Behavioral and physiological examination of spatial attention in visuomotor integration

Sensory motor integration is one of the most basic problems in cognitive neuroscience and the affect of attention on it is still largely unexplored. I will address this issue using spatial stimulus-response compatibility effects as a paradigm case. The occurrence of spatial stimulus-response compatibility effects is among the most robust, replicable findings in experimental psychology. Despite over 50 years of research, however, the extent of these effects and their neural bases remain to be completely characterized. This dissertation is a series of experiments designed to elucidate the circumstances under which spatial attention influences sensorimotor integration and the neural correlates of these effects. The methods employed include behavioral paradigms, hemodynamic (functional magnetic resonance imaging; fMRI) and physiological (transcranial magnetic stimulation; TMS) measures in normal subjects, as well as behavioral analyses in the split- and acallosal-brains.;Chapter 1 examined spatial attention in a lateralized simple reaction time paradigm aimed at measuring interhemispheric transfer time. Experiment 1 replicated the results of Anzola et al. (1977) demonstrating no effect of arms crossing on measures of interhemispheric transfer time, when varied between subjects. Experiment 2 demonstrated a significant effect of arms crossing on measures of interhemispheric transfer time, when arms position varied within subjects. Chapter 2 used the same paradigm to consider the role of the corpus callosum in mediating the spatial attention effects observed in chapter 1. Both the split- and acallosal-brain demonstrated the same effect of spatial attention as in normal subjects, indicating that the corpus callosum does not mediate this aspect of spatial attention in the intact brain. Chapter 3 used fMRI to examine the neural correlates of spatial compatibility effects revealing bilateral activations of the dorsal premotor and posterior parietal cortices. Chapter 4 used TMS to show the functional relevance of the posterior parietal cortex in mediating the spatial compatibility effects observed in chapter 3. The results indicate that the left superior parietal lobule is selectively involved in mediating compatible stimulus-response associations. Finally, chapter 5 used event-related fMRI to consider the neural correlates of yet another effect of attention on sensorimotor integration, namely, the neural coactivation that occurs during parallel processing of redundant sensory stimuli (divided attention) in simple reaction time. The results indicate a role for the inferior parietal lobule, a classical attentional area, in the case of bilateral, redundant visual targets that are processed very quickly.;Taken together, these findings (1) suggest that the influence of spatial attention is ubiquitous, occurring even in the simplest of experimental tasks, (2) suggest separate neural architectures for compatible and incompatible stimulus-response mappings and (3) highlight the different roles of the superior and inferior parietal lobules in mediating visuospatial and divided attention, respectively.