Dynamics of Learning in the Open Loop VOR

We present our preliminary results on motor adaptation of the angular vestibulo-ocular reflex (aVOR) in response to passive impulsive head rotations at constant acceleration (460 deg/s2). Human healthy subjects were repeatedly subjected to a 20 degrees yaw rotation (using a rotating chair) while they tried to maintain fixation on a visual target. We used an incremental velocity error signal in which target moved partially with the head, during rotations, causing adaptation of the initial eye velocity. We analyzed only the first 100 msec of the aVOR, i.e. the open loop portion of the response. In order to better understand the multiple-timescales dynamics of motor learning subjects were adapted to a aVOR gain reduction period followed by a shorter reverse adaptation block of trials, and a subsequent no-error feedback period which caused a recovery toward the initially adapted state. Adaptation mechanisms have been successfully described using a two hidden states model, in which a fast state learns quickly from motor error, but has poor retention, and a slow state that learns slowly but has a stronger retention. We modeled our data using such two-states model finding an underestimation of the spontaneous recovery trend.