A better understanding of memory consolidation and contributory factors is necessary to determine how it applies to the field of education. The following is a review of three studies on memory consolidation in the performance of different motor skill tasks by different population groups using a variety of independent variables.
Study #1
Purpose of the Study
Terpening et al. (2012) aimed to investigate the relationship between certain characteristics of sleep and the ability to learn and correctly perform a motor skill, namely sequential finger-tapping. The researchers recognized the limited number of studies done thus far on the neurological disturbances that occur in patients with Parkinson’s disease and other degenerative disorders. They also noted the lack of research on memory consolidation as a function of sleep, a phenomenon that changes across the lifespan. The current study offered additional insights into how sleep-dependent skill consolidation and memory is affected by both increasing age and the presence of degenerative disease, as well the features of sleep that best assist in performance of the chosen skill. The findings may be useful in developing alternative treatments in the future.
Tasks Performed
Sequential finger-tapping entailed using the non-dominant hand to tap five numbers in the correct sequence as fast as possible. The sequence was 4, 1, 3, 2 and 4. During trials that occurred two hours before the participants’ routine bedtime, the correct sequence was shown on the screen and thus did not require memory work among the participants. Each key press corresponded to a box appearing on the screen but did not indicate whether the sequence was correct. Each of 12 trials lasted 30 seconds with 30-second breaks in between and scored as incorrect or correct sequence. Participants were not made aware of the six early and late retest trials that would be conducted after a night’s sleep, specifically 30 minutes after waking up the following morning, to prevent task rehearsal which constitutes bias. The trials as well as overnight sleep took place in a sleep laboratory. Study groups consisted of healthy seniors as the control group and seniors with Parkinson’s disease as the experimental group.
Performance Measurement
Pre-training, post-training, early retest, and late retest learning scores and improvement in skills overnight were used to measure learning and performance. Pre-training score was the average number of sequences tapped correctly during the first three of the 12 trials while post-training score was the average correct sequences tapped during the last three trials. Pre- and post-training error rates were the average number of incorrectly-tapped sequences during the first three and last three trials respectively. Similarly, the early retest and late retest scores and error rates corresponded to the mean scores and error rates in the first three and last three trials respectively. Characteristics of sleep were based on the results of polysomnography and included the total duration of sleep, length of time of stage 2 sleep, duration of short-wave sleep, rapid-eye movement sleep duration, onset of waking after sleep, and efficiency of sleep. Overnight skill improvement is derived from comparisons between the learning scores at early retests and learning scores at post-training as well as late retests and post-training learning scores.
Study Findings
Data analysis revealed that both control and experimental groups had low error rates at pre- and post-training with the differences deemed statistically insignificant. The average number of correctly tapped sequences also did not show significant variation between the two groups. When comparisons were done between pre- and post-training and early and late retest, the number of sequences tapped correctly were significantly higher during late retest in both groups with the variances between groups insignificant. There were no significant differences in error rates during both training and retest between the two groups. In comparison with baseline, however, the control group exhibited better performance during late retest while in the experimental group there was no significant difference in baseline and retest results. Between the two groups, no significant associations were found between performance and any sleep characteristic but in the control group slow-wave sleep had a positive correlation with better performance during late retest. There were no significant differences in length of short-wave sleep among all participants. This observation was not noted in the experimental group but in the latter there was a positive correlation between late-retest performance and the daily dose equivalent of L-Dopa.
Explanation of Findings
The researchers explained that based on the findings, the absence of overall improvement or deterioration in task performance between the two groups implied that memory trace was stable or consolidated among healthy patients and patients suffering from Parkinson’s disease. When only healthy participants are considered, there was late retest performance improvement from baseline which was associated with longer short-wave sleep. The findings also suggest that a higher daily dose equivalent of L-Dopa improves the learning and performance of a skill. Study results support the findings in some studies and also contradict those of others showing that knowledge in this area is not yet well-established. The researchers pointed to the lack of control over several variables, sampling biases, and the nature of the selected task as possible explanations for the differences in findings.
Study #2
Purpose of the Study
On the other hand, Shea et al. (2001) wanted to determine whether motor skill performance improved as a function of the length of time interval between practice sessions. The reason for choosing this study was to fill a gap in knowledge. The researchers noted that prior studies often conducted experiments within one day because of practical considerations such as the costs of equipment and venue as well as the availability and convenience of participants. Moreover, there was no existing theoretical framework showing the relationship between skill acquisition and time interval of practice sessions. Two tasks were used in the study to investigate whether the influence of time interval can be generalized across different types of tasks.
Tasks Performed
The study consisted of two experiments, the first investigating a continuous balance task and a discrete-timing task with a 20-minute interval between sessions and the second involving the same tasks but with a 24-hour interval between sessions. Continuous balance was measured by a stabilometer, which required participants to stand on a platform and maintain their balance to keep it in a horizontal position for as long as 90 seconds as was the duration of each trial. The discrete-timing task involved tapping, with the right hand, four keys on a keyboard in the correct sequence. The key was to tap the right sequence with the shortest interval between each tap leading to the shortest length of time between the first and last taps ensuring that it falls within the given time limit. An incorrect sequence corresponds to a repeat trial.
Performance Measurement
In Experiment #2, there were three discrete timing tasks. All involved the same number sequence but with different time limits with regard to the length of time between the first and last taps. The participants had to finish 3 sessions composed of 12 trials for each task variation before taking the retention test. Two groups performed the tasks with one group having a ten-minute interval between sessions allowing them to finish all sessions in one day. The second group performed one session a day so that the experiment finished in three days. The retention test involved twelve trials on a selected task variation. Performance was measured by global error or the amount of variation between the actual and required time interval for the first and last press of keys in the sequence.
Study Findings
Statistical analyses showed that in the first experiment, there was in increase in proficiency between the first and second practice sessions. However, the group with the two-day session had better performance during the trials and retention tests with regard to root mean square error. It was also noted that for both groups, significant improvements were noted during the retention trials held 24 hours after the last session. The second experiment also showed better performance in the group that practiced for three days both during acquisition and retention. This means that they had significantly less global errors than the group with one day practice. Overall, there was improvement in performance between the first task variation and the succeeding variations.
Explanation of Findings
The results of the study indicate that better performance is achieved with longer spacing between practice sessions. This implies that longer rest periods enhance memory consolidation. Results also show that this is not only true for continuous tasks but also for discrete motor tasks. The study validates in human participants the applicability of the hypothesis in memory consolidation made with animal models with regard to motor tasks. This has implications for the design and conduct of skills training for both categories of tasks used in the experiments.
Study # 3
Purpose of the Study
Sugawara et al. (2012) studied the influence of praise as a form of social reward on skill consolidation or performance after the practice has ended. While many studies were done on the effect of praise on online performance or during practice, none were conducted on skill consolidation or offline performance. The researchers hypothesized that social reward has a direct impact on skill consolidation as opposed to social reward serving as motivation for more practice, which is an indirect effect.
Tasks Performed
Participants were asked to learn a sequence of finger taps. After the practice session, they were divided into three groups. The first group called Self Group was asked to watch a video wherein the experiment evaluators verbally praised the participants’ skill performance. The second group called Other Group watched the same video except that they were told it was an assessment of another group. The third group called No-Praise Group did not watch the video or receive any form of praise. Twenty-four hours after, the participants were asked to take part in a retention test. Participants were also asked to perform control tasks without praise on the second day. These included random finger-tapping sequences that did not require practice and also a test of working memory.
Performance Measurement
The number of correct finger-tap sequences in each 30-second trial was the measure of performance used. Participants’ perceived happiness following the video was measured by subjective assessment. A seven-point happiness scale ranging from very unhappy to very happy was developed for the study. Significant happiness levels were ratings above the midpoint of ratings for the Self Group and Other Group. To ensure that the Self Group regarded the video as a form of praise and that the Other Group did not regard it as praise, both groups were asked to rate the videos they watched. The ratings showed a significant difference between the two groups, with the Self Group significantly perceiving the video as more pleasant than the Other Group.
Study Findings
Data analysis showed among the three groups, there were no significant differences in sequential finger-tapping online task performance measured at the end of practice on the first day. The researchers also noted that performance generally improved in all groups when comparing end-of-training scores and retest scores. However, performance was significantly better in the Self Group compared to the Other Group and No-Praise Group. To eliminate the effect of gender on consolidation, further statistical analysis showed no significant differences in scores between males and females.
Participants who, on their own, practiced the finger-tapping sequence after the practice sessions were excluded as were those who were suspicious of the intent of the video presented. Confounding variables such as duration of sleep, quality of sleep, fatigue, alertness, and concentration were also analyzed and found to have no significant effect on the results. Thus, the motor skill improvements can be attributed with confidence to the use of social reward or praise rather than to any other variable.
Explanation of Findings
After controlling for all possible variables that could influence offline memory consolidation, the study provides convincing evidence that social reward in the form of verbal praise delivered through a video enhanced retention and better skill performance. Although gender, sleep, additional practice after the sessions, concentration, alertness, and fatigue provide alternative explanations for the effects noted, all were statistically analyzed and showed no significant effect on offline performance.
Similarities and Differences between the Studies
All three studies used memory consolidation as a dependent variable and measured in post-test or skill retention tests following a period of practice or skill acquisition stage. This means that in learning motor skills, sufficient time must be provided for trials in order for the task to be committed to memory. However, memory has to be consolidated to achieve retention. The differences of the studies are the independent variables used to influence retention and therefore memory consolidation. These included the presence of degenerative illness such as Parkinson’s, giving social reward, and lengthening the time interval between practice and the retention test.
Conclusion
Memory consolidation and its effect on motor skills learning as well as retention are influenced by many factors. Among healthy older adults, longer short-wave sleep was associated with better retention while in older adults with Parkinson’s it was associated with higher daily doses of medications that improved the neurologic functioning. Delivering a retention test one day following practice compared is also beneficial to consolidation, learning, and performance. Last, giving social rewards is also found to positively affect memory consolidation. Thus, consolidation seems to be a function of physiologic and psychosocial factors as well as the structure of training delivery. In all the participants of the three studies, however, improvements in performance were noted with practice. In addition, the findings of the second study regarding the benefits of a 24-hour delay between practice trials and retention test were validated in the first and third studies. These factors should be considered when designing and implementing motor skills trainings to various groups across the lifespan.
References
Charles, H., Lai, Q., Black, C., & Hoon, J. (2000). Spacing practice sesssions across days benefits the learning of motor skills. Human Movement Science, 19(5), 737-760. Retrieved from http://dx.doi.org/10.1016/S0167-9457(00)00021-X
Sugawara, S., Tanaka, S., Okazaki, S., & Katsumi, W. (2012). Social rewards enhance offline improvements in motor skills. PLoS ONE, 7(11): e48174. doi: 10.1371/journal.pone.004817.
Terpening, Z., Naismith, S., Melehan, K., Gittins, C., Bolitho, S., & Lewis, S.J. (2013). The contribution of nocturnal sleep to the consolidation of motor skill jearning in healthy ageing and Parkinson’s disease. Journal of Sleep Research, 22(4), 398-405. doi: 10.1111/jsr.12028.
