April 1976
What is it to Perceive?
J. J. Gibson, Cornell University
The World Wide Web distribution of James Gibson’s “Purple Perils” is for scholarly use with the understanding that Gibson did not intend them for publication. References to these essays must cite them explicitly as unpublished manuscripts. Copies may be circulated if this statement is included on each copy.
The verb to perceive has two meanings, one being that of ordinary usage and the other coming from a puzzle in philosophy and psychology:
1. To perceive X means simply to be in touch with it, to be able to cope with it, or to be aware of it in the environment.
2. To perceive X means to have an experience corresponding to X, or a percept of it, or a content of awareness, or of consciousness. This implies that there is a mental X besides the actual X. The second meaning is troublesome.
The two meanings need to be kept separate in the investigation of perceiving. The act of a perceiver and the content of his mind should not be confused.
Cases to consider:
a) When a person has a hallucination of X or claims to see a ghost of X, or dreams of it, I argue that the term “perceive” should not be used at all.
b) When an observer “perceives” himself, or another person, or part of the room, in a mirror there is perception based on optical information and we can say that he perceives a virtual object, person, or place. It is an “optical” object but not a “substantial” object since it has no surface (This is vastly preferable to saying it is not “real”, which is slippery). Virtual surfaces can be distinguished from substantial surfaces by exploratory perception.
c) When an observer reports perceiving a surface layout in a laboratory experiment such as the “optical tunnel” or the “visual cliff”, we can say, similarly, that he “perceives” it but that the tunnel, i.e., the surface, is not substantial, and that the cliff does not afford falling-off.
d) When an observer looks at a picture of X, I assume that there is optical information to specify at least some of the features of X and that (if he picks up the information) he “perceives” a virtual X but in the special sense of a mediated perception or perception at second hand. In this case, there is always information to specify the display as such, that is, the picture surface as well as the surface of X. This is the proper meaning of a depiction.
Note that the virtual X in a mirror, or in a laboratory display, or in a picture is not a “mental” or “subjective” entity. Looking at mirrors, displays, or pictures surely does not involve making or having an “internal representation” of X. Note that a picture can specify all sorts of virtual objects. A photograph or painting can display the information for a surface layout that (1) exists but is out of sight, such as a living person, or Niagara Falls. Or it may be a layout of surfaces that (2) have gone out of existence, such as Henry VIII, or the house I once lived in which burned down. A drawing or painting may specify a surface layout that (3) will exist, such as the house my builder is going to construct. Or the nonphotographic picture may specify a layout that (4) might exist if someone designed or invented or created it, such as a “dream house” or a new machine. Or the picture might specify a layout that (5) would only exist if different laws of nature held, such as a unicorn, an angel, or a castle in the skies.
The theory that a “mental image” of X is confronted or obtained when one remembers X, or recalls it, or imagines it, or visualizes it gets its justification from the facts about pictures listed above. An artist can, it is true, make a drawing from “life”, or from “memory” or from “imagination”. But this does not imply that to remember, recall, imagine, or visualize is to make a mental drawing.
Perhaps to perceive is to be directly aware of substantial things in the environment that exist whether or not they are temporarily in sight, including things that have been and will be seen as well as the surfaces that are seen and felt now at the point of observation. Direct perception comes from picking up unedited information in stimulation over time, not from getting pictorial information. Then to recall would mean to be aware of things that have ceased to exist and to expect would mean to be aware of things that will exist. Neither of these are substantial. To imagine would mean to be aware of things that might exist, or that one hopes or fears exist.
Note. Nothing in the above applies to human verbal learning or verbal memory, nor to verbal knowledge. When words are applied to knowledge the problem becomes different.