Inducing motor skill improvements with a declarative task

Abstract

During sequence learning, individuals show motor-skill acquisition and an ability to verbally describe items within the sequence. We disrupted this latter, declarative component by having participants learn a word list immediately after sequence learning. This induced off-line skill improvements. We conclude that off-line memory processing relies not only on the engagement of neuroplastic mechanisms but also on the disengagement of an interaction between declarative and procedural memory systems.

Figure 1. Experimental Design

Participants were trained, tested (skill₁) on the SRTT, and then either learnt a list of words or were asked to state the number of vowels within nonsense letter strings. Following a 12-hr interval participants were retested (skill₂) on the SRTT, and finally asked to declaratively recall items from the sequence. Skill was measured by comparing the response times of the sequential trials (white blocks) against those of the random trials (gray blocks). The interval between testing (skill₁) and word list learning was extended to 4-hr in one control group while in another the interval between testing and retesting was reduced to 30 minutes.

Figure 2. Off-line learning and sequence recall

(a) Participants initial (skill₁, gray boxes) and later performance on the SRTT (skill₂, black boxes), with associated sequential (square±sem) and random (circle±sem) response times. Following word list learning there was only a fall in sequential response times (paired t-test, t(11) = 6.15, P<0.0001); with no significant change in the random response times (circle±sem, paired t-test, t(11) = 1.79, P = 0.1). Following vowel counting, there was a similar non-specific fall in both sequential (paired t-test, t(11) = 2.54, P<0.05) and random (paired t-test, t(11) = 2.36, P<0.05) response times. (b) These response time changes translated into differential off-line improvements: off-line improvements were induced following word list learning but not following vowel counting (unpaired t-test, t(22) = 2.5, P<0.05). (c) The declarative component of the SRTT was disrupted by learning a word list immediately after the SRTT: those learning a word list recalled on average 4.0±0.8 items (mean±sem) of the 12-item sequence; whereas, those stating the number of vowels within nonsense letter strings were able to recall on average 7.3±0.9 sequence items (unpaired t-test, t(22) = 2.8, P<0.05).