Perspectivist approaches to natural language processing: a survey

In Artificial Intelligence research, perspectivism is an approach to machine learning that aims at leveraging data annotated by different individuals in order to model varied perspectives that influence their opinions and world view. We present the first survey of datasets and methods relevant to perspectivism in Natural Language Processing (NLP). We review datasets in which individual annotator labels are preserved, as well as research papers focused on analysing and modelling human perspectives for NLP tasks. Our analysis is based on targeted questions that aim to surface how different perspectives are taken into account, what the novelties and advantages of perspectivist approaches/methods are, and the limitations of these works. Most of the included works have a perspectivist goal, even if some of them do not explicitly discuss perspectivism. A sizeable portion of these works are focused on highly subjective phenomena in natural language where humans show divergent understandings and interpretations, for example in the annotation of toxic and otherwise undesirable language. However, in seemingly objective tasks too, human raters often show systematic disagreement. Through the framework of perspectivism we summarize the solutions proposed to extract and model different points of view, and how to evaluate and explain perspectivist models. Finally, we list the key concepts that emerge from the analysis of the sources and several important observations on the impact of perspectivist approaches on future research in NLP.