In the light of the forgoing analysis, the definition of perception may be reformulated as follows: Perception is the direct and immediate awareness of external entities resulting from the extraction of entity-imposed order in energy gradients absorbed by a receptor system.
The Physical Basis of Perception:
(1) For perception, the important fact about entities is that they are invariant centers in an otherwise changing world.
(2) What are directly processed in perception are the effects of the interaction between objects and energy,
(3) For perception to be made possible, the required net result of the interaction between energy and object is that the object remains unaltered, whereas the energy emerging from the object encounter contains a new structure imposed by the object; energy structure being defined in this context as: the pattern of distribution of energy defined in terms of the energy’s quality, magnitude and direction relative to a specified point or surface.
(4) Perception at a distance requires that the energy structure emerging from the object encounter be carried away from the objects without undergoing a distortion in the medium carrying the energy structure and in which the objects are immersed.
(5) For perception, an object consists of a structurally coherent, spatially segregated; temporally enduring existent. The fact about objects that is of primary importance is that they are spatially bounded, which means that they are physically defined by boundaries that segregate them from one another The reason why boundaries are so important for perception is that the object boundary is the physical line across which energy effects change.
(6) Perception is made possible only when object boundaries yield energy {78} boundaries. To the extent that this causal relationship holds, object structure defines energy structure.
(7) Reciprocal to the fact that object structure can define energy structure is the fact that energy structure can specify object structure and environmental layout.
(8) An energy pattern or event is said to physically specify-a physical object or event when there exists a causal and one-to-one relationship between the order in the physical object or event and the order in the energy pattern or event.
(9) Perception is made possible when energy gradients contain the physical specifications of object order.
(10) The concept of “specification” identifies the causal basis for the objectivity of perception, i.e., for the fact that perception consists of an immediate awareness of environmental order. Gibson’s “General Hypothesis of Psychophysical Correspondence,” which asserts,:
“That for every aspect or property of the phenomenal world of an individual in contact with his environment, however subtle, there is a variable of the energy flux at his receptors, however complex, with which the phenomenal property would correspond if a psychophysical experiment could be performed” (Gibson, 1959)
[This principle] identifies the causal link between object attributes and perceptual attributes, in that these latter are mediated by the attributes of energy gradients causally connected to object attributes. In short, the order contained in the changing energy gradients at the receptor specifies the external physical order, and is the physical cause of the perception of the external physical object order
The Physiological Basis of Perception:
(1) Object perception requires the display, absorption, and extraction {79} of object-specifying attributes of energy structure.
(2) The absorption and display of energy structure is achieved by means of sensory receptor organs each of which is selectively sensitive to a particular form of energy. Energy-dependent object attributes can be registered only by those receptor organs that are selectively sensitive to the specific form of energy upon which the object attribute depends. Energy independent object attributes can be equally registered by different receptor organs each sensitive to different forms of energy. The registration of energy-independent object attributes cuts across sense modalities and, thereby, permits cross-modality integration (e.g., the alternative or simultaneous visual, tactile, and, for bats, acoustical registration of shape). The registration of energy-dependent object attributes is modality-exclusive and precludes cross-modality integration (i.e., precludes the “seeing” of loudness or the “hearing” of color). These facts identify the physical and physiological basis of the philosophical distinction between the so-called “primary” and “secondary” sense qualities. The “primary” sense qualities correspond to the forms in which we perceive energy-independent object attributes. The “secondary” sense qualities correspond to the forms in which we perceive energy-dependent object attributes. Although some object attributes may be energy-independent, our perception of any object attributes is always energy-dependent. Furthermore, since both categories of sensory qualities correspond to the forms in which we perceive object attributes, both of these sensory categories have equal epistemological status.
(3) The specifications of objects are not fully contained in stationary samples of energy patterns. The full specifications of objects can only be obtained from a moving sample of the available energy structure. {80}
(4) Perception, therefore, requires a mobile receptor organ. Moving pickup of energy structure is a precondition for perception. This is because the invariant features which define objects are specified in the relational invariants in the ordered transformations of changing energy patterns displayed at the receptor and resulting from a moving sample of the available energy structure.
(5) The receptor apparatus, when understood in functional terms, is a device for picking up and displaying the pattern or order contained in changing energy gradients. Since it is the order that is fundamental, and not the form in which the order is carried, the receptor system may intercept patterns carried as a temporal order in an energy event, and display these patterns in terms of spatial adjacencies (e.g., as occurs at the basilar membrane). Or, spatial order in an energy pattern may be displayed in terms of temporal adjacencies (e.g., as in the case of optical, tactile, and acoustical scanning).
(6) The perception of objects depends upon the registration of object boundaries or contours. The specifications for these are contained in energy boundaries. An energy boundary may be defined as a line across which energy effects change.
(7) The sensory system must selectively extract those invariants of energy boundaries that specify the constant features of object boundaries. These invariants are extracted by means of the registration of energy ratios across energy boundaries. By responding to energy ratios, the sensory system is able to optimize its sensitivity to object-specifying energy boundaries, by maximizing the constancy of sensory effects over the widest possible range of changes in overall energy. {81}
(8) Perception requires the existence of physiological mechanisms that specifically and selectively isolate externally caused patterns of neural excitation. By virtue of the fact that externally caused energy gradients produce neural excitation patterns which, in their relational aspects, differ from neural excitations of endogenous origin, our sensory systems are able to selectively filter, segregate, or neutralize endogenous patterns of neural excitation so that such patterns become inadequate to produce and sustain conscious experiences. The criterion which seems to be employed, is that all excitations patterns which are not systematically translated or do not systematically co-vary with receptor movement, and which remain stabilized in the presence of receptor movement, are treated as receptor-specific and do not yield exteroception.
(This last point is my answer to the popular but erroneous conclusion, drawn from Johannes Muller’s Doctrine of the “Specific Energies of Nerves,” which is generally offered as proof that perception must be a wholly subjective process since our sensory systems cannot, according to this doctrine, differentiate between endogenous and exogenous causes of excitation.)
(9) Sensory adaptation can be understood as the effects of active mechanisms that tend to alter the sensory system’s criterion of adequate stimulation for perception by neutralizing sensor effects that are caused by neural activation patterns that are either strictly energy-specific or receptor-specific. Energy specific effects are those that do not vary as a function of directionality, i.e., which are equal or which do not change precipitously as a function of receptor registration of directionality. Adaptation to overall energy amplitude or intensity or to any omnidirectional energy component, such as a specific energy frequency, represents sensory {82} adaptation to energy-specific effects. Adaptation to systematic distortions of energy contour curvature, or to systematic spectral contour fringes, as are caused by wearing displacing optical prisms (see Gibson, 1933; Kohler, 1962), or adaptation to orientation-specific global energy shifts, such as those produced by wearing split-field colored goggles (Kohler, 1962), or the perceptual instability and disappearance of “fixed” retinal images (see Heckenmueller, 1965), are three examples of sensory adaptation to receptor specific stimulation.
(10) In general, it may be concluded that the physiological basis of perception consists of innate mechanisms which function so as to selectively isolate the invariant features of externally caused energy contours or boundaries, and to isolate changing patterns defined by these contours.
The Psychological Basis of Perception
(1) The process of perception is the primary means by which the perceiving animal regulates its life-serving behavior. Perception is not a passive physiological state or by-product. It is an active conscious process the purpose of which is two-fold: 1- the maintenance of cognitive contact with reality, and 2- regulation of self-generated action in accordance with that cognitive contact.
(2) Consciousness, qua life process, implies selective purposive actions which requires selective cognitive processing. This entails a process of selective conscious focus, i.e., attention. Attentional processes play an active role in determining which components of available energy patterns will be processed so as to bring the organism into greater cognitive contact with that part of the external world giving rise to those selected components.
(3) Perceptual control of behavior requires a conscious awareness of the {83} distinction between “self” and “external world,” i.e., the proprioceptive/ exteroceptive distinction. The perceptual differentiation that is the form in which this distinction is experienced is based upon the organism’s capacity to discriminate between those sensory effects over which he has control and those effects independent of his control.
(4) The physical basis of this distinction cannot be traced to any energy patterns acting on the receptor system, for there are no patterns which are caused by the organism’s acting (i.e., self-generated movements) that cannot also be produced by the organism being acted upon (i.e., passively imposed movements). Furthermore, the physiological basis for the perception of this distinction cannot be traced to sensory effects of muscular action or joint articulation, since coordinated conscious control of movement is possible in the absence of muscle and joint “sensation” (i.e., sensory motor feedback). Furthermore, qua mere responses to mechanical contraction, muscle and joint, afferance is as much a reaction to change as are the afferent patterns from any other receptor system, and, therefore, cannot in itself account for the awareness of self-generated action. Finally, since the awareness of the propriospecific/exterospecific distinction depends upon and presupposes awareness of self-generated action, awareness of this latter cannot itself depend upon proprioception. I conclude, therefore, that awareness of self, qua causal agent, does not have a sensory receptor origin, but is a consciously detectable efference. Once this efference is attended to in conjunction with the sensory effects caused by this self generated action, these two conscious components are automatically integrated to produce the perception of self-generated action. The awareness of self-control provides the basis for the discovery of the external world. Self-generated action produces two {84} categories of sensory effects: 1. Those sensory effects that are independent of self-generated action are automatically integrated as exterospecific, and perceived as an independent external existence. 2. Those sensory effects that are dependent upon self-generated action are automatically integrated as propriospecific, and are perceived as “self.” These facts are not experienced as two separate perceptions, but are perceived as two discriminable aspects of every perception (Gibson, 1970).
(5) Directed attention causes the organism to notice things which were previously unnoticed. Our perceptions are the automatic forms in which the order in energy patterns, once noticed, are consciously retained. It is the order in changing energy patterns that is “given” to the sensory system, and it is these ordered patterns to which the organism attends, and which are automatically integrated and retained in the form of the perception of objects.
(6) Whenever a changing energy pattern produces the perception of a specific geometrical layout of object surfaces, it is invariably due to the existence and detection of a specifiable invariant order in the physical energy patterns being picked up by the receptors. It is this invariant order in the energy patterns that that is the psychophysical correspondent of the perceived object. The order in these patterns is the fact isolated and integrated as a perception. Outside of the order in stimulus patterns, the organism has no direct cognitive contact with physical object order. But only insofar as this stimulus order is physically connected to the object order by virtue of physical laws of object/energy interaction, can the organism use the invariants in the stimulus order to guide himself about the world of physical objects.
(7) It is the patterns in energy gradients that are detected, extracted, {85} and integrated to produce our perceptions of objects. Once we understand how objects cause the order in the absorbed energy patterns, we can recreate the patterns in the absence of these objects, and thereby produce identical perceptions. The resulting perceptions are the same because the external physical order, to which our perceptions correspond, namely, the physically imposed order in changing energy gradients, is the same.
(8) Given the inherent limitations on the number of units which can be attended to and processed, perceptual development is made possible by a process of streamlining and automatizing conscious control of differentiation and integration. This process of automatizing conscious processes is called learning. Perceptual learning makes it possible, for example, for an individual to carry out perceptual integrations under conditions of incomplete object specification. After the individual has discovered a particular perceptual fact about the world, such as its spatial object layout, he can gradually learn how to detect this order given fewer, smaller, and more restricted energy samples. Such detection is also greatly aided in humans by virtue of their capacity to abstract, thus allowing men to consciously shift their “point of view” until an order in the perceived pattern is detected. But although abstraction and conceptualization can guide perception, it is not the cause of perception in man. Furthermore, conceptualization is itself genetically dependent upon and presupposes the prior achievement of the perceptual level of awareness.
(9) Once we recognize that objects are perceived by means of the absorption, detection and integration of ordered features of changing energy patterns, and that whenever a perception is produced, the detection of a corresponding external order can be shown to be the cause of the perception, {86} and that the same order in energy patterns yield the same perceptions, even though the physical cause of these patterns may differ; and that unique perceptions are always caused by the existence of unique orders in energy patterns but are not necessarily caused by the existence of unique objects, we can dispense with the self-contradictory and misleading concept of “perceptual illusion.”
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