It’s not a stereo effect. It’s a simple doubling of the scent receptors.
You make a reasonable argument.
And yet, I’ve never seen a discussion of a snake’s tongue or sense of smell that doesn’t mention the tips being used to perceive the direction of the scent. If this is an incorrect belief about snakes, then it seems to be extremely wide spread.
Yes of course. In actual fact people (and other animals) do instinctively move their sense organs in order to hear, see smell, etc, better. That is my point.
The “paradigm” I was referring to is one that infects popular science accounts of perception, and, until very recently, dominated the research literature too. Your actual perceptual behavior isn’t affected by it, but the behavior of science writers and actual scientists is. Experiments on human perception often went to great lengths to keep their subjects’ heads (and eyes, or whatever) still, and, inevitably, found that human perception in the lab was a lot less capable than it seemed to be in normal experience. For a long time the conclusion drawn was that normal experience must be wrong (like the famous, though apocryphal story of the bumblebee being unable to fly).
Actually, this sort of thing has still not died out, even in the research literature, but it is now, thankfully, under challenge and in retreat.
I think this answers dracoi’s point too.
Mind you, I am not saying that a snake derives no perceptual benefit whatsoever from having the relevant sensory organs separated at the ends of its forked tongue. I am just saying that this plays a relatively minor role in the snake’s spatio-olfactory perception compared to the role played by moving its head and tongue about. (And the same applies to the separation of nostrils, ears, and even eyes in other animals with paired organs, including humans.) When people make a big deal about the spatial-sensory role played by the anatomical separation of the organs, yet ignore the role of movement, they are (inadvertently) being quite seriously misleading.
Do you have any cites for the separation to play a relatively minor role compared to head movement for both vision and hearing? My understanding is that it is the combination of both factors. For example, there is a fairly significant minority of people who cannot watch 3D movies for too long without experiencing physical discomfort, including nausea, because of the sensory they get from receiving 3D information from the separation of the eyes, but not from turning their heads and other clues.
You have to keep in mind that as you turn your head, the separation effect remains and is integrated into the process.
Not only that, but the various senses complement each other in order to establish spatial perceptions.
Coming back to the question of separation of sensors, there is some information, such as high speed movement, where you cannot turn your head fast enough to compensate for lack of stereo viewing.
For audio spacial perception, there seem to be many factors, including changes in pitch, the difference between the sound being transmitted through the head vs. coming directly.
It’s my understanding that the audio spacial perception process is far too complex to be as definitive as you are in claiming one of the factors to be “minor.”
Also other evolutionary advantages:
- short, direct route to the lungs. If nostrils were spread out, you would need small tubes connecting each of them to the lungs. Hard to do in an already crowded skull.
- location near the mouth allows sharing the throat between the breathing and the eating systems. Less space needed in the neck.
- built-in redundancy: nostrils close together mean that both lungs can be supplied from either nostril (handy when one is congested). And being near the mouth means that if both are congested, humans can still survive breathing through their mouth.
It strikes me that odors are continual (over multiple seconds at least), wheras sounds can be one-time only or discontinuous things. Which would imply that it’s always possible to move the scent organ around to get directional info on smells, but for sounds that might not be an option.
Also, in the real world, wind affects scent a lot, so most of the time the direction of any scent farther than a few feet away is just ‘upwind’.
There was a study at Stanford that showed why we need 2 nostrils - read it here
It has to do with the two nostrils switching roles - one lets in air slower and the other faster - they switch roles throughout the day . The faster one absorbs the highly diffusive smells and the slower ones absorbs the slow diffusing smells thus giving us a complete spectrum of the smells.
If this is the only purpose of 2 nostrils - spacing them apart seems to add no value.