578 A 578 Contextual Interference Effect: Elaborative Processing or Forgetting���Reconstruction? A Post Hoc Analysis of Transcranial Magnetic Stimulation���Induced Effects on Motor Learning Chien-Ho (Janice) Lin1,3, Beth E. Fisher1,2, Carolee J. Winstein1,2, Allan D. Wu3, James Gordon1 1Division of Biokinesiology and Physical Therapy, School of Dentistry, University of Southern California, Los Angeles. 2Department of Neurology, Keck School of Medicine, University of Southern California, Los Angeles. 3Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles. ABSTRACT. The elaborative-processing and forgetting���recon- struction hypotheses are the 2 principal explanations for the contextual interference (CI) effect. The present authors��� purpose was to identify which of these 2 hypotheses better accounts for the CI effect. They synchronized single transcranial magnetic stimulation (TMS) pulses to each intertrial interval to modulate information processing during Blocked and Random Practice conditions. Participants practiced 3 arm tasks with either a Blocked or Random Practice order. The 3 stimulation conditions (No TMS, TMS, Sham TMS) by 2-practice order (Blocked, Random) between-participant design resulted in 6 experimental groups. Without TMS, motor learning increased under Random Practice. With TMS, this learning benefit diminished. These results support the elaborative-processing hypothesis by showing that perturbing information processing, evoked by Random Practice, deteriorates the learning benefit. Unlike the prediction of the forgetting��� reconstruction hypothesis, adding perturbation during Blocked Practice did not significantly enhance motor learning. Keywords: contextual interference, motor learning, transcranial magnetic stimulation (TMS) t is well established that when individuals learn multiple or multiple variants of the same task, Random Practice leads to better retention than Blocked Practice. This phenomenon is known as the Contextual Interference (CI) effect (Lee & Magill, 1983 Shea & Morgan, 1979). It has long been of interest to motor-learning theorists to understand the information���processing mechanisms under- lying this phenomenon. Two principal explanations for the CI effect are (a) the elaborative-processing hypoth- esis and (b) the forgetting���reconstruction hypothesis. The elaborative-processing hypothesis holds that Random Practice forces the learner into more elaborate process- ing, such as intertask comparisons and embellishment of task-relevant information (Shea & Morgan Shea & Titzer, 1993 Shea & Zimny, 1983, 1988). More elaborate infor- mation processing is thought to result in more comprehen- sive and readily retrievable memory traces. According to the elaborative-processing hypothesis, the interval prior to the next movement trial (i.e., intertrial interval) is a likely time during which intertask comparisons are made and the elaboration occurs. The forgetting���reconstruction hypothesis suggests that a previously constructed action plan is more likely to be available in working memory during Blocked Practice, because the same task is practiced repeatedly (Lee & Magill, 1983, 1985). Random Practice, however, forces the learner to abandon the action plan constructed previously because he or she has to perform a different task on the next trial. The forgetting that ensues requires the learner to actively reconstruct the action plan the next time the initial task is practiced, resulting in a stronger memory representation of the practiced tasks (Lee & Magill, 1983, 1985). As with the elaborative-processing hypothesis, forgetting and recon- struction of the action plan are likely to occur in the interval prior to the next movement trial. In the present experiment, we tried to distinguish which of the two hypotheses better accounts for the CI effect by applying transcranial magnetic stimulation (TMS) pulse delivered to the motor representation of the primary muscles of the trained tasks. TMS is a technique that can enhance or inhibit central reorganization (Ziemann, Hallett, & Cohen, 1998) and information processing (Boroojerdi et al., 2001 Flitman et al., 1998) by noninva- sive focal stimulation of the human brain (Hallett, 2000). Unique to the TMS technique is its temporal resolution (in milliseconds), which allows researchers to directly perturb hypothetical information processing evoked during motor control and learning. This technique has been applied to enhance or inhibit information processing during skill acquisition (Berardelli et al., 1994 Pascual-Leone, Brasil- Neto, Valls-Sole, Cohen, & Hallett, 1992 Taylor, Wagen- er, & Colebatch, 1995 Ziemann, Ilic, Pauli, Meintzschel, & Ruge, 2004). In the present study, single disruptive TMS pulses were synchronized to each intertrial interval to modulate information processes under Blocked and Random Prac- tice conditions. The key question is whether practice with TMS interferes with retention or enhances retention when compared with practice without TMS. This experimental manipulation should lead to one of two results, depending on whether elaborative processing or forgetting���reconstruc- tion provides a better explanation for the CI effect (see Figure 1). If elaborative processing accounts for the CI effect, then the advantage of Random Practice should be diminished by the TMS, because TMS perturbs elaborative processing during the intertrial interval (see Figure 1A, left). Motor learning under the Blocked Practice condition will not be affected, because little or no elaborative processes are evoked during Blocked Practice (see Figure 1A, right). On the other hand, if forgetting reconstruction accounts for Itasks Correspondence address: James Gordon, Division of Biokine- siology and Physical Therapy, School of Dentistry, University of Southern California, CHP155, 1540 E. Alcazar Street, Los Ange- les, CA 90033, USA. E-mail address: jamesgor@usc.edu Journal of Motor Behavior, 2008, Vol. 40, No. 6, 578���586 Copyright �� 2008 Heldref Publications

Contextual Interference Effect November 2008, Vol. 40, No. 6 579 the CI effect, then Blocked Practice should become more like Random Practice, because TMS applied during the intertrial interval ensues reconstruction of the action plan even during Blocked Practice, in which the same task is practiced repeatedly (see Figure 1B, right). Motor learning under Random Practice is not expected to be enhanced significantly by TMS perturbation, because forgetting and reconstruction of action plans have already been evoked by Random Practice (see Figure 1B, left). Method Participants Participants were 60 healthy, right-handed volunteers (18���38 years old) who were naive to the task and whom we recruited (see Table 1). All participants gave written informed consent and participated in the study under a protocol approved by the Institutional Review Board of the University of Southern California Health Sciences Campus. Participants were excluded from the study if there were contraindications for TMS (Wassermann, 1998), including the presence of a pacemaker, metal in the head, pregnancy, neurological disorder, current use of stimulants or medications known to lower seizure threshold, and per- sonal or family history of a seizure disorder. There were no adverse effects reported by any of the participants who received TMS. Instrumentation and Task A lightweight lever affixed to a frictionless vertical axle was attached to a table and positioned parallel to the floor. A handle at the end of the lever was adjusted to accom- modate the length of participants��� forearms. A linear poten- tiometer was attached to a transducer at the base of the vertical axle. Signals from the transducer were converted to a digital signal and sampled at 1,000 Hz. A LabView-based (LabView, National Instruments) custom-made software program (Weekley, 2004) was applied to manipulate the movement pattern, the timeline of each event, and data storage for each trial. The participants��� task was to move the lever with their dominant arm at the correct speed and distance to replicate a goal movement pattern that was displayed on the computer monitor before each trial (see Figure 2). The participant was required to learn three arm patterns, each comprising two elbow extension���flexion reversal movements (see Figure 2). Participants were allowed up to 5 s to perform each movement. The actual time to complete a movement was variable and depended on how fast the participant moved, whereas the other interval times (e.g., feedback delay) were fixed (see Figure 3). During the acquisition phase of the experiment, participants were presented with feedback after each movement trial. The feedback included (a) an overall error score, root mean square error (RMSE), repre- senting the difference between the goal movement pattern and the participant���s response, and (b) a graphic represen- tation of the participant���s response superimposed on the goal movement pattern. All participants received written instructions and additional verbal information about the experiment. The timeline of each event of a single trial is illustrated in Figure 3. Experimental Design and Procedure Participants were randomized to one of six practice condi- tions: No TMS control (Blocked, Random), TMS (Blocked��� TMS, Random���TMS), and Sham TMS (Blocked���Sham TMS, Random���Sham TMS see Table 1). There were no sig- nificant group differences for age, gender, or baseline motor performance (see Block 1, Figure 4). The resting motor threshold prior to motor practice did not differ significantly between the Blocked���TMS and Random���TMS groups. The Sham TMS condition (coil was applied to the scalp, nor- mal clicking noise was present, but no magnetic pulse was applied) was implemented to control for the nonspecific effects such as the stimulating coil noise and scalp sensa- tion during the TMS procedure. The investigators were not blinded to the group assignment. Testing took place during 2 consecutive days, with acqui- sition and immediate retention phases on Day 1 and a delayed retention phase on Day 2. The three arm patterns (see Figure 2) were practiced in either a Blocked or Ran- dom Practice order for 144 trials. During Blocked Practice, there were 48 movement trials of each arm pattern, and the order of patterns was counterbalanced across participants. During Random Practice, the three patterns were practiced in a nonrepetitive manner within each 48-trial set the ran- domization scheme was the same for all Random Practice participants. The retention tests consisted of No feedback FIGURE 1. Predicted results of the experimental manipu- lation based on (A) elaborative-processing hypothesis and (B) forgetting���reconstruction hypothesis. TMS = transcra- nial magnetic stimulation. ACBCBACABAC.. AAA.. BBB.. CCC.. ACBCBACABAC.. AAA.. BBB.. CCC.. TMS TMS TMS TMS Random practice TMS disrupts elaborate processes g Learning reduced Blocked practice Little or no elaborate processes to disrupt g Learning not affected Random practice Forgetting has already been induced by random pratice g Learning is minimally or not enhanced Blocked practice TMS perturbation induces forgetting g Learning enhanced Elaborate hypothesis Forgetting hypothesis A B