The study of learning has long held a central position in the field of comparative psychology. Here we present a survey of the past 20 years of comparative learning research, covering publications from 1994 to 2013. We selected seven journals with a strong focus on comparative learning, and identified five major topics of study represented by the publications in those journals: non-associative learning, associative learning, perceptual/object learning, social learning, and neural correlates of learning. Of these topics, associative learning was by far the most popular, comprising about 85% of the research in comparative learning. We therefore subdivided this topic into seven subcategories of research questions, which included causal reasoning, compound cue interactions, extinction, stimulus control, outcome learning and motivation, spatial learning, and temporal integration or timing. The number of publications addressing each topic or research question, as well as the number of citations received by these publications, was examined for the combined seven journals across the 20 year period of review. The subject of spatial learning has grown rapidly over the past 20 years, and has attracted robust interest by researchers both in and outside of the field of comparative psychology. Although much less popular in terms of publication number, recent growth was also identified for studies of causal reasoning, social learning, and perceptual or object learning.
