Adaptation to visuomotor transformations: consolidation, interference, and forgetting

Abstract

The paradigm task A-->task B-->task A, which varies the time interval between task A and task B, has been used extensively to investigate the consolidation of motor memory. Consolidation is defined as resistance to retrograde interference (interference by task B on initial learning of task A). Consolidation has been demonstrated for simple skills, motor sequencing, and learning of force fields. In contrast, evidence to date suggests that visuomotor learning does not consolidate. We have shown previously that adaptation to a 30 degrees screen-cursor rotation is faster and more complete on relearning 24 hr later. This improvement is prevented if a 30 degrees counter-rotation is learned 5 min after the original rotation. Here, we sought to identify conditions under which rotation learning becomes resistant to interference by a counter-rotation. In experiment 1, we found that interference persists even when the counter-rotation is learned 24 hr after the initial rotation. In experiment 2, we removed potential anterograde interference (interference by task B on relearning of task A) by introducing washout blocks before all of the learning blocks. In contrast to experiment 1, we found resistance to interference (i.e., consolidation) when the counter-rotation was learned after 24 hr but not after 5 min. In experiment 3, we doubled the amount of initial rotation learning and found resistance to interference even after 5 min. Our results suggest that persistent interference is attributable to anterograde effects on memory retrieval. When anterograde effects are removed, rotation learning consolidates both over time and with increased initial training.

Figure 1.

Experiment 1. A-D, Rotation learning (open circles and dashed lines) and relearning (filled circles and solid lines) curves for groups 1-4, respectively. Learning is shown by the progressive reduction in the directional error at peak velocity (in degrees) across cycles. Points, representing the group average with SE for each cycle, are fitted by a double-exponential function. Cycles 2-11, which were used in the analysis, are enclosed by a box. Repeated-measures ANOVA showed no main effect of session (learning vs relearning) on directional error (F_(1,40) = 1.13; p > 0.05). However, there was a significant difference between groups (F_(3,40) = 15.54; p < 0.0001) and a significant session × group interaction (F_(3,40) = 5.97; p < 0.0018). This interaction was driven entirely by the control group (group 1), which showed a substantial decrease of directional error with relearning. E, Percentage change in rotation learning from the learning to the relearning session. Bars represent mean percentage change and SE for each group. ANOVA revealed an effect of group (F_(3,20) = 9.10; p = 0.0005), and post hoc tests showed significant differences (p < 0.0083) between the control group and the other three groups but not among the other three groups.

Figure 2.

Experiment 2. A-C, Rotation learning and relearning curves with washout. Repeated-measures ANOVA revealed a significant effect of session (learning vs relearning) on directional error (F_(1,30) = 10.828; p = 0.0026). There was no significant effect of group (F_(1,30) = 0.097; p = 0.9075) nor a significant session × group interaction (F_(3,30) = 0.439; p = 0.649). D, Percentage change in learning from the learning to the relearning session. ANOVA revealed a main effect of group (F_(2,15) = 4.17; p = 0.03). Post hoc tests showed a significant difference (p < 0.016) between the control and the 5 min interference group but not between the control group and the 24 hr interference group (p > 0.05).

Figure 3.

Experiment 3. A-C, Rotation learning and relearning curves with extended training and washout. Repeated-measures ANOVA revealed a significant effect of session (learning vs relearning) on directional error (F_(1,30) = 21.16; p < 0.0001). There was no significant effect of group (F_(2,30) = 1.87; p = 0.17) nor a significant session × group interaction (F_(3,30) = 0.009; p = 0.99). D, Percentage change in rotation learning from the learning to the relearning session. ANOVA revealed no significant difference between groups (F_(2,15) = 0.046; p = 0.95).