Monday, November 30, 2009

The Helen Keller Fallacy


A persistent misconception about smell is that blind people develop keener noses as compensation for their loss of vision. Because she is so often cited in this regard I think of it as the Helen Keller Fallacy. It’s an idea so deeply soaked into American culture that it appears in comic books: check out Daredevil sometime.

Helen Keller did indeed use her nose well—to recognize people and familiar places.
I used to be able to smell Duluth and St. Louis miles off by their breweries, and the fumes of the whiskey stills of Peoria, Illinois, used to wake me up at night if we passed within smelling distance of it.
That’s cool. But it’s something plenty of sighted people have experienced as well. Keller herself admitted this:
I have not, indeed, the all-knowing scent of the hound or the wild animal.
She also said “In my experience smell is most important . . .” This is understandable; deprived of sight and sound it’s only natural that her perception of the world became more olfactory.

In What the Nose Knows I summarized twenty years worth of scientific studies:
Without exception, they find that the blind are no more sensitive than the sighted—both groups detect odors at about the same concentration.
I found that in half the studies blind people were better at naming odors:
Even here, their success depended on cognitive factors such as memory rather than hyper-acute perception.
Having no access to visual cues, blind people become skilled at naming odors and may even do it better than sighted people. But this is a matter of the brain adapting, not of the nose becoming supersensitive.

Given my opinion, this paper in a recent issue of Neuropsychologia grabbed my attention:
“Odour discrimination and identification are improved in early blindness.”
It’s by a group of researchers in Belgium led by Isabel Cuevas, who works at the Catholic University of Louvain’s Neural Rehabilitation Engineering Laboratory. (Whoa.)

They compared the odor identification abilities of 13 blind men and 13 age-matched sighted men using a set of 30 everyday sort of smells: strawberry, rose, mint, etc. First, they presented a smell and asked the test subject to name it. Here the blind performed significantly better than sighted subjects. 

Next, they asked subjects to place the smell in a semantic category (fruit, flower, plant or other). Here again the blind did significantly better than sighted subjects but their advantage was less than in the free-identification test.

Finally, subjects were asked to identify the odor from a six-item multiple choice list. Here there was no difference in performance between the blind and sighted subjects.

As Cuevas et al. put it, these results indicate that the blind show “enhanced access to semantic information (including the name) from perceived odours” and that they are able to “access this information more efficiently from olfactory inputs.” Fair enough: this is a good example of cognitive compensation. But it is not evidence for compensation at a purely sensory level.

The Belgium team also found that blind subjects were better at discriminating odors, i.e., were better at making same/different judgments when presented with a pair of odors. Cuevas and colleagues argue that this is more of a perceptual skill than a cognitive one, but I’m not convinced. Same/different judgments involve attention and short term memory which are higher-order cognitive skills. 

Unfortunately, the subjects were not tested for olfactory sensitivity which is the purest expression of the compensation hypothesis (“blindness results in a super-sensitive nose”). Still, this is a well done study that explores several facets of olfactory talent. And it leaves me convinced that the Helen Keller Fallacy is just that.

6 comments:

Ed C said...

I think you're interpreting "keener noses" and "super-sensitive nose" too literally. I agree that the odor receptors in the nose are genetically determined and not likely to improve as a result of accident or disease. But people who talk about the blind having a better sense of smell probably mean the blind are able to infer more about the world from smell. And those inferences use exactly the higher order cognitive skills you describe.

Avery Gilbert said...

Ed C:

I guess we read trends in pop culture differently. I find that people attribute to super-smellers and the blind amazing powers of odor sensitivity. Daredevil wouldn't be so awesome if he had a normally sensitive nose but thought like a perfumer. The (cognitive) inferences of a trained nose--be it Helen Keller's or Jean-Claude Ellena's--are remarkable but keeness, like visual acuity, can be measured separately. I think the Belgians and I agree on this.

Ed C said...

I won't defend Daredevil or his creators. He came along after I stopped reading comics. And I've tried but never managaged an interest in graphic novels. I think I've seen pieces of the movie on TV. I gather that he is supposed to have qualitatively different abilities than the rest of us - perhaps the ability to locate moving enemies in space by super resolution of changing smells? Or is that his super hearing? Or is his skin super sensitive to air currents? Maybe there could be a whole conference of sensory psychologists on "The Daredevil Fallacies."

But I find Helen Keller's article on smell both believeable and inspirational. My own blog on the subject was a couple of weeks before yours, so I wasn't trying to pick a fight. http://community.basenotes.net/blog.php?b=666
I actually think we're in violent agreement :)

Avery Gilbert said...

Ed C:

Just back from reading your very interesting piece on Basenotes. (Had I known I would have linked to it.) Amusing to see you contrast me with Diane Ackerman. Another way we differ is that she's one of the Old Original Proust Boosters . . . She called to interview me back when she was writing ANHOTS but I demurred. Fairly or not, something about her rubbed me the wrong way and even then I knew I would someday write my own smell book. Anyway she got the last laugh by quoting me from an article in GQ! Ah, good times.

Regarding our views, I think "violent agreement" captures it well. Perfumers have normal noses like the rest of us--riddled with specific anosmias--but they have a flair for dealing with smell conceptually. Combined with extensive sensory training, they are able to accomplish what the rest of us can't. Trying to pin down the psychological dimensions of this talent is what got me interested in olfactory mental imagery and synaesthesia. I plan to blog soon on OMI.

FWIW Daredevil was blinded as a kid and developed a supersensitive nose by compensation. I seem to recall one frame where he tracks down a sniper by following the scent trail of the bullet. Now that's olfactory sensitivity!

+Q Perfume Blog said...

what about using zinc to improve the sense of smell?
also a fairy tale?

Ed C said...

I found this article on zinc nanoparticles as possible enhancers for smell
http://www.rsc.org/chemistryworld/Issues/2009/August/ColumnThecrucible.asp
I can only see the abstract of the original article on line. But the work was done on rats and not people.

Zinc nanoparticles are not the same thing as the organo-zinc compound that is used in Zicam and - possibly- causes anosmia.

This looks like a great topic for a new blog entry, Dr. Avery.