It refers to a predilection or bias to, or predomination by, one side or the other, not exclusive use of course.
Yes, my reply was intended to contemn the concept. A very close friend whose left hemisphere is significantly physically damaged functions with a dominant right hemisphere in a way that would seem to fit the "left brain" stereotype. All generalizations are stupid.
That happens because the brain is able to rewire itself. It doesn't mean there is no such thing as right or left brained. Nobody is saying that one side does everything and can't ever do things the other side normally does. But it remains true that the right side is
predominately responsible for some functions and the left side for others, in normal working brains.
I take it your self-referential statement disparaging generalisations is meant to be ironic?
