watched the movie nor received praise. Participant happiness after watching the clips was subjectively assessed using a seven-point scale (1 = very unhappy, 4 = neutral, 7 = very happy) and the ratings were significantly higher (happier) than 4 (the midpoint) in the Self group (black bar; one-sample t-test, t16 = 12.11, p,0.0001) and the Other group (gray bar; one-sample t-test, t12 = 4.58, p,0.001). To control out the positive word effect [22], we directly compared the happiness rate of both Self and Other groups. We were interested in the effect of the direction of the positive evaluation because when the positive evaluation is directed to ‘‘Self’’, it should be perceived as praise, whereas it should not be when the positive evaluation is directed to ‘‘Other’’. Indeed, participants in the Self group rated the movies as significantly more pleasant than those in the Other group (unpaired t-test, t29 = 2.50, p,0.05), indicating the successful manipulation of praise in present study. An analysis of variance (ANOVA) showed that performance at the end of training on day 1 did not significantly differ between the groups (F2,45 = 0.02, p = 0.98; Figure 3A). In all groups, performance significantly improved between the end of training on day 1 and the retest on day 2 (F1,45 = 267.36, p,0.0001), confirming the offline improvement on the trained sequence (16, 17, 24–26). The rate of offline improvement differed significantly between the three groups (F2,45 = 3.53, p,0.05). Improvement was significantly greater in the Self group (19.9561.85%; Figure 3B) than in the Other group (14.3761.33%, Dunnett’s test, p,0.05) and the No-praise group (13.1461.82%, p,0.05), indicating that praise enhanced skill consolidation. Because several evidences showed that sex of the participants influence the consolidation and recall of different types of memory [23–25], it is possible that sex of participants interacted with the effect of praise in the offline performance improvements. Therefore, we conducted an additional ANOVA with Group (Self vs Other vs No-praise) and Sex (Male vs Female) as independent variables in the offline improvement. No significant main effect of Sex (F1,42 = .05, p = .94) or interaction between Group and Sex (F2,42 = .62, p = .52) was observed, while the effect of praise was significant (F2,42 = 4.90, p,.05). Although present study was not designed to investigate the effect of sex differences, these results indicate that the effect of praise contributed to the offline improvements in motor skill independently of participants’ sex. Figure 1. Experimental design. All participants were initially trained on a sequential finger-tapping task. They were then divided into three groups according to whether they received praise for their own training performance (Self group), praise for another participant’s training performance (Other group), or no praise (No-praise group). The next day, participants completed a surprise retest of the trained sequence, a non-trained sequence (NEW), randomly-ordered tapping (RAN), and a working memory (WM) task. doi:10.1371/journal.pone.0048174.g001 Praise Enhances Offline Skill Improvements In present study, we excluded a total of ten participants from the above-mentioned analyses because they suspected the movie (n = 5) or additionally practiced after the end of practice (n = 5). To evaluate the trend in the performance improvement of these excluded participants, we conducted an additional analysis of offline improvement rates in extra-experimental rehearsal group and suspicion group in comparison with that in the inclusion group (n = 48). According post-hoc test, relative to the average offline improvement rate of included participants (15.9461.06%), that in extra-experimental rehearsal group was significantly higher (25.6662.97%, p,.05, ANOVA with Dunnett’s test) while that in participants who suspected for the movie did not significantly differ (16.9662.55%, p = .94). These data suggest that extra- experimental rehearsal enhance the skill performance through additional exercise, and that suspicion for the movie per se did not influence the praise-related enhancement effect in skill consolida- tion. Performance on control tasks An alternative explanation for the Self group’s improvement was an increase in general motivation due to praise. To investigate this, the participants were asked to perform a non-trained sequence, a randomly-ordered tapping task, and a working memory task on day 2. There were no significant group differences in performance on either the non-trained sequence (Self, 22.1260.92; Other, 21.9861.03; No-praise, 23.2760.97 sequenc- es per trial; ANOVA: F2,45 = 0.52, p = 0.60) or the randomly- ordered tapping task (Self, 70.1661.91; Other, 67.8961.65; No- praise, 69.7062.76 buttons per trial; F2,45 = 0.30, p = 0.74). For the working memory task, there were no significant differences between the three groups in either reaction time (Self, 922647 ms; Other, 912635 ms; No-praise, 877625 ms; F2,33 = 0.47, p = 0.63) or accuracy (the number of correct responses relative to all responses) (Self, 0.7160.03; Other, 0.8060.03; No- praise, 0.7460.03; F2,33 = 1.77, p = 0.19). Sleep duration and quality during the night after training Neither sleep duration (measured by subjective reports) nor actimetry measures differed between the groups (Subjective report, F2,45 = 0.02, p = 0.98; Actimetry, F2,45 = 0.52, p = 0.60). There were also no significant differences between the three groups in sleep quality, as calculated from physical activity during the night after training (Actimetry, F2,45 = 0.49, p = 0.62). Alertness, concentration, and fatigue during training and retest Finally, there were no significant differences between the three groups for any of subjective ratings (sleepiness, concentration, and fatigue, ANOVA, p values $0.06), indicating that the differences in offline improvement between the groups were not caused by differences in subjective states during training or retest periods. Discussion The purpose of this study was to investigate whether praise following motor training enhances skill consolidation. All groups showed offline skill improvements between the end of training and the retest 24 h later, confirming the results of previous studies [17,19,20]. Furthermore, our data indicated that praise following motor training enhances consolidation of the learned sequence since the rate of offline improvement was significantly greater in the Self group than in the Other or No-praise groups. As the evaluation video clips viewed by the Self and Other groups were identical except for the instructions indicating to whom the praise PLOS ONE | www.plosone.org 2 November 2012 | Volume 7 | Issue 11 | e48174