The paucity of basic behavioral research with humans was highlighted almost 40 years ago (Findley, 1966). A recent search of the basic behavioral research journals by the present authors indicated that this situation remains, with only approximately 15% of the research using human participants. It may seem surprising that so few studies use human participants given the apparent practical advantages of doing so. Human participants are readily available, extensively pre-trained, can use a range of complex apparatus and require no feeding or housing. In reality, however, the use of human participants involves a number of practical difficulties: humans generally will not agree to participate in research involving a large number of sessions or sessions lasting more than two to three hours; it is difficult to gain within-session compliance as a result of the often repetitive and simplistic nature of the tasks; and it is often unclear whether the experimental results are a product of the experimentally-arranged contingencies or the instructions given to the participants. Another difficulty, that which is addressed here, lies in the identification of a suitable experimental outcome that will serve as a reinforcer.