Visual Imagery and Consciousness
Nigel J.T. Thomas
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http://www.imagery-imagination.com/viac.htm
Introduction
For most people visual mental imagery is a common, frequent experience. We often recall past events, or imagine possible ones, by forming mental images. Our dreams may also consist largely of mental imagery. Indeed, many philosophers and psychologists have held that, together with immediate perceptual experience, imagery makes up the entirety of consciousness (although clearly not just visual imagery, but also imagery in other sense modes, especially inner speech, auditory or vocal-motor imagery of spoken words). If we are to fully understand consciousness, we will certainly need to understand mental imagery.
Philosophers have studied mental imagery for many centuries, experimental psychologists have studied it for well over a hundred years, and more recently it has attracted the attention of cognitive scientists and neuroscientists, but many basic questions still remain unresolved. There is controversy not only over what cognitive and neural mechanisms are responsible for imagery, but also over its function (if any) in cognition. Some regard mental imagery (or some closely related notion, such as "perceptual symbols" or "image schemata") to be the necessary vehicle for all thought; some regard it as important only for certain types of cognitive task (such as judging spatial relationships); and yet others regard it as a functionally insignificant conscious epiphenomenon of the unconscious cognitive processes that really constitute our thinking.
Like percepts, mental images bear intentionality. That is to say, they are always images (or percepts) of something or other, of some (real or imaginary) "object." (Some philosophers regard intentionality and consciousness as very closely related phenomena.) However, unlike percepts, images occur in the absence of their object. You cannot perceive a cat when no cat is present, but you can imagine a cat (or any other perceptible thing) at any time. Furthermore, (mistakes aside) you cannot perceive a cat to be other than where and how it actually is, but, whenever you want to, you can imagine (i.e., form an image of) a cat as anywhere, or in any condition. Images thus seem well suited to function as mental representations, allowing us to think of things as they currently are not, and thus to recall the past, plan for the future, fantasize about the unreal, and speculate about the unknown. Since ancient times, this has generally been believed to be their cognitive function.
Defining Imagery: Experience or Representation?
Mental imagery is commonly defined as a form of experience: quasi-perceptual experience, experience that subjectively resembles the experience we have when we actually perceive something (see glossary). This implies that we are unlikely to be able to understand imaginal consciousness unless we understand perceptual consciousness (and perhaps vice-versa). Unfortunately, we do not yet have such an understanding (or, at least, one that is generally agreed upon). It also, however, implies that imagery is always and necessarily conscious: if something is not consciously experienced it cannot be mental imagery.
If, on the other hand, mental imagery is defined as being a form of mental representation, as some contemporary cognitive theorists suggest, the tight conceptual linkage between imagery and consciousness is broken, and it becomes conceivable that images (imaginal representations) might sometimes play a role in cognition without our being consciously aware of them. There is some evidence suggesting that this does indeed occur. For instance, experimental studies of verbal memory have found that nouns for which it is easy to think of a corresponding image (mostly words for concrete things, such as "dog," "ship," or "skyscraper") are more readily remembered than nouns for which it is difficult to think of an image (mostly abstractions, such as "truth," "nation," or "size"). However, this mnemonic effect of "imagability" seems to occur quite regardless of whether any relevant images are actually consciously experienced (or, at least, of whether the subjects report or recall experiencing them). One interpretation of this finding is that image representations may be spontaneously evoked by the concrete words, and may play a role in making these words more memorable, even when they do not rise to consciousness.
Unlike the experiential conception of imagery with which we started, this representational conception suggests that we might be able to understand the nature and function of imagery without giving any attention to the fact that it is (at least sometimes) consciously experienced, and, in fact, most empirical and theoretical cognitive science research on imagery over the past few decades has proceeded on that assumption. The problem of the imaginal consciousness has, very largely, been ignored or set aside, while questions and controversies about its representational function (and, more recently, its neural instantiation) have been pursued enthusiastically. Furthermore, little if any attention has been given to the question of why we should be conscious of some of our image representations and (supposedly) not others.
But in any case, imagery probably cannot be satisfactorily understood purely in terms of its representational function. It is difficult or impossible to differentiate it from other forms of actual or possible mental representation, without either, on the one hand, begging some very controversial questions about its nature (about whether, for example, the relevant representations are somehow picture-like), or, on the other hand, appealing to the experiential conception of imagery. We could (and perhaps should) say that mental images are just those mental representations whose presence to mind has the potential to give rise to quasi-perceptual experiences. If so, however, the representational conception of imagery becomes conceptually dependent upon the experiential conception, and we cannot even begin truly to understand imagery unless we take its conscious nature into account.
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