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. 2019 Oct 2;8:e48810. doi: 10.7554/eLife.48810

Figure 5. EEG-Analysis of choice-relevant information after wins and losses.

(a) Standardized coefficients from multi-level regression models relating EEG activity at Fz and Cz electrodes to the opponents’ overall switch rate (A), the n-1 opponent switch/no-switch choice (B), the n-1 players’ switch/no-switch choice, and the interaction between (A) and (B) for each time point and separately for post-win (upper panel) and post-loss (lower panel) trials. Shaded areas around each line indicate within-subject standard errors around coefficients. As coefficients for opponent-related predictors showed a marked, win/loss flip in sign, we again reversed the label of the post-loss predictors (see section Strategy for Testing Main Prediction and Figures 2 and 3; for signed coefficients, see Figure 5—figure supplement 2). For illustrative purposes, colored bars at the bottom of each panel indicate the time points for which the coefficients were significantly different from zero (p<0.05, uncorrected). See text for statistical tests of the predicted differences between coefficients for post-win and post-loss trials. The insert shows the topographic maps of coefficients that result from fitting the same model for each electrode separately. Prior to rendering, coefficients were z-scored across all coefficients and conditions to achieve a common scale. (b) Average ERPs for post-win and post-loss trials, showing the standard, feedback-related wave form, including the feedback-related negativity (i.e., the early, negative deflection on post-loss trials). Detailed ERP results are presented in Figure 5—figure supplement 3.

Figure 5.

Figure 5—figure supplement 1. Controlling for Upcoming Switch and n-1 Stimulus/Response Positions.

Figure 5—figure supplement 1.

The supplement shows the results of the same analysis as in Figure 5, but adding potentially relevant control variables. It is possible that the feedback-related differences for the history/context coefficients shown in Figure 5 are due to the fact that feedback affects the probability of an upcoming switch. For example, the EEG effects may reflect preparatory processes associated with an upcoming switch, such as the allocation of effort. As shown, information about the upcoming switch/no-switch choice was reliably reflected in the EEG signal (t = 2.67). However, different from the history/context variables, the coefficient associated with the upcoming choice was not affected by post-win/-loss feedback (t = 0.68). This pattern is consistent with (Donahue et al., 2013) who have found that frontal and parietal neurons code past choices in a feedback-contingent manner, but represent the upcoming choice in a manner that is not conditioned on previous-trial feedback. As additional control analyses, we also added n-1 stimulus position and response locations to ensure that none of the effects of interest are driven by such lower-level effects. As evident, the overall pattern of history/context effects remains the same when controlling these potential influences.
Figure 5—figure supplement 2. Signed predictors.

Figure 5—figure supplement 2.

In Figure 5, we had reversed the labels for the opponent-related predictors because our predictions referred to the amount of information about the competitive context, not how exactly that information is expressed in the EEG signal. This supplement presents the same analyses as in Figure 5, however plotted using the original predictors (i.e., without reversing labels on post-loss trials). Results reveal a clear distinction between post-loss and post-win signals. For all opponent-related predictors, the effect on the EEG signal was not only reduced following losses, it was also flipped in sign relative to post-win trials. Note, that opponents’ local and global switch behavior has very different implications for the subject’s behavior depending on whether one is currently winning or losing (e.g., see Figure 1b). Thus, one might speculate that this flip in sign is indicative of the win/loss-contingent difference in interpretation (or behavioral implication) of the information provided through the opponent.
Figure 5—figure supplement 3. Event-related potentials.

Figure 5—figure supplement 3.

The supplement shows event related potentials (ERPs) in terms of grand average EEG activity for electrodes Fz and Cz grouped by all factors used in the EEG analysis: the opponent’s overall switch rate (20,50,75%), the n-1 opponent switch/no-switch choice, and the n-1 player’s switch/no-switch choice. The EEG signal was low-pass filtered (Butterworth, 25 Hz), time-locked to the onset of feedback, and subtracted from the average across the 200 ms baseline period prior to the feedback signal. The shaded area indicates within-subject 95% confidence intervals around the average signal. Following the feedback (200 to 300 ms after the onset), we observed a typical feedback-related negativity (FRN), with a peak that was more negative for loss feedback compared to win feedback. Consistent with the results of the main analysis, the FRN was affected by the combination of feedback and context variables: The FRN amplitude was most negative for unexpected opponent switch or repeat choices, that is for opponent switch choices for 25% switch-rate opponents and (to a lesser degree) for repeat choices when facing 75% switch-rate opponents). The fact that we generally find a larger negativity during the typical FRN time range (200 to 300 ms after the onset of feedback) following loss trials is consistent with a negative prediction error account.