II The Physical Basis of Perception


As our definition states, perception is the awareness of entities.  The existence of entities, therefore, is the first fundamental physical fact making perception possible.  An entity may be defined, in this context, as a structurally coherent, spatially segregated, temporally enduring existent.  As I will show later, the most important fact about entities is that they are constant or invariant centers in an otherwise changing world.  It is the fact that entities possess invariant features that makes possible the perception of entities.  If nothing were invariant, if everything were in constant Hereclitian flux, neither the existence of entities nor the process of perception would be possible.  Without invariant properties of entities with respect to our perception of those entities, one could not even perceive change, for change is the alteration of entities.  The perception of change requires the perception of that which changes, i.e., the perception of entities. (Even at the sensational, pre-entity, level of awareness, the appreciation of change requires the isolation of some existent that changes, be it a “tone”, a “tickle”, or a “blur”.)

Perception is the product of an interaction between objects and organisms.  Perception is, as we shall see, a preliminary to controlled action.  Functionally, the purpose of perception is to provide the organism with knowledge about objects in order to permit the organism to regulate its {7} behavior with respect to these objects.  In order to control its interaction with objects.  Organisms must have immediate knowledge of what objects are, i.e., what their present forms and locations are.  Perception, therefore, must be achieved without structurally altering the objects of perception.  If entities were structurally altered by the process of perception, the process would be self-defeating, for then that which one wished to perceive would no longer exist in the same state, location, or form at the end of the perceptual process.

The means by which objects are perceived, therefore, cannot and does not consist of directly processing objects themselves.  What is directly processed in perception are the effects of the interaction between objects and energy.


Energy is the second fundamental physical fact in the universe making perception possible.  Perception requires the existence of some form of energy capable of interacting with at least some of the existing entities.  The energy must interact in such a manner that some of the entities remain structurally unaltered.  To the degree that entities interact with energy in this manner, the entities will produce lawful changes in the energy stream (or energy event sequence).  Any particular component of the energy stream may be altered in a number of ways: energy may be partially or wholly absorbed, reflected, refracted, diffracted, or transmitted.

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.  What I mean by energy structure, in this {8} context, is the pattern of distribution of energy defined in terms of the energy’s quality, magnitude and direction relative to a defined point or surface.  (This will be clarified later.)


The existence of energy “structured” by entities is a physical precondition for all modes of perception.  But there exists a third fundamental physical fact that makes possible the perception of objects at a distance from the perceiver.  This is the fact that objects are generally dispersed in a medium which, for the most part, transmits or supports in an undistorted fashion certain forms of energy structure caused by the actions of entities.  On Earth, the two major media that satisfy these conditions are air and water.

Briefly stated then, the fundamental physical facts making perception possible are:

(1) Objects exist dispersed in a medium.

(2) Energy exists and interacts with objects producing no structural changes in the objects.

(3) The objects alter, in a physically lawful manner, the structure of the energy with which they interact.

(4) The resulting energy structure is carried away from the objects and remains undistorted by the medium surrounding the objects.

Object Structure and Energy Structure.

The environment surrounding an organism contains what Gibson (1966) calls a “nested structure”.  There are large objects.  Attached to these are smaller objects or smaller parts of these large objects.  These smaller objects have their own attached structures or parts.  For example, a terrain contains mountains which {9} contain boulders and trees that contain smaller stones or flakes or leaves; these contain surface markings and textures…and so on.  There is then, a hierarchy of structure.  The higher levels (macrostructure) contain the lower levels., (microstructure).

For perception, the most important fact about these objects and components composing the environment at any level of structure, is that these components are spatially bounded, which means that they are physically defined by boundaries that separate them from one another.  The reason shy boundaries are so important for perception, is that energy is affected differently by different entities and by different components of the same entity.  The object boundary is the line across which energy effect change.  Perception is made possible when object boundaries yield energy boundaries.  When this relationship holds, object structure defines energy structure.

The ”Specification” of Objects

Reciprocal to the fact that object structure can define energy structure, is the fact that energy structure can specify object structure and environmental layout.   In fact, perception requires that energy gradients contain the physical specification of object layout or structural order.

I will define physical specification as follows:  an energy pattern or event is said to specify a physical object or event when there exists a causal and one-to-one relationship between the order in the object or physical event and the order in the energy pattern or event.  (By “physical,” I mean, in this context, a change associated with an object other than merely an energy change.)

Please note that physical specification defines a relationship between energy gradients and patterns of the one hand, and object structures, {10} attributes and relationships with each other.  Physical specification is a necessary but not a sufficient condition for defining perception.  For perception is also necessarily characterized by what I will call epistemological object specification, consisting of a causal and one-to-one relationship between the physical object order and the phenomenal order (or “sensory order”).

The concept linking physical specification and epistemological specification is Gibson’s “General Hypothesis of Psychophysical Correspondence.

The explicit hypothesis is 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, p.465.)

The state of awareness (or “phenomenal” state) that satisfies the above psychophysical criterion of being “in contact with [ones] environment” is what Gibson means by perception.

Epistemologically, when I say that perceptions specify the existence of entities, I mean that perceptions are objective forms of knowledge in the sense that there exists a one-to-one correspondence and causal connection between the attributes, however subtle, of perceptions, and the attributes, however complex, of objects.  The concept of “specification” identifies the causal basis for the objectivity of perception as the form of [immediate awareness of environmental order.  Gibson’s “General Hypothesis” 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 {11} order, and is the physical cause of the perception of the external physical object order.

Specification and Invariance

Objects are not specifiable by static energy gradients, Object specification requires changing energy gradients.  The invariant features that define objects are specified in the relational invariants in the ordered transformations of changing energy patterns resulting from a moving sample of the available energy structure.  It is J.  J.  Gibson who first recognized the fundamentality of this fact to the process of perception.  Gibson is the only leading theorist to grasp as axiomatic the fact that, by the very nature of perception, receptor stimulation must carry the specifications for environmental layout.  Perception is a process of extracting these specifications.  Any other cause of conscious awareness or phenomenal experience is not perception.

(I will briefly mention at this point that the Gibsonian theory of perception, which I am advocating in this paper adds that the extraction of object-specific energy pattern invariants requires that the organism must obtain a changing energy gradient by controlled self-initiated movements of its receptor organs.  Passively imposed changing energy gradients may contain the specifications of objects, but only actively induced changing gradients will make possible the extraction of these specification.  This will be discussed in more detail later.)

Energy-dependent and Energy-independent Object Attributes.  Under the topic of energy, it was mentioned that energy can be affected by objects in a number of ways.  For instance, energy may be absorbed, reflected, or transmitted by an object.  The attributes of an object responsible for its {12} characteristic response to energy are identified by special physical terms.  For example, the property of an object to selectively absorb certain frequencies of light energy is called the object’s spectral absorbency.  The capacity of an object to resist deformation by the application of mechanical force is called variously, depending upon how the force is applied, rigidity, tensile strength, compression strength, or shearing strength.  Objects also possess such properties as thermal conductivity, acoustical absorbency, albedo, refractive index, mechanical resiliency, optical transparency, electrical resistance, etc.

All of these attributes of objects are called “properties” because they depend upon the action of something besides the object itself for their actualization.  As Helmholtz (1889) expressed it:

[A] property or quality can never depend upon the nature of one agent alone, but exists only in relation to, and dependent on, the nature of some second object, which is acted upon.  (p.  76.)

(Until energy acts upon an object, the object’s energy responsive properties exist only as potentialities.  It is important, therefore, to note that when energy acts on objects, certain attributes of the objects become actualized which were previously merely potentialities.  Attributes of objects that manifest themselves under the action of energy, I will call energy-dependent object attributes.

Whenever energy interacts with objects, two sets of interdependent facts are simultaneously revealed: 1) facts about the nature of the objects, and 2) facts about the nature of the energy.  For example, the physicist can determine the spectral composition of a light source (energy) by passing the light systematically through a series of spectral filters (objects) of known selective spectral absorbency.  Or, alternatively, the physicist {13} can determine the spectral absorbency of a gelatin filter (object) by exposing it systematically to light sources (energy) of known spectral composition.

When we perceive, however, we are not aware of the interaction between objects and energy.  We do not perceive the attributes of energy as such; we perceive the attributes of objects by means of the absorption of energy.  Object/energy interaction is necessary for the perception of any object attribute, but only some object attributes are energy-dependent.  Some attributes of objects are not dependent for their existence or actualization upon the action of a particular form of energy.   Such object attributes I will call energy-independent (for that form of energy).

For example, the boundary conditions or spatial relations of an object are (for most objects) independent of the existence of light energy.  This does not mean, of course, that such objects cannot interact with light, for these objects may be capable of such interaction.  Furthermore, the interaction with light energy will be determined by the nature of the constituents within the object’s boundary or perimeter, (a fact which makes possible the perception of an objects “shape”).  But none of this contradicts the fact that an object’s shape can be (and usually is) independent of the existence or action of light energy.  Relative to light, therefore, object shape is energy-independent.  This does not mean, of course, that all object shape is independent of all energy forms.  Physics has discovered that magnetic, gravitational, and thermal energy (to name but a few) determine the shapes of all entities.

Neither do I mean to assert that all shape as such is independent of light energy.  Shadows, for example, are spatially bounded effects (not {14} themselves objects of course) that possess light-dependent “shapes.” Shadows are always of objects and are therefore jointly determined by the location, distance, directionality and sometimes wavelength of light energy as well as by the shapes of the objects of which they are the shadows.

Philosophical Note: Primary and Secondary Sense Qualities

The Physical Basis for the Distinction Between “Primary” and “Secondary” Sense Qualities

The distinction I have drawn between energy-dependent and energy-independent object attributes allows us to unravel one of the subtle paradoxes contained in the ancient philosophical distinction between “primary” and “secondary” sense qualities.  The qualities of color, pitch, brightness, and warmth (to name but a few) have been classified by some philosophers as “secondary” sense qualities, having a different epistemological status (the sensualists would say a higher status, the rationalists would say a lower status) than such sense qualities as shape, locus, space and time, which have been classified as “primary.”

It is possible to show, however, that both of these sets of sense qualities (or perceptual forms) have equally objective epistemological status, and that the distinction between them can be traced to the fact that they correspond to separate categories of facts about objects.  The so-called “primary” sense qualities , such as shape, locus, time, and space, correspond to facts about entities which are energy-independent, and which , therefore, remain constant over energy changes and remain constant regardless of the form of energy used to perceive these facts; and , therefore, remain constant regardless of which sense modality we employ to perceive these facts.  These facts are not exclusively accessible to any one particular sensory mode. {15} They are not exclusively accessible through vision, or through touch, or through hearing only.  They are facts that cut across our sense modalities and, therefore, seem non-sensory or independent of our senses.  This is the main reason, I believe, why we do not have separate names for these sense qualities, on the one hand, and for the object attributes to which they correspond, on the other.

In contrast, the so-called “secondary” sense qualities, such as brightness, color, warmth, pitch, etc., correspond to facts about entities which are energy-dependent and which, therefore, change as energy changes and depend upon the form of energy used to perceive them, and therefore depend upon which sense modality is used to perceive them.  It is for these reasons that man has more readily identified the dependence of “secondary” sensory qualities on our sensory systems, and has come to call the perceptual forms by different names than those referring to the objective correspondents of these forms.  Hence, brightness was identified as the form in which we perceive relative intensity differences in luminous sources; color was identified as the form in which we perceive contrasting rations of frequencies of light; pitch was identified as the form in which we perceive the relative frequency of acoustical energy; warmth was identified as the form in which we perceive the relative direction of the flow of thermal energy across body regions.

Each “secondary” sensory quality implicitly corresponds to a particular form of energy.   Brightness: light intensity; color: light frequency; warmth: thermal flow; pitch: acoustical frequency; loudness: acoustical intensity.  Notice, however, that such a chart cannot be made for the “primary” sensory qualities precisely because these are energy-independent attributes of objects. {16}

The two categories of sense qualities have the same epistemological status precisely because the difference between these two categories has an objective base in and corresponds to a physical difference between two categories of object attributes, viz., energy-dependent and energy-independent attributes.

This does not mean, however, that “primary” sense qualities are energy-independent.  On the contrary, all perceptual forms are both energy-dependent and object-dependent.  All perceptual forms are the product of absorbing and processing energy gradients resulting from object/energy interaction.  Where there are no objects, there are no perceptual forms.  Where there is no energy there are no perceptual forms.  The distinction between the two categories of sensory qualities is not to be understood in terms of the dependence or non-dependence of each on our sense organs, but rather has its base in the energy-dependence or independence of the attributes of the energy-dependent and energy-independent object attributes are perceived in different sensory forms.

Latest revision of this page:  April 19, 2014 3:49 pm

1 Response to II The Physical Basis of Perception

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