Dissociations between perceived and actual success in goal-directed movements

Abstract

Purpose. Last year, we developed an experiment intended as a very simple model of injury or stroke in which the subject, after first practicing a speeded touching movement, was required to perform the movement but with their elbow physically constrained. We found that subjects' objective performance suffered little and recovered quickly after constraint but that their predictions of success decreased markedly and remained depressed. Moreover, when the constraint was removed, subjects continued to underestimate their actual success. Typical explanations for this “dissociation” between performance and perceived performance emphasize the awkwardness of the constrained movement. Here we examine if similar effects occur after moving with the non-dominant hand. Methods. Participants (n=8) made fast reaches (35 cm, 250ms) with their index finger to touch a target (circular, 0.4 cm) on a horizontal touchscreen. Before each trial, participants estimated their chances (0–100%) of hitting the target. Participants performed three blocks: B₁) 40 trials with dominant hand, B₂) 30 trials, non-dominant hand, and B₃) 30 trials, dominant hand. Analysis. We calculated within-subject averages of endpoint errors in the last 20 trials of each block to estimate the objective probability O_i of hitting the target at asymptotic performance in B_i. We averaged subjective estimates over the same ranges to obtain corresponding subjective probabilities S_i. Results. Statistical tests indicated that O₁>O₂<O₃ and S₁>S₂<S₃ : participants showed lower accuracy and lower estimates for the non-dominant hand. Unlike the estimates following the joint constraint, participants' estimates for the dominant hand rapidly recovered after moving with the non-dominant hand. Conclusions. Restraining the arm's degrees of freedom leads to a pronounced, erroneous decrease in perceived motor performance that persists after constraint removal. However, an aftereffect was not found after moving with the non-dominant hand, so it cannot be a simple residual effect of perceiving one's performance on non-routine movements as awkward.

Footnotes

 Support: NIH NS047178-01A1 (UW), NIH EY08266 (LTM).