The Greebles refers to an invented category of novel objects used as stimuli in psychological studies of object and face recognition. They were named by the psychologist Robert Abelson. The greebles were created for Isabel Gauthier's dissertation work at Yale, so as to share constraints with faces: they have a small number of parts in a common configuration. Greebles have appeared in psychology textbooks, and in more than 25 scientific articles on perception (see below). They are often used in mental rotation task experiments.