The False Dichotomy of Imagery
Nigel J.T. Thomas
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Source: http://www.imagery-imagination.com/pyl-com.htm
Pylyshyn's return to the fray of the imagery debate is very welcome. In typically trenchant fashion he sets forth the serious conceptual and empirical problems afflicting pictorial (including "quasi-pictorial") theories of imagery, showing how even vaunted neuro-imaging evidence fails to support it. Despite its surface appeal, pictorialism is almost certainly false.
However, much as I value Pylyshyn's new contribution, I fear his re-entry into the debate may serve to further entrench a false dichotomy that seems firmly established in the minds of most cognitive scientists, and in the textbooks: the view that we are faced with a stark choice between some form of pictorialist theory of imagery1, or, alternatively, a "propositional" theory wherein imagery (quasi-perceptual experiences and associated empirical effects) is identified with descriptions couched in a computational language of thought (Fodor's (1975) mentalese). Pylyshyn is reticent about his positive theory of imagery (indeed, I think it has never been expounded in detail2), but clearly, under the guise of "the null hypothesis," he wants to sell us the same "propositional" descriptionist theory long associated with his name.
Because its details remain so underspecified, and because mentalese is supposed, ex hypothesis, to be able to represent anything that we can conceive, there are very few empirical constraints on descriptionism as it stands. Virtually any conceivable empirical observation could be accommodated without too much strain. Probably largely because of this lack of empirical content, descriptionism has remained unpopular, despite all the problems of pictorialism.
There is a worse problem, however. Mentalese is conceived by analogy to natural languages such as English and to computer programming languages and representation systems set up within actual working computer programs. Inasmuch as the symbols of such systems represent anything in the outside world, they do so by convention or by stipulation, which requires beings with minds to be around to do the stipulating or to settle upon the conventions. The whole point of mentalese, however, is to explain how minds are possible. Fodor postulated it largely to explain the constitutive intentionality of thought, the fact that thoughts, including mental images, are semantically meaningful, are thoughts or images of something or other. Thus, to explain mentalese semantics as stipulative or conventional would be viciously circular.
Admittedly, a lot of philosophical effort, over the last quarter century, has gone into trying to devise a naturalistic semantics for mentalese, one not dependent upon stipulation or convention. But this work has not even begun to converge upon any generally acceptable theory. The literature has become a casuistical morass, where every positive proposal (the underlying idea often, now, obscured beneath a mass of accumulated modifications) seems decisively refuted, even thoroughly incoherent, from the perspective of its rivals3. If a naturally meaningful mentalese really could exist, it would explain an awful lot, but then again, so would a homunculus. It is past due time to admit that the quest for such a language is hopeless. Certainly we cannot take the conceptual legitimacy of mentalese for granted.
This need not threaten computational theories of specific cognitive competencies and performances, which rarely need to invoke intentionality. Once we drop the requirement that computational cognitive representations should bear or ground intentionality, less problematic accounts of them become available (e.g. Cummins, 1996; Horst, 1996). However, the descriptionist is not just explaining competencies and performances, he is trying to explain imagery, a quintessentially intentional and conscious phenomenon (Sartre, 1948; Thomas, in press). (Some philosophers hold that consciousness may be explicable in terms of representations, but these proposals rely upon the representations bearing intentionality (Lycan, 2000)..
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