Abstract/Summary

Multiple conflicting claims have been made about the function of the superior parietal lobule (SPL), but no consensus reached. This thesis investigates the functionality of the SPL by challenging existing attention shifting hypotheses and proposing an alternative visual separation hypothesis, in which the perception of changing distances between objects relative to each other is potentially supported in the SPL. Replicating Vandenberghe et al. (2001), activation was observed in the SPL for conditions containing a fixed and displacing element, and minimal activation in the conditions containing only fixed elements. However, a key condition consisting of attention shifts to a single displacing stimulus failed to activate the SPL, which was not compatible with the shifting spatial attention hypothesis. In contrast, the proposed visual separation hypothesis correctly predicted no significant activation in SPL because there was no perception of changing distances between elements. Although, for two conditions, the results could not be explained by this hypothesis: in these two conditions multiple objects displaced in unison and there were no changes in separation. It was proposed that the stimuli’s abrupt displacement to new locations might be responsible for these unexpected results by disrupting the natural occurrence of adaptation. This was further explored in experiment 2, where displacing stimuli comprising of multiple elements again activated the SPL whereas smoothly translating stimuli consisting of multiple elements did not, these results supported the visual separation hypothesis. Experiment 3 explored visual separation further by examining two components: interobject distance and visual angle. Using complex visual stimuli, results showed that the SPL is particularly sensitive to relative changes to interobject distance and visual angle. Finally, these experimental results and previous ones were overlaid on a SPL parcellation (Wang et al., 2015) showing that activation produced by perceiving visual separation was not concentrated in one subregion of SPL, but rather across multiple subregions.