See PERCEPTION. perception, the extraction and use of information about one’s environment (exteroception) and one’s own body (interoception). The various external senses – sight, hearing, touch, smell, and taste – though they overlap to some extent, are distinguished by the kind of information (e.g., about light, sound, temperature, pressure) they deliver. Proprioception, perception of the self, concerns stimuli arising within, and carrying information about, one’s own body – e.g., acceleration, position, and orientation of the limbs. There are distinguishable stages in the extraction and use of sensory information, one (an earlier stage) corresponding to our perception of objects (and events), the other, a later stage, to the perception of facts about these objects. We see, e.g., both the cat on the sofa (an object) and that the cat is on the sofa (a fact). Seeing an object (or event) – a cat on the sofa, a person on the street, or a vehicle’s movement – does not require that the object (event) be identified or recognized in any particular way (perhaps, though this is controversial, in any way whatsoever). One can, e.g., see a cat on the sofa and mistake it for a rumpled sweater. Airplane lights are often misidentified as stars, and one can see the movement of an object either as the movement of oneself or (under some viewing conditions) as expansion (or contraction). Seeing objects and events is, in this sense, non-epistemic: one can see O without knowing (or believing) that it is O that one is seeing. Seeing facts, on the other hand, is epistemic; one cannot see that there is a cat on the sofa without, thereby, coming to know that there is a cat on the sofa. Seeing a fact is coming to know the fact in some visual way. One can see objects – the fly in one’s soup, e.g., – without realizing that there is a fly in one’s soup (thinking, perhaps, it is a bean or a crouton); but to see a fact, the fact that there is a fly in one’s soup is, necessarily, to know it is a fly. This distinction applies to the other sense modalities as well. One can hear the telephone ringing without realizing that it is the telephone (perhaps it’s the TV or the doorbell), but to hear a fact, that it is the telephone (that is ringing), is, of necessity, to know that it is the telephone that is ringing.
The other ways we have of describing what we perceive are primarily variations on these two fundamental themes. In seeing where (he went), when (he left), who (went with him), and how he was dressed, e.g., we are describing the perception of some fact of a certain sort without revealing exactly which fact it is. If Martha saw where he went, then Martha saw (hence, came to know) some fact having to do with where he went, some fact of the form ‘he went there’. In speaking of states and conditions (the condition of his room, her injury), and properties (the color of his tie, the height of the building), we sometimes, as in the case of objects, mean to be describing a non-epistemic perceptual act, one that carries no implications for what (if anything) is known. In other cases, as with facts, we mean to be describing the acquisition of some piece of knowledge. One can see or hear a word without recognizing it as a word (it might be in a foreign language), but can one see a misprint and not know it is a misprint? It obviously depends on what one uses ‘misprint’ to refer to: an object (a word that is misprinted) or a fact (the fact that it is misprinted).
In examining and evaluating theories (whether philosophical or psychological) of perception it is essential to distinguish fact perception from object perception. For a theory might be a plausible theory about the perception of objects (e.g., psychological theories of ‘early vision’) but not at all plausible about our perception of facts. Fact perception, involving, as it does, knowledge (and, hence, belief) brings into play the entire cognitive system (memory, concepts, etc.) in a way the former does not. Perceptual relativity – e.g., the idea that what we perceive is relative to our language, our conceptual scheme, or the scientific theories we have available to ‘interpret’ phenomena – is quite implausible as a theory about our perception of objects. A person lacking a word for, say, kumquats, lacking this concept, lacking a scientific way of classifying these objects (are they a fruit? a vegetable? an animal?), can still see, touch, smell, and taste kumquats. Perception of objects does not depend on, and is therefore not relative to, the observer’s linguistic, conceptual, cognitive, and scientific assets or shortcomings. Fact perception, however, is another matter. Clearly one cannot see that there are kumquats in the basket (as opposed to seeing the objects, the kumquats, in the basket) if one has no idea of, no concept of, what a kumquat is. Seeing facts is much more sensitive (and, hence, relative) to the conceptual resources, the background knowledge and scientific theories, of the observer, and this difference must be kept in mind in evaluating claims about perceptual relativity. Though it does not make objects invisible, ignorance does tend to make facts perceptually inaccessible. There are characteristic experiences associated with the different senses. Tasting a kumquat is not at all like seeing a kumquat although the same object is perceived (indeed, the same fact – that it is a kumquat – may be perceived). The difference, of course, is in the subjective experience one has in perceiving the kumquat. A causal theory of perception (of objects) holds that the perceptual object, what it is we see, taste, smell, or whatever, is that object that causes us to have this subjective experience. Perceiving an object is that object’s causing (in the right way) one to have an experience of the appropriate sort. I see a bean in my soup if it is, in fact (whether I know it or not is irrelevant), a bean in my soup that is causing me to have this visual experience. I taste a bean if, in point of fact, it is a bean that is causing me to have the kind of taste experience I am now having. If it is (unknown to me) a bug, not a bean, that is causing these experiences, then I am (unwittingly) seeing and tasting a bug – perhaps a bug that looks and tastes like a bean. What object we see (taste, smell, etc.) is determined by the causal facts in question. What we know and believe, how we interpret the experience, is irrelevant, although it will, of course, determine what we say we see and taste. The same is to be said, with appropriate changes, for our perception of facts (the most significant change being the replacement of belief for experience). I see that there is a bug in my soup if the fact that there is a bug in my soup causes me to believe that there is a bug in my soup. I can taste that there is a bug in my soup when this fact causes me to have this belief via some taste sensation.
A causal theory of perception is more than the claim that the physical objects we perceive cause us to have experiences and beliefs. This much is fairly obvious. It is the claim that this causal relation is constitutive of perception, that necessarily, if S sees O, then O causes a certain sort of experience in S. It is, according to this theory, impossible, on conceptual grounds, to perceive something with which one has no causal contact. If, e.g., future events do not cause present events, if there is no backward causation, then we cannot perceive future events and objects. Whether or not future facts can be perceived (or known) depends on how liberally the causal condition on knowledge is interpreted.
Though conceding that there is a world of mind-independent objects (trees, stars, people) that cause us to have experiences, some philosophers – traditionally called representative realists – argue that we nonetheless do not directly perceive these external objects. What we directly perceive are the effects these objects have on us – an internal image, idea, or impression, a more or less (depending on conditions of observation) accurate representation of the external reality that helps produce it. This subjective, directly apprehended object has been called by various names: a sensation, percept, sensedatum, sensum, and sometimes, to emphasize its representational aspect, Vorstellung (German, ‘representation’). Just as the images appearing on a television screen represent their remote causes (the events occurring at some distant concert hall or playing field), the images (visual, auditory, etc.) that occur in the mind, the sensedata of which we are directly aware in normal perception, represent (or sometimes, when things are not working right, misrepresent) their external physical causes.
The representative realist typically invokes arguments from illusion, facts about hallucination, and temporal considerations to support his view. Hallucinations are supposed to illustrate the way we can have the same kind of experience we have when (as we commonly say) we see a real bug without there being a real bug (in our soup or anywhere else) causing us to have the experience. When we hallucinate, the bug we ‘see’ is, in fact, a figment of our own imagination, an image (i.e., sense-datum) in the mind that, because it shares some of the properties of a real bug (shape, color, etc.), we might mistake