The Nervous System Uses Nonspecific Motor Learning in Response to Random Perturbations of Varying Nature

Abstract

We constantly make small errors during movement and use them to adapt our future movements. Movement experiments often probe this error-driven learning by perturbing movements and analyzing the after-effects. Past studies have applied perturbations of varying nature such as visual disturbances, position- or velocity-dependent forces and modified inertia properties of the limb. However, little is known about how the specific nature of a perturbation influences subsequent movements. For a single perturbation trial, the nature of a perturbation may be highly uncertain to the nervous system, given that it receives only noisy information. One hypothesis is that the nervous system can use this rough estimate to partially correct for the perturbation on the next trial. Alternatively, the nervous system could ignore uncertain information about the nature of the perturbation and resort to a nonspecific adaptation. To study how the brain estimates and responds to incomplete sensory information, we test these two hypotheses using a trial-by-trial adaptation experiment. On each trial, the nature of the perturbation was chosen from six distinct types, including a visuomotor rotation and different force fields. We observed that corrective forces aiming to oppose the perturbation in the following trial were independent of the nature of the perturbation. Our results suggest that the nervous system uses a nonspecific strategy when it has high uncertainty about the nature of perturbations during trial-by-trial learning.

Structural learning in feedforward and feedback control

“…Learning to learn has also been observed in motor tasks such as a visuomotor rotation task (Welch et al 1993) and a treadmill task (Mulavara et al 2009). Hence, such feature extraction may be a universal technique that the brain exploits to facilitate learning (Braun et al 2009b;Wolpert et al 2011).…”

Pushing attention to one side: Force field adaptation alters neural correlates of orienting and disengagement of spatial attention

“…The force profiles, velocity and kinematic profiles were resampled to 100 data points evenly spread in the y‐direction between movement start and the reach at target extent. For each participant, we subtracted the average baseline force profile from each channel trial to correct for pre‐existing biases in direction‐dependant forces (Stockinger, Focke, & Stein, ; Wei, Wert, & Körding, ). To characterise feedforward adaptation, we analysed the mean perpendicular force exerted against the channel wall divided by mean hand speed in the baseline‐corrected channel trial force profiles.…”

Saccadic adaptation to a systematically varying disturbance

“…First, we assessed whether the oculomotor system indeed showed a discernible and reproducible response that had structural features related to the disturbance. In fact, the system may respond in an unspecific way (e.g., Wei et al 2010), for example, fluctuating around the mean of the surreptitious target displacement generated by the disturbance. Second, in parameterizing and fitting the observed response-that, as we show, was related to the disturbance-we sought a sensitive and reliable estimation procedure to obtain its parameters without requiring several repetitions of the experimental runs.…”