Targeting is a skill that involves the accurate projection of an object to a target; this requires accurate integration of visual information with spatial and motor skills. Targeting tasks demonstrate a consistent male advantage. Contrary to popular belief, this male advantage is not accounted for by participants throwing experience or their size. The factors that mediate or account for the sex difference observed in targeting accuracy have not yet been identified. This dissertation addresses issues following from two prominent theories that attempt to explain this sex difference. The first theory proposes that the male advantage on targeting accuracy is due to the tasks proxemic and/or motoric characteristics, whereas the second theory proposes that the sex difference in targeting accuracy is due to differential exposure to androgenic or estrogenic sex hormone concentrations. The first and second studies in this dissertation follow from the first theory, examining whether changing the motoric or proxemic characteristics of targeting tasks will mediate the sex difference. The third study is related to the second theory; it examines the relations among direct and indirect measures of prenatal and circulating sex hormone concentrations and targeting accuracy within samples of men and women. Collectively the results from studies 1 and 2 indicate that the proxemic and motoric characteristics are related to the sex difference on targeting tasks; specifically, targeting tasks must involve only fine motor movements and be performed in intrapersonal space in order for the male advantage to be negated.<p>The results from study 3 indicate that men who were exposed to relatively high prenatal testosterone concentrations and continue to have relatively high circulating testosterone concentrations perform less accurately on targeting tasks than do all other groups of men. The results from study 3 also indicate that women exposed to relatively high prenatal testosterone concentrations target significantly more accurately than women that were exposed to relatively low prenatal testosterone concentrations. As well, the results showed that women who use oral contraceptives target significantly more accurately when they are not currently taking the exogenous estrogen supplements (menstrual phase) than when they are taking the supplements (midluteal phase). These results are discussed in light of the two prominent theories explaining the sex difference in targeting accuracy. A synthesized theory is proposed, and directions for future research are discussed.

Thèse--Faculté de médecine de Paris.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Randall M. Parker. Vita. Includes bibliographical references. Also available from UMI.

Thesis (Ph. D.) in Psychology--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 217-242).

Thesis (Psy. D.)--Indiana University of Pennsylvania. / Includes bibliographical references.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 104-121). Also available in print.

The ageing brain undergoes many structural changes. High resolution imaging with MRI has allowed visualisation and quantification of many aspects of this neurological degeneration. One particular feature of the ageing brain is the increased presence of hyperintensities. These can be clearly visualised with T2-weighted imaging. Manual scoring of these lesions is time consuming and prone to inter- and intra-observers variability. We developed automatic methods for quantification and classification of the hyperintensity volumes using T1-weighted and fluid attenuation inversion recovery images of Aberdeen Birth Cohort of 1936. The hyperintensities were classified into different brain regions given by the local Scheltens’ scale, i.e., grey matter, infratentorial, deep white matter and periventricular white matter. The automatically generated hyperintensity volumes were compared with the local scores and investigated in relation to respiratory function and smoking history. Ageing is also associated with cognitive decline. We investigated the role of the structural complexity of ageing brains in the life course changes of cognitive ability. We hypothesised that fractal descriptors of white matter would be associated with childhood IQ, suggesting early cognitive maturation, better fluid cognitive performance and less decline in late life. This was done using fractal measures of white matter structure. Our results show that the automatic quantification and classification methods provide a promising alternative to manual grading with strong correlations (p<.05). The automatic hyperintensity volumes broadly show the same pattern association as shown by the local scores when investigating with the respiratory function, and stronger correlations with daily cigarette consumption and smoking burden than did the local scores. The results of fractal measures of brain complexity demonstrate the potential of fractal measures as an estimate of structural maturation.

This thesis aimed to investigate the individual and combined effects of brain magnetic resonance imaging (MRI) markers of the two commonest age-related brain pathologies associated with dementia on longitudinal cognitive ability in normal ageing. Participants were 106 members of the Aberdeen 1921 Birth Cohort (ABC21), for whom childhood intelligence and serial measures of cognitive ability age 78-81 were available. Cerebrovascular disease was measured as white matter hyperintensities (WMH) at baseline (age 78-79) and over two successive time points; age 79-80 years and age 80-81 years using a visual scoring method. All participants had some WMH and these were most abundant in the frontal lobes. WMH increased in burden on followup and the greatest increase was seen in the parietal lobes, even allowing for participant drop-out, which was greater in those with more WMH at baseline. The effect of WMH on cognitive ability showed significant negative cross-sectional associations but there was no relationship between increase in WMH burden and longitudinal cognitive decline, either using linear regression analyses or latent growth curve modelling. Both WMH and childhood intelligence contribute significantly to late life fluid cognitive ability, but not to the trajectory of age-related change in fluid intelligence. Age was the strongest predictor of the cognitive trajectory from 78 to 81 years, even within the narrow age range of the ABC21 sample. Combined analysis of the influence of whole brain volume and WMH showed that the main predictor of dementia and death over 7 years follow-up of ABC21 was reduced viii brain fraction (< 73% of total brain volume normalised to intra-cranial volume). While WMH contributed to a diagnosis of dementia, they did not predict mortality. Comparison of manual and automated methods of hippocampal segmentation demonstrated that the automated method (FreeSurfer) systematically over-estimated volumes compared with a manual method (MRIcro) but that both methods were correlated. There were significant positive relationships between hippocampal volume and a variety of cognitive abilities, but these relationships were most significant for the left hippocampus. A final model of the influence of WMH (as a measure of cerebrovascular disease) and hippocampal volume (as a measure of Alzheimer‘s pathology) on lifelong cognitive change from age 11 to age 78 showed that both WMH and hippocampal volume had negative effects on late life fluid intelligence but that only the effect of hippocampal volume was significant. The conclusions of this work are that WMH are age-related and while they have a negative association with fluid intelligence, the main predictor of lifelong cognitive decline is hippocampal volume, an imaging marker of Alzheimer‘s pathology. The flowchart in next page is demonstrated a schematic summary of the thesis.

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