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.
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:
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.