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 9
Source: http://cogprints.org/5018/1/im-im-cp.htm
Evidence that visual illusions can be induced through imagery also raises difficulties for description theory. Berbaum and Chung (1981) found that the Müller-Lyer illusion could be induced (i.e. a presented straight line seemed to vary in length) when the inducing parts of the stimulus (arrowheads or wings on the line ends) were only imagined. Wallace (1984) reported similar findings with the Ponzo, Wundt and Hering illusions. These experiments depend on the subjects making subjective reports about subtle changes in the appearance of the stimulus, and the results can plausibly be discounted as the result of experimental demand (Predebon & Wenderoth, 1985; Reisberg & Morris, 1985). However, the experimental design used by Pressey and Wilson (1974) to demonstrate that a version of the Poggendorff illusion can be induced through imagery is not nearly so vulnerable to this sort of criticism; neither is that used by Kosslyn, Sukel, and Bly (1999, expt. 3) to demonstrate an imagery version of the "oblique effect". (See Finke, 1989, for discussion of evidence for imagery induced versions of other illusions.)
If such illusions truly can be induced through imagery, it raises a serious problem for description theory. The "cognitive impenetrability" of all these illusions (the fact that the illusion persists even when we "know better") is surely, from a computationalist perspective, excellent evidence that they arise in modularized perceptual input systems (Fodor, 1983). But Pylyshyn (1978) was determined to deny that imagery effects involve such systems. His whole commitment to description theory hung on the view that imagery arises entirely from "propositional" mentalese representations in the "central systems", and is thoroughly "cognitively penetrable".
Neuropsychological findings seem to reinforce this point. There is now much evidence that visual imagery depends on activity in parts of the brain otherwise considered to be dedicated to visual perception (Farah, 1988; Kosslyn, 1994). Such parts would naturally be construed, on the Pylyshyn-Fodor view, as embodying just the sort of "cognitively impenetrable" (Pylyshyn, 1978), "informationally encapsulated" (Fodor, 1983) input modules that are supposed not to participate in imagery. Furthermore, Bisiach and Berti (1990) argue that (quite apart from the conceptual problems alluded to in §2.1.1) the very notion of language-like, "mentalese" representation is neuropsychologically implausible.
2.4.3 Perceptual Activity Theory Confronts the Experimental Facts
Given the undeveloped state of PA theory, the explanations given here must be speculative. The intent is merely to show that PA theory is not obviously inadequate to the empirical facts against which the other theories measure themselves.
PA theory should have little difficulty with evidence suggesting the involvement of specifically perceptual mechanisms in imagery, as presented in the previous sub-section. Schemata and perceptual instruments are supposed to subserve both perception and imagery. It is entirely to be expected that quirks and defects of their functioning would show up in both modes, and that at least some of the same brain areas would be involved.
Kosslyn et al. (1976) explain imagery's mnemonic effects in terms of Paivio's "Dual Coding" theory (1971, 1986, 1991), which posits two interacting systems of memory, one linguistic/conceptual and the other imaginal. As neither picture theory nor PA theory assimilates imagery to linguistic/conceptual representation, both may appeal to dual coding theory in this regard.
Mental scanning is readily explained by PA theory's claim that imagery consists in covertly going through the motions of the equivalent perceptual process. If we steadily scan our gaze across a real scene, it will take longer to move through a large visual angle than a smaller one. It is thus to be expected that if subjects covertly go through the motions of such scanning (as they are constrained to do in the relevant experiments, either by explicit instructions or experimental conditions) they will also take longer the larger the angle. Even if actual head and eye movements are suppressed, the schema's abortive attempt to initiate and control them should follow a comparable temporal course to real visual scanning. Similar considerations apply to size/inspection time effects. Other things being equal, it takes longer to pick out small details of a scene or object before us than it does to pick out large ones; we may have to peer, or move closer. Likewise, it will take longer to covertly go through the motions of picking out smaller details8.
PA theory also seems well adapted to explaining interference between imagery and perceptual tasks: Interference occurs when each task simultaneously makes conflicting demands upon the same perceptual instrument, or upon different instruments that share some of the same anatomical resources. It has long been recognized that it is not adequate to analyze the complex findings in this area in terms of a simple categorization of tasks according to sense mode. The PA account suggests the possibility of a finer grained, more explanatorily powerful categorization. However, the details must await advances in our knowledge of the perceptual instruments.
Mental rotation is more problematic. Neisser (1976) suggests that it should be understood as the product of schemata specialized for the perception of rotating objects; or perhaps we might better say, schemata that invoke perceptual instruments specialized for estimation of rotational motion. These suggestions, however, fail to explain why a subject's mental rotations (within a particular experimental paradigm) always seem to go at a specific preferred speed (Hampson & Morris, 1978). It may be better to follow Kosslyn's recent suggestion (1994) that the effect is controlled by the motor system, and that what we are imagining is successive orientations of the object as if we were physically turning it. Of course, Kosslyn interprets this in terms of the creation of a succession of differently oriented pictures on the visual buffer, but PA theory can equally well invoke such a succession of imaginings.
Unlike picture theory, PA theory addresses both haptic and visual imagery in formally similar explanatory terms. Indeed, our account of PA theory in §2.3.1 developed the example of haptics before extending the approach to the other modes. Thus the homology between experimental findings on the haptic imagery of the blind and on the mainly visual imagery of the sighted is unsurprising for the PA theorist, and presents none of the special problems that it raises for picture theory.
The difficulties that subjects have in reinterpreting images also make sense in PA terms. We know that the interpretation that we see depends on the way in which we look at the figures; in particular, on how we direct our attention spatially (Stark & Ellis, 1981; Tsal & Kolbert, 1985). For PA theory it is precisely such ways of looking that get stored in visual memory and are reactivated as imagery. If we are only exposed to an unfamiliar figure long enough for us to successfully undertake one of the possible ways of looking at and so interpreting it, only that one way will be stored, and our subsequent imagery will involve recapitulating only that one way, giving us access only to the one interpretation.
3 Imagination
Many diverse ideas are associated with the idea of imagination. My purpose here is merely to document the centrality of three of them to the folk/Romantic conception: non-rationality (or non-discursive thinking), creativity, and imagery. I will particularly consider the views of the best known English Romantic poets: Blake, Wordsworth, Coleridge, Shelley, and Keats. It is these writers, rather than any philosophers or psychologists, who have done most to shape the "folk" conception in its ideologically significant form.
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
 |