Fig. 2.

An example of an EEG feature used to predict the subsequent free ride or cooperation decision. (a) The cross hair within the feature indicates the time and frequency of the maximum ERSP. (b) As depicted in the lower part of the figure, each feature vector was defined according to five types of information: electrode location, time_max, frequency_max, average ERSP amplitude, and max ERSP amplitude. When we tested prediction performance with a combination of two features (feature¹ at electrode¹, time_max¹, and frequency_max¹: [ERSP_max¹, ERSP_avg¹] and feature² at electrode², time_max², and frequency_max²: [ERSP_max², ERSP_avg²]), the information from the two features was concatenated in parallel (predictor: [ERSP_max¹, ERSP_avg¹, ERSP_max², ERSP_avg²]).