Re: Re. Bird Brains

[Mickey Rowe <rowe@psych.ucsb.edu>]

"Adrian Thomas" <adrian.thomas@zoology.oxford.ac.uk> wrote:

> when asked to pick it out [birds] move their heads until the image
> currently on the retina coincides with the memorised image. That is
> why biirds bob their heads, and peer at things through one eye with
> their head held still at an odd angle.

The subject of bird head-bobbing reared its, um... head here a few
months back in relation to a question of whether or not theropods
might have bobbed their heads when they walked.  If you weren't here
in September of 1999 you might want to look at messages with "Doin the
Theropod Nod" in the subject.  Anyhoo, I'd like to reiterate that
birds also move their heads in odd ways because they generally have
more areas of retinal specialization than we do.  Most birds have two
foveas in each eye, and at least some birds (e.g. the pigeon, _Columba
livia_) have large sections of their eyes dominated by particular
receptor subtypes.  When a bird looks at something from a different
direction it is not only getting a different geometrical perspective
-- it may be essentially looking at the object with a different set of
spatial and spectral filters.  I confess, that I'm not aware of Marian
Dawkins' work.  Adrian, do you know if/how this potentially
confounding factor was controlled for in these "snap-shot image
recognition" studies?

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)