Article Figures & Data
Figures
- Figure 1.
Experimental task. a, Each participant slid his hand across a tabletop to hit visual targets. Vision of the hand was occluded by a mirror, which reflected a back-projected visual image to create the illusion that the hand and visual targets were coplanar. b, Two- (top) and four- (bottom) target sets used in experiments. On each trial, one target was pseudorandomly selected. The participant reached from a central start location, attempting to “slice” through the target with the cursor. A trial was complete when the radial distance of the movement exceeded 10 cm, indicated here by a dotted ring. c, Task design in Experiment 1 to assess savings. Veridical feedback was provided in the baseline and washout blocks. The visual feedback was perturbed during the two rotation blocks, with the size of the perturbation the same in each of these blocks.
- Figure 2.
Savings is only observed with large perturbations. a, Heading angle of the hand relative to the target during last five baseline and first 20 trials of Rotation 1 (blue) and Rotation 2 (red) in Experiment 1. The data for the two rotation blocks are displayed in a superimposed manner for the four perturbation sizes. Note the different scaling of the vertical axis for each group. The 45° and 60° groups show faster relearning for the second rotation; this savings effect is absent for the 15° and 30° groups. b, Mean learning rate from an exponential function independently fit to all trials in Rotation 1 and Rotation 2. c, Difference score measure of savings (Rotation 2 − Rotation 1). Data are mean ± SEM. *Significant difference. ns, Not significant.
- Figure 3.
Gains from savings are abolished by instructions to aim directly for the target. a, Trial schematic for Experiment 2, denoting the verbal intervention following the seventh trial of the Rotation 2 block. For the following 2 trials (blue bar), participants were instructed to aim and reach directly for the target. b, Left, Behavior during the Rotation 2 block for the two-target 45° group. There is an initial period of rapid relearning, followed by a sharp change in hand angle in response to the verbal intervention. Right, Difference score between the first 6 trials of Rotation 1 and Rotation 2 blocks (red) and between the average heading angle for the 2 intervention trials and the 2 trials preceding the intervention (blue). c, Time course of hand angles for the 45° (top) and 30° (bottom) groups in the four-target groups. Savings score (d), defined by the difference between the first 12 trials of the Rotation 1 and Rotation 2 blocks and (e), verbal intervention scores (using the 4 intervention trials and 4 preintervention trials). While savings was only reliable for the 45° group, there was a drop in hand angle following the verbal intervention for both groups. Data are mean ± SEM. *Significant difference. ns, Not significant.
- Figure 4.
Savings assessed with aiming report task in Experiment 3. a, Left, Task schematic. Numbers were visible in ascending and descending manner around the target. Participant verbally reported the number corresponding to his/her aiming location and then performed the reach. Right, Assuming performance (heading angle) is the composite of an explicit aiming strategy and implicit adaptation, the magnitude of the latter can be estimated via subtraction. b, Overall behavior for 15° (left) and 45° (right) groups. c, Mean aiming reports (red) and implicit adaptation (blue, estimated via subtraction). Participants were instructed to aim directly for the target in the final washout block. d, Aiming reports over the first 30 trials, superimposed for Rotation 1 and Rotation 2. e, Savings difference scores for each measure. Data are mean ± SEM. *Significant difference. ns, Not significant.
- Figure 5.
Control of aiming strategy by an arbitrary color cue. a, Interleaved design of Experiment 4 in which the cursor changed color on rotation trials (depicted in blue). The cursor remained white on no-rotation trials (depicted in red). b, c, Heading angle for groups exposed to 45° and 15° rotations, respectively. Note the difference in the scale of the y-axis. d, Blue bars represent mean of the cued trials, limited to those that immediately preceded an uncued trial. Red bars represent mean of uncued trials. e, Baseline subtracted hand angle on the first trial for Rotation 1 and Rotation 2. The color cue prompted the use of an aiming strategy for the 45° group, even before the participants had experienced errors caused by the perturbation in Rotation 2. Data are mean ± SEM. *Significant difference. ns, Not significant.
- Figure 6.
Inappropriate recall of aiming strategies in response to a novel perturbation. a, In Experiment 5, all participants were exposed to a novel −30° rotation after completing a training block with either a 45° or 15° rotation, followed by a washout block. b, Heading angle for the last 10 trials of the washout block and all trials of the Rotation 2 block. The 45° group initially responded to the perturbation by moving in the wrong direction and, after a few trials, reversed direction, reducing error faster than the 15° group. c, Enhanced picture of behavior over the first four trials of the Rotation 2 block, showing performance of each individual (dots). Note the expanded vertical axis relative to b. d, Mean learning rate from an exponential fit of all trials in Rotation 2 block, showing faster learning of the rotation for the 45° group. Data are mean ± SEM. *Significant difference.
