Friday, 8 November 2013

Knowing Absence

Towards an alternative theory of the role of representation in perception.

“You don't merely think that the tomato has a back, or judge or infer that it is there. You have a sense, a visual sense, of its presence. In what does the visual sense of the presence of the hidden parts of the thing consist, if it does not consist in the fact that we see them? This is the problem of perceptual presence—or better: the problem of presence in absence. The object shows up for visual consciousness precisely as unseen. […] The thing that needs explaining is not that we mistakenly take ourselves to see something that we don't see. The puzzle is that we take ourselves to have a sense of the presence in perception of something that is manifestly out of view." —Alva Noë

Here contemporary philosopher of perception, Alva Noë, outlines the the issue of what he terms "presence in absence." Whilst I do not agree with all of Noë’s theories, his avoidance of any reliance upon cognitive representational states is very much to his credit. Nonetheless, in rejecting these unsubstantiated phantoms, these spectral darlings of much scientific and philosophical presupposition, he pays little regard to the role of other forms of representation (the only kind for which proof exists) that are so vital for an explanation of our ability to conceive of absence and, arguably, of perception itself.

Noë is right, I think, to identify a significant philosophical issue with the question of absence, of our capacity to account for the parts of the things that are currently out of view. For him the answer to this paradox lies in our "sensorimotor understanding” and “conceptual knowledge" of the things that we see that "brings the world into focus for perceptual consciousness" and that "discloses the world to us." He writes:

"To perceive something, you must understand it, and to understand it you must, in a way, already know it, you must have already made its acquaintance.
There are no novel experiences. The conditions of novelty are, in effect, the conditions of invisibility. To experience something, you must comprehend it by the familiarizing work of the understanding. You must master it. Domesticated it. Know it."

But how should we interpret this “understanding”, this “perceiving”, this "knowing"? If I reach for what I know is a fresh tomato only to find that it is fake then quite evidently there was something I didn’t know that I now know. Moreover, if the new knowledge contradicts the assumed knowledge – the preconception - then I think it would be right to say that I have encountered an unexpected, if not novel, experience. If someone pops their head around my door to say hello, I know that I’m not looking at a disembodied head. But I’m not convinced that the best explanation for what I perceive is provided by reference to my sensorimotor understanding or even to my conceptual knowledge. What the explanation requires is my capacity to answer the question – should it ever arise – “To what is the head attached?”

For an organism to be surprised - for novelty even - there has to be a capacity for expectation. Without an expectation of presence it is inconceivable that an absence could be registered. A vixen doesn't register the absence of an inexistent fox cub any more than we might detect the absence of the future. Or, to paraphrase Noë: to expect something, you must have already made its acquaintance. But, as we have already seen, to be acquainted with something, does not necessitate knowing it in any substantive sense. To be acquainted with something may be to know nothing more than what to expect when becoming reacquainted with it – to be aware of what features, attributes or properties one would miss if they were absent. In order for this to be possible we need not assume representational mental states nor require sensorimotor understanding but merely a capacity for registering a disagreement between the current perception and whatever residual cognitive capacities (memories) remain of the thing as previously encountered.

But to conclude the explanation here would be to neglect the most important part of the story. What needs explaining is the nature of this capacity to register absence. Advocates of representational states will simply assert that we possess cognitive representations that allow us to perceive absence. But as Noë rightly argues, an absence is not something that can figure as a mental state, let alone a representational mental state because "What they [neurons] can’t do is fire in such a way as to signal that a hidden feature is present”

The reason that our capacity to produce representations is so vital to an understanding of absence is because perception is conditional upon our capacity to represent things. For sophisticated representation users like ourselves this capacity most often manifests itself as one or other of a vast repertoire of representational actions: an exclamation, a description, a raised eyebrow, a shrug, a song, a dance, a movie, a poem. But it need not be the case that we actually produce a representation. We need only be capable of doing so.

So, when Noë says that we have a “visual sense” of the hidden parts of the tomato he is not implying – although he might be mistaken as implying - that we literally have a sensory capacity to detect absence. Not even the Large Hadron Collider at CERN has sensors capable of detecting absence. Absence is undetectable. What we “sense”, or better still, what we are capable of doing when we look at the world is representing the things that we see. Furthermore, we know how to offer representational best guesses about the things that we can’t see. But this knowledge isn’t so much a knowledge of the fullness of things - it is a knowledge of how to represent them in whatever partial or limited form they are encountered. Very often the accuracy of our representational capacities is borne out by further investigation. Sometimes not. Sometimes the back of the tomato turns out to have a bite out of it.


simon bill said...

Neurons don't 'signify the absence of a feature by failing…to modulate their activity'. That's like proving God exists by praying to God to prove he's there by doing nothing if he's definitely there. And neurons don't 'modulate their receptive field' anyway. The receptive field of a sensory neuron 'modulates' the neuron I suppose, if by that you mean it excites it.

Jim Hamlyn said...

That’s exactly right Simon. Perhaps it was a mistake on my part to quote Noë on that point because he’s very obviously blurring facts that should be made as crystal clear as possible. Unfortunately Noë tends to be rather unscrupulous with his terminology – take his frequent use of the term “visual sense” as case in point. He can't literally mean that we have a sensory capacity to detect these absences. He must surely be referring to something occurring on a cognitive level not on a sensory level. Presumably he is using “sense” in the way that we might use the word "awareness" but it’s certainly sloppy for him to be so imprecise.

The other major issue that we might identify with the quote is with the term “signify.” Neurons don’t signify. If Noë does indeed reject mental representation then he’s contradicting himself there.

In his defense I think the point he was trying to make was that neurons don’t fire in response to nothing. But if the quote is undermining the point I’m trying to make then perhaps I should remove it.

Jim Hamlyn said...

The quote was:

“Neurons can modulate their receptive field; they signify the absence of a feature by failing in any way to modulate their activity. What they can’t do is fire in such a way as to signal that a hidden feature is present”

Now removed.

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