Wednesday, November 21, 2012

Olfactory White: Whale or Minnow?









Peter Apps said...

I am just wondering, doesn't olfactory adaptation generate "olfactory white" when it makes a previously obtrusive odour sink into the general background after a few minutes of exposure ?

Peter Apps

Avery Gilbert said...

Peter Apps:

By analogy with visual white, which is composed of wavelengths from across the visible spectrum, olfactory "white" is composed of molecules with a wide range of odor characters. And, like the color white, or like white noise, olfactory "white" is very perceptible.

Olfactory adaptation, as you correctly note, reduces the perceived intensity of only the over-exposed molecule, making it harder to detect. So adapted odor and olfactory white odor aren't really parallels.

Your question does raise a fair point about Sobel's paper: they could have done more to describe what olfactory white actually smells like.

Peter Apps said...

My hand waving model is that Sobel's mixtures are simplifications of the chemical background (what Tristam Wyatt calls the chemical cacophony)which also contains compounds from all regions of odour space. In the chemical cacophony the concentrations of the individual components have not been carefully adjusted to bring them all to about the same odour intensity, instead the sensitivity of the nose to each adjusts itself by adaptation to bring each to a similar intensity, producing a white odour background against which a change in odour (that primitively signalled predator, food or sex etc) will stand out clearly. My hand-waving visual analogy is with putting on a pair of tinted spectacles - within seconds you cannot see the tint, or going into a tungsten-lighted room from outdoor sunlight.

Best regards Peter Apps

Avery Gilbert said...

Peter Apps:

OK, now I see where you’re going with this:

If olfactory adaptation tunes down each specific smell in the “chemical cacophony” around us to the same intensity level, then we should be smelling olfactory white (according to Sobel’s functional definition).

Yes, but . . .

what olfactory adaptation does is dial down the intensity of an on-going odor to the point where one is no longer aware of it.

In other words, sensory adaptation is about zeroing out background (to make new stimuli more detectable), not tuning all available stimuli to an equal level of perceivable impact.

This edges into cognition: e.g., being told a smell is toxic keeps us from adapting as quickly as we otherwise would.

Plus, the brain actively interprets and filters signals out of cacophony, which is why we can follow a conversation in a loud cocktail party even though the sonic frequency chart is chaotic.

The intense background odor at a typical fragrance company surprises first-time visitors. Yet perfumers make nuanced judgments in it all day long, by ignoring/tuning out/adapting to the background.

In my experience, this background smell—a mix of everything on the stockroom shelves—is consistent from company to company. Thus my speculation that Sobel’s olfactory white might be what some of us say “smells like the office.”

Peter Apps said...

Thank you for the feedback.

When you say;



I agree completely - I am suggesting that the mechanism of olfactory adaptation is the neurological complement of Weiss et al's dilution steps, and that perceptually the end results are the same; a bland, weak odour that is very difficult to describe and which is nearly impossible to differentiate from all the other background odours.

To use the office analogy; doesn't everyone's office smell the same to the people that sit in it all day, although they all smell different (for a few minutes at least) to a visitor ?

Peter Apps

Bharathi said...

If the olfactory white is due to the adaptive mechanism of the olfactory system, it also means that it cannot be used as a smell neutralizer in public washrooms. What other applications could it have?