For Experiment 1, participants were asked to either try to remember all items equally (baseline condition), or to try especially hard to remember the first item in the sequence (prioritisation condition). For the prioritisation condition, 2 notional points were awarded for correctly recalling the first item, if tested. One point was awarded for the 2nd and 3rd position as well as all three positions in the baseline condition, though these points were not linked to a reward.
3.4.1 Method
Participants. 87 (47 girls) participants took part in Experiment 1 (Mean age
= 8.98, SD = 0.95, Range = 7.5 - 10.47). Of this dataset, 15 children were excluded due to having special educational needs, and an additional 3 children were excluded due to being distracted on the primary tasks. Finally, 1 child was excluded due to lacking data for both conditions of the primary task. The final sample used for primary task analysis had 68 participants (Mean age = 9.02, SD
= 0.92, Range = 7.5 - 10.47). There were 21 eight year olds (Mean age = 7.94, SD = 0.27, Range = 7.5 - 8.43), 22 nine year olds (Mean age = 8.89, SD = 0.3, Range = 8.5 - 9.43), and 25 ten year olds (Mean age = 10.05, SD = 0.32, Range
= 9.57 - 10.47).
Materials & Procedure. See General Methods (above) for a description of the materials, procedure and analysis plan.
3.4.2 Results
3.4.2.1 Primary task analysis
Proportion correct by condition and age group for the primary task is illustrated in Figure 3.2. A condition (prioritisation, baseline; within) x serial position (1, 2, 3; within) x age group (8, 9, 10; between) mixed ANOVA was carried out. There was no main effect of condition: F(1, 65) = 0.65, p = .42, η2p < .01, ηG2 < .01.
The main effect of year was significant but small: F(2, 65) = 3.39, p = .04, η2p
= .094, η2G = .035. Finally, there was a substantial main effect of serial position:
F(2, 130) = 46.56, p < .001, ηp2 = .42, η2G = .18. None of the interactions were significant (all ps > 0.59).
Bayes Factor analysis revealed that the most likely model given the data had effects of age group and serial position (6.58 times more likely than a model with
Figure 3.2: Serial position curves for Experiment 1 by age group and condition for the primary task. Error bars show standard error. The horizontal dotted line shows chance performance. The unfilled grey shapes show the raw data (see Weissgerber et al., 2015).
effects of age, serial position, and condition.) However, this model was only 1.03 times more likely than a model with effects of serial position only.
Planned pair wise comparisons revealed a non-significant difference between serial positions 1 and 2 (t(67) = -0.77, p = .45, BF = 0.18, d = -0.09). The Bayes Factor analysis showed that the null model was 5.6 times more likely than the alternate model. Positions 1 and 3 significantly differed with performance at position 3 being higher (t(67) = -8.09, p < .001, BF > 10000, d = -0.98). Equally, positions 2 and 3 differed significantly with higher performance at position 3 (t(67) = -7.6, p < .001, BF > 10000, d = -0.92).
8 year-olds and 9 year-olds did not differ significantly (t(40.6) = -1.08, p = .29, BF = 0.48, d = -0.33), nor did 9 year-olds and 10 year-olds (t(44) = -1.45, p = .27, BF = 0.68, d = -0.42). 8 year-olds and 10 year-olds, on the other hand, did differ significantly in performance with 10 year-olds performing better than 8-year-olds (t(43.89) = -2.67, p = .037, BF = 4.45, d = -0.78).
Table 3.1: Standardised and unstandardised coefficients for predicting the difference in performance at position 1 between the prioritisation and baseline conditions.
B SE Beta p-value
Intercept 0.043 0.28 0.88
FDR 0.16 0.23 0.11 0.49
BDR -0.029 0.18 -0.03 0.87
Corsi -0.0022 0.21 -0.0019 0.99 Odd-one-out -0.066 0.17 -0.074 0.69
Age -0.011 0.031 -0.051 0.73
3.4.2.2 Individual differences analysis
While no overall effect of prioritisation was observed there could be an effect for some participants that is related to individual differences in WM. This was tested with a linear regression predicting the difference in performance for the first item between the prioritisation and baseline conditions. One participant was excluded from this analysis due to having not completed the Corsi task. Table 3.1 shows the results of this analysis. Clearly none of the predictors were related to the boost at the prioritised position. The R2adj for this model was .01.
Bayes Factor analyses also supported the absence of a relationship between the additional WM measures and the prioritisation boost. The intercept-only model was 3.6 times more likely than any alternative model.
3.4.3 Discussion
The analyses of the primary visual WM task showed no effect of condition; telling children to try especially hard to remember the first item did not improve memory for that item. There was an effect of year-group driven by the difference between the youngest (7 to 8) and oldest (9 to 10) groups, however, the Bayes Factor analysis did not support including the effect of year. In addition, there were no
interactions with age, such that older children were no more able to utilize the instructions than the youngest children.
The individual difference analyses further supported the suggestion that children are unable to prioritise items in visual WM. If the ability to prioritise is emerging at the ages we tested then we would expect those children with the most developed WM abilities to show a prioritisation effect. This would be revealed if our additional WM measures related to the difference in performance at position 1 between the prioritisation and baseline conditions. Instead none of the measures were related to this difference in performance. Thus, while some participant performed better at position 1 in the prioritisation condition this is likely due to random fluctuations in performance rather than meaningful developmental changes. As predicted, there was a large effect of serial position with recall from the final position relatively more accurate than from the first two positions. This recency effect is larger than those observed when an entire visual sequence is recalled (Hitch et al., 1988; Pickering et al., 1998), instead resembling the effects observed using a precision-based single item probe (Burnett Heyes et al., 2012).
These results provide the first suggestion that, unlike adults (Hu et al., 2014, 2016), 7 to 10 year-olds are unable to prioritise the first item in a sequential visual WM task. In contrast, like adults, they do clearly show improved recall of the final sequence item. These findings might indicate a developmental contrast between controlled, effortful processing on the one hand, and relatively effortless and automatic processing on the other. However, one possible alternative account of the outcomes from Experiment 1 is simply that children were not sufficiently motivated or that they forgot the prioritisation instructions. To address this concern and establish whether the Experiment 1 findings replicate, we increased the motivation to prioritise in Experiment 2 by adjusting the notional points rewarded for the prioritised item, and telling participants that if they got enough points they would be given a reward upon completion of the task. In addition, participants were shown an instruction screen every 10 trials reminding them
which item in the sequence they should try especially hard to remember.