some of the most commonly used machine learning algorithms include support vector machines (svm), naive bayes, and maximum entropy. deep learning, which is under the unsupervised family of machine learning, is also widely employed in emotion recognition. well-known deep learning algorithms include different architectures of artificial neural network (ann) such as convolutional neural network (cnn), long short-term memory (lstm), and extreme learning machine (elm). the popularity of deep learning approaches in the domain of emotion recognition may be mainly attributed to its success in related applications such as in computer vision, speech recognition, and natural language processing (nlp).