Reward expectation regulates brain responses to task-relevant and task-irrelevant emotional words: ERP evidence

Abstract

We investigated the effect of reward expectation on the processing of emotional words in two experiments using event-related potentials (ERPs). A cue indicating the reward condition of each trial (incentive vs non-incentive) was followed by the presentation of a negative or neutral word, the target. Participants were asked to discriminate the emotional content of the target word in Experiment 1 and to discriminate the color of the target word in Experiment 2, rendering the emotionality of the target word task-relevant in Experiment 1, but task-irrelevant in Experiment 2. The negative bias effect, in terms of the amplitude difference between ERPs for negative and neutral targets, was modulated by the task-set. In Experiment 1, P31 and early posterior negativity revealed a larger negative bias effect in the incentive condition than that in the non-incentive condition. However, in Experiment 2, P31 revealed a diminished negative bias effect in the incentive condition compared with that in the non-incentive condition. These results indicate that reward expectation improves top-down attentional concentration to task-relevant information, with enhanced sensitivity to the emotional content of target words when emotionality is task-relevant, but with reduced differential brain responses to emotional words when their content is task-irrelevant.

Keywords: reward expectation; emotional Stroop; negative bias; event-related potential.

Fig. 1.

Example of the trial sequence in Experiments 1 and 2. The task in Experiment 1 was to discriminate the emotional content of the target word, while the task in Experiment 2 was to discriminate the color of target word, which was colored in red or in green in the actual display.

Fig. 2.

Grand average waveforms at the midline electrodes showing the potentials produced in response to the presentation of the target stimulus in Experiment 1. The topographies of the P3₁ potential are shown on the right. Positive voltage is plotted downwards. For all waveforms, rewarded trials are represented in red lines, and non-rewarded trials are in black lines. Negative conditions are plotted in solid lines, and neutral conditions are plotted in dotted lines.

Fig. 3.

Grand average waveforms at the midline electrodes showing the potentials produced in response to the presentation of the target stimulus in Experiment 2. The topographies of the P3₁ potential are shown on the right. Positive voltage is plotted downwards.

Fig. 4.

Grand average waveforms at the P4 electrode showing the EPN component in response to the target in Experiment 1 (the left one) and in Experiment 2 (the right one). Positive voltage is plotted downwards.