In his own (with colleagues) EEG studies,left-handers fell into three
groups: those whose cortical organization is like right-handers, those
whose organization is reverse, and those who have language and spatial
abilities in both hemispheres.
Does that mean they learn differently? He didn't really address that
except for noting that one group of lefties do have more problems in
learning and coordination (see below). Interestingly, there is a tendency
for some activities to have a greater proportion of lefties (as compared to
the general population), e.g., fencing, chess, math, art, and architecture.
And since left-handers tend to be more ambidextrous, there's a tendency for
them to excel in some sports like soccer. (Although noting these
tendencies, Ornstein emphasizes how little difference there is between
normal lefties and righties.)
On the addiction connection, Ornstein says that "in almost any group of
people with psychological problems, there are more left-handers than
normal" (p. 156). It seems, he says, that this is because there are two
sources of left-handedness: genetic and brain damage. If it's genetic,
then there shouldn't be any differences in health problems, but brain
trauma/damage especially while in the womb or during birth can affect
different parts of the brain which in turn can cause a change from
right-handedness to left-handedness. It's this group of lefties that
suffer from extra health problems, including among others alcoholism. And
when this group is added to the genetic group, their average of
health/psychological problems is a little higher than that of righties.
For other sources, Ornstein cites 5 studies of M. Annett, and for accident
proneness, he mentions S. Coren's work.
Charles Nelson
c.nelson who-is-at mail.utexas.edu