The Multidimensional Spectrum of Imagination
Nigel J.T. Thomas
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Page 7
Source : http://www.imagery-imagination.com/spectrum.htm
Reestablishing Continuity: 5. Absence and its Consequences
I will return to McGinn's point about absence, but let us grant it, provisionally. The things we perceive are really there, whereas the things we imagine are not. I think this apparently conceptual truth is actually what underpins several of his other suggested criteria of differentiation between perception and imagery: saturation,occlusion, thought, and observation. These four, at least inasmuch as they appear to be differences in kind rather than of degree, are consequences of the more fundamental fact of the absence of the imagined object.
Let us begin with saturation. McGinn's view, to recap, is that visual perceptual experience is "saturated" in the sense that "every point of the visual field is such that some quality manifest there, whereas this is not true of the [mental] image" (p. 25). It does indeed seem to be the case that imagery is not saturated in this sense. My mental image of a Jackson Pollock painting (for example), no matter how vivid it is and how well I know the work, almost certainly does not specify what color appears at every single point on the canvas, and it does not need to do so in order to be a recognizable and serviceable image of the painting.
However, my visual experience in front of an actual Pollock canvas differs, in the relevant regard, not because of any fact about my instantaneous visual experience, but because of the fact that as soon as I want to know the color at any arbitrary point, I can quickly turn my attention there and find it. It is the physical world that is saturated with qualities (colors in particular), not my instantaneous perceptual experience of it.
If I were to stand far enough back, I could get an optical image of the whole canvas on my retina, but I would still not thereby be experiencing the color at every point simultaneously. As we have seen, the peripheral parts of the retina has very few color sensitive cone cells, and does not seem to be capable of differentiating colors at all. I would have to stand very far away from a typically large Pollock if I wanted to get an image of the whole canvas on my fovea. Remember, foveal vision, whereby we see rich color and fine detail, comprises only about 2° of visual angle. Clearly nobody could make out much of the intricate detail of Pollock's paint splatters if the painting were far enough away to look "about the size of a thumbnail [held] at arm's length" (Richardson & Spivey, 2004). If I were close enough to the canvas to discriminate all the artistically relevant detail, its retinal image would greatly overflow my fovea, and it would be physiologically impossible for me to take in information about the color at every point on the canvas without moving my eyes to foveate (i.e., point my fovea directly at) different areas in turn. We do not normally notice that we are getting no color information from the peripheral visual field, but that is because we normally move our eyes so frequently and automatically.
Of course, the visible world, the external, physical world around us, does seem to be saturated, colored all over, but that is because it is colored all over. Some color quality is indeed manifested at every visible point (or else it would not be visible), and, as soon as I turn my eyes to foveate any of those points, I cannot avoidseeing the color there (even if I have no particular interest in it at that moment, and am currently much more concerned with, say, shape). Our visual perceptual experience seems saturated with qualities because the world we are experiencing is itself saturated (in the relevant sense). When we are merely imagining, by contrast, there is no (relevant) external world there to force us to experience color in this way, and it becomes possible to shift our attentional viewpoint around an imagined object or scene, paying attention, perhaps, to shapes or spatial relationships, without taking the trouble to imagine what color would manifest itself at every point. The apparently complete saturation of perceptual experience, then, arises from the physical presence of whatever is being perceived, and imagery can be, and often is, experienced as unsaturated because the physical absence of whatever is being imagined allows it to be.
Imagery's lack of the power of occlusion also seems to be a fairly straightforward consequence of the absence of imagined objects. Things we perceive are really there, where we see them to be, so of course they block the light that would otherwise come to us from whatever is behind them. Imaginary things are not there at all, so they do not block any light.
There is a little more that should be said, however, because imagery does have some power to cause us to fail to see things that we would otherwise see. There may even be rare individuals who sometimes experience imagery as partially or even fully occlusive. Be that as it may, even the rest of us, if we are devoting some of our attentional effort to maintaining an image in consciousness, are likely to miss seeing things that we might otherwise have seen. Keeping a visual image in mind generally reduces people's ability to detect and discriminate visual stimuli (Segal & Fusella, 1970; Craver-Lemley & Reeves, 1992; Craver-Lemley & Arterberry, 2001). No doubt this is not actual occlusion – no light is being blocked; rather, the effect is probably closely related to the inattentional blindness we discussed earlier – but the difference between a mental image and an opaque object, in respect of their powers to prevent us from seeing things, is not quite as absolute as we might at first be tempted to think.
The absence of imagined objects also explains McGinn's observations about thought. Yes, if we have an image in mind but then start to think about some other, unrelated topic, the image is likely to go away. As McGinn rightly sees, mental images are only sustained in consciousness by an effortful, ongoing act of attention, and our attention has, ex hypothesis, turned elsewhere. But images are not unique in this regard. If we become sufficiently engrossed in some train of thought we may equally well cease to pay attention to what is before our open eyes, and thus cease to be conscious of it (inattentionally blind). It may well be true that it takes a greater degree of absorption in our thoughts to make the world go away than it does to make a mental image go away, but this is clearly a difference of degree, quite consistent with the continuum view. The sense of a more absolute, qualitative difference between the perceptual and imaginal effects of being absorbed in thought arises, I think, because when we eventually turn our attention back to the visible world, we immediately see that the same world is still there (still present, not absent), constraining us to have much the same sorts of visual experiences as we were having before. This (reinforced, perhaps, by the knowledge that the light has been pouring into our eyes all along, and that that, from the Cartesian, passivist point of view, ought to be sufficient for seeing) invites the questionable inference that we have been seeing the scene in front of us all along, even when we were not actually aware of it. By contrast, any mental image we may have had before becoming otherwise engrossed will be utterly gone, and can be recalled only with effort, if at all. There is thus not the same temptation to think that we might somehow have been unconsciously experiencing it the whole time.
McGinn's claim about observation is also, I think, a consequence of the fact that the objects of perception are materially present to us, whilst the objects of imagination are absent or non-existent. Sartre and Wittgenstein both argued that we can never learn anything new from our imagery, because an image contains nothing but what the imager put there, which must already have been in their mind (Sartre, 1940 ch. 1; Wittgenstein, 1967 §§627, 632). This is misleading, however. It is as if one were to say that if someone knows all the axioms and definitions of Euclidean geometry, they automatically know all of its theorems. In fact, of course, the theorems must be inferred, and this is not trivial. Kosslyn (1980, 1994) and Taylor (1981), have independently pointed out that imagery can sustain a form of inference: the information about the appearances of things that is stored in one's memory may entail facts of which one is unaware, and, in many cases, these facts can best be discovered by forming and examining a mental image. One of Kosslyn's favorite examples is the question "What shape are a German Shepherd dog's ears?" He has provided persuasive experimental evidence that people confronted with a question like this will often answer it by recalling a mental image of a German Shepherd, and "seeing" the shape of the ears in their image (Kosslyn, 1976a,b, 1980).
McGinn concedes this point to Kosslyn, but nonetheless insists that Sartre's and Wittgenstein's argument still points to an important truth. Drawing out fresh implications from what we already know is, after all, only one of the ways, and not the most important or fundamental way, in which we increase our knowledge. Through the use of my senses, through observing the world around me, I constantly get to know things that could not possibly have been inferred from what was already in my head. I find out, for instance, the color of a berry on a bush – whether it is unripe and green, or ripe and reddish – by looking at it. Somehow, through perception, new information comes from the berry itself into my mind. This sort of knowledge gain can never come through mere imagination, because, of course, when I merely imagine a berry there is no berry to draw any information from. Although we can imagine something in its absence, we can only perceive something, and thereby draw new information from it, if it is actually there.
So is absence (and the differences with respect to saturation, occlusion, thought, and observation that flow from it) the true criterion of demarcation between imagery and perception? To say that we perceive something is normally to imply that it is present to be perceived. Imagery, by contrast, has often been defined (by me, amongst others) as quasi-perceptual experience of something in the absence of that something (McKellar, 1957; Richardson, 1969; Finke, 1989; Thomas, 2008, 2009a). This is a genuine difference between imagination and perception, but, despite appearances, it is, once again, really a difference of degree. It only appears otherwise when we fix our attention firmly on the far opposite ends of the continuum of perceptual/imaginative experience: "plain as day" veridical perception at one end, and "pure," totally stimulus-independent imagery at the other. As McGinn recognizes (he devotes a whole chapter to the matter), there is a whole range of forms of "imaginative perception" in between: mistaking a bush for a bear in the darkness; seeing the shapes of animals or angels in the clouds; mistakenly recognizing a stranger as an acquaintance; seeing an ambiguous drawing as depicting a duck (or a rabbit); recognizing the politician in the caricature; seeing paint on canvas as a portrait of Napoleon; and so on and on. These are all cases of seeing something as something else: something is present to the senses, but it is not quite what we take (or deliberately fancy) it to be. (Although even veridical seeing is seeing as: seeing something as what it in fact is.) The imagination, here, is not entirely free, but is constrained, to a greater or lesser degree, by what is present to the senses. We are not going to mistake that bush for a giraffe, or take the duck-rabbit figure to depict a motorcycle, and although that cloud might equally well be seen as very like a whale, a weasel or a camel, it is certainly nothing like a hollyhock.
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