Learning to imitate novel motion sequences

Abstract

Many imitative behaviors entail complex sequences of component actions that must be recalled and performed in the proper order. It is well known that imitation of complex actions tends to improve with repeated opportunities to observe and execute the target behavior. But what actually makes this practice-based improvement possible? To address this question, we had subjects view and then reproduce sequences of connected, randomly directed motions of a disc. Even a single repetition of a motion sequence substantially reduced errors in reproduction. Improvement seemed to follow a power law, with accuracy in reproducing each motion segment improving by an amount proportional to the current error for that segment. Analysis of the pauses separating a reproduction's segments suggests that with learning, multiple segments in memory are grouped into more compact representations. To test overt performance's contribution to repetition-based improvement, we compared subjects' performance when they reproduced the stimulus trajectory after each repetition to when they did so only once, after the final repetition. Performance was similar following the final repetition in both conditions, indicating that seeing the model, without actual imitation, was sufficient for learning--even in the absence of an explicit error signal. In another experiment, subjects viewed three presentations of each model, with the second presentation given in forward (start to end) or backward (end to start) order. Performance was significantly better when all three presentations were in the same, consistent order, suggesting that repetition reinforced some temporal aspects of a trajectory as it was being learned, and not merely a better representation of the static shape traced by the motion of the disc. These results provide a first look into explicit learning of sequential, nonverbal material, which is central to many tasks of daily life.

Motion trajectory information and agency influence motor learning during observational practice

“…They rated their agreement using a 7-point Likert scale (upper anchor 3 = strongly agreed, lower anchor -3 = strongly disagreed, 0 = neither agreed nor disagreed). Insert Figure 7 about here As predicted, and compared to the control group, the experimental groups learned relative timing by acquiring early (1, 2) and late (5) segments, which confirmed segmentspecific motion trajectory information was coded (Agam, et al, 2007). This finding is important because although we expected no difference between the experimental groups, the results show the agency instructions did not interfere with the acquisition of timing (Shanks & Johnstone, 1999).…”

Eye movements and imitation learning: Intentional disruption of expectation

“…To examine the contribution of prediction errors to sequence learning (Kumaran & Maguire, 2007), we adapted an imitation task in which learning has been well characterized, behaviorally (Agam, Bullock, & Sekuler, 2005; Agam, Galperin, Gold, & Sekuler, 2007; Maryott & Sekuler, 2009) and electrophysiologically (Agam, Huang, & Sekuler, 2010; Agam & Sekuler, 2007). In our adaptation of this task, during repeated presentations of a random sequence of motion directions, we measured (i) the eye movements that subjects made while observing the random motion sequence, as well as (ii) the fidelity with which subjects later reproduced that sequence from memory.…”

Violations of newly-learned predictions elicit two distinct P3 components

“…A fully detailed analysis of the behavioral results is beyond the scope of this paper, as such analyses of closely-related experiments have been previously published (Agam et al, 2007; Maryott et al, 2011), and the focus of this paper is on the neural responses to new, familiar, and deviant sequence items.…”