Priors Engaged in Long-Latency Responses to Mechanical Perturbations Suggest a Rapid Update in State Estimation
Figure 4
A: Average elbow motion from one exemplar subject when step perturbations were expected (top) and when ramp-profiles were presented in blocked manner (bottom). Displays use the same color code as in Figure 3 B. The three black traces correspond to 1 Nm, 2 Nm and 3 Nm step-torques. The vertical black dashed line is the reversal time averaged across responses to all step-torque perturbations. Blue and red dashed lines represent the reversal times of ramp-up and ramp-down perturbations. The inset shows the initial elbow displacement for the different perturbation profiles and magnitude (average ± SD across subjects). The gray rectangle emphasizes that the initial joint displacement across ramp-up (down) perturbations and the 1 Nm (3 Nm) step were similar for the first ∼10 ms. B: Same as A from the model simulations. C: Timing of the corrective response measured in joint coordinates based on the elbow reversal time (TE, black) and in Cartesian coordinate based on the first hand speed minimum (TH, gray) for each perturbation profile (1, 2 and 3 Nm step torques; RD, ramp-down; RU, ramp-up; mean ± SD across subject). Orange dots represent the joint reversal time computed from model simulation. Times were measured for each subject and simulations relative to the mean across responses to the step torque perturbations. Single (double) star(s) indicate significant differences at the level P<0.05 (P<0.01). D: Effect of context on the timing of the corrective response for the ramp-down and ramp-up torque profiles with the same color code as in panel A.