distributed representations

[Elizabeth Bates]

I respectfully disagree with Max Coltheart that brain damage usually or even
often yields discrete and domain-specific performance decrements.  to be
sure, such cases have been reported -- and indeed, their "news value" often
lies in the surprisingly discrete nature of the patient's profile.  but
such case studies typically fail to recognize issues like the peaks and
valleys that might have been there premorbidly, i.e. in the "man that used
to be".  also, we often fail to recognize that by choosing those patients
with "interesting" profiles against an unspecified number of background
patients with "uninteresting" profiles, we are capitalizing on chance
distributions across a number of noisy domains.  given 1000 patients
who are normally distributed across 100 tasks, I have a pretty solid
chance of finding a good number of striking "double dissociations" and
even more "single dissociations" entirely by chance.  For a simulation
that makes EXACTLY that point (coupled with a detailed critique of a
"real" study of 20 patients that make this very error), see Bates,
Appelbaum and Allard, "Statistical constraints on the use of single
case studies in neuropsychological research", in the last issue of
Brain and Language. -liz bates