Automated emotion classification in the early stages of cortical processing: An MEG study

Highlights

• The automated classification of human emotions is feasible in very early time-intervals within 100–300 ms post-stimulus.

• MEG is well suited to automatically classify human emotions very early with high performances.

• This study suggests that the human brain might differentiate emotional versus neutral stimuli within 100–150 ms.

• Our study is the first to automatically classify human emotions very early, at least 700 ms earlier than in other studies.

Abstract

Purpose

Here we aimed to automatically classify human emotion earlier than is typically attempted. There is increasing evidence that the human brain differentiates emotional categories within 100–300 ms after stimulus onset. Therefore, here we evaluate the possibility of automatically classifying human emotions within the first 300 ms after the stimulus and identify the time-interval of the highest classification performance.

Methods

To address this issue, MEG signals of 17 healthy volunteers were recorded in response to three different picture stimuli (pleasant, unpleasant, and neutral pictures). Six Linear Discriminant Analysis (LDA) classifiers were used based on two binary comparisons (pleasant versus neutral and unpleasant versus neutral) and three different time-intervals (100–150 ms, 150–200 ms, and 200–300 ms post-stimulus). The selection of the feature subsets was performed by Genetic Algorithm and LDA.

Results

We demonstrated significant classification performances in both comparisons. The best classification performance was achieved with a median AUC of 0.83 (95 %- CI [0.71; 0.87]) classifying brain responses evoked by unpleasant and neutral stimuli within 100–150 ms, which is at least 850 ms earlier than attempted by other studies.

Conclusion

Our results indicate that using the proposed algorithm, brain emotional responses can be significantly classified at very early stages of cortical processing (within 300 ms). Moreover, our results suggest that emotional processing in the human brain occurs within the first 100–150 ms.