The work in our lab focuses on how action is represented in brain. To produce any simple response, a vast array of information must be specified, including the timing in magnitude of the activation of multiple sets of muscles. Yet when we choose an action, these concerns are often invisible to us, and we are only aware of the goal-states.
We have examined this topic using a range of tasks and experimental techniques. We have looked at sequence learning tasks in which individuals produce series of responses, often despite being unaware that there is a sequence. Behaviorally, we have shown that people can encode sequences of abstract goals and that this knowledge can transfer to performance under conditions in which a completely different set of movements is required. We have also looked at neural activation during the task using PET and fMRI and found that a system of regions increases activation during motor learning. This system changes depending on whether the learning takes place under single-task conditions, when explicit awareness of the sequence often occurs, or dual-task conditions, when people seldom report becoming aware of the sequence.
A second line of study involves the production of bimanual movements. In many cases, it is very difficult to move the two hands to accomplish distinct goals. For example, there is the classic task of patting your head and rubbing your stomach, which often gives people trouble (at least the first 2 or 3 times). In other cases, such as when we eat with a knife and fork, or tie our shoes, the two hands move differently, in a coordinated fashion, and we do not notice any crosstalk or interference. What makes bimanual movement hard? It does not seem to relate to the movements themselves, but instead it seems to stem from some sort of conflict between goals.
To examine these phenomena further, we ask subjects to perform bimanual movements, using different stimuli and different S-R mappings. Our results show that it is neither the movements nor the stimuli themselves that cause bimanual interference but conflict between S-R mapping rules. We are striving to link this work with our ongoing dual-task work. Although the two topics are usually studied seperately, our findings suggest a possibly important similarity. Interference between simultaneously performed actions does not result from input or output properties considered in isolation. Rather, the limitations appear to be central and abstract.
Diedrichsen, J., Grafton, S. T., Albert, N., Hazeltine, E., & Ivry, R. B. (2006). Goal-selection and movement-related conflict during bimanual reaching movements. Cerebral Cortex.
Hazeltine, E. (2005). Response-response compatibility during bimanual movements: Evidence for the conceptual coding of action.
Diedrichsen, J., Ivry, R. B. , Hazeltine, E., Kennerley, S., & Cohen, A. (2003). Bimanual interference associated with the selection of target locations. Journal of Experimental Psychology: Human Perception and Performance, 29, 64-77.
Kennerley, S., Diedrichsen, J., Hazeltine, E., Semjen, A., & Ivry, R. B. (2002). Callosotomy patients exhibit temporal uncoupling during continuous bimanual movements. Nature Neuroscience, 5, 376-381.
Diedrichsen, J., Hazeltine, E., Kennerley, S. & Ivry, R. B. (2001). Absence of bimanual interference during directly-cued actions. Psychological Science, 12, 493-498.
Jorn Diedrichsen studies bimanual interference and motor learning.
Rich Ivry and his lab study motor control using a wide range of experimental techniques and behavioral tasks.
David Rosenbaum investigates timing and motor planning using a variety of ingenious behavioral tasks.
Reza Shadmehr has pioneered force field learning tasks to uncover important clues about how motor programs are acquired and consolidated.
Dan Willingham studies sequence learning using the serial reaction time task to learn how actions are represented.
