Conceptualization in pigeons: The evolution of a paradigm.

Keller and Schoenfeld (1950) proposed a unique behavioral perspective on conceptualization. They suggested that concepts refer solely to an organism's behavior and to the conditions under which it occurs; as such, conceptual behavior need be neither verbal nor uniquely human. Herrnstein and Loveland (1964) advanced that behavioral perspective by deploying an elegant training procedure to teach visual concepts to pigeons. Keller and Schoenfeld's perspective and Herrnstein and Loveland's methodology have inspired my own research into conceptualization by pigeons. Using a system of arbitrary visual tokens, my colleagues and I have built ever-expanding nonverbal "vocabularies" in pigeons through a variety of different concept learning tasks. Pigeons have reliably categorized as many as 2000 individual photographs from as many as 16 different human object categories, even without the benefit of seeing an item twice. Our formal model of conceptualization effectively embraces 25 years of empirical evidence as well as generates novel predictions for both pigeon and human conceptual behavior. Comparative study should continue to elucidate the commonalities and disparities between human and nonhuman conceptual behavior; it should also explicate the relationship between associative learning, object recognition, conceptualization, and language.