KR-withdrawal and self-paced motor performance

The purpose of this study was to examine the effects of KR-withdrawal on performance and the chronological profile of KR-delivery following the self-paced procedure and the blank trial technique. 120 participants were randomly separated into 12 groups and practiced finding an 8-in. line with no fixed starting and ending points. Appropriate 12 x 3 (groups by blocks of trials) analyses of variance and a prior contrasts were conducted to analyze all dependent variables (absolute error, variable error, movement time, KR-delay, post-KR interval, and KR-delay by post-KR interval ratio). The results indicated that (a) accuracy decreased significantly when KR was withdrawn early in practice, while the effects of KR-withdrawal later in practice affected accuracy differently. (b) Early in practice, participants performed at the same level of consistency even when KR was withdrawn; however, later in practice, the participants were less variable. (c) Movement time, KR-delay, and post-KR-interval were affected differently during early and later stages of practice. (d) Moderate to high correlations between absolute error and post-KR intervals may indicate the development of mechanisms for error detection.