In a first experiment, the authors found that eye velocity during pursuit initiation was higher for a target associated with a larger reward. This finding is in line with the results obtained for saccadic eye movements, i.e. larger reward elicits faster eye movements (Takikawa et al. 2002).
Finally, the influence of reward on smooth pursuit learning was also investigated. In smooth pursuit experiment, learning is induced by a change in target direction 250ms after target motion onset. After a few trials, the eyes start to move in the new direction before the target does. Learning appeared to be faster and larger when the large reward target was presented compared to the small reward target.
One way to probe the learning is to suddenly remove the change in target direction in order to observe the predictive motor response (catch trials). If the amount of reward influenced the learning, one would expect that the response in probe trials with similar reward would depend on the amount of reward in learning trials (reward in probe and learning trials could vary independently). In the probe trials, the response only depended on the reward at the end of those trials, not whether the learning took place with a small or large reward target. This suggest that the amount of learning was not influenced by the reward size during the learning.
All in all, this paper highlights the differential role that reward can have on motor behavior. It largely biases target selection while it has a minor influence on motor behavior and motor learning.
Shadmehr, R., Orban de Xivry, J.-J., Xu-Wilson, M., & Shih, T.-Y. (2010). Temporal Discounting of Reward and the Cost of Time in Motor Control. Journal of Neuroscience, 30(31), 10507-10516. doi:10.1523/JNEUROSCI.1343-10.2010
Joshua, M., & Lisberger, S. G. (2012). Reward Action in the Initiation of Smooth Pursuit Eye Movements. Journal of Neuroscience, 32(8), 2856-2867. doi:10.1523/JNEUROSCI.4676-11.2012
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