Article Figures & Data
Figures
- Figure 1.
Combining memory load and acoustic degradation in a memory paradigm. A schematic trial of the adapted Sternberg task is shown in the top left. Memory load, operationalized as number of items to be retained [2, 4, or 6 items, flanked by bandpassed noise (BPN) to ensure presentation of 6 auditory events]; speech degradation of the presented items in a given trial, operationalized as the number of bands used for spectral degradation (16, 8, or only 4 bands). The bottom right indicates the vocoding filter frequencies and bandwidths. The color coding indicates the hypothesized parametric change of alpha power during stimulus-free delay.
- Figure 2.
Time–frequency response during encoding, delay, and retrieval phases. All panels show t values (N = 18) for parametric effects of memory load (top row) and degradation (bottom row), separately for the encoding phase (left column), delay phase (middle column), and the retrieval phase (right column). Waveforms at the top schematically indicate the presented sound. Top and bottom rows show time–frequency plots of t values, averaged across sensors that belong to the respective significant cluster. Positive t values (i.e., more alpha activity for higher load or more severe degradation, respectively) are shown in hot colors and negative values in cold colors. Line plot, For the delay period (middle panels), the distribution of memory load (black) and degradation (red) effect sizes over frequencies confirms an alpha peak for both effects. The sensors contributing to the significant memory load and degradation clusters are indicated by dots in the series of sensor topographies over time (left middle).
- Figure 3.
Alpha enhancement during delay and relation to response time. A, Mean alpha power change during delay (8–13 Hz, 0.4–1 s; the inset sensor topography shows the used sensors; those sensors were part of both the memory load cluster and the degradation cluster). Means ± 1 within-subject standard error are displayed. Note the cumulative effects of memory load (memory load, left to right) and degradation (less number of bands, also left to right). B, Subadditivity and superadditivity of alpha power. Alpha power (data identical to A) replotted as a two-dimensional function along the two manipulated dimensions (load, more items; degradation, less number of bands). Note the alpha overshoot (red) for most severe degradation/highest number of items and alpha undershoot (blue) for least degradation/least number of items. C, Mean response time per condition. Means ± 1 within-subject standard error are displayed. D, Scatter plot of mean response time (x-axis; data identical to C) versus mean alpha power during delay (y-axis; data identical to A) with linear regression line.
- Figure 4.
Source localization of alpha enhancement during delay. Top row illustrates the source-level cluster (p < 0.05) exhibiting an overall alpha power enhancement compared with baseline, with t values from the significant cluster displayed on a standard MR template. Bottom row shows the data plotted on the automatic anatomical labeling atlas. Sup, superior; Inf, inferior.
