Are Theories of Imagery Theories of Imagination? An Active Perception Approach to Conscious Mental Content
Nigel J.T. Thomas
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Source: http://cogprints.org/5018/1/im-im-cp.htm
With Morris and Hampson (1983), I take there to be three types of imagery theory extant in the Cognitive Science literature. I shall refer to them as "description theory", "picture theory", and "perceptual activity [or PA] theory". However, we might better understand these as paradigms (Kuhn, 1970), or, better still, as research programs (in the sense of Lakatos, 1978), rather than as static and unitary theories. Although research programs are characterized by certain core commitments, which suggest particular lines of investigation and explanatory strategies, different theoretical elaborations can be constructed around these cores to account (with varying degrees of strain) for almost any empirical evidence that is likely to arise. Thus, in the course of its development a single vigorous research program may encompass a number of well elaborated and quite diverse theoretical positions, whose detailed empirical commitments may differ considerably. In the case of the pictorialist research program we see this even within its relatively recent evolution: Contrast the very different versions of picture theory given by Kosslyn in his two major statements on the subject (Kosslyn 1980, 1994). In the light of this, we should not expect to be able to make a definitive choice between the three imagery research programs solely on the basis of empirical evidence. Rational choice between programs (or paradigms) depends not just upon empirical adequacy, but also on judgements about factors like the elegance and consistency of the theoretical elaborations needed to assimilate the evidence, and the scope and promise of the core ideas (Lakatos, 1978).
2.1 Picture Theory
Picture theory has a very long history, going back to Plato or even Democritus (Thomas, 1987), and until quite recently it was almost universally accepted (White, 1990). All versions hold that having visual imagery involves having entities, in the head or in the mind, which are like, or functionally equivalent to, inner pictures. These pictures are thought of as being composed of copies or remnants of earlier sense impressions, complexes of visual sensations, which were themselves picture like. "Picture" is, of course, strictly appropriate only to copies in the visual mode (upon which most discussions of imagery concentrate), but, if this sort of account really works for the visual, then it seems at least initially plausible that similar "copy" theories could be devised for the other sensory modes (Matthews, 1969).
2.1.1 Contemporary "Quasi-Pictorial" Theory
Picture theory came under severe philosophical attack in the middle years of this century (e.g. Sartre, 1936/1962; Ryle, 1949; Wittgenstein, 1953) for being committed to an implausible, Cartesian view of the mind. However, in the opinion of many, Kosslyn (1975, 1980, 1994) has succeeded, in the teeth of trenchant and sophisticated objections from such description theorists as Pylyshyn (1973, 1978, 1979, 1981) and Hinton (1979), in showing that his computational version of picture theory is both coherent and empirically credible.
At least, Tye (1991) seems to have convincingly demonstrated that it is coherent given the assumption that computational data structures of some type are a proper model for conscious and intentionalistic mental contents. Kosslyn implicitly shares this assumption--let us call it computational mentalism, or CM--with the descriptionists. Indeed, most discussions of cognitive theory conflate the notion of a mental (intentional) content with that of a computational representation, failing to distinguish the CM dogma from the view that brain function may best be understood and simulated computationally1. However, one can consistently accept the latter position (and even a form of "strong AI") whilst rejecting CM, and there may be good reasons to do so (Slezak, 1999; Cummins 1989, 1996). CM faces the symbol grounding problem, the problem of understanding how computational states can acquire intrinsic intentional content (Harnad, 1990), and it is not at all clear that this problem is soluble2. If CM is false (as I believe) then both the description theory of imagery and the computational version of picture theory defended by Kosslyn and Tye are profoundly compromised. However, the critiques of these theories that follow below will not depend upon prior rejection of CM. Many people accept CM, and it is at the foundations of theinformation processing paradigm, which views the task of a theory of perception as, essentially, to give an account of how the information implicit in states of the sense organs is converted into a canonically "mental", consciously available, data format or formats. Kosslyn's fundamental disagreement with the descriptionists is over what sorts of format might be able to fill this role.
The quasi-pictorial theory of imagery [Based on Kosslyn (1980 p. 6)]. The system is considering whether a fox has pointed ears. A "quasi-picture" is constructed in the visual buffer, on the basis of a description in LTM, and the "mind's eye" analyses it to extract the required information.
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