Abstract

This doctoral thesis employed a psychophysical approach to investigate the relationship between goal-directed eye and hand movements, visual attention, and visual working memory. To establish a solid methodological basis for investigating visual attention, the first study compared the strengths and weaknesses of a set of discrimination stimuli frequently used in attention research (Chapter 2.1). Based on the results, we used a novel pink noise stimulus for approaching the following research questions concerning visual attention. In the second study, we investigated the dependence of attentional orienting on oculomotor programming (Chapter 2.2). Motivated by the claim that attention can only be allocated to locations reachable by saccadic eye movements, we measured visual sensitivity – a proxy for visual attention – within and beyond the oculomotor range using an eye abduction paradigm. Contrary to previous findings, we found that attention can be shifted without restriction to locations to which saccades cannot be executed, ruling out the necessity to program a saccadic eye movement as a prerequisite for spatial attention. The third study attempted to resolve the longstanding debate as to whether eye and hand movement targets are selected by a single attentional mechanism or by independent, effector-specific systems (Chapter 2.3). Results revealed that during simultaneous eye and hand movements, attention – an index of motor target selection – was allocated in parallel to the saccade and the reach targets. Motor target selection mechanisms moreover did not compete for attentional resources at any time during movement preparation, demonstrating that separate, effector-specific mechanisms attentionally select eye and hand movement targets. The fourth study tested the assumption of effector-specific selection mechanisms in the framework of visual working memory (Chapter 2.4). Participants memorized several locations and performed eye, hand, or simultaneous eye-hand movements during the maintenance interval. When participants performed an eye and a hand movement simultaneously to distinct locations, memory at both motor targets was enhanced with no tradeoff between the two. This suggests that the two effector systems improve working memory at their selected motor targets independently. In the final study, we dissociated the relative contributions of the two highly interdependent parameters, task relevance and oculomotor selection, to the memory benefits consistently observed at eye movement targets (Chapter 2.5). Participants memorized shapes while simultaneously either avoiding or selecting a specific location as a delayed saccade target. While oculomotor selection was consistently associated with an increased working memory performance, mere task relevance was not, indicating that the frequently reported memory benefits for task-relevant items might, in fact, be caused by oculomotor selection. In summary, goal-directed eye and hand movements selectively boost the visual processing of the currently most relevant information, and likewise bias our memory capacities according to behavioral priority. The observed motor-induced enhancements in both the attention and working memory domains appear to be independent and effector-specific, allowing for the most flexible assignment of our limited cognitive resources as we traverse through our crowded environment.