Robert M. Kohl

Specificity and Variability of Practice

The specificity of learning principle proposes that motor skills are specific and only superficially resemble other similar skills or variations of the same skill. On the other hand, the variability of practice hypothesis derived from schema theory proposes that experiences with task variations are vital to the development of the memories (schemata) responsible for response production and learning. This paper contrasts these two positions in two experiments aimed at determining the influence of providing variable and/or specific acquisition experiences on the retention of a force production task. The results clearly indicated that acquisition practice with variations of the criterion task leads to better retention than practice on the criterion task alone. This finding is contrary to a strict interpretation of the specificity of learning principle and suggests that paradigms investigating schema notions should be expanded to include potential impacts of variability of practice on tasks experienced during acquisition.

Composition of Practice: Influence on the Retention of Motor Skills

The purpose of these experiments was to investigate further the variable practice effect found by Shea and Kohl (1990). Experiment 1 was an initial attempt to determine the locus of the retention benefits demonstrated by subjects provided variable practice experiences. All groups received 20 acquisition blocks consisting of five test trials per block at a target of 150 N. The interval between test trials was either unfilled or filled, with additional trials consisting of the same target force, variable target forces, or practice on an unrelated motor task. The results indicated retention was not incremented (relative to an unfilled interval) by requiring subjects to perform an unrelated motor task in the intertest-trial interval. However, when the interest-trial interval was filled with practice on related motor tasks, retention was significantly improved. Experiment 2 assessed the impact of increasing the number of related motor tasks interpolated between test trials. The results indicated filling the intertest-trial interval with one motor task resulted in large retention benefits relative to an unfilled interval. Further increases in the number of related motor tasks (3) interpolated between test trials resulted in only modest increments to retention. The results were consistent with the elaboration perspective proposed by Shea and Zimny (1983). The elaboration perspective proposes that the simultaneous presence of related items in working memory facilitates interitem elaborative and distinctive processing that ultimately results in retention benefits.

Knowledge of Results for Motor Learning: Relationship Between Error Estimation and Knowledge of Results Frequency

Abstract The authors of the present study investigated the apparent contradiction between early and more recent views of knowledge of results (KR), the idea that how one is engaged before receiving KR may not be independent of how one uses that KR. In a 2 × 2 factorial design, participants (N = 64) practiced a simple force-production task and (a) were required, or not required, to estimate error about their previous response and (b) were provided KR either after every response (100%) or after every 5th response (20%) during acquisition. A no-KR retention test revealed an interaction between acquisition error estimation and KR frequencies. The group that received 100% KR and was required to error estimate during acquisition performed the best during retention. The 2 groups that received 20% KR performed less well. Finally, the group that received 100% KR and was not required to error estimate during acquisition performed the poorest during retention. One general interpretation of that pattern of results is that motor learning is an increasing function of the degree to which participants use KR to test response hypotheses (J. A. Adams, 1971; R. A. Schmidt, 1975). Practicing simple responses coupled with error estimation may embody response hypotheses that can be tested with KR, thus benefiting motor learning most under a 100% KR condition. Practicing simple responses without error estimation is less likely to embody response hypothesis, however, which may increase the probability that participants will use KR to guide upcoming responses, thus attenuating motor learning under a 100% KR condition. The authors conclude, therefore, that how one is engaged before receiving KR may not be independent of how one uses KR.

Mechanism involvement during skill imagery.

Explanations of the effects of initial mental imagery practice on the subsequent performance of a motor task may be divided into two categories. In-flow explanations propose that proprioceptive feedback generated during imagery practice serves as the underlying mechanism while outflow explanations claim that cognitive operations (e.g., motor programs) generated during skill imagery serve as the basis for physical performance. A test of these two models was conducted by comparing unilateral and bilateral transfer in a rotary pursuit task following either imagery or physical practice (cf. Wallace, 1977). The results showed that all transfer groups produced positive transfer relative to a no-practice control group. Further, unilateral transfer was greater than bilateral transfer for physical practice. There was no difference between unilateral and bilateral transfer for imagery practice. These data were interpreted as evidence for an outflow explanation of skill imagery.

Pew (1966) Revisited: Acquisition of Hierarchical Control as a Function of Observational Practice.

Two experiments are reported that utilized a task similar to one developed by Pew (1966) in which subjects controlled the position of a continually moving cursor by alternately pressing two response keys. Experiments I and 2 replicated Pews findings. That is, over acquisition trials, subjects exhibited an increase in their rate of responding, an increase in response rhythmicity, and a reduction in error. After a 24-hr retention interval, it was demonstrated that the rate and rhythmicity of responding for the observation practice groups were indistinguishable from those of the actual practice groups. In general, however, as the demands of the task (cursor acceleration rate and/or target amplitude) were increased, there was a tendency for the absolute differences in error between the actual and observation practice groups to increase, These data support the notion that subjects may choose appropriate response/control schemes (i.e., open-loop and hierarchical control) without actual practice experiences.

Bilateral transfer as a function of mental imagery.

Three experiments are reported which investigate the role of mental imagery in the bilateral transfer from right to Ie ft hand of rotary pursuit skill. In Experiment 1 both mental imagery and physical rehearsal showed significant positive transfer relative to a control condition. However, work decrement may have accumulated and transferred in the physical rehearsal group thereby depressing this groups left-hand performance. Experiment 2 was conducted under conditions designed to allow work decrement to dissipate prior to transfer to the contralateral limb. The data still showed no difference between physical rehearsal and mental imagery. One interpretation of these data is that work decrement was present under both the physical rehearsal and mental imagery manipulations in Experiment 1. The data from Experiment 3 confirmed this interpretation as well as replicated the positive transfer effects found for mental imagery in Experiments 1 and 2. The data are discussed in terms of central versus peripheral explanatory mechanisms.

Alternating Actual and Imagery Practice: Preliminary Theoretical Considerations

The main purpose of the following experiments was to reexamine the acquisition effects of alternating actual and imagery practice on retention. This was accomplished by making retention comparisons between groups that either alternated actual and imagery practice, alternated actual practice and rest, employed all actual or all imagery practice, or performed an unrelated task (the control) during acquisition. Results from Experiment 1 indicated that the actual practice and the alternating actual and imagery practice groups produced equivalent scores that were greater than the equivalent scores of the imagery practice and alternating actual practice and rest groups. All experimental groups performed better than the control. Because the retention test was identical to the actual practice protocol, practice specificity may have biased the retention relative standings in favor of the actual practice group. Experiment 2 was identical to Experiment 1 except subjects were transferred to a contralateral limb retention test. Results indicated that the alternating actual and imagery practice group produced better retention scores than the equivalent retention scores of the actual practice and imagery practice groups. These three groups produced higher retention scores than the alternating actual practice and rest group, which was better than the control. These results support the notion that alternating actual and imagery practice facilitates motor learning and suggest that practice specificity may be a factor in response imagery experiments. Based on the notion that actual and imagery practice activate shared and unique mechanisms, several hypotheses were offered to explain these results.

The Scheduling of Knowledge of Results

The experiments outlined in this article were performed so that the acquisition effects of KR scheduling on no-KR retention could be determined. In Experiment 1, the group that alternated between 12 KR and 12 no-KR responses produced better retention than both the group that alternated between 6 KR and 6 no-KR responses and an all-KR group. The partial KR group that performed the best on retention also received the least number of reversals from KR to no-KR responses, however. In Experiment 2, when acquisition KR reversals ere held constant for partial KR groups, groups that received either random KR scheduling or all KR produced similar and better retention that groups who received blocked KR scheduling. These results were reconciled with KR frequency experiments by proposing that memory processes invoked by KR protocols decrease from KR frequency, to reversal, to scheduling conditions.

After-contraction phenomenon : influences on performance and learning

Three experiments investigated the influence of an after-contraction phenomenon on the performance and learning of a dynamic force-production task. The after-contraction effect refers to an involuntary potentiation (induced by a sustained precontraction) that is thought to summate with voluntary motor commands to bias subsequent responding. The precontraction involved a brief (20 s) static contraction. The subsequent influence of the precontraction on a dynamic force-production task was assessed. Experiments 1 and 2 were aimed at demonstrating the direct impact of the precontraction intensity on the magnitude and decay of the after-contraction effect. The results indicated that as the intensity of the precontraction increased, the magnitude of the induced bias increased. In Experiment 3, the indirect influence on subsequent retention of varying the precontraction intensity during acquisition was investigated. The results indicated that the performance of subjects experiencing varying precontraction intensities during acquisition was inferior to that of subjects experiencing a constant precontraction intensity, but the performance of the varied precontraction intensities group was superior on the test of retention. It is noted that the paradoxical reversal from acquisition to retention is similar to that found in contextual interference experiments and may arise from similar mechanisms.

Individual differences in skilled performance following imagery of bilateral skill.

The present study examined individual differences related to imagery about bilateral skill. 100 males were pretested on the Betts and Gordon scales for competency of imagery and the Eysenck Personality Inventory (to assess introversion-extraversion), and randomly assigned to an experimental or control group. Experimental subjects were given 15 30-sec. sessions performing rotary pursuit, 5 min. rest, and 15 30-sec. trials with the non-dominant hand. Controls received identical treatment but recited the multiplication table instead of generating mental imagery. As expected, skill imagery facilitated bilateral transfer of pursuit tracking. Limited support for competency in generating imagery as a prerequisite for effective imagery of one skill was given only to the extent that subjects who could control imagery, practiced mental imagery, and were given 10 to 15 physical practice trials, performed better than those with less control. Contrary to prediction, there was no evidence of personality effects either in correlations of personality scores with performance or in a post hoc analysis of variance in which subjects were assigned to treatment versus control and extravert versus introvert groups.