Introducing Bidirectional Ordinal Classifier Cascades Based on a Pain Intensity Recognition Scenario

Abstract

Ordinal classifier cascades (OCCs) are popular machine learning tools in the area of ordinal classification. OCCs constitute specific classification ensemble schemes that work in sequential manner. Each of the ensemble’s members either provides the architecture’s final prediction, or moves the current input to the next ensemble member. In the current study, we first confirm the fact that the direction of OCCs can have a high impact on the distribution of its predictions. Subsequently, we introduce and analyse our proposed bidirectional combination of OCCs. More precisely, based on a person-independent pain intensity scenario, we provide an ablation study, including the evaluation of different OCCs, as well as different popular error correcting output codes (ECOC) models. The provided outcomes show that our proposed straightforward approach significantly outperforms common OCCs, with respect to the accuracy and mean absolute error performance measures. Moreover, our results indicate that, while our proposed bidirectional OCCs are less complex in general, they are able to compete with and even outperform most of the analysed ECOC models.