Greg Detre
for 11 on Wednesday 17 May 00
Daniel Dennett
in many ways, Dennett complements McGinn nicely � he agrees that there is a naturalistic explanation for consciousness, but he also believes it to be accessible to us, cognitively open � however, the pains he goes to to make clear exactly how his model is different from our standard misconceptions is evidence of our finite capacity to understand
trying to debunk the hangover from cartesian dualism that there is a single, central locus in the brain which the rest of the brain reports to � he calls this position cartesian materialism
for instance, we assume that the afferent sensory inputs and the efferent motor signal outputs must meet somewhere specific in the middle � the top of the neural hierarchy
this is another way of expressing the (fallacious) idea that there is a homunculus in our brain, watching our visual world on TV screen in the Cartesian theatre inside our brain, and directing our action
descartes sensibly posited the pineal gland as the pinnacle of his hierarchy, where he thought information from all the senses flowed into and all the motor commands emanated from � it was a good area to pick anatomically, because it was fairly central, slightly towards the back, with inputs from most of the brain, and even more interestingly, it�s one of the few areas in the brain which isn�t lateralised, that is to say that it isn�t mirrored on both sides, but rather sits alone on the mid-line separating the left and right hemispheres � this neatly avoids the problem of how we unify the two semi-autonomous halves of our brain.
this pineal gland, or homunculus or whatever you want to call it, is a personification of consciousness and the subjective. but when you think about it, it can�t be like this - because what would the inside of the homunculus� brain look like? it�s an infinite regress. this seems to be one of the barriers to understanding consciousness, that �there�s no one at home�
Poppel � button-pushing times to auditory and visual stimuli � used external behaviour as his end-point
wherever the stimuli go when they�re being processed in the brain, they all end up following the same route down an efferent nerve to my finger
but the problem comes when you try and trace it back further down the line of processing � where in the brain was I conscious of the sound or flash of light?
Cartesian materialism = the view that there is a crucial finishing line or boundary somewhere in the brain, marking a place where the order of arrival equals the order of �presentation� in experience, because what happens there is what you�re conscious of
neo-Laffer curve
attacks an analogous notion in Reaganomics about revenue against tax rate:
that there must be a single point where government revenue is maximised
just because the extreme ends of the curve are clear, there is no reason why the unknown part of the curve in the middle has to take a smooth course
Dennett uses the analogy of the information processing in the nervous system as continual �editorial revision� (this is slightly problematic, since it conjures up a readership, which is exactly the image he�s trying to dispel)
all cognition is accomplished by parallel processes of interpretation and elaboration of sensory inputs
rapid saccades are edited out early in the processing from eyeball to consciousness
Julesz� 1971 random dot stereograms �/span> perception of depth
you see a shape emerge in 3 dimensions �/span> impressive editorial process in the brain that compares and collates the information from each eye, on the basis of lowest-level coincidences of saliency (individual dots)
experiments on dubbing � where you see the actor lips making the motions for �from left to right� and yet you hear the soundtrack say �from reft to light�
according to Dennett, in the artificially induced editorial contest between the contributions from the eyes and the ears, the eyes win, in this case
I think there�s also a point to be made about the subject�s expectations in that experiments, but we can take his point about parallel sensory processing tracks
he makes a further point that additions, incorporations emendations + overwritings occur � in various orders
he�ll come back to this point about the supposedly linear narrative stream of consciousness
the novel feature of the MD (multiple drafts) model is: feature detections or discriminations only have to be made once
there is no need for the information or observation to be sent elsewhere to be rediscriminated, represented or logged for the benefit of the audience in the Cartesian theatre � because there isn�t one
�it is always an open question whether any particular content thus discriminated will eventually appear as an element in conscious experience, and it is a confusion to ask when it became conscious�
�these distributed content-discriminations yield, over the course of time, something rather like a narrative stream or sequence, subject to continual editing by many processes distributed around in the brain, and continuing indefinitely into the future�
�this stream of contents is only rather like a narrative because of its multiplicity; at any point in time there are multiple �drafts� of narrative fragments at various stages of editing in various places in the brain�
this narrative evolves, degrades, gets over-written etc. so probing this stream at different places/times produces different results
there is no canonical, inert, final version that is the actual stream of consciousness of the subject, whether or not the experimenter or the subject can gain access to it
phi = when you get a sensation of motion when you see a succession of still pictures, i.e. television and cinema
simplest case: if 2 or more spots separated by up to 4� of visual angle are briefly lit in rapid succession, you�ll see a single spot move back and forth
things start getting trickier when you change the colour of the spot as it moves (and add a tiny time interval between the 2 spots)
as it turns out, it seems to us that the spot swaps colour half-way through its trajectory � which led Goodman (whose idea this was in the first place) to wonder how we�re able to fill in the spot�s colour and trajectory before the second flash occurs
ignore precognition
how does the brain interpose the illusory content between the conscious experience of the red spot and the conscious experience of the green spot?
the principle of causes preceding effects does still hold, you�ll be glad to hear � one process waiting for information from another must indeed wait for that information
straw poll: since what you consciously experience is first red, then red-turning-to-green and finally green, it (�surely�) follows that your consciousness of the whole event must be delayed until after the green spot is perceived � right?
Orwellian: the Ministry of Truth continually re-writes the history books, footage etc.
if all evidence consistently corroborates a story, we assume that story to be true
�he who controls the past, controls the present�
Stalinesque: the newspapers and textbooks faithfully record the fabricated show trials
but the show trials themselves depict falsehood
Dennett�s aim is to show that though these distinctions are unproblematic at macroscopic time scales, we have problems trying to apply them to microscopic time intervals, like our rapidly flashing coloured spot phi phenomenon
in the Orwellian account, there is a recognisable objective reality � however, that reality is distorted by memory (post-experiential or memory revision)
resist operationalism � what we remember (or is recorded by history) is what really happened
e.g. insert the memory of a guy with pink hair at last week�s seminar
in the Stalinesque account, the memories are laid down accurately, but the perceptions at the time are misinformed (pre-experiential or perceptual revision)
e.g. special 3D projector that makes it look like at the time like there�s a guy with pink hair in that empty seat
when you reject Cartesian materialism, the temporal order of discriminations cannot be what fixes the subjective order in experience
this is our explanation for how we see the red spot becoming the green spot in mid-trajectory, seemingly without having to wait to see the green spot
somehow, the information from the green spot (its colour and location) has to be used by the brain to create the �edited� version that the subjects report
but there is no way we can determine whether this is a Stalinesque or Orwellian revision, since it could be either � and there is no way that a scientist, even in the future, could determine which by brain-scanning either
they tell exactly the same story, other than where they place the mythical Great Divide
contemporary analogy
in the world of publishing, there is no longer a hard-edged distinction between pre- and post-publication editing
since word-processing and email often lead to there being >1 draft of an article in circulation � fixing a moment of publication, and thus calling one of the drafts of an article the canonical text of record is almost arbitrary, since most of the intended readers will have read an early draft � the �published� version is archival and inert
if one wants to settle on some moment of processing in the brain as the moment of consciousness, this has to be arbitrary
one can draw a line in the stream of processing in the brain, but there are no functional differences that could motivate declaring all prior stages and revisions to be unconscious or preconscious adjustments, and all subsequent emendations to the content to be post-experiential memory contamination � the distinction lapses in close quarters
problematic meaning of �projection�
do we mean by it what Hobbes thought, that after light struck the eye and produced there a kind of motion in the brain, this led something to rebound somehow back into the world?
= a projection into physical space
projection by the observer of the sound to that point in space
= the observer projects the sound in phenomenal space
distinction between logical space as represented in/by the brain, and actual distance between neurons
same with time
people want to preserve the reality/appearances distinction for consciousness
resist operationalism: that what happened is whatever you remember to have happened
�/span> bizarre objectively subjective (the way things actually, objectively seem to you even if they don�t seem to seem that way to you)
supposedly unconscious intelligent action = rolling consciousness with memory loss
Pandemonium program � worked on the basis of clamouring demons, low-level agents played off against each other probabilitistically
what determines whether we are conscious of something being processed or not?
what implications does this have for AI, specifically vision research?
should we try and replicate the multiple drafts model, i.e. not bother to bring it all together � no, because our program isn�t conscious � but isn�t this the way the animal kingdom does it? ah yes, but there is no sense of the frog seeing the fly � that is an illusion, a mentality which we ascribe to it because its perception is so intimately tied to (what appears to us to be intentional) action � mind you, even that sort of low-level non-conscious fly-noticing on a grander scale would satisfy us, or would it � it�s object recognition I suppose we want � no, we would be happy if our program were simply able to recognise two similar objects as being similar
if mind is a river, and each of the multiple drafts a swirling eddy or current, then what is consciousness � the surface?
does this render our spontaneity just an orwellian imagined/fabricated construct?