Note on “Unstructured” Stimulation

February 1958

Note on “Unstructured” Stimulation

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 References to these essays must cite them explicitly as unpublished manuscripts.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 notion of unstructured stimulation is much favored by some recent investigators of perception (e.g. Sherif’s textbook, Rorschach studies, etc.). It seems to be derived from Gestalt theory (although it is not explicit in Koffka (?)).

For vision , it is applied to nonsense patterns, ink-blots, etc. (Cf. also the verbal “summator” of Skinner). I suggest that it is just a contradiction in terms when so applied. The homogeneous optic array can justly be called unstructured, but not a differentiated array. A continuous pitch (or white noise) can be called unstructured (in time) but not a changing sequence of sounds. Apart from these pure cases, stimulation is always structured. One might assert, in fact, that the variables of structure are the information – carrying variables of stimulation (ordinal stimulation) and that the variables of frequency and intensity as such are not informative in general. (They are “sensory”.)

The visual stimulus from an ink-blot, say, has a structure just as much as does that from a tree, or a photograph, or a page of print. It has a different structure, that is all. The structure of a static array (the adjacent order) may not specify objects; may both specify symbols; may not specify anything, but it is still a structure. It may be “regular” (described by a rule) or not “regular” (i.e., not described by any known rule). It may be “random” (so-called). The structure may be ambiguous or contradictory. But it is there to be analyzed. It may not convey meaning to the perceiver because (a) it does not specify anything, or (b) the perceiver is not sensitive to the specifying variable of structures. In either case, it is loosely said to be “meaningless”.

The notion that the individual structures the stimulation which excited his sense organs is another prevalent one, which is more directly borrowed from Gestalt theory (sensory organization). Strictly speaking, it is also contradictory; an organism cannot influence the stimulation in the flux of energy around it — all it can do is select some variables of stimulation to register than others (or seek out certain forms of stimulation rather than others). What the Gestalt theorists meant (and said) was that the organism structures the neural excitations aroused by stimulation. This is a reasonable hypothesis, although debatable. Note that whenever stimulation is structured, and to the extent that this structure is registered by sense-organs , the hypothesis of the “structuring” of excitations is unnecessary (unparsimonious).

Hence, one can study (a) experience or behavior in conditions of true unstructured stimulation (homogeneous array or unchanging sound), or one can “impoverish” or “reduce” stimulation (but this is not so simple as it sounds, these terms being hard to define; reducing intensity is not the same as reducing pattern or structure). More of the above study is necessary. The notion that the more one impoverishes thesensory process, the more one can reveal the perceptual process has not worked out well in practice.

Or (b) one can study perception with structured stimulation, the variables of which are not however, responded to by the subject. This is the problem of perceptual learning (or development, in the case of young animals).