Semi-Daily Journal

Brad deLong writes:

> She's learning that watching movies is an activity that
> takes place primarily in the visual cortext, while reading
> takes place primarily in the forebrain.

First, I would like to applaud Brad deLong for taking the study of cognition (and cognitive neuroscience) as seriously as he does. I think his is one of the few blogs where I have seen visual illusions brought up for discussion.

Unfortunately, I am short of time this morning, but I have to point out three infelicities of the quoted passage.
The first point is that when you say "the visual cortex" (note spelling) a lot of people might have a foggy image in mind of the visual cortex as the being this tiny sliver of the brain at the very back (in the occiptial lobe). As it turns out, that's sort of correct for *primary* visual cortex, but even there, the foggy notion is probably inaccurate since primary visual cortex (aka "V1") is very folded up and buried in a sulcus that isn't visible from the "outside" in the usual "brain shot" you see in textbooks. A related point is that we have now found and studied a lot more visual cortex than that, to the point that where neuroscientists like Marty Sereno would argue that about 50% of the cerebral cortex is at least moderately active under complex visual stimulation even during a passive viewing task. For that matter, both reading and watching video do a pretty good job of activating an extensive portion of the (greater) visual cortex.

A second point is that the term "forebrain" in neuroscience doesn't mean what I think deLong thingks it means (e.g., frontal or pre-frontal cortex), but would be used to refer to all of the cerebral cortex plus the thalamus and the hypothalamus. Now, the reason why this isn't pure pedantry is that we also now know that language processing involves a substantial amount of activity in the cerebellum, which is most emphatically not part of the forebrain and which before too long ago was basically thought to just be brain tissue that helped you walk and chew gum simultaneously or something. The story turns out to be way more complex than that, especially since the prefrontal cortex of primates (at least) has extensive direct connectivity with the cerebellum. Why this is true is, of course, an area of very active debate and research. One thing to point out, though, is that old textbooks will also tell you that the human brain contains about 10 billion neurons. That turns out to be an estimate for the cortex alone; the cerebellum by itself may have five times as many,

OK, so what I think Brad deLong really meant was that reading affords (or even encourages) a richer variety of so-called executive processes to be put into play; you aren't just a passive observer, but can alter a lot of things about your reading that make a big difference in what you get out of it. I think this is also already more true of watching video than you might suppose, and I think technology is going to help us close this gap even further. Lots of kids now are already very adept at using the remote to blow off commercials. PVRs like TiVo and DVD players now make it pretty easy to skip around in and between video streams. The next generation of kids is going to do things with these toys that will alarm their parents in the extreme.

Yikes; gotta go. But the point here is not that reading doesn't have a priviledged position among cognitive activities (it sure does, at least in *my* house :-)), but that we shouldn't be too glib about talking about these advantages or assigning them to neural structures.

Thanks, Johnathan. That was really great.

Thanks, Johnathan. That was really great.