Task-dependent modulation of aftereffects during visuomotor adaptation

Introduction Implicit motor adaptation is widely described as having a fixed ceiling of 12–15° that does not scale with perturbation size when explicit strategies are suppressed. We examined how this ceiling changes when participants experience two different visuomotor rotation magnitudes (24° and 48°) under gradual versus error-clamped schedules.

Methods Forty-one participants adapted to 24° and 48° rotations in counterbalanced order across two sessions. Perturbations were introduced either gradually (stepped increments designed to minimize the awareness of the visuomotor perturbation) or via error-clamp (constant clamped feedback that eliminates explicit aiming). Immediate aftereffects were measured during the first four no-feedback trials after each exposure.

Results In the gradual groups, aftereffects scaled strongly with the perturbation size (first exposure: 12.7° after 24° vs. 24.8° after 48°, t(19)=6.06, p<0.001; second exposure: 24.4° vs. 16.3°). In the error-clamped groups, aftereffects remained ∼11–14° regardless of whether participants had just experienced a 24° or 48° clamp (all ps>0.18).

Conclusions When visuomotor adaptation occurs gradually, implicit aftereffects are flexibly modulated based on the rotation size. When the adaptation occurs under the error-clamped condition, aftereffects are fixed at approximately 13° irrespective of the rotation size. These results indicate that the “fixed ceiling” effect known to follow implicit adaptation may be task dependent.