Re: Study shows brain can learn without really trying

From: Dace (edace@earthlink.net)
Date: Fri Nov 30 2001 - 02:42:30 GMT

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    From: "Dace" <edace@earthlink.net>
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    Subject: Re: Study shows brain can learn without really trying
    Date: Thu, 29 Nov 2001 18:42:30 -0800
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    Vincent:

    > <I did accept at
    > > least one argument against Sheldrake, regarding the ability of birds and
    > > fish to see 360 degrees around. However, it turns out they actually
    can't
    > > see all around them, as I discovered later. Didn't need to yield on
    that
    > > one after all.>
    > >
    >
    > Birds don't need to see directly behind them, because flying
    > immediately behind another bird is no good aerodynamically (much harder to
    > fly in the disturbed air). For aerodynamic purposes then, birds fly to
    one
    > side of each other (the classic case being the flying V of Geese), which
    > puts birds well within their field of vision, which is indeed not 360, but
    > far greater than ours. I don't know but I'd venture the same general
    point
    > probably applies to fish. I think it was disputed, but I recall a misread
    > of a piece about Cichlids as well.

    Disputed, exactly. The authors of that piece never demonstrated how
    environment determined color patterns on the cichlids' scales. I never made
    any claims regarding the traits that could be explained by natural
    selection.

    As to the geese, no, they cannot see birds flying in formation behind them.
    Sheldrake passed this on to me when I queried him about it:

    >>>
    Canada geese, for example, have a visual field for each eye of 135, with a
    40 overlap in front of the head. In other words they have 40 binocular
    vision . They also have a blind area at the back of the head of 58.
    (Heppner, F.H., Convissar, J.L., Moonan, D.E. and Anderson, J.G.T.
    (1985)Visual angle and formation flight in Canada geese (Branta canadensis).
    Auk, 102, 195-198). They cannot possibly see anything in this blind zone:
    the back of the head blocks the view, just as the backs of our heads block
    our view behind, however much we try to look backwards by swivelling our
    eyes. Geese generally fly in V formations, and the angle of the V is often
    around 30 to 40. (L.L. Gould and F.H. Heppner (1974) The vee formation of
    Canada geese. Auk 91, 494-506) This means that geese are able to see the
    birds in front of them, but not those in the line behind them, unless they
    turn their heads by about 45. Nevertheless, flocks that fly in Vs, as many
    geese and ducks do, can still be coordinated visually by following the
    leader.
    >>>

    Ted

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