Comments on: A clue! A clue!

A clue! A clue!

grateful — Mon, 12 Jul 2004 14:17:17 -0800

What does blue smell like? A novel theory contends that humans smell the frequency of a molecule, rather than shape (full study, pdf). In fact, there is no evidence to support either theory, leading to the question, how do humans smell? Inspired by bonehead.

By: kenko

kenko — Mon, 12 Jul 2004 14:20:45 -0800

What does blue smell like?

By: kenko

kenko — Mon, 12 Jul 2004 14:22:01 -0800

oh crap, I didn't see the "inspired by bonehead" thing there. Or rather, overlooked it. In any case, the answer I'm sure you're expecting is "terrible".

By: mr_crash_davis

mr_crash_davis — Mon, 12 Jul 2004 14:22:05 -0800

"...how do humans smell?" Terrible.

By: Witty

Witty — Mon, 12 Jul 2004 14:23:51 -0800

"...how do humans smell?" Terrible.

By: kenko

kenko — Mon, 12 Jul 2004 14:26:10 -0800

Man, we're on a roll here. Try the veal, it's delicious.

By: esch

esch — Mon, 12 Jul 2004 14:26:29 -0800

"...how do humans smell?" With their noses.

By: Pretty_Generic

Pretty_Generic — Mon, 12 Jul 2004 14:26:51 -0800

"...how do humans smell?" Terrible.

By: DevilsAdvocate

DevilsAdvocate — Mon, 12 Jul 2004 14:36:51 -0800

To begin with, there's no one single frequency of a molecule. Even a simple molecule such as water (with only three atoms) has three vibrational modes, each one with a different frequency, and three rotational modes, most likely each with its own frequency as well. More complex molecules have correspondingly more vibrational modes, each with its own frequency. In fairness to the abstract grateful links to, the authors don't claim that molecules do have just one single frequency that determines a molecule's smell; rather, that seems to be a mischaracterization by grateful. More importantly is the lack of any proposed mechanism by which the frequencies of a molecule could be distinguished. Biomolecules which essentially act upon a certain of molecule (and this is an oversimplification, because it's not just shape that's detected) are present in virtually every living cell, and are much more widespread than simply giving a sense of taste or smell--they're called receptors. Structures which act upon certain frequencies--in humans, in the eyes and ears--are more specialized and much less common. I'm not aware of any olfactory cells which would have any sort of structure suited to detecting frequency. (Which is not, of course, a proof that it can't be the mechanism for smell, but it makes one highly skeptical.) For more information about the commonly accepted mechanism of smell, google on olfactory receptor.

By: mdn

mdn — Mon, 12 Jul 2004 14:37:02 -0800

weird, I just posted about this yesterday on my website... it's interesting stuff.

By: Outlawyr

Outlawyr — Mon, 12 Jul 2004 14:41:56 -0800

"...how do humans smell?" Terrible. Sorry, I couldn't resist

By: Smart Dalek

Smart Dalek — Mon, 12 Jul 2004 14:52:42 -0800

"...how do humans smell?" In too many ways, if you ask me! Everything they touch turns to shit! They're ungrateful, they disrespect their elders, and they have no sense of architecture whatsoever! Talk about your wasted potential!

By: dagny

dagny — Mon, 12 Jul 2004 15:17:14 -0800

Reminds me of Ralph (I think) in an episode of The Simpsons: My finger smells like purple!

By: mr_roboto

mr_roboto — Mon, 12 Jul 2004 15:33:04 -0800

More importantly is the lack of any proposed mechanism by which the frequencies of a molecule could be distinguished. This just isn't true. Turin has, in fact, proposed a detailed mechanism. You can find a full-text link to his 1996 paper here. Briefly, he suggests that odorant molecules fill a tunneling gap in receptor proteins which use redox chemistry to generate a tunneling current. The current flows only when a molecule with a proper vibrational absorption band fills the gap. A series of receptor molecules, each tuned to a different wavelength, can serve as a rudimentary spectroscope. This is not unlike the way the other spectral senses work: receptors in the eyes are tuned to a fixed set of colors (rather than a continuous spectrum), and those in the ear are arranged along the cochlea, which acts to deconvolve sound into component frequencies. As for the actual presence of proteins capable of performing these functions, I don't think we have any structures for olfactory receptors: membrane proteins are notoriously difficult structural subjects. Turin, however, makes sequence homology arguments that those proteins identified as receptors would be capable of performing the necessary electrochemistry. Whether or not Turin is right, he certainly has come up with an ingenious and well-considered putative mechanism.

By: twsf

twsf — Mon, 12 Jul 2004 15:43:31 -0800

I highly recommend Chandler Burr's great, underappreciated book on Luca Turin and the larger topic, The Emperor of Scent.

By: adrianhon

adrianhon — Mon, 12 Jul 2004 16:08:44 -0800

I also highly recommend the paper by Keller & Vosshall (2004) in Nature Neuroscience which finds no evidence whatsoever for Turin's theory, and also the accompanying editorial in that issue. Here's a press release from Rockefeller University about their findings. Following are some excerpts from the Nat Neuro editorial (I would love to post all of it but it's probably illegal): "The paper by Keller and Vosshall on page 337 of this issue is unusual; it describes a refutation of a theory that, while provocative, has almost no credence in scientific circles. The only reason for the authors to do the study, or for Nature Neuroscience to publish it, is the extraordinary—and inappropriate—degree of publicity that the theory has received from uncritical journalists." "...The magician James Randi, debunker of paranormal claims, once said that if you claim to have a goat in your back yard, people will probably believe you, but if you say you have a unicorn, you must expect closer scrutiny. The editors at Nature used to classify manuscripts on a 'zoological scale' that ranged from goats to unicorns, and Turin's paper was toward the far end of that scale. Despite the forcefulness of his assertions, most scientists in the field were unconvinced by his proposal. Thus his paper was rejected by Nature, and it was eventually published (without review, according to Turin's own account) by Chemical Senses in 1996. Turin's theory would probably have vanished into obscurity but for two coincidences. First, one of his former students had become a producer for the BBC, and she decided to make a TV documentary about him. Second, he had a chance encounter with writer Chandler Burr, who was so taken with the theory that he wrote a popular book about it. The Emperor of Scent, which appeared in 2002, is effectively a mouthpiece for Turin's views, and it is intensely hostile to the scientific establishment. It has attracted wide attention, and with the exception of a scathing review in this journal from Avery Gilbert2, the reviews have been almost uniformly favorable. The book is seductively written, and it was recently reissued in paperback, complete with a readers' guide to promote book club discussions." "...In some sense it does not matter whether the public believes in the vibrational theory of olfaction; the truth will eventually come out. But of course this is not just about olfaction. It is about the public credibility of the scientific process and the biases that affect science reporting in the popular press. It is disturbing that Emperor of Scent received so much favorable publicity from reviewers who were ill qualified to judge its scientific content. The New York Times and The Washington Post, for instance, assigned it to their movie critic and fashion critic, respectively. The media loves controversy, and ever since David and Goliath, the story of a lone hero taking on the establishment has had enduring appeal. Of course, radical ideas from outside the mainstream do occasionally turn out to be right. Of course scientists are sometimes excessively attached to conventional ideas. But in science at least, the mainstream view is usually based on the accumulation of evidence over many years. Journalists are trained to report both sides of any argument, but this can be misleading when both sides are not equally credible. A mature body of scientific theory is like a large building, and the impulse to demolish it is often little more than a form of intellectual vandalism, an expression of frustration by those who did not succeed as architects. Some buildings outlive their usefulness, of course, but the threshold for knocking them down should be high. We hope that the paper from Keller and Vosshall will serve as a reminder of why that's so."

By: uftheory

uftheory — Mon, 12 Jul 2004 16:14:22 -0800

My finger smells like purple! -dagny Perhaps your thinking of... 'Crayons taste like purple' - Ralph from Simpsons Now how about ... 'What smells like blue?' - Fry from Futurama That show was always ahead of the curve.

By: DevilsAdvocate

DevilsAdvocate — Mon, 12 Jul 2004 16:14:23 -0800

This just isn't true. Turin has, in fact, proposed a detailed mechanism. Fair enough; I had written that without more carefully looking at the linked article. The most tantalizing claim, in support of the vibrational theory, is that acetophenone-d8 smells different than acetophenone--the two compounds have nearly identical shapes but very different vibrational frequencies. However, the Keller and Vosshall paper in Nature Neuroscience found no distinguishable difference in smell in a double-blind test. The Turin paper doesn't describe the details under which he found that acetophenone and acetophenone-d8 were perceived as different; if it was not done under double-blind conditions, it throws that conclusion into serious doubt. Nature Neuroscience also published an editorial which very harshly criticized Turin in the same issue in which the Keller/Vosshall paper appeared. (April 2004, although you probably can't get to the full text of the paper and editorial unless you're at an institution which has a subscription.) [On preview, a bunch of excerpts from the editorial deleted upon finding that adrianhon had done the same thing.]

By: undecided

undecided — Mon, 12 Jul 2004 16:15:27 -0800

"...how do humans smell?" Purple.

By: Eekacat

Eekacat — Mon, 12 Jul 2004 16:18:20 -0800

Hey Man.... Smell My Finger

By: adrianhon

adrianhon — Mon, 12 Jul 2004 16:19:59 -0800

I left a fair bit out from the editorial, but if possible I would strongly encourage people to find and read it in its entirety, or at the least read the release from Rockefeller. While IAAN (I am a neuroscientist) I do not specialise in olfaction. However, based on what I know of sensory perception and signal transduction in humans and other animals, Turin's theory and proposed mechanism sound distinctly improbable, and I am convinced by Keller and Vosshall's study that he is basically wrong.

By: chicobangs

chicobangs — Mon, 12 Jul 2004 16:24:10 -0800

"How terrible do humans smell?" Wait, I told it wrong.

By: mr_roboto

mr_roboto — Mon, 12 Jul 2004 16:39:01 -0800

Turin's theory and proposed mechanism sound distinctly improbable.... Well, I'd certainly agree it sounds improbable; that's why I called it "ingenious" :)

By: euphorb

euphorb — Mon, 12 Jul 2004 16:50:27 -0800

This is not unlike the way the other spectral senses work: receptors in the eyes are tuned to a fixed set of colors (rather than a continuous spectrum)... Umm, no.

By: Ethereal Bligh

Ethereal Bligh — Mon, 12 Jul 2004 16:56:35 -0800

Oh, boy. Color vision. Almost no lay person has a correct conceptual understanding of color vision. But it's possible (probable?) that Mr. Roboto roughly knew what he was talking about, he only phrased his assertion badly.

By: mr_roboto

mr_roboto — Mon, 12 Jul 2004 17:07:48 -0800

Umm, no. Huh? I see four classes of photopigments: one tuned to a peak transmission wavelength of 410 nm, one to 498 nm, one to 534 nm, and one to 564 nm. That's what I meant by "a fixed set of colors": rather than having receptors which are capable of performing a spectral analysis on incident light (like a spectrophotometer), our minds perceive color by combining four filtered data channels (like some high-end CCD cameras). Sorry for any lack of clarity. Is your objection that there's some overlap in the pass bands of the filters?

By: mr_roboto

mr_roboto — Mon, 12 Jul 2004 17:14:41 -0800

And, or course, in defending myself, I confused transmission and absorbance, so that's all pretty much garbled... I mean, it still makes sense, but you know, it's an absorbance band, not a pass band, and it's not exactly filtering (well, it is in a camera, but not in an eye), and I'm gonna stop digging the hole now.

By: Ethereal Bligh

Ethereal Bligh — Mon, 12 Jul 2004 17:19:18 -0800

Well, the 420nm receptor, the "rod", is not combined with the others for the perception of color. But, otherwise, yeah, you knew what you meant, it just sounded like you may have been saying something else. By the way, the Voyager CD included color photographs, which is really weird (and possibly stupid) if you think about it. However, it also included a way to decode them. Furthermore what this says about human color vision implies a great deal about Earth's environment! Which is cool. Perhaps you know: are there any cameras that are photospectrometers at every point of resolution? I guess you'd also need the spectra of the illuminating light, although it'd probably be derivable from the data.

By: mr_roboto

mr_roboto — Mon, 12 Jul 2004 17:33:08 -0800

I think you'd be interested in imaging spectrographs. The most sophisticated examples of these are custom-built devices used in astronomy.

By: Ethereal Bligh

Ethereal Bligh — Mon, 12 Jul 2004 18:05:12 -0800

Thanks for that link. I'm guessing the resolution can't be very good for imaging? I'm not a graphic artist or photographer, but I do know a bit about color vision and related problems; and the idea of a camera that's a spectrograph at every point of resolution, with a flat-broad spectrum illuminating light, seems really cool to me.

By: amberglow

amberglow — Mon, 12 Jul 2004 19:07:44 -0800

would this be related to the air smelling like it's going to snow (right before it does)?

By: amberglow

amberglow — Mon, 12 Jul 2004 20:12:52 -0800

ok, i guess not. "...how do humans smell?" Terrible. : >