdf: 2200854 bytes, checksum: 84ddec2d50b9ddbd892dccbd71453358 (MD5) / Approved for entry into archive by Georgia Fernandes(georgia@bce.unb.br) on 2009-01-28T11:18:22Z (GMT) No. of bitstreams: 2 TESE_2008_DenisePradoAlvarenga_anexos.pdf: 4956925 bytes, checksum: 0ea693ab71cf1ad447c9a5c50bccb7f8 (MD5) TESE_2008_DenisePradoAlvarenga.pdf: 2200854 bytes, checksum: 84ddec2d50b9ddbd892dccbd71453358 (MD5) / Made available in DSpace on 2009-01-28T11:18:22Z (GMT). No. of bitstreams: 2 TESE_2008_DenisePradoAlvarenga_anexos.pdf: 4956925 bytes, checksum: 0ea693ab71cf1ad447c9a5c50bccb7f8 (MD5) TESE_2008_DenisePradoAlvarenga.pdf: 2200854 bytes, checksum: 84ddec2d50b9ddbd892dccbd71453358 (MD5) / OBJETIVO: Estudar preenchimento perceptual de lesão retínica produzida por corioretinite. Embora exista área de escotoma com déficit de impulsos visuais, pacientes com tais lesões percebem o campo visual de forma ininterrupta, sugerindo a existência de fenômeno de preenchimento perceptual nessas regiões danificadas pela corioretinite. MÉTODOS: Foram selecionados 14 pacientes com lesão retínica monocular, extra-macular e cicatrizada, cuja exata localização foi determinada por campimetria computadorizada. Os experimentos utilizaram um programa de computador, que gerava um estímulo cinza (1° x 1° e 33cd/m² de luminância), numa área cinza homogênea ao redor, com luminância de 28 cd/m². Os testes foram realizados monocularmente. Experimento 1- escotoma artificial foi programado para ser projetado na borda da lesão e em dois outros pontos de mesma excentricidade e normais. Experimento 2- escotoma artificial foi programado para ser projetado na área correspondente à lesão no olho contralateral e em dois outros pontos controles. Nesse experimento todos os pacientes foram classificados em três subgrupos, de acordo com a posição do estímulo na retina em: central, nasal superior a 15° de excentricidade e temporal superior a 15° de excentricidade. Cada posição foi testada 36 vezes. O protocolo foi aprovado pelo Comitê de Ética em pesquisa da Universidade de Brasília e todos os pacientes assinaram o Termo de Consentimento Livre e Esclarecido. RESULTADOS: Experimento 1 – Não houve diferenças significativas entre as médias de latências de preenchimento (p>0,05). Experimento 2 – As latências de preenchimento das áreas correspondentes à lesão foram inferiores às das áreas controle (p<0,05). A diferença entre o estímulo central e temporal superior a 15° de excentricidade foi significativa (p<0,05), porém entre o estímulo central e nasal superior a 15° de excentricidade não foi significativa (p>0,05). Na comparação de ambos os experimentos, houve diferença significativa entre as médias de latências de preenchimento para o estímulo posicionado nas áreas correspondente à lesão e nas bordas da lesão. CONCLUSÕES: (i) As alterações neuronais ocorridas nas bordas das lesões influenciaram o preenchimento perceptual dentro da área do escotoma; (ii) O preenchimento perceptual é facilitado na área correspondente à lesão retínica; (iii). Os mecanismos neuronais envolvidos na facilitação devem ser semelhantes aos descritos para a deaferenciação do córtex somatosensorial; (iv) A assimetria da representação das colunas de dominância ocular no córtex cerebral contribuiu para aumentar as latências de preenchimento perceptual de escotoma artificial projetado no córtex contralateral, em relação ao projetado no córtex ipsilateral; (v) Os resultados sugerem a existência: de mecanismos de interpolação neuronal na reorganização do mapa retinotópico cortical e de fatores cognitivos, como a atenção, ambos envolvidos no processo de preenchimento perceptual de escotomas adquiridos. _______________________________________________________________________________ ABSTRACT / PURPOSE: To study the perceptual filling-in from retinochoroiditis scotoma in 14 patients. Although with visual inputs deficit, patients with such as chronic lesions perceive the visual field uninterrupted, suggesting completion of the damaged regions by perceptual filling-in process. METHODS: The exact localization of the lesions was determined by standard automated perimetry. In the experiments, the target and surround stimulus were grey; the surround area with a luminance of 28 cd/m², target with 33 cd/m². The target was a 1° square patch. Experiment 1 - Artificial scotomas were programmed to be projected just outside the edge of retinal lesion and at two another equidistant points, in the visual field of the same eye. Experiment 2 - targets were projected inside the scotoma corresponding area in the fellow eye, and at two control points. In this experiment, patients were classified in three groups, according to the tested retina: central; nasal beyond 15 degrees; temporal beyond 15 degrees of excentricity. Each position was tested 36 times. All subjects gave their informed consent and the Brasília University's Human Research Ethics Committee has approved this protocol. RESULTS: Experiment 1 - There was no significant difference in perceptual filling-in latencies (p>0.05). Experiment 2 – There was faster perceptual filling-in latencies (p<0.05) at the scotoma corresponding area than at the control points. Although the difference between central and temporal targets beyond 15 degrees was significant (p<0.05): the difference between central and nasal targets beyond 15 degrees was not significant (p>0.05). Comparing the experiments, there was significant difference in perceptual filling-in latencies at the scotoma corresponding area and at the edge of lesion (p<0,05). CONCLUSIONS: Any neuronal changes occurring at the edge of the lesion only affected filling-in within the scotoma area; perceptual filling-in is facilitated at the corresponding area of retinal scotomas; the neural mechanisms of this visual facilitation might be similar to those found following somatosensory cortex partial deafferentation. The ocular dominance cortex column asymmetry of peripheral retina added with partial cortical deafferentation contributes to longer filling-in latency of targets projected into contralateral cortex when compared to ipsilateral cortex; the data combined show that there is strong evidence for interpolation in retinopically organized areas . It is likely that cognitive factors such as attention are involved in the perceptual filling-in of acquired scotomas.

Understanding of visual scenes takes place within very brief episodes known as fixations. To explore the extent of the scene, the eye shifts between fixation locations at intervals of roughly 300 ms. Currently, it is a matter of open inquiry as to what factors influence the timing of these movements. This thesis focuses on understanding the mechanisms that govern the rapid adjustment of fixation and saccade timings when novel stimulus information is encountered during a fixation. In part I, I use an experimental technique known as the fixation-contingent scene quality paradigm to control the quality of incoming visual scene information. This approach is used to assess how fixation timing adapts to moment-by-moment changes in the quality level of the stimulus. I find that quality changes tend to result in an increase in fixation durations and this occurs whether the quality is increased or decreased. Using distributional analytic techniques, I argue that these results reflect the combined influence of a rapid surprise related process and a slower acting encoding related influence. In part II, I study how fixation durations are influenced by the underlying saccade programming mechanisms. An important assumption within the eye-movement control literature is that there exists a threshold called the point-of-no-return. Once this point has been reached, a saccade may no longer be modified or cancelled. I adapt a classic psychophysical technique known as the double-step procedure to study the point-of-no-return within scene viewing tasks. I also provide a measurement of the saccadic dead time, the last point in time that a saccade may be modified. In Part III, a formal model of fixation durations in high-level tasks is presented. I build on recent modelling work and develop a formal account for the early-surprise late-encoding modulation account of fixation durations in scene viewing tasks. The model is tested against data observed in Part I of the thesis. I demonstrate that the model does a very good job of predicting these distributions with relatively few assumptions. In summary, I use experimental techniques in combination with computational modelling to reveal how a composite of low-level (saccade programming) and high-level (information processing) considerations can, and must, be taken into consideration when understanding eye-movement control behaviour in scene viewing tasks.

Hallucinations are often considered a sign of psychotic illness, but are also common in other diagnostic groups and individuals without mental health problems. This thesis uses Perceptual Control Theory (PCT), a cybernetic model which explains behaviour and cognition in terms of control processes regulating ongoing perception according to internally represented goals, as a theoretical framework to understand hallucinations. First, a theoretical/conceptual paper (Paper 1) examines how PCT provides an integrated account of (i) the mechanisms responsible for the formation of hallucinations, (ii) their phenomenological heterogeneity, (iii) the interaction between these mechanisms and environmental factors that might contribute to the formation of hallucinations, and (iv) the processes leading to different affective reactions to hallucinatory experiences (e.g. distress). The main implications of this model are discussed in the context of pertinent theoretical and empirical literature, and relevant clinical and research implications are considered. Second, this thesis includes an empirical investigation (Paper 2) examining two PCT-informed hypotheses in a cross-section of 22 clinical and 18 non-clinical individuals with auditory verbal hallucinations (“hearing voices”), namely (i) that the content of voices will be thematically linked to the participants’ personal goals, and (ii) that affective reactions to voices will depend on the extent to which voices facilitate and/or interfere with important personal goals. The analysis revealed that 82.5% of participants reported voices that thematically matched at least one of their reported goals. As predicted, affective reactions to voices were strongly associated with measures of interference and facilitation of goals, even when controlling for important covariates (e.g. participants’ history of mental health difficulties; voices’ content, frequency and duration).Finally, a critical evaluation is provided (Paper 3), where the methodological strengths and limitations of the work presented in the present thesis are discussed with the aim to reflect on the research process, and inform future investigations into the topics considered in this thesis.