What is the effect of age in use-dependent learning?

• Angelica Suescun, Neuroscience, University of Delaware

• Jonathan Wood, Physical Therapy, University of Delaware

From sports training to rehabilitation, repetition is a core component of practice. However, the impact of aging on the ability to learn from repeated practice is unknown. Repeated practice biases future movements to be more like prior, repeated movements, a process called “use-dependent learning”. Use-dependent learning is driven by distinct cognitive processes: goal selection (choosing the movement’s objective) and movement trajectory selection (specifying movement direction or curvature). Repeated practice of a goal makes it more likely for that goal to be selected again (i.e., goal-selection bias). Repeated practice of a movement trajectory produces a bias such that subsequent trajectories appear more like recently repeated trajectories (i.e., trajectory-selection bias). We tested the impact of age on the goal- and trajectory-selection biases, individually. Three younger (Mean age = 20.0 years) and four older adults (57.3 years) performed reaching movements to various targets. To induce use-dependent learning, most reaches (84%) were made to a frequent target. Our measure of use-dependent learning was the reach direction to infrequent targets, which appeared randomly at either 45 or 90 degrees away from the frequent target. Use-dependent learning is greater when movements are more biased towards the repeated targets. We distinguished between goal- and trajectory-selection biases using a timed response paradigm: Participants were trained to initiate their reach on the last of 4 equally spaced auditory tones. After training, the targets appeared either 150ms or 500ms before the last tone. We assumed that less time to prepare a movement (150ms condition) prompts goal-selection biases, while more time (500ms condition) allows the trajectory-selection biases to emerge. Older adults displayed an increased goal-selection bias and decreased trajectory-selection bias relative to younger adults. If these results hold in a larger sample, it will imply that age impairs both goal selection and movement trajectory selection.