1 2 Fractionation of the Visuomotor Feedback Response to 3 Directions of Movement and Perturbation

36 Recent studies have highlighted the modulation and control of feedback gains as support 37 for optimal feedback control. While many experiments contrast feedback gains across 38 different environments, only a few have demonstrated the appropriate modulation of 39 feedback gains from one movement to the next. Here we extend previous work by 40 examining whether different visuomotor feedback gains can be learned for different 41 directions of movement or perturbation directions in the same posture. To do this we 42 measure visuomotor responses (involuntary motor responses to shifts in the visual 43 feedback of the hand) during reaching movements. Previous work has demonstrated that 44 these feedback responses can be modulated depending on the statistical distributions of 45 the environment. Specifically, feedback gains were up-regulated for task-relevant 46 environments and down-regulated for task-irrelevant environments. Using these two 47 statistical distributions, the first experiment examined whether these feedback responses 48 could be independently modulated for the same limb posture for two directions of 49 movement (same limb posture but on either an inward or outward movement), while the 50 second examined whether the feedback responses could modulate, within a single 51 movement, to perturbations to the left or right of the reach. Both experiments 52 demonstrated that visuomotor feedback responses could be learned independently such 53 that the response was appropriate for the environment. This work demonstrates that 54 feedback gains can be simultaneously tuned (up-regulated and down-regulated) 55 depending on the state of the body and the environment. The results indicate the degree to 56 which feedback responses can be fractionated in order to adapt to the world. 57