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Although no one can say with certainty how conscious experience is realized in relation to the brain's activity, all the evidence seems to indicate that it must occur somewhere downstream from the LGN (lateral geniculate nucleus). The reason I say "downstream" is because the optic nerve connecting the retina to the LGN is an afferent nerve through which information is passed in one direction only.

The retina is, of course, an integral part of the overall nervous system, but it's activity seems to be primarily in preparation for sending information to the brain. Within the retina, there is a complex system of intercellular inhibition which seems to be a means of regulating any given cell's response in relation to that of neighboring cells. Another aspect of this preparatory activity is the transformation of graded potentials to action potentials which is analogous to transforming analog signals to digital. This may be a way to minimize errors during the transmission of the signal. In addition to this, the mind distinguishes between neural signals from different sense organs not according to any characteristic of the signals themselves but according to which pathway conveys the signal to the brain. That rules out the possibility that neural signals are somehow transporting phenomenal qualities from the outside world.

In my opinion, all of these physiological facts seem to be more consistent with the sense-data theories which were predominant prior to the 20th century. John Searle is an example of modern philosophy's opposition to sense-data theories. He claims that our conscious experience gives us direct access to the objects of perception (see Intentionality, p.45), but he also makes some assertions which seem to oppose the possibility of such a theory. For example, he recognizes that perceived attributes are distinct from how the "world really is" (Intentionality, p.75). He also acknowledges the causal nature of physiology and even asserts that visual experience occurs within the brain:

"Notice that this story is a causal account, it tells us how the visual experience is caused by the firing of a vast number of neurons in literally millions of synapses. But where, then, is the visual experience in this account? It is right there in the brain where these processes have been going on. That is, the visual experience is caused by the functioning of the brain in response to external optical stimulation of the visual system, but it is also realized in the structure of the brain." (Intentionality, p.267)

If visual experience occurs within the dark recesses of the cranium and has no means to access the world as it is upstream from the LGN, it's difficult to imagine in what sense we can be said to have a direct access to the objects of perception. Michael Tye is another philosopher opposed to sense-data theory, and according to his account, consciousness is "transparent". Of course, he gives no physiological explanation how that might be possible.

My question is: Among the philosophers who make similar claims, such as to having direct access to the objects of perception or that consciousness is transparent, are there any that have attempted to explain that in physiological terms?

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Searle isn't contradicting himself. We need to distinguish the content of an experience from the nature of the experience itself. Direct realism is a thesis about the content; the bit in the section you've quoted looks to be about the nature of the experience.

Direct realists say the content of my thought of the tree outside my window is the tree itself. This is in contrast to sense-datum theorists who say that the content of my thought is not the tree itself, but merely my mental representation of the tree.

However, saying that the content of my thought is the tree, isn't yet to have said anything at all about the ontology of the thought that has the tree as its content. What is this thing the thought? That's what Searle is answering in the bit you've quoted. "The visual experience" is the name, Searle is saying, of the whole complicated process of environmental interaction between the tree, light, and the extraordinarily complicated organization of my nervous system. I think he's making the point that these complicated physiological cum environmental changes constitute the experience, rather than cause it. Just like each of the buildings on campus constitute the university, but none of the buildings is the cause of the university.

  • Thanks for the answer. Howard Robinson says, "[Descartes] makes it quite clear that ideas possess what he calls 'objective reality', which means that it is part of their essential nature to have an object—that is, to be of something. This contradicts [the conception] that sense-contents possess no intrinsic intentionality." This suggests that intentionalists should agree with the sense-data theorists with respect to content and perhaps with respect to the ontology of the experience as well. Is there no real debate then? Is it just a question of terminology and emphasis? – user3017 Mar 30 '16 at 19:54
  • That's an excellent question. Where is the reference to Robinson? I would usually think of Hume rather than Descartes as an example of a sense-datum theorist, but I'm not an expert on the matter. Certainly, the difference between direct realists and sense datum theorists is supposed to be that sense-datum theorists suffer the "no good inference" problem, i.e. that they can't be certain that their mental representations correspond to the world, whereas the direct realists aren't supposed to have that problem. Robinson might be arguing that that isn't right though, I'd have to check. – shane Mar 30 '16 at 19:58
  • Page 11 of Perception. But Robinson aside, the "no good inference" problem always struck me as rather superficial, because even before encountering Robinson, I never imagined that sense-data philosophers ever imagined it to be anything else but intentional. – user3017 Mar 30 '16 at 20:03
  • Let me take a look, and if I'll see if I can get back to you in a few days. I've not read Perception, but I don't think Robinson would be too worried about the problem anyway, since he's an idealist. There's no need to make an inference, hence no need to worry about whether the inference is a good one or not! – shane Mar 30 '16 at 20:08
  • If the content of perception is the thing in itself as you, how does it make sense for Searle to speak of phenomenal properties which don't belong to it? To what could those properties belong except to a mental image representing the object perceived? But he expressly rejects that idea. Unless Searle and everyone else is essentially a sense-data theorist with a possible emphasis on intentionality, I'm still looking for a physiological account for the opposing view. – user3017 Mar 31 '16 at 1:21
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Many current theories of perception http://theconversation.com/how-do-our-brains-reconstruct-the-visual-world-49276 shape it more as the Ancient Greeks did than the way Newtonian physics does. Something goes out from the mind and meets reality rather than coming into the mind and getting encoded. Of course, we know the light comes to us, but the idea of what is to be seen seems to meet it halfway, in the brain, as the visual field is being turned into information. The same seems to be true of all the senses to some degree.

Optical illusions and related Apophenias tell us that the originating assumption of what we are going to see has more reality for us than the actual input:

  • We see faces and snakes where they clearly are not present.
  • We notice dogs in clouds (not tables).
  • We hear the exact same sound pattern as different phonemes in different contexts.
  • Colors seem to spread into white space.
  • The mp3 process discards information and we cannot hear the difference it, but if they discard a little too much, we don't hear a lack of something, but totally unrelated (schwooshing) patterns invade the sound as a whole.
  • We miss doubled words when reading, and may have a hard time seeing them even when they are pointed out.

It seems obvious that we project our intentions on the data well before it reaches the point of really thinking. All this error is explained by the success it enables. By being a little too aggressive with our assumptions, we can see things we are looking for faster than we can ordinarily interpret them. It is common for some reaction times to be shorter than would be possible if the brain were to fully interpret the input.

Sensory content is clearly afferent, but we do not passively receive information. In fact, unexpected information can fail to register. For many, that means the best theory is that the brain is reaching out into its pool of data to confirm suspicions about what is present. It is not simply observing the patterns that are present and deducing the layout of the world. If there is no suspicion, we may fail to perceive the otherwise obvious. Change blindness seems to be quite the norm.

This implies that the ideas of things that are to be checked for may originate in the mind and then get shaped by testing against the outside world, instead of getting incorporated from sense-data. They are sculpted rather than molded or drawn. Inappropriate assumptions are made and then removed when they are found not to fit into the model we are testing against.

In that sense, you can say that reaction timing and eye tracking physiology supports the idea that sensory impressions and interpretations are not built up from the data, but originate in the mind, and must be more available to it than sensory data.

  • Thanks for the answer, but I don't know what it has to do with what I was asking. – user3017 Mar 31 '16 at 0:56
  • If the objects of perception are internal objects projected onto reality, rather than external objects internalized from reality then the mind has direct access to them. – user9166 Mar 31 '16 at 18:29
  • Via reaction timing, and in certain other cases we can trace this happening in physiology -- we start the reaction when we establish the expectation and not after we have the perception, then we subvert it if the expectation fails. So it is the expectation, which is fully accessible to the mind, that is the real object of perception. – user9166 Mar 31 '16 at 18:39
  • I don't disagree with that. However, it looks like Searle was a poor example for me to have chosen, because I was trying to give an example of somebody who believes that we have a direct access to external objects--if any such philosopher exist. The idea that the mind has direct access to internal object seems to be indistinguishable from the sense-data theories. – user3017 Mar 31 '16 at 18:55
  • You asked "Among the philosophers who make similar claims, such as to having direct access to the objects of perception or that consciousness is transparent, are there any that have attempted to explain that in physiological terms?" The answer is yes, if you listen to what they actually mean by those statements. If you purposely misunderstand them, then no. Not even Plato, Leibniz or Berkeley imply the mind has access to anything but ideas. The question is whether the idea comes first and seeks the object, or sense data accumulate and create the idea. – user9166 Apr 4 '16 at 6:28

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