Abstract
What does it mean to hear a sound? What does it mean to perceive anything? Sound has no objective reality, such as "vibration." Of two people together, one may hear a sound and one may not. We know only that their actions-their judgments-differ. Such comparison underlies all discriminations. In experiments on concept learning, for example, pigeons peck when they are shown a slide containing human beings and do not peck when the slide contains no humans. The experimenters judge beforehand whether the slides contain human beings or not, and the pigeons' concept of human being is determined by the comparison between the experimenters' judgments and the pigeons' pecking or not. Similarly, to tell which of two people is hearing or deaf, an observer that can hear must judge whether their behavior corresponds with the observer's judgments. In an experiment by Lubinski and Thompson (Behavioral and Brain Sciences, 16, 627-680, 1993), in which pigeons pecked at different keys depending on which of two different drugs they had received beforehand, the experimenters judged which drug had been injected, and the pigeons' pecking corresponded to the experimenters' judgments. If two persons' judgments differ, they can only resolve the difference by deciding that one of them is mistaken. If no one is there to hear a tree fall in the forest, from the point of view of a science of behavior, it made no sound.