The Role of Sleep in Motor Skill Learning Timothy Rickard, Denise Cai, Cory Rieth, Jason Jones, & Colin Ard University of California, San Diego

Motor skill performance exhibits a roughly 20% improvement following sleep. Motor skill performance exhibits a roughly 20% improvement following sleep. The dominant explanation is the sleep consolidation (sleep learning) hypothesis. The dominant explanation is the sleep consolidation (sleep learning) hypothesis. a.k.a., “The get something for nothing theory of learning.” a.k.a., “The get something for nothing theory of learning.”

Experiment 1: Replication of Walker et al. (2002) Training session: Twelve 30 second practice blocks on a 5-key sequential finger tapping task, with a 30 second break between each block. Sequence: Test session: Two additional 30 second blocks of the same task. Awake group: Trained at 10 am in the morning, tested at 10 pm the same night. Sleep group: Trained at 10 pm at night, tested at 10 am the next morning. Subjects slept at home. Subjects who reported less than 6 hours of sleep (sleep group), who napped (awake group) or who practiced between sessions were removed, yielding 16 subjects per group. No group differences in Stanford Sleep Inventory given after the test.

Their conclusion: There is a memory consolidation mechanism specific to sleep that enhances subsequent performance. Walker et al. results: For the sleep group, tapping speed was about 20% faster on the two test blocks than on the last two training blocks (sleep enhancement). For the awake group, there was no enhancement effect.

Three points of caution, however: 1) Data averaging in those studies may mask true effects of the delay between sessions in at least two ways: -block-level reactive inhibition 2) Session-level fatigue may be occurring 3) Their awake vs. sleep design confounds the critical group by session interaction with respect to both time-of-day (circadian rhythms) and time-since-sleep.

Summary of results so far: 1)When data are analyzed in a way that is free of averaging and reactive inhibition effects, there is no sleep facilitation effect. 2)There is still a relative sleep advantage, but it now takes the form of forgetting (slowing) for the awake group, with no observed slowing for the sleep group.

Two points of caution noted earlier: 1) Data averaging in those studies may mask true effects of the delay between sessions in at least two ways: -session fatigue -block-level reactive inhibition 2) Their awake vs. sleep design confounds the critical sleep effect with respect to both time-of-day (circadian rhythms) and time-since-sleep.

Can time-of-day explain the relative sleep advantage?

Limitations 1)Lots of data had to be ignored to eliminate the enhancement effect. 2)Time-of-day effects remain. 3)Only two test blocks. Need design that: 1)Does not require elimination of data. 2)Equates time of day effects for the two groups. 3)Eliminates or reduces the reactive inhibition effect. 4)Provides additional test blocks to evaluate the possibility of faster learning after sleep.

Experiment 2: Massed versus spaced practice effects Two groups, each given 6 minutes of training and an identical 6 minute test 24 hours later. Massed practice group: 12 blocks of 30 seconds on / 30 seconds off in each session. Spaced practice group: 36 block of 10 seconds on / 30 seconds off in each session. For the massed group we expected to replicate prior enhancement results with 24 hour delay. The spaced group allows us to minimize the effects of within-block reactive inhibition without having to eliminate any data. Will enhancement still be observed?

Summary of Experiment 2 Massed practice group replicates earlier 24 hr. enhancement result. Massed practice group replicates earlier 24 hr. enhancement result. Based on performance of the spaced practice group, there is no evidence that motor skill learning occurs during sleep. Based on performance of the spaced practice group, there is no evidence that motor skill learning occurs during sleep. These results converges with results for the rotary pursuit task (Adams, 1952). These results converges with results for the rotary pursuit task (Adams, 1952).

Experiment 3: A test of the time-of-day account for wake vs. sleep comparison We controlled for time-of-day but manipulated duration of the delay between sessions. We controlled for time-of-day but manipulated duration of the delay between sessions. 8-hour group (awake): trained at 10 am, tested a 6 pm. 8-hour group (awake): trained at 10 am, tested a 6 pm. 32-hour group (1 night of sleep): trained at 10 am, tested a 6 pm next day. 32-hour group (1 night of sleep): trained at 10 am, tested a 6 pm next day. 56-hour group: (2 night of sleep): trained at 10 am, tested a 6 pm two days later. 56-hour group: (2 night of sleep): trained at 10 am, tested a 6 pm two days later.

So what is the role of sleep in motor skill learning? Sleep may be completely inert with respect to motor skill consolidation, but stay tuned…