Friday, September 24, 2010

Space in the Causal Theory of Perception

John Smythies has kindly provided some of Lord Russell’s actual utterances about how he conceived the relationship between physical space and perceptual space in his book Human Knowledge: Its Scope and Limits, a basic and even now classic source for philosophical analysis of this topic. The first passage is from the chapter “Mind and Matter”:
The objects of perception which I take to be ‘external’ to me, such as coloured surfaces that I see, are only ‘external’ in my private space . . . When on a common-sense basis, people talk of the gulf between mind and matter, what they really have in mind is the gulf between a tactual percept, and a ‘thought’—e.g. a memory, a pleasure, or a volition. But this, as we have seen, is a division within the mental world; the percept is as mental as the ‘thought’. (Simon and Schuster edition, p. 228)
The second excerpt is from the previous chapter, “Space in Psychology”:
All this [the physiological account of perception], I say, has long been a commonplace, but it has a consequence that has not been adequately recognised, namely that the space in which the physical table is located must be different from the space we know by experience. (p. 222)

In these two passages Russell does not refer to the theory of perception as such, that is, the “physical theory of perception” as he calls it in the chapter “Physics and Experience,” or “causal theory of perception” in his book The Analysis of Matter, devoting a chapter to it under that name. Russell makes explicit reference once again to the proverbial table which so often serves as an example in these armchair exegeses (perhaps being a pedagogical tradition dating from medieval scholasticism?):

The colored surface that I see when I look at a table has a spatial position in the space of my visual field; it exists only where eyes and nerves and brain exist to cause the energy of photons to undergo certain transformations. (The ‘where’ in this sentence is a ‘where’ in physical space.) The table as a physical object, consisting of electrons, positrons, and neutrons, lies outside my experience, and if there is a space which contains both it and my perceptual space, then in that space the physical table must be wholly external to my perceptual space. This conclusion is inevitable if we accept the view as to the physical causation of sensations which is forced on us by physiology . . . . (p. 220f)
In saying that the conclusion “is inevitable,” I would refer to my recent remarks about data “demanding” one theory over another, because the inevitability of the conclusion (= theory) here not only depends upon but is in a sense "demanded" by the causal chain of empirical events, all save the last, arguably, as at most a percipient can only report that he indeed “sees the light” (pun intended), but no observer can also see his visual space and independently verify that it exists (yes, just the sort of argument that behaviorists used to use against what they miscalled "introspection"). Of course Russell was an avowed monist so it is reasonable to assume that dualism plays no part in the “physical causation of sensations” to which he refers.

Russell is at pains to say that confusion has resulted from conflating different senses of the word “space.” (p. 201), but assures us that percepts are nonetheless in the brain: “Percepts, considered causally, are between events in afferent nerves (stimulus) and events in efferent nerves (reaction); their location in the causal chains is the same as that of certain events in the brain.” (p. 209)

So without evidence to the contrary, it seems reasonable to assume that when Russell refers to two different spaces (physical and perceptual) he means space not in the cosmological sense, but in sense 11 of the word space in OED, “Specific or limited extent,” because he is claiming that perceptual space is “private,” or conversely, that it is separate from external physical space, i.e., external to the body.

In spite of that, I suspect that Russell may have conflated two senses of “space,” because merely in separating perceptual space from physical space he seems to be using sense 11 of “space,” yet elsewhere in the context of his argument seems to be employing OED sense 7, “Physical extent or area; extent in two or three dimensions.” They are not synonymous senses of the word.

Lord Brain basically just restates Russell’s main point, and while Broad (1923) says it is “possible” to have “a space-like whole of more than three dimensions, in which sensa of all kinds, and scientific objects literally have places,” and that “scientific space would be one kind of section of such a quasi-space, and e.g. a visual field would be another kind of section of the same quasi-space,” he does not seem to explain (1) the necessity of such a “space-like whole” nor (2) how it is “possible.” By referring to "places," again Broad seems to be using sense 11, not sense 7 of the word "space."

Where then does this leave us, as other than Broad’s imaginative proposal, what compelling evidence is there to support it since he put forth the idea 1923?

Sunday, September 19, 2010

Quote of the Day

Esse est percipi (to be is to be perceived).

--George Berkeley as quoted by John Archibald Wheeler in "Law without Law"
(from Quantum Theory and Measurement, 1983)

Saturday, September 18, 2010

"Seeing is Believing": The Visual Cortex in "Fortune" Magazine

Many years ago my theoretical physicist crony Nick Herbert sent me a clipping from Fortune magazine that reproduced the picture above. Knowing that it would needle me, Herbert wrote on the clipping the words "seeing is believing" with reference to the caption that claims that "visual images [are] transported intact to the brain." The picture was reproduced from an article that had then recently appeared in Science magazine by Russell DeValois and his research team at UC Berkeley. It shows both the pattern the monkey looked at and the corresponding "image" of it in the monkey cortex.

"What's wrong with this picture," as the expression goes?

Friday, September 17, 2010

"Biologico-Teleological Considerations as to Space" (Ernst Mach)

Just for a little historical perspective on our topic, I am appending an excerpt from Ernst Mach's book, Analysis of Sensations (1897), the beginning of Chapter 9 entitled "Biologico-Teleological Considerations as to Space":

We have already repeatedly had occasion to notice how very different the system of our space-sensations--our physiological space, if we may use the expression--is from geometrical (by which is here meant Euclidean) space. This is true, not only as regards visual space, but also as regards the blind man's tactual space in comparison with geometrical space. Geometrical space is of the same nature everywhere and in all directions, it is unlimited and (in Riemann's sense) infinite. Visual space is bounded and finite, and, what is more, its extension is different in different directions, as a glance at the flattened "vault of heaven" teaches us. Bodies shrink when they are removed to a distance; when they are brought near they are englarged: in these features visual space resembles many constructions of the metageometricians rather than Euclidean space. The difference between "above" and "below," between "before" and "behind," and also, strictly speaking, between "right and left," is common to tactual space and visual space. In geometrical space there are no such
differences. (p. 181f)

By "physiological space," presumably Mach means that which is customarily called "perceptual space" (or "phenomenal space") today, including but not being confined to visual sensations. His use of the term "visual space" to denote just the visual component of perceptual space supports my previous contention that this term has long been used for the space of visual sensations (at least in science, if not philosophy). Rather than relating some of the characteristics of VS to projective geometry, Mach relates them to metageometry (i.e., what today is called non-Euclidean geometry). Other characteristics that he notes (e.g., left and right) as departing from Euclidean space are now considered to be topological properties of space.

In a previous chapter Mach notes that "optical space" [a term he uses synonymously with "visual space"] represents geometrical space (Euclid's space) in a sort of relievo-perspective." (p. 169) There is a wealth of other observations and points about visual/perceptual space in Mach's book, and I highly recommend it for that reason, and as ostensibly being the first to propose that VS is non-Euclidean, though not apparently on the basis of curvature, but on the basis of it being like a perspective projection.

Friday, September 10, 2010

Quotes of the Day

ἀγεωμέτρητος μηδεὶς εἰσίτω. (Let no one ignorant of geometry enter here.)
Motto above Plato's Academy
"The man convinced against his will is of his first opinion still," says Hudibras.
Plato's Gorgias
We must begin with the mistake and transform it into what is true. That is, we must uncover the source of error; otherwise hearing what is true won't help us. It cannot penetrate when something is taking its place. To convince someone of what is true, it is not enough to state it; we must find the road from error to truth.
It is Berkeley's merit to have realized that the Cartesian-Newtonian philosophers, seeking to account for a seeable world, succeded only in substituting a world that could in no sense be seen. He realized that they had substituted a theory of optics for a theory of visual perception.
L. Susan Stebbing

Friday, September 3, 2010

The very basic topology of the visual field

This topic may best be approached by examining the basic visual field that we experience in the complete dark, or in the Ganzfeld situation (i.e. with one half of a ping-pong ball placed over each eye). The former delivers a flat featureless black expanse: the latter a “cloudy” featureless white expanse. If we examine these with the eyes directed forward, we note that the field has a center straight ahead and a boundless periphery. Then we can turn our eyes from one side to the other. With the eyes directed to the side we notice that the center of the visual field remains where it was, now to one side of our new fixation point, which is near the rim. Note that these ‘eyes’ that we feel (experience) moving from side to side are not the eyes of the physical body but are the eyes of the body-image).

Next we can introduce structure by opening our eyes, gazing at a lit lamp bulb, and closing our eyes again. An after-image (AI) appears. This possesses some intrinsic properties—i.e. extension, shape, and colour—and extrinsic properties i.e. location at a particular position in the visual field, as well as topological and geometrical relations with other after-images in the same field. For example, one AI can be spatially BETWEEN two other AIs. Three AIs can form a triangle: four AIs can form a square, etc.. The edge of an AI can form a Jordan curve. Moreover, when we move our eyes we notice that the AIs move too to stay in the focus of attention.

These simple observations establish the important point that visual (phenomenal) space is a genuine space. A genuine space may be defined as that in which an entitiy can move about in. Tennis balls move in physical space A. After-images, as well as the eyes of the body-image, move about in phenomenal space B.

Two different genuine spaces in a cosmos can be related in three ways;—

i. A and B are different cross-sections in a higher-dimensional space C (Broad’s 1923 theory: since elaborated by others).

ii. B is a subset of A (as in the Identity Theory).

iii. A and B have no spatial relations and only causal ones (Price’s 1953 theory)

iv. Nevertheless, in all three cases, we are dealing with real spaces, and not imaginary, mathematical, phase spaces, etc.

Wednesday, September 1, 2010

Qualia and Consciousness

Rama had Paul MacGeoch forwarded me this link that features Francis Crick and his apostlte Christoph Koch talking about consciousness and "qualia":

With all due respect to them, I find their remarks to be some of the most philosophically naive and historically uninformed on these topics I have yet to hear. With so-called "qualia" all they seem to have done is rediscover what Christian von Ehrenfels called "Gestalt qualities" over 100 years ago, and consciousness is scarcely even a scientific concept the way they use it, apparently unaware as they seem to be that it is the starting point of all scientific investigation rather than something secondary or superflous that automata lack. Not once do they even mention the visual world in their discussion of visual consciousness (whatever that is), let alone its structure.