In the theta frequency, the interaction between spectral power in the left temporal region and age was a significant predictor of performance on TMT-B. As before, adding IAF did not contribute to the model (AIC: 541.25 for the full and 539.73 for the reduced model; AIC difference = 1.51; F(1,48) = 0.44, p = .51) and was removed. The model accounted for 46% of the variance (adjusted R2; F(3,49) = 15.87, p < .001; interaction: β = −0.71, SE = 0.19, t = −3.79, p < 0.001; age: β = 1.25, SE = 0.26, t = 4.74, p < .001; power: β = −6.12, SE = 3.15, t = −1.94, p = 0.06). Figure 3d shows a similar pattern: for older participants, increased slow wave power was associated with better performance.
