Off-line learning of motor skill memory: A double dissociation of goal and movement

Abstract

Acquiring a new skill requires learning multiple aspects of a task simultaneously. For example, learning a piano sonata requires learning the musical notes and being able to implement this goal by learning the appropriate sequence of finger movements. After practice, skill continues to develop off-line during a period of consolidation. Here we show that different aspects of a procedural memory are processed separately during consolidation: Only the movement sequence is enhanced over the day; whereas only the goal is enhanced over a night of sleep. This double dissociation suggests that distinct systems, enhancing different aspects of a procedural memory, support improvements during consolidation. Consolidation is not a single process; instead, there are multiple routes to off-line learning, and the engagement of these distinct mechanisms is determined by when consolidation takes place. movement control ͉ procedural learning ͉ consolidation ͉ sleep C lassically, a distinction has been made between how a movement is performed and the spatial target or goal of the movement (1). For example, a pianist makes a series of finger movements to fulfill the goal of playing notes in a sonata. Enhanced knowledge of either the finger movements or the goal of these movements can produce an increase in skill (2-4). During practice, distinct mechanisms may be engaged to support the simultaneous acquisition of both components (5-7). Skill can also develop off-line, between practice sessions, during consolidation (8, 9). Skill enhancement during consolidation, like practice, may involve the simultaneous enhancement of both the goal and the movement. Alternatively, the principles operating during consolidation may differ from those during practice: Skill components may be enhanced separately. This result would imply that the mechanisms engaged simultaneously during practice are engaged separately during consolidation.It is possible to distinguish between the goal and the movement components of skill in a procedural sequence learning task (2). In the present experiment, participants acquired skill in the serial reaction time task (SRTT). In this task, a visual cue can appear at any one of four positions arranged horizontally on a computer screen (10). Each screen position corresponds to a button on a response box. A trial begins when a cue appears. The participant presses the appropriate response button, ending the trial, and after a short fixed delay, another cue is presented. Unbeknownst to the participant, the visual cues follow a specific spatial pattern that is learned as both a sequence of finger movements and as a sequence of response buttons to push, or goals (2-4). After training with one hand, these two skill components can be distinguished by probing skill with the untrained hand (Fig. 1). By switching hands, the same finger is no longer associated with the same response. So, although the same sequence of response buttons is required, this goal is achieved by using a different set of finger movements. Thus the goal remain...

Motor sequence consolidation: constrained by critical time windows or competing components

“…Nonetheless, the time of retesting may influence the expression of off-line improvements. However contrasting improvements over a 12-hr interval -shown in an earlier study -against those that developed over the 24-hr intervals of the current study showed that goal and movement-based improvements can be equally expressed at 8am and at 8pm (Cohen et al 2005). Thus, time-of-day seems unlikely to have influenced the expression of offline learning.…”

“…Off-line improvements can be modified by a participant's ability to recall segments of the sequence (Robertson et al 2004). Those reporting four or less items consistently show goal-based improvements over a night of sleep and movement-based improvements over wake (Cohen et al 2005). We wished to examine the development of both types of improvement over a 24hr interval.…”

“…The expression of off-line improvements may be influenced by the timeof-day of retesting. To quantitatively address this issue we contrasted improvements in this study against those which developed over 12-hr intervals in an earlier study (Cohen et al 2005). Two groups were drawn from the earlier study.…”

“…24-hr vs. 12-hr) there should be: (1) similar improvements when retesting took place at the same time of day (e.g., 8pm) and (2) substantially different improvements when retesting took place at different times of day (e.g., 8pm vs. 8am) for the same skill component (goal or movement). To explore this issue we contrasted the improvements over the 24-hr intervals described here against those which developed over 12-hr intervals described in earlier work (Cohen et al 2005). There was no significant difference in the goal-based improvements which develop from 8pm to 8am as compared to 8pm to 8pm (unpaired t-test, t(18) = 0.588, p = 0.564).…”

“…During consolidation however, skill components are differentially processed: skill represented in an egocentric coordinate frame is enhanced over wake, whereas skill represented in an allocentric coordinate frame is enhanced over a night of sleep (Cohen et al 2005). A 24-hr interval containing a normal sleep-wake cycle may support the development of improvements within both the egocentric and allocentric co-ordinate frames.…”