Imagery and Imagination
Amy Kind
Page 2
Source: http://www.iep.utm.edu/imagery/
b. The Argument from Introspection
It is also important to note that the imagery debate is not a debate over whether we “think in words” or “think in images.” To see this, it will be useful to consider the argument from introspection that is directed at descriptionalism. When we introspect, it seems to us that our mental images look like what they represent. This introspective judgment is often taken as definitive support for pictorialism, since pictorial representations look like what they represent while descriptional representations do not.
Block (1983) and Tye (1991) each argue persuasively that this argument should be rejected. Properly understood, the evidence from introspection can be seen to be neutral with respect to the imagery debate. To see this, we need to distinguish the experience of imaging from the representation that underlies or accounts for this experience. Consider the following analogy: Suppose you were to come across a box on whose surface was displayed a crude black and white image of a rabbit in a meadow. You might then ask: What is going on inside this box to account for the rabbit-image? One possibility is that some sort of slide projector inside the box projects the rabbit-image onto the box’s surface. If this were the case, then what underlies the image would be a pictorial process. But another possibility is that a computer inside the box produces the rabbit-image by way of binary code – strings of 0s and 1s that turn certain pixels on the surface of the box to black, certain pixels to gray, and so on, such that the rabbit image appears. If this were the case, then what underlies the image would be a non-pictorial process.
As this analogy suggests, the pictorialists claim that underlying the experience of mental imagery is some sort of representation that is pictorial in nature while the descriptionalists claim that underlying the experience of mental imagery is some sort of representation that is descriptional or linguistic in nature. By distinguishing between experiences and the underlying representations, we undercut the force of the introspective judgment that lies at the heart of the argument from introspection, namely, that mental images look like what they represent.
Pictorialists and descriptionalists alike thus accept that we sometimes think in images. In other words, pictorialists and descriptionalists agree that we have certain imagistic experiences, that we experience what we would call “imaging.” When we introspect, when we look within, it seems to us as if we are experiencing mental pictures. But the experience is one thing, the representation that accounts for this experience another. The pictorialists think that the introspective data should be interpreted just as it seems—our mind manipulates representations that are pictorial in nature. The pictorialist view thus offers us a unified conception of our experiences and the representations that underlie them. In contrast, the descriptionalists think that the introspective data is misleading in a certain sense; our experiences are not quite as they seem. Insofar as it seems to us that we have certain mental representations that are pictorial in nature, we are the victims of an illusion.
In defending descriptionalism against the argument from introspection, Tye (1991) makes the further point that all that introspection really suggests is that imaging is like perception: “to assert that a mental image of my brother, say, looks to me like my brother is merely to assert that my imagistic experience is like the perceptual experience I undergo when I view my brother with my eyes.” Empirical experiments have tended to confirm introspective reports that imaging resembles perceiving. Perky (1910) placed a number of people in a room, facing a screen, and asked them to produce mental images of various ordinary objects on the screen. The subjects were not aware of the fact that, after they had reported that they were engaged in the requested imaging (of a banana, for example), an image of a banana was lightly projected onto the screen. The projected image was slowly increased in intensity until, eventually, it was visible to any newcomer entering the room. Nonetheless, the subjects never realized that they were seeing an image of a banana. The only differences that they noted in their subjective experiences were changes in the size and the orientation of the banana they had been imaging. In this highly controlled setting at least, seeing was mistaken for visual imaging.
Additional empirical evidence strongly suggests that the mechanisms underlying imagery and underlying perception are the same. (For an overview of some such experiments, see Finke and Shepard 1986.) One set of important results was generated by Kosslyn (1993), who demonstrated using positron emission tomography (PET) that areas of the brain activated when we engage in object recognition are also activated when we produce visual mental imagery. Other important results come from studies on patients who have suffered damage to parts of their visual system. Bisiach and Luzzatti (1978) studied patients who suffer from hemi-neglect, i.e., patients who ignore objects in one half of their visual field. These patients were discovered also to neglect objects in the same half when producing mental images. To give another example, prosopagnosiacs, who cannot recognize faces, have been shown to suffer from similar difficulties when interpreting mental imagery (Levine, Warach, and Farah 1985).
Given the totality of the evidence, both introspective and empirical, it seems reasonable to assume that the representations underlying the experience of imagery are like the representations that underlie the experience of perception. Importantly, however, the representations that underlie the experience of perception may themselves be descriptional in nature. Thus, without a theory of the nature of the representation underlying perceptual experience, evidence connecting mental imagery with perception cannot be taken as support for pictorialism.
c. Objections to Pictorialism
While the above considerations suggest that the argument from introspection should be rejected, they do not entail the truth of descriptionalism. So why would anyone embrace descriptionalism? One influential consideration, as noted earlier, comes from the seeming incompatibility of pictorialism and materialism. This problem, at least in part, is what Block (1983) has called the No Seeum Objection: when we look in the brain, we do not see any pictures.
Of course, when we look in the brain, we do not see any descriptions either. But, in contrast to the pictorialists, the descriptionalists seem to have an easy response to the No Seeum charge. Sterelny (1986) notes that, since sentences are not medium-dependent, accounting for descriptional representations in the brain is unproblematic: “Sentences can come as sound waves, marks on paper, electrical pulses, punched cards, and so on. Why not then as patterns of neural firings as well?”
Interestingly, Block (1983) argues that we can extend this sort of response to protect pictorialism from the No Seeum objection as well. To know whether you are looking at a descriptional representation, you must be familiar with the representational medium that is in use. Block proposes that the pictorialist can adopt this same line of reasoning. What makes something the sort of representation that it is, regardless of whether it is pictorial or descriptional, depends in large part on the system of representation in which it functions. Thus, until we know more about how the representational system of the brain works, we are unlikely even to be able to tell which structures in the brain are representations, let alone what sort of representations they are.
Descriptionalism has also been thought to gain support from the Paraphernalia Objection to pictorialism: even if we were to discover pictures in the brain, these pictures could not play a role in our cognitive processes unless there were an internal eye to see the pictures, and since there is no such internal eye, pictorialism must be false. (See Rey 1981, Block 1983 for discussion of this objection.) Dennett (1969) voices the Paraphernalia objection by way of an apt analogy:
Imagine a fool putting a television camera on his car and connecting it to a small receiver under the bonnet so the engine could ‘see where it is going’. The madness in this is that although an image has been provided, no provision has been made for anyone or anything analogous to a perceiver to watch the image.
According to the Paraphernalia objection, the pictorialist is like this fool. Block (1983) and Kosslyn (1980) each suggest responses that the pictorialist can make to this objection; in short, the basic strategy is to invoke mechanistic explanation.
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