Effect of stimulus contrast and attention on PSDs and slopes. (A) Mean PSD (left) and mean PSD slopes (right) during the stimulus period (200 ms–400 ms after stimulus onset) for different stimulus contrasts (indicated in the second column). The traces corresponding to the lowest (0%; black) and highest contrast (100%, lightest gray) are plotted thicker for clarity. The insets in the first and third columns show the change in power (in decibels) from the baseline period (300–100 ms before stimulus onset) for the different contrast conditions to highlight the suppression of alpha power at about 10 Hz and increase in gamma power above 30 Hz. The black markings over the frequency axis denote the frequencies at which the difference in the slopes is statistically significant (⁠⁠; Bonferroni corrected; ANOVA). SEMs are omitted for clarity. (B) Mean PSD and corresponding slopes during the baseline period (300–100 ms before stimulus onset) and stimulus period (200–400 ms after stimulus onset; only 100% contrast condition is shown) when attention was directed inside (Attention IN) or outside (Attention OUT) the receptive field. The insets in the first and third columns show the change in power (in decibels) from the Attention OUT baseline condition.