Dissociating Oscillatory Alpha Activity and Aperiodic EEG Dynamics in Visual Working Memory

Visual working memory (VWM) allows visual information to be temporarily maintained, but its capacity is limited. Alpha-band EEG activity is often interpreted as a neural marker of VWM. However, traditional band-limited analyses may mix oscillatory alpha activity with the broadband aperiodic component of the EEG signal. Because of that, this thesis examines whether oscillatory and aperiodic EEG activity show different patterns during encoding and maintenance in VWM. Behavioral and EEG data were analyzed from a sequential delayed-estimation color-wheel task. Here, participants remembered one, three or five colored items. Later, participants reported the color of a probed item. Behavioral performance was assessed using absolute recall error. EEG analyses tested aperiodic phase differences, posterior alpha modulations and whether traditional alpha effects remained in decomposed oscillatory alpha peak amplitude. Absolute recall errors increased with set size. This confirmed a clear memory-load effect. The aperiodic exponent was higher during encoding than maintenance, suggesting phase-specific modulation of broadband neural activity during memory formation. Traditional posterior alpha values were more negative during maintenance than encoding. This indicates stronger baseline-relative alpha suppression. However, this encoding-maintenance pattern was much weaker when alpha was estimated as decomposed oscillatory peak amplitude. Overall, the results show that VWM is reflected in both aperiodic and alpha-band dynamics. At the same time, they are also showing that conclusions about alpha modulation depend on how alpha activity is operationalized. This supports a resource- based account, where higher load reduces memory precision.