The Concept of the Stimulus. A Revised Formulation of the Alternatives

May 1968

The Concept of the Stimulus. A Revised Formulation of the Alternatives

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 References to these essays must cite them explicitly as unpublished manuscripts.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 conflicting definitions of the term stimulus in psychology (Gibson, 1960) has led to a logical discussion (Hocutt, 1967; Gibson, 1967). But the question of the “circularity” of the definition of the concept is only one question; there are several others. The principle theoretical issues seem to be the following.

1. Should the stimulus be defined only in terms of energy at receptors or in terms of objects and events in the world? This is the issue that began with the distinction between the proximal and the distalstimulus, accepted by some perceptionists but not by the behaviorists.

2. Should the stimulus be defined as effective energy at a receptor or a mosaic of receptors, or extended to mean the available array and flow of energy at the surface of an organism? If the first, then the stimulus is response-producing; if the second, then the organism can be understood to explore, obtain, and select the stimulation to which response will be made. This is the issue of “passive” or “active” perception in its fundamental form. This is also where the question arises of whether a potential stimulus is or is not actually a stimulus (is the term logically reciprocal with response?).

3. Even if we conceive of stimulation as a patterned and transforming array of energy (either currently effective or explored over the course of time) is it no more than neutral physical energy, or must we allow that it comprises information in some sense of that term? This is the issue of whether stimulation and experience are fundamentally meaningless or are intrinsically meaningful. Should we distinguish between stimulus energy and stimulus information? The sense-datum controversy in theories of perception arises here.

4. If the concept of information in the flowing array of stimulus energy is allowed, do we define such information as affording mere discrimination or differential reaction (an item being “what it is not, but might have been”) or do we define it as having environmental reference and ecological validity? Do invariants of stimulation specify sources in the environment or do they generally not do so? This is when the undeveloped disciplines of ecological optics, acoustics, etc. come in, and here lie the empirical questions that could settle the central problem of epistemology. Moreover the question of whether perceptual activity is a process of constructing an internal copy of the environment or one of detecting the environment depends on this issue.


Gibson, The concept of the stimulus in psychology. Amer. Psychol., 1960, 15, 694-703.

Hocutt, On the alleged circularity of Skinner’s concept of stimulus. Psychol. Rev., 1967, 74, 530-532.

Gibson, On the proper meaning of the term “stimulus”. Psychol. Rev., 1967, 74, 533-534.

Gibson, New reasons for realism. Synthese, 1967, 17, 162-172.