  There are still many challenges of emotion recognition using physiological
data despite the substantial progress made recently. In this paper, we
attempted to address two major challenges. First, in order to deal with the
sparsely-labeled physiological data, we first decomposed the raw physiological
data using signal spectrum analysis, based on which we extracted both
complexity and energy features. Such a procedure helped reduce noise and
improve feature extraction effectiveness. Second, in order to improve the
explainability of the machine learning models in emotion recognition with
physiological data, we proposed Light Gradient Boosting Machine (LightGBM) and
SHapley Additive exPlanations (SHAP) for emotion prediction and model
explanation, respectively. The LightGBM model outperformed the eXtreme Gradient
Boosting (XGBoost) model on the public Database for Emotion Analysis using
Physiological signals (DEAP) with f1-scores of 0.814, 0.823, and 0.860 for
binary classification of valence, arousal, and liking, respectively, with
cross-subject validation using eight peripheral physiological signals.
Furthermore, the SHAP model was able to identify the most important features in
emotion recognition, and revealed the relationships between the predictor
variables and the response variables in terms of their main effects and
interaction effects. Therefore, the results of the proposed model not only had
good performance using peripheral physiological data, but also gave more
insights into the underlying mechanisms in recognizing emotions.
