How Many Minds? Individuating Mental Tokens in the Split-Brain Subject

Abstract

The "split-brain" cases raise numerous difficult and fascinating questions: questions about our own self-knowledge, about the limits of introspection and phenomenology, about personal identity, and about the nature of consciousness and of mind. While the phenomenon is therefore of relevance to many areas of psychological inquiry, my dissertation explores the split-brain studies from the perspective of theoretical psychology.

The dissertation uses the split-brain cases to develop criteria for individuating mental tokens, and then applies those criteria back to the split-brain subjects themselves, ultimately arguing that split-brain subjects have two minds and two streams of consciousness apiece. Because the dissertation defends a particular account of the constitutive conditions for mental tokens against competing functionalist accounts, it also ends up being about the proper form for functionalist theories of the mental to take.

I argue throughout that psychofunctionalists who are realists about mental phenomena should accept that the constitutive conditions for mental tokens are partly neural. In particular I argue that, within an organism, multiple neural events that sustain mental phenomena causally independently of each other in some relevant sense cannot be identified with a unique mental token, regardless of how unified that organism's behavior may seem.