This study aimed to define the optimum dosage of MI required to improve the effectiveness of learning a novel motor task. The question we proposed at the beginning of the study was how much training would be enough to produce a significant enhancement in performance and to compare the improvement between the three groups of CG with no MI practice, LD of MI, and HD of MI.
After analyzing the two dependent variables of time and errors, after treatment (8th session), there was a gradual decrease in the mean amount of time taken for the CG and LD groups in comparison to the 1st session. Moreover, between the CG and LD groups, the latter improved the most (20 seconds on average to finish the task on day 8). However, there was no significant difference between the two measurement periods in the HD group. These results were consistent with those of another study in which the MI time was between 10 and 80 minutes. They stated that MI is better than none and that too much MI would lead to a loss of concentration and exertion of participants (13). In this study the HD group, specifically starting from session five, participants reported tiredness and loss of concentration by the end of the session. Previous research has shown that too much practice might have adverse effects in terms of the number of sessions (the frequency) not only the time for a single session (13).
In this study, the largest reduction in time started to occur by day 2 for LD and day 3 for CG but with no improvement for the HD group. These findings are supported by a systematic review which concluded that the largest improvement was seen after three training sessions (4). Moreover, seven studies from the same systematic review (4) stated that a significant improvement was seen in healthy individuals’ performance in the first week of treatment. This agrees with our findings regarding the day-to-day statistical reduction in errors between the 2nd and 3rd and 3rd and 4th days for LD with no further changes for the preceding day.
Regarding the number of errors, there was a statistically significant gradual decrease between session one and all the preceding sessions in both CG and LD groups. However, no statistically significant difference was observed in the HD group. Compared with the CG, the LD performed better in terms of error reduction. This reduction started on day 2 in both groups; however, it fluctuated in the CG.
With MI practice, in this study, the LD group outperformed the CG group in the time needed to complete the task. This finding answered part of the suggested question that was proposed earlier in the study regarding the amount of training needed to improve performance. This is in line with a study that found that MI can enhance the benefits, even partially replacing, of physical training to achieve improvement (29). It was found that task-related MI can influence the actual execution speed of motor tasks, which means that the speed of the task should be equal to what an individual is rehearsing (30).
Furthermore, the performance of tasks can be enhanced by working on both motivational and cognitive components of activity while performing mental practice. However, it has been proposed that in rehabilitation, most of the attention is given to the physical component of the movement rather than to the motivation of the participant. According to this theory, the use of MI will improve the ability to acquire skills (16, 31). The improvement in the CG can be attributed to the amount of physical practice of the mirror tracing task. In addition, according to the different motor learning theories, this may be attributed to the task being new in that the participants made more errors during early sessions, so there was more scope for improvement by the end (32). A different reason might be the interest of participants as they might have been more enthusiastic about the task itself (33).
One more explanation for this improvement is the rapid modulation of the nervous system to adapt to new mental demands (10–12, 34). There were so many factors that could affect the performance of the participants that this study put into consideration such as the surrounding environment, familiarity with the test, and the ability to perform the MI itself (2). Regarding motor learning and performance, there are factors to be considered, one of which is arousal where the individual should be in a mental state that simulates the task intended to be learned (35).
Limitations
The small sample size was due to a shortage of time and the challenging process of recruitment among students. The dropout of students caused an uneven number of participants in all 3 groups that was due to different and tight scheduling. During the task, the investigator encountered difficulties in counting errors. The criteria stated that each time a participant crossed a line, it was considered an error. However, some participants remained at the same point in the drawing for a few seconds, making it challenging to differentiate the lines. Additionally, some participants drew lines outside the designated shape and continued to do so, leading to confusion about whether to count it as a single error or multiple errors, as they were no longer inside the shape.
Suggestions for Future Research
This study is consistent with the literature to a great extent. However, to repeat it modifications are recommended. First, concerning the participants, a larger sample size will strengthen the results and improve the generalizability of the study. Second, the time factor is important for providing a chance to overcome any attritions and dropouts. More time will be needed in terms of recruitment and availability to collect more data. Third, it is suggested to use a computerized tracing method to improve the sensitivity of error tracking.
Clinical Implications
This study assessed two aspects of applying different MI dosages. First, the intensity was measured for several seconds. Second, the frequency was represented by the number of sessions. The findings showed that the greater change occurred between sessions 3 or 4 out of 9 sessions which implies that lower frequencies can cause a greater change than expected. Additionally, there was a beneficial effect in the low-dose group in terms of time and errors which indicates that a greater dose is not necessarily better in terms of effectiveness and improvement.
These findings apply to healthy populations in the age range of 18–35 years, as stated in the inclusion criteria. If replicated with a clinical population, guidance on both frequency and intensity will need further research.