Influence of the inter-reach-interval on motor learning.

Previous studies have demonstrated changes in motor memories with the passage of time on the order of hours. We sought to further this work by determining the influence that time on the order of seconds has on motor learning by changing the duration between successive reaches (inter-reach-interval (IRI)). Human subjects made reaching movements to visual targets while holding onto a robotic manipulandum that presented a viscous curl field. We tested four experimental groups that differed with respect to the IRI (0.5, 5, 10 or 20 s). The 0.5 s IRI group performed significantly worse with respect to a learning index than the other groups over the first set of 192 reaches. Each group demonstrated significant learning during the first set. There was no significant difference with respect to the learning index between the 5, 10 and 20 s IRI groups. During the second and third set of 192 reaches the 0.5 s IRI group's performance became indistinguishable from the other groups indicating that with continued training the initial deficit in performance could be overcome.