Theories are often supported by unquestioned assumptions. One of the oldest unquestioned assumptions in philosophy concerns the nature of perceptual stimuli, namely, that sense-data are immediately perceived and that sensation consists in the sequential processing of “motions” immediately pressed upon the eye. Originating in Plato’s Theaetetus, this idea reached maturation in Descartes and was then taken up by Locke under the concept of primary and secondary qualities. According to these thinkers, sensible ideas (sense-data) are immediate impressions upon the eye which communicate the motion of light particles through the nerve conduits so that they may be processed and deposited onto the internal mental theater for subjective viewing. It is important to note that the conduit metaphor assumes that perception can only perceive the atomic sequence of impacts upon the eye; any nonimmediate mental perception is the result of “inference”. In other words, there is a “bottleneck” of immediacy that cannot be overcome without higher-order cognitive acts. Moreover, sense-data are private in that the primary qualities “appear” differently for different people in accordance with their individuality. The logic of this conduit metaphor was radicalized by Berkelely in his extreme sense-data empiricism. In the First Dialogue, he writes:
Philonous. It seems then, that by sensible things you mean those only which can be perceived immediately by sense.
Phil. Doth it follow from this, that though I see one part of the sky red, and another blue, and that my reason doth thence evidently conclude that there must be some cause of that diversity of colours, yet that cause cannot be said to be a sensible thing, or perceived by the sense of seeing?
Phil. This point then is agreed between, that sensible things are those only which are immediately perceived by sense. You will further inform me, whether we immediately perceive by sight any thing beside light, and colours, and figures: or by hearing any thing but sounds: by the palate, any thing besides tastes: by the smell, besides odours: or by the touch, more than tangible qualities.
Phil. Sensible things therefore are nothing else but so many sensible qualities [immediately perceived], or combinations of sensible qualities.
Our discourse proceeded altogether concerning sensible things, which you defined to be the things we immediately perceive by our senses. Whatever other qualities therefore you speak of, as distinct from these, I know nothing of them, neither do they at all belong to the point in dispute.
As a good empiricist, Berkeley radicalized the logic of the conduit metaphor for visual perception. If there is nothing “in” the mind-container other than impressions formed by the immediate perception of sensible things, and if sensible things cannot exist without a perceiving mind, then we have no rational recourse for knowing anything about an extrasensory material world composed of primary qualities not dependent on the mind. Thus, the ultimate substance of reality is Mind or spirit, for we can never escape the confines of our mental container.
The essence of the conduit/container metaphor consists in understanding the perceptual process in terms of an immediate communication of sense-data across the nerve-conduits into the “container” or “theater” of the mind. Accordingly, the very nature of the perceptual stimulus ensures that the mind can never rationally proceed beyond the causal immediacy of private sense-data. Because the perceptual stimulus is assumed to consist of immediate impressions upon the retina, any perception of motion must be inferred from the two-dimensional patterns of light, which are then transduced into sense-data. For Berkelely, the radicalization of this logic leads to the proposal that we have no rational recourse for getting “outside” of the internal theater of sense-data, for what we “perceive” is not the primary real, but rather, the secondary quality of “how it appears” subjectively.
Upon reflection however, we can see that the flatness or “immediacy” of sensory input is usually presupposed only after thinking about perception in terms of a frozen snapshot of reality. Ecological information, however, does not exist exclusively in an instantaneous slice of time for, as J.J. Gibson points out, “Animals and men [directly] perceive motions, events, episodes, and whole sequences” (1966, p. 276). Thus, the information we perceive in the environment has both successive and adjacent order. For Gibson, it is a mistake to think of persisting patterns as being a separate stimulus; biologically speaking, “Transformations of pattern are just stimulating as patterns are…motion is immediately detected by animals, not secondarily deduced from change of position”( ibid., p. 40). Accordingly, the brain is not in the business of continuously constructing a mind bogglingly detailed phenomenal model from spots of sensations differing in brightness and color. If this were true, Gibson sardonically notes that “the fact of perception [would be] almost miraculous”. Instead, Gibson theorizes that the nervous system directly “picks up” or behaviorally “resonates” to the ecological information available in the environment, particularly in respect to changes in the layout of surfaces, changes in the color and texture of surfaces, and changes of existence of surfaces. As Mark Rowlands nicely puts it,
information is simply optical structure-together with the deformation in this structure generated in a nomothetic way from the environmental layout and events. This optical structure is not similar in any way to the environment, but it is specific to it. That is, optical structure is nominally dependent upon environmental structure. Because the structure in the optic array is specific to its environmental sources, an observer whose perceptual system detects some optical structure is therefore aware of what this specifies. Thus, the perceiver is aware of the environment not the array. Therefore, once we describe the input for perception in terms of a structured optic array, we are committed to the idea that there is enough information directly available in the organism’s visual input to give that organism useful knowledge about the nature of its environment. Postulation of additional information processing would, to this extent, be superfluous. (1995, p. 9)
The logic of Gibsonian information processing goes counter to the thesis of radical sensory immediacy. Under the Gibsonian framework, perception is not constituted by the processing of sense-data through the bottleneck of retinal immediacy. Instead, the perceptual system is capable of a first-order perception of whole sequences in the environment. By proposing that the transformations of pattern within the ambient optic array contain both sequential and adjacent order, the notion that perception consists of immediate detection and transduction of motion across the two-dimensional retina loses its status as an unquestioned assumption. Accordingly, the Gibsonian framework argues that perception is grounded by ecological information, not sensory immediacy. And because ecological information is temporally extended, the classic model of immediacy is overcome by supposing that animals are capable of directly resonating to such information. As it turns out then, we are not trapped within the theater of our minds; access to reality is quite pedestrian.