Article Figures & Data
Figures
- Figure 1.
A novel utility of the allocentric memory of a target position. a, Allocentric memory in terms of the background frame has been believed to be useful in memorizing “where to go” in delayed reaching when a blank (delay) is as long as 2 s (left). We propose a novel use of the allocentric memory in an immediate reach (right). We hypothesize that the allocentric memory is essential for dissociating error attributable to the motor system (red arrow) from error attributable to target motion by encoding “where I intended to go” (dotted circle). b, Basic design of the experiments. A large apparent error (black arrow) was introduced using a lateral displacing prism. The frame remained still (left) or was displaced in the direction of prism displacement (ipsilateral shift, middle) or in the opposite direction (contralateral shift, right) during a reaching movement. Assuming that our hypothesis is correct, the original target position decoded in terms of the frame would shift with the frame (dotted circle), and the motor error (red arrow) would be underestimated in the ipsilateral condition and overestimated in the contralateral condition.
- Figure 2.
Task procedures. Each column schematically shows the status of the visual field (oval shape) and the position of the hand relative to the button and the screen. The shutters opened at 0 (Start) when the participant pressed the button. A target and background figures appeared after a random delay (900–1200 ms) at 1. Vision was blocked from 2 (Release) to 3 (Touch) and allowed again for 300 ms. The background figures were presented both before (encoding) and after (decoding) the reach in experiments 1–3 (a); they were presented only after the reach in experiment 4 (b).
- Figure 3.
Effects of ipsilateral and contralateral shifts of the background (experiment 1). The data from an individual participant (a–c) and from all participants (d–f) are shown. Each circle represents the median of two (a–c) and 12 (d–f, 2 directions × 6 participants) responses plotted against trial sequence (abscissa). Errors in the direction of prism displacement (right or left) are indicated as positive. The thick black lines indicate the model predictions using model equation in Materials and Methods. Note the difference in the asymptotes during the exposure period (red dotted lines) and in the aftereffects (black arrows) across three conditions: ipsilateral shift (a, d), no-shift (b, e), and contralateral shift (c, f). The gray shaded areas in d–f show the 25th and 75th percentiles. g, h, Distributions of the asymptotes during the exposure period (g) and aftereffects during the posttest period (h) estimated for each session (n = 12). Each box plot shows the 10th, 25th, 50th, 75th, and 90th percentiles. Brackets with asterisks indicate significant differences (*p < 0.05; **p < 0.01; ***p < 0.001) after corrections for multiple comparisons (Ryan's method after one-way repeated-measures ANOVA).
- Figure 4.
Effects of the size of the background (experiment 2) on cancelling. a, Illustrations of background figures of different sizes. The size of the center square was 0 (no background), 8, 40, 80, or 120 mm. The top and bottom panels show the rightward shift of the background between the encoding (top) and decoding (bottom) phases. The vertical lines show the size of the shift (20 mm). b–f, Prism adaptation with five different sizes of background. Note the maximal cancelling effects at 40 mm. Each circle represents the median of 12 responses (6 participants × 2 directions). g, h, Distributions of the asymptotes during the exposure period (g) and aftereffects during the posttest period (h). The daggers in h show that the mean aftereffect was significantly different from zero after correction for multiple comparisons (†p < 0.05; ‡p < 0.01; t test, Bonferroni's correction). Other conventions are the same as in Figure 3.
- Figure 5.
Effects of the complexity of the background on cancelling (experiment 3). a, Illustrations of background figures with different complexities: no background, a single line, parallel lines, a single square, triple squares, and multiple squares. The size of the center figure was fixed at 80 mm. b–g, Prism adaptation with background figures of different complexities. Note the maximal cancelling effects with multiple squares. Each circle represents the median of 12 responses (12 participants × 1 direction). h, i, Distributions of the asymptotes during the exposure period (h) and aftereffects during the posttest period (i). Other conventions are the same as in Figure 3.
- Figure 6.
Necessity of the background during the encoding phase (experiment 4) for cancelling. a–c, Prism adaptation in the ipsilateral shift (a), post-presentation (b), and no background conditions. Note the contrast between the ipsilateral shift condition and the post-presentation condition. Each circle represents the median of 12 responses (6 participants × 2 directions). d, e, Distributions of the asymptotes during the exposure period (d) and aftereffects during the post-test period (e). Other conventions are the same as in Figure 3.
