Online research in philosophy

David Marr's theory of vision has been widely cited by philosophers and psychologists. I have three projects in this paper. First, I try to offer a perspicuous characterization of Marr's theory. Next, I consider the implications of Marr's work for some currently popular philosophies of psychology, specifically, the "hegemony of neurophysiology view", the theories of Jerry Fodor, Daniel Dennett, and Stephen Stich, and the view that perception is permeated by belief. In the last section, I consider what the phenomenon of vision must be like for Marr's project to succeed.

The paper presents an extended argument for the claim that mental content impacts the computational individuation of a cognitive system (section 2). The argument starts with the observation that a cognitive system may simultaneously implement a variety of different syntactic structures, but that the computational identity of a cognitive system is given by only one of these implemented syntactic structures. It is then asked what are the features that determine which of implemented syntactic structures is the computational structure of the system, and it is contended that these features are certain aspects of mental content. The argument helps (section 3) to reassess the thesis known as computational externalism, namely, the thesis that computational theories of cognition make essential reference to features in the individual's environment. It is suggested that the familiar arguments for computational externalism?which rest on thought experiments and on exegesis of Marr's theories of vision?are unconvincing, but that they can be improved. A reconstruction of the visex/audex thought experiment is offered in section 3.1. An outline of a novel interpretation of Marr's theories of vision is presented in section 3.2. The corrected arguments support the claim that computational theories of cognition are intentional. Computational externalism is still pending, however, upon the thesis that psychological content is extrinsic.

This paper considers the implications of David Marr's computational theory of vision for the issues of individualism and methodological solipsism. A recent argument that the theory is nonindividualistic is shown to be similar to Gibson's arguments for "direct perception." The paper argues that a complete analysis of Marr's theory must take into account Marr's rejection of Gibson's approach, and that such an analysis shows Marr's theory to be consistent with methodological solipsism as a research strategy.

The role of content in computational accounts of cognition is a matter of some controversy. An early prominent view held that the explanatory relevance of content consists in its supervenience on the the formal properties of computational states (see, e.g., Fodor 1980). For reasons that derive from the familiar Twin Earth thought experiments, it is usually thought that if content is to supervene on formal properties, it must be narrow; that is, it must not be the sort of content that determines reference and truth-conditions. An interesting alternative to this view has recently been proposed by Egan (1995). According to Egan, the explanatory role of content is such that contents must in general be broad to be explanatorily relevant. But Egan’s view involves a non-realist interpretation of content assignments. I will argue here that this non-realism about contents is undermotivated. A realist variation on her view of the explanatory role of content, however, would survive this criticism. This realist variation, I suggest, shares with the views of other commentators on Marr’s theory (e.g., Burge 1986; Shapiro 1993; forthcoming) certain commitments concerning the supervenience base of visual contents and processes. I will argue, however, that these commitments beg important questions regarding the individuation of cognitive states and processes. I conclude, contrary to Burge and Shapiro, that Marr’s theory does not favor anti-individualism.