Students were allowed to copy a figure at the training day (TR) and 24 h later they were asked to draw it again. A memory index was calculated. The first analysis was to assess the children performance on TR day. We noticed that around 85% of the participants copied the figure completely, whereas 12% missed copying 1 element and 3% missed copying 2 elements. However, when we compared the memory index between participants who copied the figure completely, those who missed 1 element and those who missed 2, the one-way ANOVA did not reveal significant differences between these three groups, neither for weak controls (F (2,53) = 1.24, p = 0.30) nor for strong controls (F (2,55) = 0.04, p = 0.96).

Figure 1a shows the performance in the graphical LTM test for students from CTRw, which obtained a Memory Index of about 0.5 and significantly less than 0.6 (One-sample t-test against 0.5 value, p > 0.05; against 0.6 value p < 0.05; for all CTRw groups). We observed an improvement of the Memory Index for students who experienced the exam 1 h after the copying of the figure in the TR day (Student’s t-test; EXM Condition +1 h vs CTRw, t = 3.30, p < 0.01). The other EXM groups, whose students had the exam previous to the copying of the figure (−4, −1, −0.5, or −0 h) or at other times after it (+0.5 h or +2 h), showed similar Memory Indices in comparison to their respective control groups (EXM vs. respective CTRw, p > 0.05). Figure 1b shows the performance in the graphical LTM test from CTRs, which obtained a Memory Index of about 0.6 and significantly greater than 0.5 (One-sample t-test: against 0.6 value p > 0.05; against 0.5 value p < 0.05; for all CTRs groups). In contrast to the improvement in memory retrieval observed in Fig. 1a, the presence of an exam either before (−1 or −0.5 h) or after (+0, +0.5, or +1 h) the copying of the figure, significantly decreased the memory index of the EXM groups with respect to their corresponding CTRs groups (Student’s t-test; EXM vs respective CTRs, at condition −1 h: t = 2.33, p < 0.05; −0.5 h: t = 2.24, p < 0.05; +0 h: t = 3.98, p < 0.001; +0.5 h: t = 2.92, p < 0.01; +1 h: t = 2.78, p < 0.01). However, when the exam was taken 4 h previous to the figure copy or 4 h after it, the impairment of LTM was not observed (EXM vs respective CTRs, p > 0.05).

Fig. 1 Exam effects on unrelated graphical long-term memory could be beneficial or deleterious. A schematic representation of the experimental protocol is presented on the top of the figure: students were asked to copy Rey Osterrieth´s figure and they had or not (CTR) an exam before or after it. The figure copy is time zero and the time condition described for the exams are relative to it and expressed in hours. LTM of this figure was tested 24 h later. a Memory Index is shown as mean ± SEM for weak retrieval CTR groups (CTRw, white bars) and for that groups which had one exam at different times around copying of the figure (EXM groups, black bars). b Memory Index is shown as mean ± SEM for strong retrieval CTR groups (CTRs, light gray bars) and for that groups which had one exam at different times around copying of the figure (EXM groups, black bars). In all cases the number of participants is written in each bar. Student’s t-test, CTR vs. corresponding EXM group, *p < 0.05, **p < 0.01, ***p < 0.001 Full size image

Then, we analyzed possible sex differences in memory index using two-way analysis of variance (ANOVA). In Fig. 2a we assessed differences applying control group (CTRw/CTRs) x gender (M/F) ANOVA. We found a significant main effect of control type, F (1,258) = 57.13, p < 0.0001, but no main effect of gender, F (1, 258) = 0.02, p = 0.88, neither significant interaction, F (1, 258) = 1.97, p = 0.16. These results showed that beyond the differences between CTRw and CTRs no significant differences were observed between masculine (M) and feminine (F) students in each one. The following two-way ANOVA analysis was made considering group condition (EXM/CTRw or EXM/CTRs) x gender (M/F) for different time point evaluated. The increment in the Memory Index induced by the exam 1 h after the copying of figure observed in weak retrieval students, was similar for M and F, since the analysis only revealed a main effect of exam, F (1, 56) = 11.89, p < 0.01 (gender: F (1, 56) = 0.04, p = 0.84; interaction: F (1, 56) = 7.75 e−5, p = 0.99; Fig. 2b). Moreover, the decrement induced by the exam 1 h after the copying of figure in strong retrieval students was similar for M and F too (exam: F (1, 83) = 6.61, p < 0.05, gender: F (1, 83) = 3.00 e−3, p = 0.96, interaction: F (1, 83) = 0.83, p = 0.37; Fig. 2c). Also, at those times in which the exams had no effect, for example exam 2 h after copying of the figure in weak retrieval students (Fig. 2d) or exam 4 h before it in strong retrieval students (Fig. 2e), the Memory Index did not show differences by gender. The analysis did not reveal any significant effect (at Condition +2 h in weak retrieval groups, exam: F (1, 52) = 0.43, p = 0.52, gender: F (1, 52) = 1.19, p = 0.28, interaction: F (1, 52) = 0.30, p = 0.59; at Condition −4 h in strong retrieval groups, exam: F (1, 40) = 1.78 e−4, p = 0.99, gender: F (1, 40) = 0.30, p = 0.59, interaction: F (1, 40) = 1.14, p = 0.29).

Fig. 2 Sex differences and proportion of item scores for graphical memory. a–e Memory index is shown as mean ± SEM for different groups in which masculine (M, flat bars) and feminine (F, hatched bars) students were analyzed separately. We show data for all CTRw (white bars) and CTRs (light gray bars) a, EXM groups (black bars) that had an exam 1 h after the copying of the figure (EXM, Condition +1 h) in both weak b and strong c retrieval students groups and also for those groups that had an exam 2 h after the copying of the figure (EXM, Condition +2 h) or 4 h before it (EXM, Condition -4h) in weak d and strong e retrieval students groups, respectively. Two-way ANOVA, *p < 0.05, **p < 0.01, ****p < 0.0001. f–j Score proportion is shown as mean ± SEM for different groups in which item scores (null, low, mid, and high) was analyzed. We compare the profile of CTRw (black dotted line with circles) and CTRs (gray dotted line with squares) f, EXM in Condition +1 h (black line with triangles) with its respective CTRw g or CTRs h, EXM in Condition +2 h group with its respective CTRw i and EXM in Condition -4h with its respective CTRs j. Student’s t-test. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 Full size image

Finally, we analyzed the score proportion obtained in figure's test using Student's t-test. Figure 2f shows a decreased proportion of null score (t = 5.58, p < 0.0001) and an increment in items perfectly drawn (high score; t = 6.33, p < 0.0001) in CTRs compared to CTRw. No differences were observed in the low and mid scores (p > 0.05). This same profile was observed in weak retrieval students, when EXM Condition +1 h group was compared with their respective CTRw (null score, t = 3.62, p < 0.001; high score, t = 2.54, p < 0.05; low and mid scores p > 0.05; Fig. 2g). On the other hand, the decrement of memory index observed in strong retrieval students at EXM Condition +1 h compared with their controls, relayed on the increment of null items drawn in the test and in a decrement of items perfectly drawn (null score, t = 2.76, p < 0.01; high score, t = 2.28, p < 0.05; Fig. 2h). No differences were observed in the low and in mid scores (p > 0.05). These results suggest that the amount of items drawn and the number of items faithful drawing (both draw and place were correct) are parameters sensible to exams effects. Moreover, the analysis of score proportion in those cases in which memory index was not modified, did not show differences between groups (EXM Condition +2 h vs. CTRw: all scores p > 0.05, Fig. 2i; EXM Condition -4h vs CTRs: all scores p > 0.05, Fig. 2j).