Right-footed parrots offer pointers on how the mind organizes language.
"Nous parlons avec l'hemisphere gauche!" ("We speak with the left hemisphere!") declared the French neurologist, Paul Pierre Broca in 1864. The halves of the brain watch over distinctly different tasks and, as Broca noted, speech is the provenance of the brain's left side. A century and a half later, that principle of brain function remains largely true--that is, unless you happen to be left handed. Unlike righties, some left handers use parts of their right brain for processing language.
Are these fundamental asymmetries in brain function a peculiarity of humans
or do their roots lie deep in the evolutionary history of the mind? Intrigued
by that question, Peter Snyder, a neuroscientist at Allegheny General Hospital
in Pittsburgh, went looking for a suitable animal model. Just down the street
at the National Aviary, Snyder found some perfect candidates: parrots. Right
footed African Grey parrots, Snyder says, know more words than their lefty brethren.
Here then might lie a clue to the brain's odd division of labor.
For 300 years people have noted the parrot's dexterity and tendency to favor
one foot over the other when handling food, Snyder reports. But all of the scientific
attempts to quantify this behavior were deeply flawed. Snyder therefore began
by developing the largest and most accurate study to date of parrot footedness,
encompassing the pedestrian habits of more than 500 birds. He created questionnaires
describing a set of experiments and strict guidelines for carrying them out;
he then published these both in bird magazines and on the Internet. From the
responses, Snyder concluded that parrots in general show a tendency toward left
footedness. Among one species, the Australasian Cacatuinae (cockatoo), 82% of
the birds are left-footed--close to the percentage of humans who are right handed.
That degree of lateral preference is unknown in any other vertebrate animal,
including our primate cousins.
Hoping to find a link between brain function and footedness, Snyder focused
on the best avian articulators around, the African Greys. Parrot owners reported
on the size of their Psittacinan sidekicks' vocabulary, providing lists of up
to 300 words. Amazingly, the right-footed birds had memorized a significantly
larger number of words than their left-footed counterparts. Even after adjusting
for age and for how pushy the owners were about teaching them to talk, right-footers
won wings down.
As in humans, the left side of a bird's brain controls the right side of its
body, and vice-versa. Likewise, studies in chickens show that avian memory for
categories (like words) resides in the left hemisphere. Snyder therefore suggests
that "right footedness might be a behavioral measure of preferential activation
of the contralateral (left) hemisphere." Until now there was little evidence
of a connection between motor dominance and higher cognitive functions in any
animal other than humans.
The evident link between foot preference and language skills in parrots is
especially striking because avians split off from our branch of the evolutionary
tree some 150 million years ago. Perhaps birds and people have followed a strangely
parallel evolutionary path, Snyder notes, or else they share brain asymmetries
inherited from an even older ancestor. Either way, he believes that the new
findings will improve scientists' understanding of why our brains are organized
they way they are, and of how brains adopt a preferred handedness during fetal
development. Such information could lead to new insights into the nature of
brain disorders, such as those associated with strokes and epilepsy.
Snyder plans to extend his work by directly measuring parrots' mnemonic abilities--testing
their ability to distinguish objects by color and shape, for instance, or to
count a number of objects. Such experiments have been successfully done on primates
and on one famous research parrot, Alex, but testing a large sample of parrots
will be difficult. Until now, "I don't think anybody's been crazy enough to
do this test with 80 to 100 birds," he says. "I think I may be that crazy person."
--Samuel K. Moore Posted 2/23/1998
(c) Copyright 1998 The Walt Disney Company.