Motor adaptation is reduced by symbolic compared to sensory feedback

Abstract

Motor adaptation - the process of reducing motor errors through feedback and practice - is an essential feature of human competence, allowing us to move accurately in dynamic and novel environments. Adaptation typically results from sensory feedback, with most learning driven by visual and proprioceptive feedback that arises with the movement. In humans, motor adaptation can also be driven by symbolic feedback. In the present study, we examine how implicit and explicit components of motor adaptation are modulated by symbolic feedback. We conducted three reaching experiments involving over 400 human participants to compare sensory and symbolic feedback using a task in which both types of learning processes could be operative (Experiment 1) or tasks in which learning was expected to be limited to only an explicit process (Experiments 2 and 3). Adaptation with symbolic feedback was dominated by explicit strategy use, with minimal evidence of implicit recalibration. Even when matched in terms of information content, adaptation to rotational and mirror reversal perturbations was slower in response to symbolic feedback compared to sensory feedback. Our results suggest that the abstract and indirect nature of symbolic feedback disrupts strategic reasoning and/or refinement, deepening our understanding of how feedback type influences the mechanisms of sensorimotor learning.

Figure 1.. Motor adaptation in response to symbolic feedback is dominated by strategy use.

(a) Schematic of the web-based rotational perturbation task in Experiment 1. An example of the 60° counterclockwise rotation is provided. Participants are instructed to reach in the direction that maximized points (i.e., 100 points). The left, middle, and right panels display a representative trial from the early adaptation, late adaptation, and aftereffect phases, respectively. (b) Mean time courses of hand angle (N = 184; 30°: 77 participants; 60°: 51 participants; 90°: 56 participants). Colors denote different perturbation groups (red = 30°; green = 60°; blue = 90°). Shaded error denoted SEM. Each movement cycle includes three trials (1 reach to each of the three targets). Grey horizontal lines at the bottom indicate clusters showing significant group differences. (c) Mean hand angles during early adaptation (i.e., first 10 cycles of the perturbation block), late adaptation (last 10 cycles of the perturbation block), and aftereffect phases (10 cycles of the aftereffect block). Black line denotes median ± IQR. (d) Mean time courses and (e) mean hand angles of learners (N = 112; 30°: 35 learners; 60°: 39 learners; 90°:38 learners).

Figure 2.. Symbolic feedback reduces explicit strategy use in response to a rotational perturbation.

(a, b) Schematic of the 60° visuomotor rotation task (Experiment 2). Feedback was delayed to minimize implicit recalibration. Participants were instructed to move in a direction that minimizes error. Error was conveyed via (a) symbolic feedback (score magnitude conveys the size of the angular error rounded to the nearest integer; score sign conveys direction, with negative denoting a clockwise error and positive denoting a counterclockwise error) or (b) sensory feedback (the magnitude and direction of the error are conveyed by a rotated cursor). Left and right panels denote early and late adaptation, respectively. (c) Mean time courses of hand angle (N = 110; Sensory: 53 participants; Symbolic: 57 participants). Colors denote different feedback groups (dark green = symbolic feedback; dark magenta = sensory feedback). Shaded error denoted SEM. Grey horizontal lines at the bottom indicate clusters showing significant group differences. (d) Mean hand angles during early adaptation, late adaptation, and aftereffect phases. Black line denotes median ± IQR. (d) Mean time courses and mean hand angles of learners (N = 76; Sensory: 40 learners; Symbolic: 36 learners).

Figure 3.. Symbolic feedback reduces explicit strategy use in response to a mirror perturbation.

(a, b) Schematic of the mirror-reversal perturbation task in Experiment 3. Participants were instructed to move in the direction that minimizes error. Error was conveyed via (a) symbolic feedback or (b) sensory feedback. Feedback is provided in the same manner as Experiment 2. Left and right panels denote early and late adaptation, respectively. (c) Mean time courses of hand angle (N = 121; Sensory: 50 participants; Symbolic: 71 participants). Colors denote different feedback groups (dark green = symbolic feedback; dark magenta = sensory feedback). Shaded error denoted SEM. Grey horizontal lines at the bottom indicate clusters showing significant group differences. (d) Mean hand angles during early adaptation, late adaptation, and aftereffect phases. Black line denotes median ± IQR. (d) Mean time courses and (e) mean hand angles of learners (N = 75; Sensory: 42 learners; Symbolic: 33 learners).