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published_or_final_version / Psychology / Doctoral / Doctor of Philosophy

published_or_final_version / Psychology / Master / Master of Philosophy

Eight experiments are described exploring the consequences of training eye-movements. Training is related to Findlay & Walker’s (1999) model of saccade generation, and consists of strategies for visual search and stimulus discrimination. These two components are separated in an effort to link training to the hypothesised Move and Fixate centres, respectively, within Findlay & Walker’s framework. Training directed towards the Move centre thus consistently improved visual search, and in Experiments 1-4 it was also shown that training directed towards the Fixate centre could further improve performance (in terms of target response discrimination) in an additive way over Move Training alone. Experiments 5-7 investigated the idea that training which promotes activity in the Move centre, independently, may actually be detrimental. This hypothesis draws upon the reciprocal inhibitory relationship between the Move and Fixate centres described by Findlay & Walker: training people where to look may increase activity in the Move centre and consequently hinder information processing during fixational eye movements, owing to an associated diminution of activity in the Fixate centre. Partial support for this conclusion was found. When training encouraged saccades away from a task-relevant centrally located stimulus, towards a visible saccade target in the periphery, there was evidence of premature disengagement when fixating, causing sub-optimal processing of the central stimulus in the first instance (Exp. 5). However, this effect was sensitive to changes in task (Exps. 6 & 7). This may explain why Move training did not encumber performance in a driving task (Exp. 8). Nevertheless, the findings reported herein have implications for training eye-movements in applied settings, because they suggest combined eye movement training directed towards the Move and Fixate centres in concert may produce cumulative performance gains, and offset detection failures associated with a sole emphasis on visual scanning.

The auditory system needs to be able to analyse complex acoustic waveforms. Many ecologically relevant sounds, for example speech and animal calls, vary over time. This thesis investigates how the auditory system processes sounds that occur sequentially. The focus is on how the responses of neurons in the primary auditory cortex ‘adapt’ when there are two or more tones. When two sounds are presented in quick succession, the neural response to the second sound can decrease relative to when it is presented alone. Previous two-tone experiments have not determined whether the frequency tuning of cortical suppression was determined by the receptive field of the neuron or the exact relationship between the frequencies of the two tones. In the first experiment, it is shown that forward suppression does depend on the relationship between the two tones. This confirmed that cortical forward suppression is ‘frequency specific’ at the shortest possible timescale. Sequences of interleaved tones with two different frequencies have been used to investigate the perceptual grouping of sequential sounds. A neural correlate of this auditory streaming has been demonstrated in awake monkeys, birds and bats. The second experiment investigates the responses of neurons in the primary auditory cortex of anaesthetised guinea pigs to alternating tone sequences. The responses are generally consistent with awake recordings, though adaptation was more rapid and at fast rates, responses were often poorly synchronised to the tones. In the third experiment, the way in which responses to tone sequences build up is investigated by varying the number of tones that are presented before a probe tone. The suppression that is observed is again strongest when the frequency of the two tones is similar. However, the frequencies to which a neuron preferentially responds remain irrespective of the frequency and number of preceding tones. This implies that through frequency specific adaptation neurons become more selective to their preferred stimuli in the presence of a preceding stimulus.

Prior clinical studies have documented that high blood pressure is one of the prominent risk factors leading to cerebrovascular disease and subsequent cognitive impairment. The present study aims to examine the relationship between blood pressure and brain and cognitive function in a community sample. This study recruited 41 elderly persons aged 60–70. Multiple imaging modalities were adopted to assess white matter microstructure, regional brain volume, and resting-state neural activity while a set of neuropsychological tests was used to assess cognitive function. With blood pressure measured at clinical interview, correlation and regression analyses were performed. Results showed reduced white matter integrity with increased systolic blood pressure in the splenium of the corpus callosum and inferior longitudinal fasciculus in the absence of change in brain volume or neural activity. Also, increased systolic blood pressure was found to be correlated with poorer cognitive performance in information processing speed. The results held significant after controlling age, sex, and education. These observations of the subclinical sample suggest that high blood pressure relates to subtle changes in the brain and cognitive deficits. Blood pressure control, as a relatively modifiable factor, should be taken seriously in community-dwelling elderly. / published_or_final_version / Clinical Psychology / Doctoral / Doctor of Psychology

No description available.

No description available.

No description available.

No description available.