An article by John Searle (“Minding the Brain”) in the Nov 2, 2006 edition of The New York Review of Books shows how confused most of us (including philosophers & scientists) are about something as everyday as vision. Searle reviewed Nicholas Humphrey’s book Seeing Red: a Study in Consciousness, with which he largely disagrees. In that book (based on lectures he gave at Harvard in 2004) Humphreys asks the reader to imaging they are looking at a large red screen upon which the color red is projected, and proceeds to argue that the normal interpretation of what happens when we view such a field of red is mistaken.
But what is the normal interpretation of seeing red? Searle explains it this way,
According to contemporary scientific common sense, when we look at the red screen the reflection of light waves sets up in us a series of neuronal events beginning at the retina and ending with a conscious visual experience of red. If we assume that there are no hallucinations or pathological conditions involved, the perceiver sees, and in that way perceives, the red object by having a visual experience. The perceiver sees the object, but he does not see the visual experience of the object. He consciously sees real things in the real world and not his experiences of those things. There are not two red things in the scene but just one, the red screen.
If Searle is correct that this is the standard viewpoint, then I’m with Humphrey right off the bat, for I almost don’t know where to begin with my objections. Let’s begin at the end: “There are not two red things in the scene but just one, the red screen.” It should hardly have to be pointed out that the screen is not red. Nor is the light reflected from the screen red. Photons do not have a color. Light waves do not have a color. There is simply nothing outside of the eye, and in fact outside of the brain, that is red or any other color.
We can’t even say that color equals the wavelength of visual light. Instead, the wavelength of the light striking our retinas triggers the brain to create a corresponding color experience, but it is crucial to note that the correspondence is not necessarily fixed. This is demonstrated by an optical illusion using a Rubic’s Cube, which reveals that the brain analyzes the patterns and wavelengths of light which have hit the retina before determining which color experiences to create in the visual field. In this illusion two tiles on the cube, one brightly lit on the top, the other in shade on the side, appear to be entirely different colors (eg, one blue, one yellow). Yet if a mask is placed over the entire picture except for those two tiles, they are perceived as identical in color.
Unfortunately I can’t find a link to the Rubic cube illusion. However a similar effect occurs with the Color-constancy illusion (of interest also is the accompanying paper) And this illusion shows how the brain adjusts the color of an object based on the background color. Another example of the brain editing the “raw” signals from the retina (involving shades of grey instead of color) is demonstrated with the Checker shadow illusion.
As it happen, the current issue of Scientific American contains an acticle by John S. Werner, Baingio Pinna and Lothar Spillmann which reinforces my point about color. From that article:
Many people believe that color is a defining and essential property of objects, one depending entirely on the specific wavelengths of light reflected from them. But this belief is mistaken. Color is a sensation created in the brain. If the colors we perceived depended only on the wavelength of reflected light, an object’s color would appear to change dramatically with variations in illumination throughout the day and in shadows. Instead patterns of activity in the brain render an object’s color relatively stable despite changes in its environment. — “Illusory Color and the Brain ” Scientific American, March 2007
The colors we see, then, do not come from the objects we look at, nor from the light waves/photons reflected off those objects. Instead our brain takes hints from the patterns of photons striking the retina and constructs useful color experiences for us to have. Thus Humphrey’s “red” screen is colorless. It is our brain which colors the screen red and determines it’s brightness.
Which brings us back to Searle’s claim
The perceiver sees the object, but he does not see the visual experience of the object. He consciously sees real things in the real world and not his experiences of those things.
The opposite must in fact be the case. What we see is the visual experience of a red screen created by the brain. What we do not “see” is the actual physical screen in front of us at which our eyes are aimed and from which our retinas are gathering photons. Of course, the visual experience we have of a red screen is certainly “about” the physical object in front of us, but it is not an experience of that object, nor even an experience of the photons themselves reflected off of it.
That at least is how I see it. But how about Humphrey? As Searle explains it,
Nicholas Humphrey agrees that there is a red object and a perceiver, and that light waves from the object stimulate the perceiver, but beyond that he disagrees with just about everything in the account I have just presented. He says that what I call the visual experience is really a “sensation” experienced in the eye and that the sensation is red, just as the screen is red. So there are two red things in the scene: the red object and the red sensation.
As my earlier comments make clear, I agree with Searle that there is only one red object in the scene — but maintain Searle is wrong in thinking that red object is the screen. The only thing actually “red” is Humphrey’s red sensation, although I don’t think I would say that the sensation occurs “in the eye” but rather that the visual sensation appears to occur outside of us but in fact occurs in the brain; the brain presents the visual field (or sensation) to us as if it were outside us, as if it were the “real world” instead of a sensational substitute.
Humphrey would fully agree, it appears. According to Searle’s report, Humphrey distinguishes between perception, which he defines as unconscious detection of an object by the brain, and sensation, which is necessarily conscious.
Perception is not only done by a different channel from that which produces consciousness, but more importantly, perception is unconscious. In Humphrey’s view, the sensation channel is conscious; the perception channel is totally unconscious. Indeed all consciousness consists of sensations. Humphrey thinks that the only form our consciousness can take is sensation, which for him includes mental imagery and dreams.
Although Humphrey’s terminology differs from mine, I find myself in agreement. Searle’s article continues:
His account of sensation and perception contains the following striking claims: perception and sensation are totally independent; all consciousness is sensation; perception is never conscious; and all sensation is really action. The arguments for these claims are complicated and I will not try to summarize all of them; but what follows gives the flavor of his reasoning.
He writes, “I think the weight of evidence really does suggest that sensation and perception, although they are triggered by the same event, are essentially independent takes on this event, occurring not in series but in parallel, and only interacting, if they ever do, much further down the line.” And later he says that a visual sensation “can be put to several uses…, but the one thing it is not used for is as the raw material for the perception of the world. Perception has its own quite separate channel….” He tells us that we have the illusion that sensation and perception are linked because they occur at the same time.
This makes sense of a type of experience I first had over a decade ago. At the time, I was reading a phone number off a computer screen in order to write it down on a piece of paper. I took a quick glance at screen and silently voiced the number I saw there to myself. I then wrote the number down, without looking back at the screen. Immediately after finishing I had the odd sensation of having made a mistake. I check the screen again, and realized that in reading the phone number I had transposed two of the digits. But when I looked at the piece of paper, I had written the number correctly.
It struck me then that the brain action of writing what I saw and the brain action of reading what I saw were distinct but parallel actions. I experienced what Humphrey would call an “sensation” when I read the number to myself off the screen. And yet the number I wrote on the paper did not come from from that “reading” sensation but from some parallel “perception” of the computer screen. Furthermore, when some other non-conscious activity in my brain concluded that there was a discrepancy between these other two activities, it created a conscious “feeling” of something wrong.
If I understand him correctly, Humphrey would maintain that my action of looking at the screen and writing down what I saw was an action of unconscious perception followed by an action of writing; on the other hand my action of silently voicing what I read on the screen was a conscious sensation that occurred in parallel with the other. This really does make sense to me.
At the same time, I strongly recommend Searle’s review. Although I think he’s wrong about how vision works, I do think Searle is fundamentally right in his claim that Humphrey has not solved the body/mind problem. Humphrey has presented a plausible evolutionary account (apparently I find more to recommend it than Searle does) but he has not explained how the brain creates subjective experiences. Searle explains,
Humphrey does not address that question directly; rather, he changes the subject. Our question is: How do objective third-person brain processes right here and now (as well as in earlier evolutionary times) cause our conscious states? What specific parts of brain anatomy do it and how do they work? His question is: Assuming that perception is unconscious, how might conscious sensations have evolved and what functions would they perform? His answer, in brief summary, is that they evolved by monitoring our responses to input stimuli and they function to give us a sense of “the Self.” I think he is wrong to separate perception from consciousness; all the same, some evolutionary story about consciousness must be right. But whatever evolutionary story may be proposed is an answer to a different question from the causal question. The only part of his account that even hints at an answer to the causal question is the discussion of feedback mechanisms. But he does not tell us how we get from the feedback mechanisms to qualitative subjectivity.
Humphrey’s book is can be purchased here, an article he wrote on the subject is here. Searle’s book review is here. All quotes are from Searle except for the quote from Scientific American. I should add that I have not read Humphrey’s book (yet), but I have ordered it and will undoubtedly have more to say about his ideas later.
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This has been edited since first posted, including a more accurate description of my experience of reading and writing the phone number, the addition of the quote from SI, and changing the post time-stamp to represent the date it was posted to the blog rather than the date of the unposted first draft (yes, I wrote this months ago and neglected to post it).
