Regarding Why do pigeons bob their heads?
In another thread, someone mentioned neural adaptation as the reason our eyes bounce around a lot, appear to jitter. Our brains compensate for this and give us a steady, clear image, even though our eyes are bouncing around a tiny bit, probably several times a second.
I’m wondering if this might be one reasons pigeons bob heads? To re-stimulate their saturated visual neural adaptation?
This is backwards. We do not have, or need, any “steady clear image” inside our heads in order to see properly, and our eyes do not bounce about by themselves such that the brain needs to compensate for it. Rather, the brain causes the eyes to move around (normally several times per second, as you say), in order to find the information that it wants. If we did not move our eyes we could not see (certainly not nearly as well as we do). Eye movements probably serve a number of purposes in vision, but one of then arises from the fact that, because of the way the retina is structured, the eye can only detect fine detail in a very small part of the visual field (about 2 degrees of visual angle). Thus you basically have to be looking right at something to see it clearly. This is not normally apparent, however, because moving your eyes is very quick and easy, and as soon as anything moves in your peripheral visual field (where we can detect movement quite well, but not much else) you will probably turn your eyes towards it and see clearly what it is.
We do not see images inside our heads (there are some images in there, but they are not what we see, they are just part of the processing), we see the outside world, and it appears stable not because our brains “compensate” for the movements of some image jiggling about inside our heads, but because (for the most part) it actually is stable when we are looking at it.
How this might relate to pigeon head bobbing, I am not sure. I do not know if they are doing it for visual reasons. However, there is a case in the scientific literature of a woman whose eye muscles are paralyzed. In order to have viable vision, she has to constantly make little jerky movements of her head to produce an effect something like normal eye movements. On this see http://journals.royalsociety.org/content/bp32fug91pvm838n/?p=eacc7eb9d7674b8fb78838a70994a1b4&pi=1
On the role of eye movements in vision more generally, much of the relevant material will only be available through academic libraries, but here are some links to freely available stuff (most are pdfs):
Scientific American article:
http://smc.neuralcorrelate.com/files/inpressfiles/sciam_0708.pdf
For some theoretical background presented in a relatively non-technical way:
http://nivea.psycho.univ-paris5.fr/ASSChtml/ASSC.html
More technical articles:
From Encyclopedia of Biomaterials and Biomedical Engineering (why I don’t know, but it is a good article on the study of eye movements):
http://www.eyethink.org/publications_assets/EyeTrackingEBBE.pdf
From Nature Reviews Neuroscience:
http://smc.neuralcorrelate.com/files/publications/macknik_martinez-conde_nrn08.pdf
Trends in Cognitive Sciences:
http://www.cps.utexas.edu/Research/Hayhoe/PDF%20files/hayhoe.pdf
njtt seems to be talking past you.
Anyway, I think head-bobbing is way too big a movement than is necessary to stimulate neurons. I’m firmly in the parallax crowd.
Why do pigeons bob their heads?
Because they wish to be more like a good woman?
There seems to be some confusion about one point: pigeons bob thier head in order to stabilize their gaze by having the head stable in space between the bobbing motions.
The gaze does move a lot, indeed. As njtt nicely explained, we constantly look a t the word thurh a succession of quick eye movements (saccades). However, good visual acquity requires that our eyes remain stable the rest of the time. This is what gaze stabilization reflex such as vestibulo-ocular reflex do.