Mu Suppression Is Sensitive to Observational Practice but Results in Different Patterns of Activation in Comparison with Physical Practice

Abstract

Research has shown the effectiveness of observational practice for motor learning, but there continues to be debate about the mechanisms underlying effectiveness. Although cortical processes can be moderated during observation, after both physical and observational practice, how these processes change with respect to behavioural measures of learning has not been studied. Here we compared short-term physical and observational practice during the acquisition and retention of a novel motor task to evaluate how each type of practice modulates EEG mu rhythm (8-13 Hz). Thirty healthy individuals were randomly assigned to one of three groups: (1) physical practice (PP), (2) observational practice (OP), and (3) no practice (NP) control. There were four testing stages: baseline EEG, practice, postpractice observation, and delayed retention. There was significant bilateral suppression of mu rhythm during PP but only left lateralized mu suppression during OP. In the postpractice observation phase, mu suppression was bilateral and larger after PP compared to that after OP. NP control showed no evidence of suppression and was significantly different to both the OP and PP groups. When comparing the three groups in retention, the groups did not differ with respect to tracing times, but the PP group showed fewer errors, especially in comparison to the NP group. Therefore, although the neurophysiological measures index changes in the OP group, which are similar but moderated in comparison to PP, changes in these processes are not manifest in observational practice outcomes when assessed in a delayed retention test.

Figure 1

The flower-tracing task. Each arrow represents an error. The total tracing time starts at A and ends at B.

Figure 2

Research design and research questions.

Figure 3

Mu suppression index during physical (PP) and observational practice (OP) (i.e., stage 2 testing) at the central interpolated electrodes C3, CZ, and C4. Values represent the mean log ratio of mu power at the frequency range of 8–13 Hz in the experimental condition compared to baseline. A ratio of negative value indicates suppression. Error bars represent standard error of the mean SE.

Figure 4

Mu suppression index for the PP, OP, and NP groups during postpractice observation (stage 3 testing). Error bars represent standard error of the mean (SE). Asterisks indicate significant between group differences (p < .05).

Figure 5

(a) Average number of errors across 9 blocks of retention testing (t = 9/blk) for the physical practice (PP), observational practice (OP), and no practice (NP) groups and first-day acquisition trials for the PP group (PP_acq). Error bars represent standard error (SE). ^∗PP group significantly different to NP group B1–B3. PP group significantly different to OP group (B1). (b) Average tracing time across 9 blocks of retention testing (t = 9/blk) for the physical practice (PP), observational practice (OP), and no practice (NP) groups and first-day acquisition trials for the PP group (PP_acq). Error bars represent standard error (SE). There was no interaction.

Figure 6

Average number of errors across the first 10 trials of physical practice in retention for the physical practice (PP), observational practice (OP), and no practice (NP) groups as well as during first-day acquisition for the PP group (PP_acq). Error bars represent standard error (SE). There were no group differences comparing PP_acq to the OP_ret and NP_ret.