ABSTRACT
When Kurt Koffka (1935) asked his readers to consider why we normally “see things and not the holes between them,” individual reaction differed as to whether the question was profound, trivial, misleading, or meaningless. A similar profile of opinions would probably greet a contemporary student of learning and cognition who wondered aloud why we seem to more easily associate things with each other than with the temporal or spatial holes that surround or separate them. If he or she were a persistent person, this psychologist might argue that the selfsame kind of associative bias affects the thinking of researchers, so that certain possibilities for learning have been neglected in the laboratory. Until fairly recently, for example, the study of Pavlovian conditioning in animals has concentrated on phenomena produced by closely contiguous occurrences of conditioned stimuli (CSs) and unconditioned stimuli (USs), and not on phenomena engendered by delivering USs only in the absence of some definite stimulus or by presenting discrete CSs that are never followed shortly by another event.
