Are Theories of Imagery Theories of Imagination? An Active Perception Approach to Conscious Mental Content
Nigel J.T. Thomas
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12
Page 4
Source: http://cogprints.org/5018/1/im-im-cp.htm
However, standard philosophical objections to picture theories have not necessarily been circumvented by all this (Slezak, 1993, 1995). Pace Kosslyn (1994), the theory (and, indeed, any perceptual theory of similar form) still relies on an "undischarged homunculus" (Dennett, 1978), the "mind's eye function", to interpret the surface representation. No amount of neurophysiological detail is, in itself, going to solve this problem. In fact, the basic functional organization of Kosslyn's theory (figure 1) does not differ from that of Descartes' theory of imagery, which also involves a merelyquasi-picture (see Treatise on Man and Optics in Cottingham, Stoothoff, & Murdoch, 1985). Of course, the theories do differ when we move beyond the functional level. Descartes, for example, put his "visual buffer" on the surface of the pineal gland instead of in the occipital cortex. More significantly, Descartes ascribed his mind's eye function to an immaterial, scientifically inaccessible soul, while Kosslyn clearly believes that his will eventually be explicable in purely physicalist terms. Kosslyn, to borrow Dennett's (1991) term, is a "Cartesian materialist"4. This is not an indefensible position (Attneave, 1961), but it is certainly problematic.
The specific ways in which deep representations and surface representations are stored in the Kosslyn-Shwartz program, and how various transformations of the quasi-picture are generated, need not detain us. There are many possibilities. Several different ways of implementing (symbol filled) array theories of imagery have been proposed by AI researchers since the original Kosslyn and Shwartz work; some connectionist (e.g. Julstrom & Baron, 1985; Mel, 1986, 1990; Stucki & Pollack, 1992) and some not (e.g. Glasgow & Papadias, 1992; Glasgow, 1993). These all have interesting features, but none attempt the psychological range of Kosslyn's model. The core commitment of the quasi-pictorialist research program is not to any particular details of implementation, but to the (symbol filled) array representation for the image itself, and to something resembling the functional organization of figure 1.
2.2 Description Theory
Description theory is also known amongst psychologists as "propositional theory", because the data structures that it takes to embody mental images (and percepts too) are regarded as expressing propositions descriptive of the relevant perceptual scenes. When such structures are the end product of perceptual processes, we are perceiving; when they are constructed inventively, or retrieved from memory, we experience imagery. In effect, the data structures are sentences in an inner language, "mentalese" (Fodor, 1975), and the core commitment of description theory is that such language-like representations are sufficient to account for all genuinely cognitive processes, including the experimental effects attributed to imagery. Pylyshyn, the principal advocate of description theory, explicitly and forcefully urges the view that this conception of an inner "notation" through which thoughts are "written in the mind" should be understood quite literally and realistically (Pylyshyn, 1991). Of course, description theorists consider the content of the representations involved in imagery to be perceptual, but they consider that there is nothing specifically perceptual about their format. This format does not differ from that of the representations underlying other cognitive processes. Furthermore, no specifically perceptual processing mechanisms need be active when imagery is experienced (Pylyshyn, 1978, 1984).
The earliest attempts to implement computer models of imagery phenomena were made in the Carnegie-Mellon school of Artificial Intelligence research, where the established approach was to examine people's strategies in solving logical and mathematical puzzles (largely through the analysis of protocols produced by subjects talking through their puzzle solving out loud) and then to attempt to program a computer to solve the same puzzles by a similar strategy (Newell & Simon, 1972). Baylor (1972) and Moran (1973) attempted to apply this approach to certain puzzles that people seem to solve using visual imagery. Baylor (1972) took on Guilford's (1967) "block slicing" puzzles, and devised a way of describing rectangular blocks using LISP data structures. Blocks were represented in terms of nested lists of faces, edges, and vertices (V1 through V8), and property lists holding information like edge length and face color. Using such representations, he wrote a program that solved certain of the puzzles using a sequence of steps similar to that followed by a human solver (according the protocol analysis). Moran (1973) achieved comparable results applying similar techniques to another type of imagery puzzle.
Neither Baylor nor Moran took any significant account of the experiential, quasi-perceptual nature of imagery. Neither did they give much heed to the (then very new) experimental results on rotation, scanning, etc. Later attempts to simulate imagery computationally do take account of these things (see §2.1.2), but, simultaneously, abandon treating the image representation as a sentential description. Nevertheless, description theory has continued to play a prominent role in discussions of imagery. This is very largely due to the vigorous advocacy of Pylyshyn, who initially seems to have seized on Baylor's and Moran's work as an alternative to what he took to be the naïve and unworkable pictorialist views implicit in early cognitivist research on imagery (Pylyshyn, 1973). Subsequently he turned his efforts to attacking the more explicit conception of images as "analog" representations then being developed by Kosslyn (1975, 1980), Shepard (1975), and others. In this work Pylyshyn (e.g. 1978, 1981) recommends description theory as greatly theoretically preferable to picture theory, but he does little to develop its details.
2.3 Perceptual Activity Theory and Active Vision
Versions of a PA approach to imagery were outlined by several psychologists in the 1960s and 70s, including Hebb (1968); Hochberg (1968); Sarbin and Juhasz (1970); Janssen (1976); Morgan (1979); and Neisser (1976, 1978). More recently, Ellis (1995), and Ramachandran and Hirstein (1997 p. 442) have sketched similar views. (See also Dennett [1991] on hallucination.) PA theory does not involve CM or the information processing framework. However, that does not mean that it cannot be modelled computationally. Indeed, Farley (1974) produced a computer model based on Hochberg's version of the theory (like the Baylor and Moran models, however, it has very limited psychological scope). Otherwise, there has been very little cross-fertilization between the theorists, little directly relevant experimental research (what there is being inconclusive), and little critical discussion (and consequent defense and elaboration) of any of the versions (Thomas, 1987, 1997b). As a consequence, even the best developed published exposition (Neisser, 1976) remains very sketchy.
This neglect of PA theory, however, may be mainly due to historical accident. In the 1970s, information processing theory was decidedly in the ascendant, and there was a very high profile battle between the description theorists and the quasi-pictorial theorists and their allies (the "analog-propositional dispute") over the best way to understand imagery within this framework. Consequently, most subsequent discussions treat these two approaches (plus, perhaps, some hybrid of them [e.g. Chambers, 1993)] as exhausting the alternatives. Such opposition as there was to information processing theory (and CM) mostly coalesced around the work of Gibson (1966, 1979). Unfortunately, Gibson's metatheoretical rhetoric (if not, perhaps, his positive theory--see Bickhard & Richie, 1983) emphatically rejects using the concept of mental representation (explicitly including mental imagery) within the context of perceptual theory. Thus, although Neisser's PA theory was deeply influenced by Gibson (and Gibson himself [1970, 1979 p. 256] hints at a PA view), the study of imagery has not flourished in this tradition.
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12
We Make it Easy to Succeed
Successwaves, Intl.
Brain Based Accelerated Success Audios
 |