3.1 Normal aging effects (YA vs HA comparison)
3.1.1 Behavioral results. For RT (measured in ms), main effect of condition was significant, F (1,49) = 78.418, p< .001, with participants taking longer to respond to non-retrieval (mean RT = 1562, SD = 345) compared to retrieval (mean RT = 1296, SD = 235) conditions. Main effect of group was not significant,F (1,49) = 3.798, p = .057. No significant interaction between condition and group was found, F (1,49) = .126, p = .724. For accuracy, main effect of condition was significant,F (1,49) = 4.657, p = .036, with participants performing better on non-retrieval (mean accuracy = 88 %, SD = 9.1 %) compared to retrieval (mean accuracy = 84.7 %, SD = 6.9 %) conditions. Main effect of group was not significant, F (1,49) = 0.761, p = 0.387. No significant interaction between condition and group was found,F (1,49) = 0.196, p = 0.66. Group averaged RT and accuracy scores for each condition are listed in Table 2 and plotted in Figure 1.
3.1.2 EEG results. Permutation tests on ERSPs (difference between retrieval and non-retrieval conditions) between YA and HA showed three different effects (FDR < 0.05). First, there was greater theta ERS near the left/midline parietal electrode (P1) from 628 to 701 ms post-stimulus onset in non-retrieval compared to retrieval conditions in YA, t (28) = 3.841, p < 0.001, Cohen’s d = 1.06 (retrieval: 1.96 ± 1.49 dB, non-retrieval: 2.72 ±1.48 dB), but not in HA, t (21) = 1.772, p = 0.091 (retrieval: 2.25 ± 1.75 dB, non-retrieval: 1.76 ± 2.3 dB) (Figure 2.1). Second, there was greater alpha ERD near the left centro-parietal electrode (CP3) from 555-591 ms post-stimulus onset in retrieval compared to non-retrieval conditions in YA, t (28) = 3.744, p < 0.001, Cohen’s d = 1.17 (retrieval: -0.32 ± 1.81 dB, non-retrieval: 0.5 ± 2.13 dB), but not in HA, t (21) = 0.889, p = 0.384 (retrieval: 0.14 ± 3.05 dB, non-retrieval: -0.09 ± 3 dB) (Figure 2.2). Third, there was greater high beta ERS near the right parietal electrode (P8) from 444-481 ms post-stimulus onset in non-retrieval compared to retrieval in HA, t (21) = 2.32, p = 0.03, Cohen’s d = 0.85 (retrieval: 0.11 ± 1.1 dB, non-retrieval: 0.53 ±0.77 dB), but not in YA,t (28) = 1.305, p = 0.202 (retrieval: 0.82 ± 0.69 dB, non-retrieval: 0.63 ± 0.76 dB) (Figure 2.3).
For reference, group-averaged ERSPs in different frequency bands in each condition is illustrated in Supplementary Figures 1 (YA) and 2 (HA). The differences in ERSPs between conditions within each group are included in Supplementary Figures 4 (YA) and 5 (HA). Results from all time frames (including windows with non-significant effects) for normal aging effects (YA versus HA) can be found in Supplementary Figure 7.