Multimodal Machine Learning: A Survey and Taxonomy, Tadas Baltrušaitis, Chaitanya Ahuja, and Louis-Philippe Morency, 2017IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 41 (IEEE)DOI: 10.1109/TPAMI.2017.2767267 - A survey that provides a categorization of multimodal machine learning methods, including distinct levels of fusion such as late fusion.