Does predictive cueing of encoding stimulus duration modulate alpha power and facilitate visual working memory performance in younger and older adults?

Both selective attention and visual working memory (WM) performance are vulnerable to age related decline. Older adults perform worse on, and are less able to modulate oscillatory power in the alpha frequency range (8-12 Hz) than younger adults in WM tasks involving predictive cues about ‘where’ or ‘when’ a stimulus will be present. However, no study has investigated whether alpha power is modulated by cues predicting ‘how long’ an encoding duration will be. To test this, we recorded electroencephalography (EEG) while 24 younger (aged 18-33 years) and 23 older (aged 60-77 years) adults completed a modified delay match-to-sample task where participants were cued to the duration (either 0.1 s or 0.5 s) of an encoding stimulus consisting of 4 coloured squares. We found: (1) predictive cues increased WM capacity, but long encoding duration trials led to reduced WM capacity in both age groups, compared to short encoding duration trials; (2) no evidence for differences in preparatory alpha power between predictive and neutral cues for either short or long encoding durations, but preparatory alpha suppression was weaker in older adults; (3) retention period oscillatory power differed between short and long encoding duration trials, but these differences were no longer present when comparing the trial types from the onset of the encoding stimulus; and (4) oscillatory power in the preparatory and retention periods were not related to task performance. Our results suggest that preparatory alpha power is not modulated by predictive cues towards encoding duration during visual WM, however, reductions in alpha/beta oscillatory power during visual WM retention may be linked to the encoding stimulus, rather than a process specific to WM retention.