The Imagery Debate, Pt. 1 - Background

The history of the theorization of mind can be described as a long list of analogies to different technologies. "Aristotle had a wax tablet theory of memory, . . . Leibniz saw the universe as clockworks, [and] Freud used a hydraulic model of libido flowing through the system [coupled with a] telephone-switchboard model of intelligence" (Rumelhart 205). By the 1950s and 60s, early efforts in the Artificial Intelligence community had borne enough fruit that researchers increasingly began to favor analogies to digital computers for the bases of their models. Doing so produced great strides in the psychological community and jumpstarted what has become known as the "Cognitive Revolution".

One of the most significant developments that early cognitive scientists argued for was the rejection of the conceit held by most working within behavioral psychology (then the most prominent research paradigm operating in the United States) that the mind is a blank slate. In particular, Noam Chomsky's veritable trouncing of B. F. Skinner's Verbal Behavior set the tone for much of the research that was to follow. The existence of his proposed universal "generative grammar," Chomsky argued, required as a corollary a module in the brain that could produce such universal structures. Later researchers -- particularly the philosopher Jerry Fodor -- extended this assertion of modularity to cover the brain as a whole, increasing the analogy to different hardware structures in a computer. In order for their information-processing metaphor to work, researchers claimed, the brain had to run on an underlying mathematical descriptions such as the binary code that forms the basis of computer software. Fodor prominently argued for this position in his influential 1975 monograph, The Language of Thought.

Initially, this research paradigm proved extremely successful, but at the same time, it quickly became clear that certain mental phenomena were difficult to describe in its terms. In particular, the computer researcher and philosopher Zenon W. Pylyshyn argued that recent refinements of cognitive theory required psychologists to dramatically rethink their understanding of mental imagery. In his debate-provoking 1973 article "What the Mind's Eye Tells the Mind's Brain," Pylyshyn claimed that the new research paradigm revealed imagery to be merely epiphenomenal. That is to say, mental imagery has a phenomenological or experienced reality, but it is inessential, a mere side effect of "invisible" subconscious processing to which the mind cannot be made privy. He argued that mental imagery bore roughly the same relationship to the "real" mental process as the images on a computer screen bear to the computations that occur within a computer processor.

He presented two primary arguments for this position. In the first case, he argued, those who believed in the "reality" of mental imagery implicitly reinstated the Cartesian dualism between mind and body. This position was a reaction to then-recent ground-breaking vision research, most notably the incredibly influential 1959 paper (which inspired the title of Pylyshyn's), "What the Frog's Eye Tells the Frog's Brain," in which a team of international researchers led by the MIT psychologist Jerome Lettvin showed that much important vision processing in a frog actually took place along in the frog's eye. Cells on the retina that responded to small, fast moving objects (which Lettvin et al. deemed "bug detectors") triggered the response of attacking the triggering object with the frog's tongue. The fact that the frog's eye and not the frog's brain seemed to do the work of identifying its perceptual object showed that researchers could advance mechanistic descriptions of cognitive systems that could also account for where meaning come from without needing also to posit some sort of non-mechanical "mind" which attributed meaning and made judgments. This research was then replicated (in somewhat less bug-centered terms) in many other animals including humans.

Pylyshyn claimed that those who believed in the reality of mental imagery gave up the ground that Lettvin and his colleagues had gained. He saw mental imagery as a return to dualism, arguing that the mind showed no sign of containing an additional "eye" with which to view the represented image and also reiterating the philosopher's classical critique of dualism: that it implied an infinite regression of nested homunculi. After all, if the brain required an interior structure to view the represented image, then that internal structure presumably required an observing internal structure as well, which in turn required, ad infinitum.

Pylyshyn's other major claim was that the dichotomy then posited by many vision researchers that mental content was either propositional or perceptual was too rigid. Indeed, he claimed, since perceptual content was ultimately reducible to propositional content, the distinction was meaningless. The renowned British opera director, Jonathan Miller, who was originally trained as a neurologist, made a similar (albeit softened) claim some years later:

I recently went to Cambridge to deliver a lecture, and in my apprehension I had rehearsed my arrival in a series of increasingly alarming dreams. About four nights before, I dreamed that I was parking my car in what I knew to be Trinity Lane, although it was from its visible appearance also a narrow side street behind the Santo in Padua. At the end of the lane, I could see the master of Trinity waving hospitably at me, and he was the actor Michael Horden. Now there was no sense in my dream that Horden, the actor, was playing the part, or that he had popped in between the election or anyone else's hopes. As far as I was concerned in the dream, Horden and the master were one and the same, in spite of the fact that I also knew, simultaneously, that the master and Sir Andrew Huxley were identical. The rest of the dream was so humiliating, for which I blame neither Sir Michael nor Sir Andrew, that I shall draw a veil over it. (198)

Miller's point is that his mental image of Michael Horden also contained the propositional content "master," thus blending the two categories. This, it must be stressed, is a softer claim than Pylyshyn's, Miller not being interested in proving the epiphenomenality of images, but it operates along the same vectors.

Pylyshyn's was the first salvo in what would become a proplonged debate over the nature of mental imagery.

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