Kant and the brain: A new empirical hypothesis

1. Introduction Kant claims that human cognition involves the peculiar ability to " think the particular as contained under the universal. " We generalize: we abstract, classify, or conceptualize; we think of particular individual things as belonging to general kinds: this is a bird, that a tree. We form concepts into systematic hierarchies: grizzlies and polar bears are kinds of bear; bears and dogs are kinds of mammal; and so on. Similarly we can consider an abstract feature, such as 'redness', which we have encountered in many different individual experiences, and apply it to other objects: this apple is red, that balloon is red. In Kant's terminology these are examples of judgment: the mental act of applying general concepts to particulars. This act, for Kant, involves the coordination of two mental abilities, identified in his Critique of Pure Reason as " understanding " and " imagination " respectively. In his Critique of Judgment Kant adds a new development to this theory. In the course of an analysis of judgments of beauty, Kant argues that an internal signal (of pleasure) accompanies the coordination of imagination and understanding in judging. This signal is found, he argues, not only in the purely " aesthetic judgment " of beauty but also in cognition (Kant, 1790/1987, §21). Kant here appears to propose nothing less than an additional sense, one not devoted to processing external sensory inputs, nor internal bodily signals such as balance, hunger, and so forth, but instead reporting on the processing state of the mind itself. He argues that such a signal is a prerequisite of cognition. While Kant's argument is purely philosophical, I take it his conclusion can also yield an empirical hypothesis, amenable to empirical investigation. Namely, is there any such signal in the mental processing leading to cognition? If such a signal exists, could its locus in the brain be identified? Below, I describe a candidate neuronal substrate for such a signal, and summarize ongoing experimental studies testing this idea in animal learning. I end by noting some questions raised in Kant's analysis of the human situation. For Kant's concern here is broader than the use of concepts and empirical laws already in our possession: it also concerns their discovery, formulation, and organization into a coherent system in the scientific investigation of nature. 1 1 Of course considerable detail and nuance will have to be set aside in this brief …