January 2007
Volume 20, Number 1
Presidential Column: The Eye of the Beholder
APS President Morton Ann Gernsbacher, University of Wisconsin-Madison
I’m at the 15th percentile in height for U.S. females — a ranking
I’ve held since birth. When I was growing up, there were certain occupations
(e.g., flight attendant and firefighter) for which my height rendered me ineligible,
and to this day I’m unable to reach the top shelf of most cupboards, grocery
store aisles, or overhead luggage bins. If I immigrated to Japan, I’d
rise to the 50th percentile, but if I immigrated to Holland I’d fall to
the 1st percentile.
Another way to think about my stature is that I’m at the 85th percentile
for shortness. I’m pretty facile at getting under limbo poles; I have
no qualms riding in the back seat of compact cars; and I’m chipper sitting
in coach class on long, transatlantic flights. My six-foot colleagues, who are
at the 12th percentile for shortness for U.S. males and below the 1st percentile
for U.S. females, are not nearly so san-guine in such situations.
Overhead bins and coach-class airline seats demonstrate the obvious: We differ
in height. Indeed, the average difference between males and females in height
is one of the very few sex differences on which we all can agree.
Another morphometric sex difference has recently been reported: On average,
females have thicker cortices than males — or put an-other way, males
have thinner cortices than females (Im et al., 2006; Luders et al., 2006; Preul
et al., 2006; Sowell et al., 2006). A typical effect size (across each cortical
hemisphere) is .8 of a standard deviation, which increases to 1.4 standard deviations
when scaled for total brain size (because females have smaller brains).
What’s better, having a thicker cortex or a thinner cortex? It depends
on who you ask. Some researchers have claimed that thicker cor-tices are “an
indicator of integrity of cytoarchitecture in the cortex” (Makris et al.,
2006; Goghari et al., 2006), “a general sign of cogni-tively beneficial
neuroanatomical characteristics” (Walhovd et al., 2006).
But other researchers have claimed that thicker cortices are “abnormal”
(Hardan et al., 2006), due perhaps to a “failure to myelinate” (Thompson
et al., 2005) or “exuberant arbourization” (Rauch et al., 2004).
It also depends on who you are.
If you’re a typically developing child between the ages of 8 and 20, age-related
thinning of the cortex is considered “eliminating ineffi-cient or unnecessary
dendritic connections” to allow “more effective, accurate synaptic
transmission” (O’Donnell et al., 2005). But if you’re a typically
developed adult between the ages of 18 and 93, age-related thinning of the cortex
is considered “atrophy” (Salat et al., 2004).
If you’re a child gaining motor skills over a two-year period, having
a thinner cortex is considered good; if you’re a child gaining pho-nological
processing skills over a two-year period, having a thicker cortex is considered
good (Lu et al., 2006). If you’re an adult with ex-perience in meditation,
having a thicker cortex than an adult without experience in meditation is considered
good (Lazar et al., 2005); if you’re an adult recovering from a stroke,
having a thicker cortex than an adult not recovering from a stroke is considered
good (Schaecter et al., 2006).
But if you’re autistic,1 having a thicker cortex than someone who is not
autistic is considered bad (Hardan et al., 2006) — and having a thinner
cortex than someone who is not autistic is also considered bad (Chung et al.,
2005; Hadjikhani et al., 2006a, 2006b). Your thicker cortex might be a function
of higher fluid intelligence (Dawson et al., 2006; Fjell et al., 2006); your
thinner cortex might be a function of better memory retrieval (Sowell et al.,
2001). It doesn’t matter: If you’re autistic, having either a thicker
or thinner cortex is just considered bad.
Indeed, if you’ve been diagnosed with specific attention deficit, animal
phobia, bipolar, Williams Syndrome, or schizophrenia, having a thinner, thicker,
thinner, thicker, or thinner cortex, respectively, is considered bad, bad, bad,
bad, and bad, respectively (Shaw et al., 2006; Rauch et al., 2004; Lyoo et al.,
2006; Thompson et al., 2005; Kuperberg et al., 2003, respectively).
This confluence of results could be due to different measurement algorithms
(Fischl & Dale, 2000; Lerch et al., 2005), across a variety of cortical
regions, and some studies could be tightened with better between-group matching
for factors such as total brain size, measures of cognition, even height(!).
But what is striking is that not one of the between-group differences, which
have been pathologized, is more pronounced than the difference between “normal”
males and “normal” females.
For some differences, their value lies in the eye of the beholder (http://en.wikipedia.org/wiki/The_Eye_of_the_
Beholder).
References
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Morton Ann Gernsbacher is the Vilas Research Professor and Sir Frederic C. Bartlett Professor of Psychology at the University of Wisconsin-Madison. She can be reached via email at mgernsbacher@psychologicalscience.org.
1 See Sinclair (1999; http://web.syr.edu/~jisincla/person_first.htm) to appreciate my respectful use of the term “autistic” rather than “person with autism.”
