| Possible right hemisphere dominance for the performance of visuospatial tasks has been the subject of a number of investigations. However, results have not been consistent across studies. These studies have varied in the form of the stimuli used as well as the amount of practice subjects receive. In this study, we investigated the effects of the form of the task as well as the effects of practice on any possible asymmetry of activation. To do this, we used event-related functional magnetic resonance imaging (fMRI), which allows individual task trials to be separated and analyzed individually or grouped with similar trials. In order to reduce the effects of inaccurate modeling of expected responses, we used a data-driven analysis technique called independent component analysis (ICA). ICA separates independent sources within a mixed signal, such as found in fMRI images. We first confirmed that ICA is able to determine task-related components in fMRI data when task trials are isolated and grouped based on similar characteristics. This technique was then applied to MRI results from subjects who performed a series of visuospatial tasks that varied in dimensionality and difficulty. Two groups of subjects were studied. The first group was not given any practice before the imaging session. The second group first underwent a practice session in order to become familiar with the tasks. Results show that the form of the task and amount of practice affect the patterns of activation. Dissociations in active regions of the brain were seen for the dimensionality and amount of mental manipulation in the tasks. A right hemisphere dominance was seen in the superior parietal and frontal regions for all tasks, but measures of laterality did not show significant shifts to the right. Our results indicate that the type of task used and the subject's familiarity with the stimuli can affect the amount of asymmetric activation in the brain for visuospatial tasks. |
