The Multidimensional Spectrum of Imagination
Nigel J.T. Thomas
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Page 6
Source : http://www.imagery-imagination.com/spectrum.htm
Reestablishing Continuity: 3. Attention
I have no quarrel with McGinn's contention that imagery necessarily involves attention, or what he calls "attentive intentionality." Indeed, I myself have elsewhere proposed a theory that could reasonably be nutshelled by saying that mental images are, in a sense, made of attention (Thomas, 1999a, 2008 §4.5, 2009a,b), and although not all imagery theorists go quite so far as that, they nevertheless give attentional processes an important role in their account (Kosslyn, Thompson & Ganis, 2006).
McGinn is mistaken, however, in denying that attention is also necessary for seeing. The Cartesian, passivist conception of vision may tempt us into thinking that if something is, right now, potentially visible to us ( i.e., we are awake, it is before our opened eyes, it is illuminated, nerve pathways are intact, etc.) then we ipso facto see it. In fact, however, passive reception of energies by the sense receptors, even if followed by transmission to the brain, is insufficient for perception in general, and for seeing in particular. Experimental studies have shown that, if our attention is sufficiently tied up with some other task, we may well have no conscious awareness whatsoever of even downright conspicuous objects or events that appear or occur right in front of us (Mack & Rock, 1998; Simons & Chabris, 1999). This counterintuitive but well established phenomenon is known as "inattentional blindness." Conscious visual experience depends upon the active, purposeful, attentive seeking out of environmental information, and this attentional activity plays a constitutive, and not merely incidental, role in vision.
It is important to remember that eye movements are far from being the only means by which we direct our attention. There are also numerous acts of directed attention that are carried out entirely within the brain, and at multiple levels of the visual processing hierarchy. Furthermore, visual attention is not just a matter of spatial direction or location. There are brain mechanisms that enable us to pay attention selectively to particular objects rather than just spatial locations, and even to particular aspects or features of an object, such as its shape, its color, or its motion (Reynolds & Chelazzi, 2004; Li et al., 2004; Bressler et al., 2008; McAlonan et al., 2008).
It is true that things to which we are inattentionally blind can nevertheless have some subtle effects on our behavior or behavioral dispositions (Mack & Rock, 1998; Bressan & Pizzighello, 2008). Clearly our brains are affected by them, via our eyes, and perhaps this deserves to be called seeing in some attenuated sense. That does not help the case of those who want to draw a sharp distinction between imagery and perception, however. Clearly the contrast they are trying to draw is not one between imagery and some sort of partial, automatic, subliminal registration of visual stimuli. They want to distinguish two modes of consciousness: imagination, and seeing in the full, everyday, conscious sense of the word, and that requires attention.
Attention may be all there is to imagery. It is certainly not all there is to seeing: At the very least, seeing also depends upon the appropriate stimulation of the visual receptors in the eyes. Nevertheless, attention is necessary both to imagery and to seeing, so McGinn is simply wrong to think that he can draw a sharp distinction between them on the basis of its involvement.
Reestablishing Continuity: 4. The Visual Field
On the face of things, McGinn's claim that the visual field of imagery is unrestricted has been directly refuted by experimental studies. Kosslyn (1978) reports experiments by which he claims to have actually measured "the visual angle of the mind's eye," and to have found it to be not very different from that of the bodily eyes. This is not, however, a straightforward case of the armchair philosopher being proved wrong by the experimental scientist, but, rather, a matter of dueling preconceptions. The experiments in question in fact depend upon people being asked to imagine themselves staring fixedly ahead at some scene, not turning their eyes, heads, or bodies as they normally would, and then being asked about what they can "see" in their mental image of the scene under those circumstances. The outcome is unsurprising. They "see" only as much as they would see if they were staring fixedly ahead. McGinn is clearly right to think that when the imagination is not deliberately and unnaturally constrained in this way, what it can "see" is not noticeably restricted by visual angle, or even by position: the mind's eye can quickly and easily skip around to new vantage points.
The trouble is that if the eyes are not subjected to similar unnatural restrictions, they too can easily skip around to new vantage points. Of course, if a physiologist wants to measure the visual field (i.e., the visual angle) of your eyes, then they must be held still while the measurement is made, and McGinn is certainly right to think that while the eyes themselves are thus held nearly still (or if we consider only what they could see during one very brief "snapshot" instant) their anatomically determined visual angle restricts what can be seen. However, he is not entitled to treat the imagination and the eyes asymmetrically, comparing what the imagination can encompass in its normal, free condition, over time, with what the eyes can see only while they are held carefully immobile (or only during an instant). If our standard for vision is the constrained, (relatively) immobile eye – the Cartesian, passive eye – then it deserves to be compared with an equivalently constrained imagination, as in the experiments of Kosslyn and his colleagues; if our point of comparison is to be the unconstrained imagination, then we should be comparing it with the unconstrained eye, whose physiological "visual angle," once it is set free from external constraints, places few if any limitations upon what can be seen. The eyes can flit freely about from viewpoint to viewpoint very nearly as easily as the imagination can. It is very easy to move the eyes in their sockets (indeed, much easier than it is to hold them even somewhat still), fairly easy to turn the head, and far from impossible to move the whole body. We constantly do all these things in order to bring new vistas into view. Even though it takes a lot less effort for me to imagine Timbuktu than it does for me to go and see the city, going there is by no means beyond my powers. The difference (given that no-one, I think, holds that imagination is completely effortless) is, once again, one of degree.
If it did happen to be quite impossible, in practice, for me to get to Timbuktu, that would be for merely contingent and nomological reasons, quite unsuitable for underwriting any sort of principled or conceptual distinction between imagination and perception. Although I can imagine being on Mars, I cannot get there to see it for myself, but that is only because no suitable spacecraft has yet been built. Whatever the basis for our distinction between perception and imagination may be, it isn't rocket science.
The difference in degree between imagination and perception with respect to visual field may be regarded as a consequence of the fact that the body, being subject to the laws of physics and the facts of geography, is generally more recalcitrant to the will than is the imagination. (Perhaps the mind is subject to the laws of physics too, but it certainly takes much less effort just to fire off a few action potentials than it does even to turn the head, let alone travel to Timbuktu.) We have already seen that the difference between imagination and perception with respect to will is a difference of degree rather than kind, so, of course, we should not be surprised to have found that this corollary, the difference with respect to visual field, is likewise.
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