A Direct Realist Theory of Sensory Qualities

The goal of this paper is four-fold:  1. to identify and challenge the currently dominant view of the doctrine of  primary/secondary quality dualism, 2. to trace its philosophical history,  3. to identify the intellectual implications and consequences of this doctrine, 4. to offer a theory of sensory qualities and their psychophysics that resolves this dualism and provides a direct realist solution to the understanding of sensory qualities.

It has been widely and historically believed that there are two distinct classes of sensible object qualities (most commonly referred to in modern philosophy as sensory categories).   1. One class that is characterized by the fact that its qualities can be sensed by multiple sensory organs.  Such qualities include shape, size, quantity, motion, arrangement and unity.  and  2. A second class of qualities appear to depend upon the special powers of specialized sensory organs in that such qualities cannot be sensed across multiple sense organs.  Such qualities include color, odor, savor, and sound.

Historically, there are different accounts of these different sensory  classes,   The accounts vary depending on the epistemological orientation of the philosopher.  Thus there are realist interpretations and idealist interpretations.  From an ontological perspective, there are corresponding monist interpretations and dualist interpretations.

Dualism  and Idealism

Cartesian Dualism and Primary and Secondary Properties

Cartesian dualism divided the world into two mutually exclusive and collectively exhaustive forms of being: res extensa and res cogitans.    The former was further specified as the essence of physical being qua being.  To Descartes, the essence of physical being was the property of extension or extensiveness, having the quality of extending in space.  This allowed Descartes and his subsequent adherents, to map the ‘real’ to the mathematical, not to abstract mathematics, but rather to geometry and analytic geometry, the mathematics of space.

Philosophers since the time of Descartes called the extensive properties of the world (i.e., the properties of size and shape, as well as the properties of position and locus) the ‘primary’ (or intrinsic) properties of entities, since, presumably, they represent mathematical (geometric) properties of being.  Other properties, such as warmth, color, texture, odor, etc. were rejected as not real in the primary sense, i.e. not mappable to the qualities of res extensa.  These latter qualities were said to be properties of the mind itself, i.e., properties of res cogitans.

For Descartes, although res cogitans was not part of nor physically interactive with res extensa, it was able to know physical existence, but only by it power to grasp in thought, qua res cogitans, the geometric properties of being, specifically the geometric properties of res extensa.  Thus is was for Descartes the mathematical principles of geometry (the mathematics of space and or extended objects) that conceptually unified res cogitans and res extensa.  This was a remarkable piece of mental gymnastics that saved the external world (res extensa) and the science of that world (geometry) by arguing that that science was epistemologically realized by the capacity of res cogitans to mentally grasp the validity and fundamentality of geometric laws as the laws of physical being (again, res extensa).  Thus began the serious mathematization of physics, where mathematics was not merely a tool for modeling the world but an epistemological/ontological engagement with the physical world.

Extension as the Essential Real Property of Physical Being

This doctrine of the extensible (or extended) as the ‘real’  was so deeply embedded in the Cartesian world-view, that it was directly applied to theories of perception.  Here is Thomas Reid’s understanding of Descartes’ view of perceptual evidence regarding the nature of matter:

The perceptions of sense, he thought,…by accident only, exhibit things as they are in themselves.  It is by observing this, that we must learn to throw off the prejudices of sense, and to attend with our intellect to the ideas which are by nature implanted in it.  By this means we shall understand, that the nature of matter does not consist in those things that affect our senses, such as color , or smell, or taste; but only in this, that it is something extended in length, breadth, and depth.  —Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. Of the Powers We have by Means of our External Senses. Chapter VIII: Of the Common Theory of Perception (1785), MIT Press, 1969, p. 146.

 After Descartes, the perceptual experience was thus divided into two categories of sensory qualities, named by John Locke: 1. The  primary perceptual qualities of shape, size, location, were considered primary precisely because they mapped to the Cartesian primary properties of extensive being (res extensa), or as Reid, in his analysis of Descartes, put it ‘something extended in length, breadth, and depth’.  Thus the primary qualities were thought to be objective or amenable to scientific thought.   2. The  secondary perceptual qualities of color, sound, texture,  odor, taste, warmth/cold were not part of res extensa, but part of res cogitans only, or as Reid, in his analysis of Descartes, put it ‘ the nature of matter does not consist in those things that affect our senses, such as color , or smell, or taste’.

Thus secondary qualities, ‘such as color, or smell, or taste’ were regarded by Descartes’ followers as fully subjective, having no causal basis in physical reality, and no mapping to corresponding physical properties.  Science throughout its entire history, from Descartes to the present, endorses this dualist doctrine of sensory qualities.

Locke on Primary and Secondary Qualities:

John Locke argued for a simplistic view of the distinction between primary qualities and secondary qualities of an object.  Notice: qualities of objects not qualities of our phenomenal experience of the object.   Primary quality are those intrinsic to the object.  Our perception of those qualities, for Locke, ‘resemble’ the intrinsic qualities themselves.  Here is one authors (quite reasonable) interpretation of Locke’s concept of primary qualities.

The primary qualities of an object are its intrinsic features, those it really has, including the “Bulk, Figure, Texture, and Motion” of its parts. (Essay II viii 9) …When we do perceive the primary qualities of larger objects, Locke believed, our ideas exactly resemble the qualities as they are in things. – from Britannica Philosophy Pages: Locke: The Origin of Ideas

What can it mean to say that our ideas ‘resemble’ the qualities of things?  Naively we may say that we perceive an objects shape as ‘shape’,  its texture as ‘texture’, its bulk as ‘bulk’, for there is no special term in our sensory vocabulary for distinguishing between the quality perceived and the quality as perceived, as a perceptual quality.   This much is true.   We have no way of knowing (perceiving) that a property is ‘intrinsic’ for we have only the resulting perception itself.  This perception is experienced as an external object having the primary qualities of  shape, size, distance, location, orientation, texture and other so-called ‘intrinsic’ properties.  Locke does not address the topic of how we know that our perceptions of intrinsic qualities of things are in fact intrinsic to the thing as contrasted with intrinsic to our perception or state of awareness, to our phenomenal state.   This topic is later identified and addressed by David Hume (incorrectly and to disastrous consequences.)

In addition to primary qualities, Locke also identifies what he calls secondary properties of an object. Here is one authors (again quite reasonable) interpretation of Locke’s notion of secondary qualities:

The secondary qualities of an object, on the other hand, are nothing in the thing itself but the power to produce in us the ideas of “Colors, Sounds, Smells, Tastes, etc.” (Essay II viii 10) In these cases, our ideas do not resemble their causes, which are in fact nothing other than the primary qualities of the insensible parts of things. – from Locke: The Origin of Ideas

Locke recognized that secondary qualities of objects (note again, not of our perceptions of objects) are nothing but the power in the external object to produce in our senses the ‘ideas’ of such qualities as  color, taste, smell, sound (which are actually dimensions of qualities, thus ‘red’ is a color quality of which there are many others in the dimension of color, etc.).    Unlike primary qualities, our experience of secondary qualities of objects do not ‘resemble’ their causes.  Again, what does it mean to resemble their cause?  It must mean that the cause of a perception is a one-to-one mapping (or copy) of the object’s properties to the sensory property or experience.

So, according to the Lockean doctrine of secondary sense qualities,  the experience of ‘red’ does not map to anything in the object that is intrinsically ‘red.’   So what then is the cause of the perception of ‘red’? According to Locke, it is ‘in fact nothing other than the primary qualities of the insensible parts of things.’   This is crucial, Locke does not suggest that the secondary qualities are ‘subjective’.  He argues only that their causes are not directly perceivable but do exist in the object (thus presumably not in our minds) but are of such a nature that they are both intrinsic and insensible.

Thus Locke is arguing that all perception is caused by intrinsic properties of the object of perception.  Primary qualities correspond to (are caused by) the corresponding intrinsic properties of the object (which is why such qualities ‘resemble’ those of the object).   Secondary qualities are also caused by intrinsic properties of objects.  But in this latter case the cause (the intrinsic property of the object) is not (directly) sensible, but rather is the product of the power in the external object to produce just these secondary sensory properties.  Locke assumes the reality of this intrinsic cause, but does not and cannot prove its existence .

Although Locke cannot explain how and why secondary qualities have the phenomenal qualities that they have, he insists that they are nevertheless caused by insensible properties of objects.

Hume on Secondary Sense Qualities:

Why is the issue of primary vs secondary qualities important to us?  The answer is that this very issue has given rise, through the doctrines of David Hume and his interpretation of Locke, to the foundations of modern science and of modern philosophy.   Philippe Hamou explicitly points out these powerful consequences in his essay: Qualities and Sensory Perception.  Here is a key excerpt:

In his Treatise of Human Nature, Hume contrasted the ancient metaphysics of substantial forms and occult qualities with the metaphysics of the Moderns, which he characterized as follows:

The fundamental principle of that philosophy is the opinion concerning colours, sounds, tastes, smells, heat and cold ; which it asserts to be nothing but impressions in the mind, deriv’d from the operation of external objects, and without any resemblance to the qualities of the objects. (Hume 1985: 275)

Hume evidently had in mind the definition of secondary qualities that is given in Locke’s Essay….I shall argue in what follows that Hume was fundamentally correct, and that the doctrine of secondary qualities is indeed a distinctively modern doctrine that captures something of the very essence of the new philosophical age. (from  Qualities and Sensory Perception, by Philippe Hamou)

If, as Hume suggests and as most of his followers agree, our secondary qualities are entirely subjective, then they do not inform us about the nature of the external world, of the universe in which we live, but rather only the nature of our own mind and its own internal subjective qualities.   This means that our ability to perceive the external world is limited only to the properties experienced in the form of our primary qualities.

Science, Quantification and Primary Qualities

Science has become deeply mathematised.  As we have discussed above, this is the result of Cartesian Dualism with its insistence that only res extensa is real, and that its essential property is that of geometric extension.  Thus, only geometric quantization is available as a valid technique for the study of res extensa.  Fortunately, there was Descartes (himself, a mathematician/philosopher) to develop analytic geometry and provide the intellectual tool needed for the study of ‘true reality’.  Thus science, focused on reality as particulate, passive (but reactive) and extended, has written its laws as mathematical relational quantitative expressions of an abstract content ( mass, fields and energy relative to space and time), omitting all qualitative attributes of the physical world.

Consider the most famous of all mathematical accounts of the world: E=mc2. As with any law, it describes a mathematical relationship between values of variables (energy, mass) that in the context of the equation have no other properties than quantity. (More generally, and technically, physical laws are about the co-variance of quantitative parameters.) The energy in Einstein’s equation is not warm or bright or noisy, and the matter is not heavy or sticky or obstructive. The world of physical laws – which enables predictions of quantities – is a world of quantities without qualities. – from Mathematics & Reality by Raymond Tallis, 2014

This dominant mathematical model of scientific methodology grew directly out of the the ‘New Science’ born of the Renaissance (discussed in depth elsewhere in the bioperipatetic), and deeply influenced by Cusanian Neoplatonism (the zeitgeist of the Renaissance) which deeply informed the scientists (most famously Galileo and Newton), and philosophers (most famously Rene Descartes) and later enlightenment  philosophers (most famously Locke).  The Cusanian influence on Descartes was Cusanus’ conception of the universe as the mathematical unfolding explication (explicatio) of its folded implicit (implicatio) nature:

Cusanus believes that no knowledge we have is more certain than mathematics, given that it is the construction of our own minds. Mathematical ideas are the paradigm of how the human mind unfolds a conceptual universe that parallels and forms an image of God’s unfolding of the created world. Number here refers primarily to arithmetic and geometry, to the whole numbers and to plane and solid figures. The latter are often imagined as in movement or constructing other figures. Nicholas joins enfolding/unfolding and the certainty of mathematics to the Christian tradition that everything is created in the divine word or Logos. – from Cusanus, Nicolaus [Nicolas of Cusa], 2013 revision, in the Stanford Encyclopedia of Philosophy

The influence of Cusanus on Descartes res extensa, as essentially a geometric mathematization of being intellectually grasped by res cogitans, is seen in Cusanus’ On Conjectures:

On Conjectures moves directly into arithmetic and geometry with its conjectural reflections on the decade’s embracing all number and with its ordering of reality’s oneness and otherness using the spatial diagrams P and U that employ cones and spheres. Just as the number series unfolds the unit, so the created universe unfolds God’s creating, and human concepts (such as numbers and geometric figures) unfold the oneness of the human mind. In this way a human being is truly a “second God.”- from Cusanus, Nicolaus [Nicolas of Cusa], 2013 revision, in the Stanford Encyclopedia of Philosophy.

Renaissance philosophers/scientists defined the standards upon which the ‘New Science’ was to be based, namely the world as apprehended by the primary sense qualities, the qualities the represent the spacial geometry of res extensa; thus a world without (secondary) qualities (which existed only in the mind):

This is not an accidental oversight. Galileo, who kick-started the scientific revolution, argued that colours, tastes, sounds, odours, had no place in the material world, whose book was written in mathematics. The qualities we experience were introduced by sentient beings. By contrast, physical reality itself was comprised of ‘primary qualities’, such as size, shape, location and motion, which can be expressed in mathematical terms without remainder. So the mathematized universe of physics lacks what are now (after John Locke) usually called by the slightly derogatory term ‘secondary qualities’. These resist being mathematised. – from Mathematics & Reality

Mathematics cannot express nor science formalize (or so it was and is still widely believed) the secondary qualities associated with objects.  These qualities were said by Locke to be the product of insensible intrinsic properties of objects.   Unfortunately, such properties do not (it is argued) admit to scientific expression and quantification.  As a result scientific laws appear cold, colorless and barren from an aesthetic point of view.   And is prevents physical science from addressing the value-laden nature of the external world relative to lifeforms, most relevantly, human beings.

The mathematics of light does not get anywhere near the experience of yellow, nor does the mathematical description of patterns of nerve impulses reach pain itself. This is sometimes seen as evidence that neither the colour nor the pain are really real – although it might be difficult to sell this claim to the man looking at a daffodil or a woman with toothache. – from Mathematics & Reality

Such are the consequences of a science that addresses only the geometrically quantifiable and omits as ‘unscientific’  and ‘unquantifiable’ (in spite of the later quantitative studies of secondary qualities by phychophysicists, such as Weber and Fechner) the properties of objects that underly our experience of so-called ‘secondary’ sensory qualities.   Secondary properties of objects (corresponding to secondary  sensory qualities) were omitted as ‘subjective’ or ‘unscientific’ solely because science (specifically the science of sense perception) had not been able to understand their nature and objective basis.    This is how limitations of knowledge led to limitations of methodology, a dangerous strategy.   This, in turn, led to the omission of a vast universe of physical facts, placing them arbitrarily and permanently outside of the realm of science.   This is just one element of the ‘New Science’ that led to the tragic and wholly unnecessary doctrine of mind-body dualism and the anathema of consciousness.

Modern Science (Quantum Theory) and Sensory Qualities

Modern physics, unto but perhaps not including Quantum Theory, is in full agreement with the doctrine that it is only our primary sensory properties that can be said to actually ‘inhere in the object’.  That means, that primary qualities are said to survive the absence of any form of consciousness in the universe.

We can identify at least three types of properties that we associate with an everyday object: primary, secondary and subjective properties. ‘Length’ and ‘position’ are examples of primary properties.  An object being ‘blue’ or ‘my father’s give’ are examples of secondary and subjective properties, respectively…A primary property for example, can be thought of as a property that will inhere in the object even if all conscious observers were to cease to exist in the universe.  from Quantum Theory and the Observation Problem,, by Ravi V. Gomatam, in Reclaiming Cognition: The Primacy of Action Intention and Emotion, Ed. Rafael Núñezand Walter J. Freeman, Imprint Academic , 1999, p. 185.

According to this same Humian doctrine (which I do not attribute to Locke, who clearly would not accept Hume’s interpretation of his doctrine) secondary sensory qualities or properties are said to exist only in consciousness and cannot be found as intrinsic properties of observed objects.   Therefore, their existence is dependent upon consciousness, in the absence of which secondary qualities cannot objectively exist.

By contrast, an object will not have a secondary or subjective property unless at least one conscious observer exists within the universe and perceives the object in that manner.  from Quantum Theory and the Observation Problem, p. 185.

But quantum theory, in its quest to deal only with objective primary properties of matter, may require the abandonment of Locke and Descartes with respect to the concepts of primary and secondary object properties, not in favor of objective qualities independent of consciousness, but rather in favor of subjective qualities, in that all properties of matter require some form of observation by some form of consciousness.  Since under the quantum model, all potential outcomes of a state change coexist as equally ‘true’, to actually, as contrasted with potentially , exist, to be,  in quantum theory is to be measured (or observed):

Following Locke, we have generally presumed that physics should deal only with primary properties to remain objective. Indeed the formal properties of classical physics are idealizations of primary properties…However, we discussed …the problems in treating the properties associated with quantum mechanical observables as objective properties in the sense of existing in nature with pre-determined values independent of measurement.  Indeed, if primary properties were the only conception of objective properties possible, a subjectivity unavoidably enters quantum theory.  It is therefore sometimes wondered whether quantum theory signals the end of the Cartesian divide between mind and matter.  from Quantum Theory and the Observation Problem, p. 185.

Psychophysical Paradoxes: Quantification of Sensory Qualities:

The psychological techniques of psychophysics do not escape this dualism.  For all that psychophysics can establish is correlation between physically applied ‘stimuli’ (using different forms of energy and energy patterns) and the subjects’ reports of secondary sensory phenomena or conscious experiences, quantified as ‘just-noticiable’diferences’ or, in the symbology of psychophysics, jdns.  Thus perceived color and brightness differences are roughly correlated with light wave frequency and intensity differences, respectively.  Perceived auditory tone and loudness differences are, similarly, roughly correlated with acoustical wave frequency and intensity differences, respectively.  But more importantly, sensory qualities may change while the physical ‘stimuli’ remain unchanged, and vice versa, depending on the conditions of physical stimulation and context of sensory ‘observation’.

Most significantly as a challenge to the very concept of primary sensory qualities, sensory phenomena regarding primary sensory qualities emerged that were in contradiction to the facts of physical stimulation.  The most prominent and widely studied of such phenomena are various forms of perceived motion (called ‘apparent motion’), where the physical stimuli were not moving.  If this is so, the higher significance of the so-called primary sensory qualities, in this case location and change of location, or location and coincidence.  If primary, they must be in the objects’ corresponding primary properties (as Locke held).  But in no case are primary qualities allowed to be ‘created’ in perception as sensory qualities when they do not physically exist in nor correspond to the corresponding properties of the external object of observation.

Some perceived motion was correlated with stimulus-onset-asychrony (SOA) between two identical stimuli applied to adjacent regions of the same sensory organ surface.  Other perceived motion was correlated with simultaneous stimuli varying only in energy intensity.  When reaction time to successive stimuli was measured, in cases where the first stimulus was very weak relative to the second stimulus, the first stimulus was reported as ‘phenomenally absent’.  And yet the reaction time proved that the subject must have reacted to the first ‘phenomenally absent’ stimulus.  This was often classified as a form of ‘subliminal perception’, an invalid concept emerging as an artifact of purely behavioral (stimulus-response measurement) models of human sensory systems.

So there were (at that time, using then established psychophysical techniques) no discovered laws guaranteeing that a given spatial or temporal stimulus pattern will always yield the same sensory experience, even within the same individual subject nor could certain phenomenal reports of emergent sensory experiences be physically mapped to the stimuli alone, without introducing ‘hidden’ (i.e., not externally physically measurable) internal processes and corresponding theories of these processes, usually couched in behavioral terms using behavioral vocabulary.  Thus, there emerged technical names for these anomalous sensory phenomena, such as ‘the Crawford Effect’, ‘the Broca-Sulzer Phenomenon’, ‘Phi Motion’, ‘Type A and Type B Metacontrast-Masking’ and others. All of which were inexplicable from the point of view of how physical stimulation mapped to and caused a one-for-one sensory experience or sensory quality.   For an detailed study of the failures of psychophysical experimentation and the flawed behavior theories upon which they rest, see the bioperipatetic 9-part series entitled ‘Perception, Philosophy and Neural Processing.’

Realism and Monism

Aristotle’s Realist View of Common and Special Sensory Qualities

Aristotle, who was a realist and not a dualist, recognized that things sensible are capable of being sensed by organs possessing just that capacity to sense the qualities of objects.  Thus sensible things, qua sensible, require the existence of sense organs capable of sensing those objects that are sensible.  Furthermore, sensibles were divided by Aristotle into two general categories:  1. The common sensibles. 2. The special sensibles.  The former were sensible qualities that are sensible by multiple sense organs (e.g., organs of vision, of touch, of hearing).  Examples of these were shape, size, quantity, motion and unity (of a whole or unified).  As for the common sensibles:

According to Aristotle the “common sensibles” are motion, rest, shape, magnitude, number, and unity (De Anima III.1 425a16). (Different translations might use slightly different terms here.) They are apprehended by more than one sense – sight and touch. For example, extension and roundness can be perceived by both sight and touch. – from blog Rebirth of Reason™: The Primary-Secondary Quality Distinction  by Merlin Jetson.

Thus, common sensibles were properties of objects that required only generalized sense organs but did not require specialized sense organs to sense their existence.  Generalized sense organs are sense organs of such a nature that they can sense multiple qualities of objects without having special capabilities for sensing each of these multiple qualities.  Thus the very same sense organ (the eye for example) can sense the shape, motion, size and unity of an object (a horse, for example) without having specialized shape-sensing, motion-sensing, size-sensing or unity-sensing sensing properties or powers.   As for the special sensibles:

What Aristotle called the “special perceptibles” were those grasped by one sense only, e.g. warmth, color, taste, smell and sound. Aristotle did not make the [primary-secondary-quality-distinction]. He treated all qualities of an object or body as belonging solely to the object or body. However, he gave one of the means to do it. – The Primary-Secondary Quality Distinction

 Direct Realism: What Does it Assert?

Direct realism is a view of perception that holds the following premises:   1. That perception is a power of the mind to directly grasp in conscious form the existence of objects in the world (including our physical selves as objects in the world).   2.  That what we perceive are objects in the world outside of consciousness.   3. That such objects exist independent of consciousness, and in no way depend upon conscious or the existence of consciousness for their existence.   4. That when we perceive objects, we are not perceiving any kind of mental representations, images, ideas, sense-data, sensation, or effigies, but are directly aware of the objects themselves.   5. That the perception of objects does not, qua perception, depend upon, nor is it the product of, intellectual actions of the mind, including induction, deduction, memory, recall, hypothesis, assumption, probabilistic expectations, or any form of innate ideas, templates, or filters representing any predefined (a priori) categories, models or concepts of a pre-conceived external order.   Denial of any one of these premises is at least a partial denial of direct realism.

Direct Realism: The Enlightenment – Thomas Reid

One of the first Enlightenment thinkers who wrote deeply about the human intellectual powers, including the nature of Perception, was the English philosopher Thomas Reid.  His magnum opus was entitled ‘Essays on the Intellectual Powers of Man‘.  The book consisted of eight essays, the longest of which (and the one in which  this article is concerned) is entitled: “ESSAY II. Of the Powers We Have by Means of Our External Senses.”  In this deeply reasoned essay, Reid reviews all of the dominant theories still reigning his time, including those of Descartes,  John Locke,  Bishop Berkeley, David Hume, Antony Arnauld, Leibnitz.  Reid argues from direct attention to our own perceptual experiences, which Reid calls ‘acts’, for they are not, he argues, passive phenomena, but active processes which we initiate and control through our power of attention and focus.

If, therefore, we attend to that set of our mind which we call the perception of an external object of sense, we shall find in it these three things.  First, Some conception or notion of the object perceived.  Secondly, A strong and irresistible conviction and belief of its present existence.  And, thirdly, That this conviction and belief are immediate, and not the effect of reason. –Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. pp. 111-112

Reid is observant enough of nature to realize that perception, like any cognitive function, delivers degrees of clarity and precision depending on the physical and physiological conditions within which perception emerges.

Yet, even in perception, the notion which our senses give of the object may be more or less clear, more or less distinct, in all possible degrees. –Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. p. 112

Reid goes so far as to state that perceptions may be so indistinct and and faint as to make us doubt what it is that we perceive.

There may be a perception so faint and indistinct, as to leave us in doubt whether we perceive  the object or not. . . but when the perception is in any degree clear and steady, there remains no doubt of its reality; and when the reality of the perception is ascertained, the existence of the object perceived can no longer be doubted.  –Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. p. 113

As to the request for proof that our senses give us direct awareness of the world of object existing independent of  consciousness, Reid argues from common sense:

Can any stronger proof be given, that it is the universal judgment of mankind that the evidence of senses is a kind of evidence which we may securely rest upon in the most momentous concerns of mankind; that it is a kind of evidence against which we ought not to admit any reasoning; and therefore, that to reason either for or against it, is an insult to commonsense?  –Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. p. 114

As for then common arguments for doubting our senses, Reid dismisses quickly the argument from psychopathology, agreeing that perception presupposes mental health and physiological health of the sense organs.  As for the arguments offered by philosophical skeptics, Reid has this to say:

The other exception that may be made to the principle we have laid down, is that of some philosophers who have maintained, that the testimony of sense is fallacious, and therefore ought never to be trusted.  Perhaps it might be a sufficient answer to this to say, that there is nothing so absurd which some philosophers have not maintained.  It is one thing to profess a doctrine of this kind, another seriously to believe it, and to be governed by it in the conduct of life.  It is evident, that a man who did not believe his senses, could not keep out of harm’s way an hour of his life; yet, in all the history of philosophy, we never read of any skeptic that ever stepped into fire or water because he did not believe his senses, or that showed, in the conduct of life, less trust in his senses than other men have.  This gives us just ground to apprehend, that philosophy was never able to conquer that natural belief which men have in their senses; and that all their subtle reasonings against this belief were never able to presage themselves.

It  appears, therefore, that the clear and distinct testimony of our senses carries irresistible conviction along with it, to every man in his right judgement. –Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. pp. 115-116

 Reid argues strongly against any kind of unconscious inference or reason mediated theory of perception or of any form of cognitive enrichment as a precondition for the achievement of direct perception.  On the issue that perception is accompanied by an immediate,  irresistible conviction, Reid writes:

I observed, 3dly, That this conviction is not only irresistible, but it is immediate; that is, it is not by a train of reasoning and argumentation that we come to be convinced of the existence of what we perceive; we ask no argument for the existence of the object, but that we perceive it; perception commands our belief upon its own authority, and disdains to rest its authority upon any reasoning whatsoever. -Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. p. 116

Direct Realism: Denial of Representationalism – Thomas Reid

Here Reid knows that he is opposing an almost universal doctrine shared by modern and ancient philosophers, from Plato to Hume, who hold, by contrast, that what we perceive directly are intermediate things or events.  We call them sensations, impressions, ideas, symbols of object in the external world which they somehow represent and by which (to some significant extent) they are caused.  These intermediate conscious forms are fallible in that they do not give us direct awareness of the being and nature of the objects for which they somehow stand.  It is inevitably added that some innate or acquired knowledge or the world, gained by practice or discovered by intuition, somehow corrects the senses and gives us true contact with the external world.  Reid puts it this way:

But all philosophers, from Plato to Mr. Hume, agree in this, That we do not perceive external objects immediately, and that the intermediate object of perception must be some image present to the mind.  So far there appears an unanimity, rarely to be found among philosophers on such abstruse points.

If it should be asked, Whether , according to the opinion of philosophers, we perceive the images or ideas only, and infer the existence and qualities of the external object from what we perceive in the image? or, whether we really perceive the external object as well as its image?  The answer to this question is not quite obvious. -Thomas Reid, Essays on the Intellectual Powers of Man:  Essay II. p. 124-125.

Reid then goes on to state the obvious fact that none is aware of these assumed  ideas, images, or to use today’s favorite phrase ‘sense data’.  Nor is anyone aware of engaging in any form of reasoning to interpret the images as real external objects, while at the same time retaining the awareness of both (the image and its object).

Beyond those common sense arguments, Reid adds another important dimension to the problem:  Why would man possess an imperfect organ for contacting the objective world and also possess  another power, reason, that, though just as likely to be fallible, is used to prove that the images and ideas we ‘sense’ represent real external objects?  How does reason get outside of the mind to the external world?  Reason (and presumably mental images and ideas) reside inside the mind.  So how do they escape into the objective world?  We know that Hume asked exactly these questions and led the Western world into a nearly psychotic nightmarish state of cognitive solipsism, an inescapable infinite regress of self-doubt.  This cognitive malady is the product of rationalism, a rationalism that started with Plato, and that takes the intellect (reason) to be superior in every way to the crude and unreliable awareness provided by the senses.  The intellect gives us shining ideals (residing, of course, in a the transcendent world of perfect forms), the senses only murky shadows (reflecting the crude incomplete, indeterminate realm of matter).

Direct Realism: Rand’s Rejection of Sensory Quality Dualism

Sensory quality dualism has been rejected by one of the most publically prominent direct realists,  philosopher and novelist, Ayn Rand, who, like the professional perception scientist James J. Gibson, argues that all perception is the joint product of  the nature of of our sensory system and the nature of the external object being perceived.

Ayn Rand explicitly rejects the entire distinction between primary and secondary qualities as epistemologically inappropriate.

I would not accept the distinction of primary and secondary qualities, because it leads you into enormous pitfalls.  It is not a valid distinction. – fromAyn Rand: Introduction to Objectivist Epistemology.  Expanded Second Edition, edited by Harry Binswanger and Leonard Peikoff, Meridian, 1979, p. 279.

Ayn Rand rejects the classification of qualities based on the subjective form in which we are aware of them (color, for example, being one such subjective form).  But all qualities are the product of sensory processing (processing giving rise to the perceptual level of awareness), therefore all qualities are on the same epistemological footing.  Rand writes:

We perceive light vibrations as color.  Therefore you would say the color is not in the object.  The object absorbs certain parts of the spectrum and reflects the others, and we perceive that fact of reality by means of the structure of the eye.  But then ask yourself: don’t we perceive all attributes by our means of perception—including length?  Everything we perceive is the result of our processing, which is not arbitrary or subjective.

The primary-secondary quality distinction is a long philosophical tradition which I deny totally.  Because there isn’t a single aspect, including length or spatial extension, which is perceived by us without means of perception.  Everything we perceive is perceived by some means. – from ‘Ayn Rand: Introduction to Objectivist Epistemology.  Expanded Second Edition, p. 279-280.

Some qualities, such as wave-length, can be distinguished from the form in which we perceive them, in this case color.   Some qualities cannot be distinguished from their perceive forms (e.g. length).   But it does to follow that secondary qualities are subjective, and non-objective, precisely because we perceive them in some identifiable form.  Nor does it follow that primary qualities are objective precisely because we are not aware of the forms in which we perceive them as distinguished from their intrinsic object qualities.

The primary-secondary distinction in fact starts from the idea that that which we perceive by some specific means is somehow not objective.

Now you can properly distinguish that which is in the object from the form in which you perceive that quality. But that isn’t the same thing as saying color is a secondary quality but extension is a primary quality.  That isn’t the same issue at all. . . as if one could say color isn’t in the object but extension is.

You see, it’s the classification of the attributes of reality according to how and by what means we perceive them that is wrong in that whole classification. – from ‘Ayn Rand: Introduction to Objectivist Epistemology.  Expanded Second Edition, p. 280-281.

The fallacy here is a form of what Ayn Rand has called ‘re-writing reality’.  In this case, it consists in demanding that true sense perception, true contact with the world at the level of perception, must be what David Kelley calls ‘diaphanous,’ transparent cognitively.  Such that we have not cognitive awareness of the form in which we perceive the objects qualities and the intrinsic qualities of the objects themselves.  In this case, we are experiencing ‘primary qualities.’  If we are aware of the form of our perception, such as the subjective form of color corresponding to wavelength, then our perception is declared by the self-imposed arbitrary rule, non-objective.   This is, in Ayn Rand’s view, a fatal epistemological error.   It is the fundamental error ultimately leading to the Kantian fallacy that our senses are invalid because they possess a specific identity in that they employ specific means of cognition.  In Ayn Rand’s words:

The entire apparatus of Kant’s system, like a hippopotamus engaged in belly-dancing, goes through its gyrations while resting on a single point: that man’s knowledge is not valid because his consciousness possesses identity. “His argument, in essence, ran as follows: man is limited to a consciousness of a specific nature, which perceives by specific means and no others, therefore, his consciousness is not valid; man is blind, because he has eyes—deaf, because he has ears—deluded, because he has a mind—and the things he perceives do not exist, because he perceives them.” (For the New Intellectual.) – from ‘Ayn Rand: Introduction to Objectivist Epistemology.  Expanded Second Edition, p. 80.

For Gibson, speaking at the scientific level, it is the energy structure at the receptor surfaces and its invariants under transformation that yield direct conscious awareness of the properties to which the invariants correspond.  The power to resonate to and detect this invariance is built into the sensory system.  The sensory system itself is not passive but deeply active, as it requires consciously directed attention and intensional explorations of objects. Such explorations themselves require continuous voluntary movement of the organism as well as its sensory organs in order to provide a context in which invariance under transformation can occur and simultaneously be detected.

Rand would argue that consciousness does not (and by its very nature as an organ of identification, cannot) add , remove or distort its objective cognitive content, but merely renders that content it in a subjective mental form.  The subjectivity of its form does not cause its content to be subjective, on the contrary, it is the undistorted, unmodified content that makes consciousness objective.

Both Gibson and Rand are epistemological direct realists, though they apparently disagree on the details of how realism is manifest in object perception.  And both Gibson and Rand reject sensory quality dualism, though for different reasons.

Rand rejects the view that some perceptions are of the qualities of objects as they are independently of us (primary qualities), whereas others (secondary qualities) are caused by the primary qualities, and are entirely in the mind (Rand 1990a, 279ff ). Instead, she distinguishes between the content of a perception and its form; when we perceive an object as, e.g., square and red, what we perceive are its intrinsic features in a certainform, a form that is determined by the nature of the object, the nature of our perceptual organs, and the environment. Thus, we perceive the object’s shape as square, and the reflectance properties of its surface as red; both are the result of the interaction of our perceptual organs with what is out there. Neither squareness nor redness belong either to the object apart from our mode of perception, or to our mode of perception apart from the object in its environment. Hence, these attributes are neither intrinsic nor subjective but relational and objective (Kelley 1986; Peikoff 1991).  – from  Ayn Rand, in Stanford Encyclopedia of Philosophy, article written by Neera K. Badhwar, and Roderick T. Long

The Subjectivity of All Sensory Qualities – Denied

 ‘But wait,’ one might object, ‘are not the qualities we perceive in objects part of the content of our awareness?  And since the subjective qualities of our perceptual experiences do not tell us what the corresponding qualities of the object of perception are, i.e., are not the same as the qualities of the object of perception, are they not subjective distortions that misrepresent the true reality of external things?’

By asking these questions in this way, we revisit the entire problem of primary and secondary sensory vs physical qualities and the problem of direct perception itself.  Let us begin by answering the question of the subjectivity of sensory properties.  If objectivity means that what we are uniquely aware of corresponds to a unique fact about the external world, and always corresponds to that fact, when experienced in that psychophysical form, then the experience can be said to be both objective and direct.

Truth, objectivity, are about correspondence, objectivity is about identification not about identity.  Our conscious processes and their mental products are not identical with the facts to which they correspond.  The quality of ‘red’ that we perceive in a rose (under illumination — yes there must always be energy to carry the content to the sensory system), qua sensory quality, is NOT identical to the quality to which it corresponds in the rose’s pigment in response to its illumination by the physics of the light energy.   I’m sure we’ve all heard this argument before, but do we realize the implications of this argument as against the doctrine of quality dualism?

The doctrine of quality dualism is the product of a rationalistic approach to understanding the world and its relationship to mind.  This approach makes demands on the process of cognition, before it ever studies the requirements for actual cognition for a scenting cognitive being.  True knowledge of the physical world, it is thus argued, must consist of the mind actually (somehow) holding, grasping, each fact of reality ‘as it is in itself independently of consciousness.’  Thus an object’s mass must be felt ‘as’, experienced as, mass (called ‘weight’) its expanse grasped and experienced as an extended external expanse having just the physical shape that the independent object does have.  And so on for all of the object’s intrinsic properties (insofar as they are perceivable by the naked senses).

Such a demand is absurd both epistemologically and metaphysically.  For knowledge, for ANY being possessing knowledge, is NOT a collection of ‘copied’ objects, in which all of an object’s properties appear as corresponding elements of the cognitive product.  It may be the purpose of some deeply misguided philosopher to demand such ‘direct immediate, unprocessed content’, but it is not the purpose of any cognitive organism.  Indeed such a process is not even possible in principle (unless one wants to venture into the science fiction of parallel universes, this time a universe within the mind and its parallels universe outside of the mind.)   Let us reject this fantasy trip, which, in any event, has nothing to do with real science and the real possibilities of objective epistemology.

A variant of this model-the-universe-first (or as Rand calls it ‘re-writing reality’) attitude is revealed in the common argument that the way we perceive colors (i.e., what we experience when we perceive colors) must be directly matched to a color’s (electromagnetic) physical property of wavelength and physical laws of light color mixture, such as the display of colors via chromatic filters onto a neutral background.  We know the ‘science’ of the control of projected light colors and their precise mixtures (via gelatin transparencies, for example).  And we also know the ‘science’ of the control of light absorption via opaque pigments (paints if you will).  Thus (leaving aside the strange phenomena of wave-particle dualism associated with light energy ‘packets’ or photons) a properly behaving visual system in response to color mixtures must detect the very combinations of transmission and absorption shown in color demonstrations.

Not surprisingly, physiologists and ocular micobiologists searched long and hard for a set of exactly three ‘primary’ color pigments, which they hoped to show matched in color perception the same principles known to the demonstration of color presentation through mixture of the three ‘primary’ colors (first formulated by the trichromatic theory of color vision).   Having set these standards as to what a proper, or adequate sensory system must detect and differentiate, visual scientists were (and continue to be) repeatedly amazed to find that color vision is not nearly so simple as the laws of simple color mixture, and that the subject very often does not appear to see the ‘true’ colors of objects, even in ‘simple’ color presentations.   Is the arrogance of the visual theorist blamed for this empirical mismatch?  No.  Instead, true to form, it is the senses that are blamed and accused of subjecting their owners to unfortunate ‘misleading illusions.’  Of course they are only illusions if we believe that we have the right to dictate the biological and cognitive purpose of the visual system and then go on to dictate what and how the visual system must ‘see’,  instead of empirically investigating the actual biocentric and cognitive basis of visual perception, or, as Gibson expressed it ‘to look for ourselves.’

This, in the current case of sensory quality dualism under discussion here, is exactly the same cognitive fallacy so frequently committed by philosophers who ‘want’ the senses to work a certain way (however their theories take them) and who blame the senses for failing to ‘see’ (in the current case) the secondary qualities of objects.  Thus sensory dualism is the epistemological side of physical quality dualism.  All the product of backward thinking and arrogant philosophy.  As we shall show (later in this and other articles) our sensory systems are quite capable of selectively responding to all energy information emerging from objects.  But the correspondence between conscious sensory qualities and the physical properties and relationships  in objects underlying this sensory responsiveness is far more complex that philosophers would like to believe.  Nevertheless, there is a complex causal psychophysics underlying all of human and animal perception.

Direct Realism: Gibson’s Rejection of Sensory Quality Dualism

Gibson’s objection to the Lockean distinction between primary and secondary sensory qualities is based primarily on his own work, as well as that of others, on sensory adaptation.  Gibson cites the many adaptation experiments that initially induce distortion of object perspective, color reversal or distortion, orientation distortion, and other such phenomena based on subjects wearing (over a prolonged period) spectacles that are fitted with color shifting or position shifting lenses.  The sudden appearance of ‘straight’ lines as dramatically curved or the color of the world as overlaid with blue or yellow (depending on the direction in which the subject’s eyes are oriented) all followed eventually with visual adaptation eliminating the distortion through active interaction with the external world.  The fact that both so-called primary qualities (such as shape, slant, orientation, parallelism) and secondary qualities (color, balance, etc.) are equally modified and equally adapted to, provides evidence for the assumption that there is not fundamental primacy built into the senses for objective awareness of primary qualities versus secondary qualities.  On this topic Gibson writes:

The principle [of sensory adaptation] applies not only to the qualities of objects that John Locke called secondary, but also to some that he called primary. The secondary qualities were colors, sounds, tastes, smells, and feelings of warmth and cold, and they were said to be only in us, not in the physical objects themselves.  The primary qualities were shape, size, position, duration, motion, and solidity, and they were said to be in physical objects.  Everything in this book, the reader will recognize, goes contrary to the doctrine of Locke. It is plausible but pernicious, and the attempt to refute it was begun in the first chapters.  The point of interest here is this: since after-effects in perception apply not only to colors, tastes, smells, and feelings of temperature, but also to shape, size, position, and motion, one reason for the doctrine [of sense quality duality] breaks down.  [My bracketed emphases.] — J. J. Gibson, The Senses Considered as Perceptual Systems, 1966,  p. 308.

Gibson then goes on to describe his own experiments as well as those of Kohler on sensory adaptation to visual distortion of the environment, and suggests some possible causal explanations for the principle of adaptation.  He does not commit himself to any known theory, but ends with the statement:

Whatever the process, it is a realistic one and the occasional errors of judgement are incidental to it. — J. J. Gibson, The Senses Considered, p. 309.

On the general problem of the objective and subjective characteristics of perception (qua phenomenal experience), Gibson has written:

There is a subjective aspect and an objective aspect to every phenomenal experience, but this does not mean that there is some degree of subjective determination of objective perception. The old idea that perception is determined partly from the outside and partly from the inside is nothing but a muddle of thought….If perception is essentially an act of attention, as I maintain, and is not to be confused with imagination, hallucination, or dreaming, then the perceiver does not contribute anything to the act of perception, he simply performs the act.  — Gibson in a Letter to Gunnar Johannson, 1970, p.89 – cited by Edward S. Reed, in James J. Gibson and the Psychology of Perception, p. 237.

Direct Realism: Gibson’s New Psychophysics of Perception

In fact it can be argued and proven, that all perceptual properties of objects are equally objective, in the sense that they correspond directly to the properties of objects specified in sensory information and automatically detected by our perceptual systems.  What philosophers have failed to do, since the time of Descartes, is to identify the objective referents (correspondents) of so-called secondary sensory properties.  James J. Gibson was the first to make this profound identification.  I have written in Perception, Philosophy and Neural Processing:

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.   – from Gibson, J.  J.  ‘Perception as a Function of Stimulation.’  Psychology: A Study of a Science. STUDY I. Conceptual and Systematic, Volume 1. Sensory, Perceptual and Physiological Formulations. S.  Koch (Ed.), New York: McGraw Hill.  1959, 456-5

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.

Direct Realism: A Unified Theory of Sensory Qualities

Neither Gibson nor Rand nor anyone else (to my knowledge) have tackled the difficult problem of the causal basis for our phenomenal awareness of a distinction between primary and secondary sensory qualities.  They simply assert that, whatever the underlying cause, it does not violate the principle that perceptions are objective (Rand) or realistic (Gibson).

I have thought about the possible under lying causal basis for this phenomenal distinction, and in my paper The Causal Basis of Perception: A New Integration on a Gibsonian Base (first published in 1975 and re-published in bioperipatetic) have developed my theory as a Philosophical Note entitled: Primary and Secondary Sense Qualities: The Physical Basis for the Distinction Between “Primary” and “Secondary” Sense Qualities.

Here is the full note explaining my theory as to why both primary and secondary sensory qualities  have a common unified causal basis and can be unified under a common direct realist theory of sensory qualities (for full details and background, it is recommended that one read the entire paper The Causal Basis of Perception):

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. – from  The Causal Basis of Perception, by Jack H. Schwartz, pp. 15-16 of the original master’s thesis in 1975.

Direct Realism Defended: Sensory Quality Dualism Challenged

We have shown, by citing and excerpting the key relevant writings on this topic by Descartes, Locke, Hume, Gibson, Rand and myself, that sensory quality dualism (between primary and secondary qualities or properties) is unwarranted and indeed invalid, in that it leads to a false concept of the nature of  sense perception.

We have shown by deeper analysis of the phenomena under question, plus a reassessment of historical doctrines relating to sensory qualities, and utilizing both experimentation as well as analysis, that quality dualism can be shown to be the product of incorrect theories of mind in general and of perception in particular.  The theoretical paper: The Causal Basis of Perception, is grounded on the seminal experimental and theoretical work of Professor James J. Gibson and his wife and collaborator, Professor Eleanor J. Gibson.  The work of the Gibsons goes even further to reject and refute Cartesian Dualism on theoretical,  experimental and methodological grounds.  From the arguments, empirical observations and analyses in The Causal Basis of Perception emerges a new direct realist theory of perception and of all cognitive powers of the mind where such powers are based on the evidence of sense perception.

References (Listed in reference order):

  1. Thomas Reid, Essays on the Intellectual Powers of Man: Essay II. Of the Powers We have by Means of our External Senses. Chapter VIII: Of the Common Theory of Perception (1785), MIT Press, 1969, p. 146.
  2. Garth Kemerling, Britannica Philosophy Pages: Locke: The Origin of Ideas, © 1997, 2011.
  3. Roger Bishop Jones, On Locke:  Chapter VIII Some further considerations concerning our Simple Ideas of Sensation, First edition October, 1994, Last modified March, 2009.
  4. Philippe Hamou, Qualities and Sensory Perception, The Oxford Handbook of Philosophy in Early-Modern Europe, Desmond Clarke and Catherine Wilson eds., Oxford University Press, 2009.
  5. Raymond Tallis,  Mathematics & Reality, 2014
  6. Clyde Lee Miller, Cusanus, Nicolaus [Nicolas of Cusa], in the Stanford Encyclopedia of Philosophy, 2013.
  7. On Weber and Fechner, wikipedia.com, last modified on 20 March 2015.
  8. Ravi V. Gomatam,  Quantum Theory and the Observation Problem, in Reclaiming CognitionThe Primacy of Action Intention and Emotion, Ed. Rafael Núñezand Walter J. Freeman, Imprint Academic , 1999.
  9. Jack H. Schwartz, ‘Perception and Neural Processing‘, substantially based on a experimental thesis THE NEURAL PROCESSING PERIOD AS THE BASIS OF BACKWARD VISUAL MASKING, submitted to the Department of Psychology, Brooklyn College on July 1977.
  10.  Merlin Jetson, from Blog: Rebirth of Reason™: The Primary-Secondary Quality Distinction, June 2009.
  11. Rand, Ayn, Introduction to Objectivist Epistemology.  Expanded Second Edition, edited by Harry Binswanger and Leonard Peikoff, Meridian, 1979.
  12. Neera K. Badhwar, and Roderick T. Long,  Ayn Rand, in Stanford Encyclopedia of PhilosophyFirst published Tue June 2010; Substantive Revision July 2012.
  13. James J. Gibson, The Senses Considered as Perceptual Systems, 1966.
  14. Edward S. Reed, James J. Gibson and the Psychology of Perception, Yale University Press, 1988.
  15. Gibson, J.  J.  ‘Perception as a Function of Stimulation.’  In Psychology: A Study of a Science. STUDY I. Conceptual and Systematic, Volume 1. Sensory, Perceptual and Physiological Formulations. S.  Koch (Ed.), New York: McGraw Hill.  1959, 456-5
  16. Jack H. Schwartz,  The Causal Basis of Perception: A New Integration on a Gibsonian Base,  substantially based on a theoretical thesis submitted to the Department of Psychology, Brooklyn College on September 10, 1975.

Published November 10, 2014 @ 2:20 pm.  

Latest revision:  October 23, 2015 @ 2:20 am

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