Let's get specific

OK then, if you've been reading our blog so far, you're probably wondering what the heck we're talking about. You've either read recent papers coming out of auditory cortex that suggest A1 is 'cracked', or you're sick of the cutthroat competition in vision and the grass looks greener over here. We've kept the issues pretty general so far, but I can't take any more ambiguity: so I decided (after winning Elias's vote) that I'd post two slides I used in my thesis committee meeting.


(click on figure for a bigger version)

This slide pretty much sums it up. After 26 years of research, the only thing we know for certain about the primary auditory cortex is that it is tonotopically organized. It is either testament to the fact that 'audition is more difficult than vision', or, what lack of theory can do to you.

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Let's get specific 2

Here's the next slide:



This slide is meant to illustrate all the progress we've been making in the past few years. I believe these data are a fair portrayal of the current state of the field. Data includes stuff from my own lab, and other leading labs in the field.

These data illustrate: synchronizing and non-synchronizing responses, low- and high-contrast responses, temporal and rate coding of sAM frequency, selectivity to ramped/damped stimulus waveform, presence of multi-peaked tuning, the integration time constant of neurons indicating their 'role in object processing', responses to low-probability sounds, synchronized onset responses, STRF-type mehtods providing descriptions of linear receptive fields and the mapping of arbitrary model parameters on the cortical surface.

It is becoming increasingly difficult to synthesize all these data (which on their own, are pretty well-done studies) into a cohesive picture. This lack of such a unifying picture is a matter of concern in certain circles in the field.

To a new student/uninitiated theorist, or even a relatively experienced person like myself, a read of current literature is very confusing, and any theorist attempting to understand and synthesize all the above data is bound to quickly depart in favor of greener pastures in vision and computer science.

The next slide in my talk to the thesis committee was a couple of quotes:

"The key observation is that neurophysiology and psychophysics have as their business to describe the behavior of cells or of subjects but not to explain such behavior."
- Marr, Vision, 1982

"If one just wants lots of varied evidence, one can assemble an encyclopaedia of facts, but the hypothesis that is their conjunction will be incredibly complex because the facts are so heterogenous."
- Lipton, Science, 2005

I think they hit the nail on the head (the aforementioned nail being the last one on the coffin of auditory cortex research, if we were to continue this way). All of the above results are important in themselves, they are results of testing hypotheses of themselves. Me and Elias call these 'point theories', and we believe it is misleading to go this route. But the picture is still hopeful: as long as the aspiring phenomenologist even thinks about linking up his contribution to atleast one stage below his level of description, we would have a much more cohesive picture.

Note: All the figures are taken from papers published in peer-reviewed journals. They represent contributions of many different labs. I'm not citing specific references because I feel that it's irrelevant to the discussion at hand: what's more important is the data that's out there, not who is doing what.



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JC 2: Some fine detective work

Ref.: Livingstone MS and Conway BR, Was Rembrandt Stereoblind? N Engl. J. Med. 351: 1264-1265


Abstract:
Stereopsis is an important cue for depth perception, yet it can be a hindrance to an artist trying to depict a three-dimensional scene on a flat surface. Art teachers often instruct students to close one eye in order to flatten what they see. Therefore, stereoblindness might not be a handicap — and might even be an asset — for some artists. Stereopsis requires precise alignment of the two eyes. We examined a number of self-portraits of Rembrandt,
an artist known for his astute powers of observation, and noticed that many of them show his eyes as exotropic, some to a degree that would be incompatible with normal stereopsis. We wondered whether the gaze angle of the eyes in Rembrandt’s self-portraits was random or whether the gaze deviation was systematic, as it would be if he were accurately portraying a feature of his physiognomy.

Summary:
One of Livingstone's interests is the interaction between Vision and Art. In this paper, she analyzes the self-portraits of Rembrandt in an effort to understand if an observed lateral deviation of his left eye in these paintings was intentional portrayal of a real strabismus. They analyzed high resolution images in 24 oil paintings and 12 etchings where they could quantify the position of the pupil (or center of the iris) and the extent of its deviaiton from the center. In 23 of the 24 paintings, the right eye looks toward the viewer and the left eye looks outward. In all 12 etchings, this trend is reversed, because of the method of etching: the artist first draws on a metal plate and tranfers it to paper, creating a mirror inversion. The one painting that did not show the effect, the authors guess, could either be a copy of an etching or painted by a student. Since lack of stereo-vision is an advantage to artists (as they have to paint 3D scenes on a flat surface, Rembrandt's stereo-blindness could have contributed to his greatness.

Comments:
The purpose of the JC series was also to discuss what we thought were cool papers, so I guess I'll vaguely justify this post by saying it was cool.


This is not an article in the class of Lipton, but it still shows how far some logical thinking goes. An observation of an apparent strabismus, a logical experiment to generalize the observation (to make sure it is not a proof-by-example type effort) together with a theory of how it may have helped the great Master. Again, the perfect interaction of Thinking and Experiment. Plus, I think it's really cool: like performing a forensic exam from a painting.

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Vatsun meets the Committee

Well, I'm not sure why you'd be interested in how it went, but it went well... considering my incendiary slides (which included a graphic timeline of how much the world has moved on between 1975 and 2001, while A1 still obsessed over tonotopy). Let's call the committee members A - E (for obvious reasons, plus you'll have fun guessing who they are). 'A' and 'B' kinda looked upset over my trashing of A1 research, not to mention the statement I made about vocalizations being only a subset of natural stimuli. 'C' was mostly concerned that I was a 4th year student still making too specific hypotheses. 'D' was insightful but silent mostly. 'E' was the only person interested in my two-tonepip idea.

'A' graciously defended me citing all the effort I had put into my erstwhile doomed project, and gave me credit for building a new setup etc. Other than that, I guess we'd already spoken about most other things. B's reaction was more interesting. Initially he was sceptical, perhaps even a tad outraged (especially when I commented on unsubstantiated theories of an ex-postdoc of his), but eventually, conceded that he didn't have a better idea of studying the system either, so he might as well support me. Most of my argument with him centered on the dimensionality of audition: B made the commonly made point that the 'linear' STRF is actually the second-order Weiner kernel and therefore non-sync. neurons were possibly 3rd or 4th order, and I countered with my intuition for sound which is that once frequency channels are separated, it is essentially a first -order amplitude-time system.

'C' was mostly concerned that I would not be able to graduate. He wanted me to get some data, both from my old and new projects and describe something to get out. His concern about my hypotheses being too specific was valid. And, 'C' made the very insightful suggestion that perhaps I should incorporate natural statistics into my two tone-pip stimuli.

Not much else to say about 'D' and 'E'. I should talk to them more though, they probably have more ideas than I do on these matters. We'll see how it goes.




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But Mooooooomm... there's so much variability in Biology....

You got to say the title in the voice of Eric Cartman (go see South Park).

But something struck me. The Brain isn't stochastic. Behavior isn't stochastic (not unless you believe in Free Will, and I very much doubt that). If a lion stalks a zebra and the zebra notices, barring other complications (such as maybe altruistic sheilding of a baby zebra, whatever you call those), 10 times out of 10, the zebra will run. It's a certainty, not a probability. Of course, it wouldn't work if you studied a zebra in a lab while simulating a stuffed tiger attack, that isn't variability: that's stupidity on the experimenter's part.

Sure, it depends on what level you look at. Spike trains from individual cortical neurons do appear to be stochastic. But experiments suggest that by looking over the population and measuring the mean rate, or (not to offend anyone), measuring synchrony, this stochasticity is taken care of. When you talk about behavior, it is predictable. Look at the stuff coming out of Newsome's lab these days for proof. There is one thing the brain must obey: causality.

For all the talk about physicists having it really easy (all they have to do is explain the universe, no big deal really), aren't they the guys who invented uncertainty? They found a way to deal with it. Yes, it required a paradigm shift, but you don't hear physicists whining: 'But Mooooomm... Heisenberg ruined my career...'
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Meet the Committee

No, not the sequel to Meet the Fokkers, although I'm bound to be as
hapless as Ben Stiller. I'm talking about my upcoming thesis committee
meeting where I'll renounce all material and scientific pursuits,
convert to Zen Buddhism and retire to a lonely peak of the Himalayas.

Seriously, what do I tell them? I plan to start by telling them how
after recording from over two hundred neurons, I managed to uncover 4
synchronizers and maybe 10 non synchronizers. Not the promised kind
either. Then I meticulously take down the auditory system, the cause
of all my misery. Maybe I'll spend time on the evils of phenomenology.
Then my plans for the future; more on that later.

If this blog sounds a bit out of place, don't bother. It's just a test
of the blog-by-e-mail feature.

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Is A1 dead and gone?

Maybe the field is claiming an unofficial triumph that primary auditory cortex (A1) is a solved ('cracked') problem. Most present labs are moving toward secondary areas... it's almost like unofficially accepting that it is becoming increasingly difficult to publish/get grants to do work in A1. Seriously, if I report 'interesting' spectro-temporal stuff in A1, can I even get it into JARO?

Elias claims he was being sarcastic when he told me the above, but I believe it. We've opened up so many possibilities looking in unexplored areas, that A1 is just plain boring (what, it responds to tones? Didn't we know that in 1973?). This is strange, cause Fitzpatrick published an excellent V1 anatomy paper that I presented at journal club, and Ferster came out with a great one this week in Neuron. V1 research is more saturated, but still keeps coming. Maybe V1 is more complex than A1? Aha... (if I can get that out of a self-pitying auditory neurophysiologist).

Sum up V1 in a sentence: 'robust edge detection at multiple resolutions, computational basis for parsing objects in a scene'. Sum up A1 in a sentence: 'it responds to tones'. No wait, 'tonotopically organised response to tones'. Oh, and let's not forget 'non-monotonicity'. And 'temporal processing'. How about 'A1 is actually doing object recognition because thalamus neurons are feature sensitive'. At this point, I can just quote W: 'You forgot Poland'.

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Physicist-bashing

Conversations over the past few days have yielded several statements in response to our (me/Chris/Elias) support for reductionist approaches that have benefitted physics immensely. These range from modeler-baiting ('All modeling work is crap... even I can build a crappy model in half-an-hour') to 'Did I hear that right' moments ('I do not believe in reductionism') to the incredible ('modern physics has not helped us at all'). I did expect a defence of non-reductionist approaches, but not by discrediting the efforts of physicists. Apparently, ' a lot of physicists are without jobs now'. !!!. Isn't that where you want to be? Isn't that more a tribute to the fine job physicists have done unravelling incredibly complex questions? No, apparently 'the variability in Biology is so much, those approaches wouldn't pay off' (an obvious reduction to the 'Biology is difficult' defence, see one of my earlier blogs).

So I begin to wonder, this anti-physicist thing must be pretty deep-rooted. Is this jealousy? Is this because... they have more money? No, I know some physicist friends in academia who don't make that much. In fact, it's pretty darn hard to get funding for experimental physics these days. Is it because they have... better social lives? No, they are even more pathetic geeks than we are (to wit, bumper sticker that says 'Flirt Harder, I'm a physicist'). Why?

My theory is that we are jealous... of the way they've applied reductionist approaches to a system that's equally complicated, more basic, with incredible success. Physicists would rather conjure up String theory, a purely mathematical construct, to try and answer deep questions rather than be proud of the complexity of their system. Obviously, they are doing something right... they left themselves without jobs.

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Existence proofs

Someone brought up the point that what we were doing by finding areas in the brain that respond to certain stimuli was providing 'existence proofs' that had the potential to provide constraints on future studies. I had to read up a bit to examine that claim:

http://www.mathpath.org/proof/proof.methods.htm
http://www.ams.sunysb.edu/~yildirim/handouts/proof-meth.pdf

Link 1 talks about what an existence statement is, and what the ways to prove it are. Link 2 talks about valid and invalid methods of proof in general.

An existence proof for P(x) is of the form 'there exists an x such that P(x) is true'. For example, we may want to prove 'if a is real, there exists real x that is a solution to 5x+3 = a'. A constructive proof would say, since a is real and (a-3)/5 is also real, there exists a real x such that P(x).

Two important things: the space is defined and is made known to you. If the space is undefined/not known to you, or worse, you assume a space, the solution becomes trivial because the problem is unconstrained - you can find a space such that P(x).

The brain presents a similar under-constrained problem. For example, you can ask 'show neurons such that these neurons process faces'. But you are imposing your framework by presupposing faces are represented at the level of single neurons, and you don't know the brain's framework.

The solution therefore cannot be constructive. The only other method of proof is non-constructive - to show that 'face cells' must exist as a consequence of previously known theorems. This necessarily requires a Theory of Vision - my personal bias is that it should be a mechanistic, bottom-up theory.

Proof by example is just plain wrong. For example, if I propose 'for any n, 3n is even', and show for n=4, 3n = 12, I am clearly wrong (for n=7, 3n=21 which is odd). Finding some face cells does not mean you've provided an 'existence proof' for face cells in a rigorous sense.

The point is, even an existence proof requires much more thought, and is ultimately much richer than a simple description. So in a sense, descriptions themselves are underconstrained, and may not be very useful as a prologue to more sophisticated questions. Of course some descriptions are really good and are probably true, but in a rigorous sense, we need a theory.

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Story-telling

I'm blogging a bunch today 'cause I'm behind schedule.

Elias brought up a great analogy. Some people have a talent for story-telling. In any conversation, they can link up a story beautifully, sometimes as a metaphor, sometimes as entertainment. But the point is, at the end of the conversation, the story carried meaning - it belonged and contributed to information that was exchanged. The best Science is good story-telling - when you link up multiple observations into a coherent 'story' that carries meaning and advances your understanding/conveys information.

Auditory neurophysiology is stand-up comedy.

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Is Phenomenology inherently fatalistic?

It seems so to me, atleast the descriptive-solution believers in my field. I have been called a fatalist for proposing that it is possible to have a theory of audition, but I'm not smart enough to do it. But what about the guys who throw their hands up in the air and say 'audition is complex, a grand theory is probably not going to happen. So we'll just describe what we can and move on'?

On a different note, is there such a thing/person as a phenomenologist who believes in reductionism?

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The Nature of this Blog

In three words: 'mid-PhD crisis'. When you stop thinking about doing something cool and ask why you are doing it at all. This blog is an online excerpt of lab conversations feat. Elias, serving both as a summary statement of the day's rant to us and to collect more thoughts on the matter. So if you read this, and have something relevant to say, do post.

By way of background, we feel trapped in a field that is content with describing, not explaining, phenomena. Auditory cortex research, though as old as visual cortex research, has not progressed at all (personal opinion) in it's 50-something years of existence. Some abandoned cortex in favor of sub-cortical structures to gather more insight. Others fled because the auditory system is 'a harder problem than vision' (more on that below). The few that stayed on have, well, stayed on - they haven't made much progress.

The one very valid reason for this sorry state of affairs is early fixation on the anesthetized preparation. Perhaps if people had thought of an awake prep, things would have progressed much faster. Other reasons you might commonly run into are always reduced to one of the following:

1) Audition is a far more complicated problem (the self-congratulatory, 'I'm trying so hard' answer: variations are 'Biology is so complex'/'A1 is like V4')
2) We cannot wait for a grand theory of things, we chip away and describe what we can
3) ... there is no third reason, wow

I guess what I'm saying is, auditory neurophysiologists are not phenomenologists by choice: they are phenomenologists by training.



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This is a Test

Not a wizard? Join Muggles Against Phenomenology!

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