Structural learning is enhanced by increasing blocked repetition of visuomotor perturbations

Structural learning refers to the ability to extract and generalize the underlying structure of a set of perturbations-even when the specific perturbations vary from trial to trial. In visuomotor tasks, exposure to such variable but related perturbations has been shown to speed subsequent adaptation to a new, fixed perturbation. However, many center-out reaching studies present several repetitions of each perturbation-often cycling through a set of eight targets-before switching to the next one. This raises the question of whether these repeated exposures reduce the true variability that is thought to drive structural learning. To examine how the number of consecutive repetitions influences learning, we used a center-out reaching task with two targets and trained three groups with either two, four, or eight repetitions of a particular visual feedback rotation between ±90 degrees before presenting a new, pseudorandom rotation; a control group trained in a null field. We show that the different training regimes all facilitated adaptation in the subsequent fixed rotation testing compared to the control group, but a clear dose response was limited to the eight-repetition group who benefitted most, both in feedforward and feedback control of their performance. As shown in previous research, the facilitation was present only during the early testing phase. An exploratory retention test in a subgroup showed no effects after 24 h. We discuss these findings also in the context of earlier massed- vs distributed-practice approaches.