rooms, pictures, faces, and so on. People have looked for evidence of the
"funneling" of many low-level neural responses into fewer and fewer
higher-level ones, culminating in something such as the proverbial grand-
mother cell, or some kind of multineuron network, as mentioned above. It
is evident that this will not be found in some gross anatomical division of
the brain, but rather in a more microscopic analysis.
One possible alternative to the the grandmother cell might be a fixed
set of neurons, say a few dozen, at the thin end of the "funnel", all of which
fire when Granny comes into view. And for each different recognizable
object, there would be a unique network and a funneling process that
would focus down onto that network. There are more complicated alterna-
tives along similar lines, involving networks which can be excited in differ-
ent manners, instead of in a fixed manner. Such networks would be the
"symbols" in our brains.
But is such funneling necessary? Perhaps an object being looked at is
implicitly identified by its "signature" in the visual cortex-that is, the
collected responses of simple, complex, and hypercomplex cells. Perhaps
the brain does not need any further recognizer for a particular form. This
theory, however, poses the following problem. Suppose you are looking at
a scene. It registers its signature on your visual cortex; but then how do you
get from that signature to a verbal description of the scene? For instance,
the paintings of Edouard Vuillard, a French post-impressionist, often take
a few seconds of scrutiny, and then suddenly a human figure will jump out
at you. Presumably the signature gets imprinted on the visual cortex in the
first fraction of a second-but the picture is only understood after a few
seconds. This is but one example of what is actually a common
phenomenon-a sensation of something "crystallizing" in your mind at the
moment of recognition, which takes place not when the light rays hit your
retina, but sometime later, after some part of your intelligence has had a
chance to act on the retinal signals.
The crystallization metaphor yields a pretty image derived from statis-
tical mechanics, of a myriad microscopic and uncorrelated activities in a
medium, slowly producing local regions of coherence which spread and
enlarge; in the end, the myriad small events will have performed a com-
plete structural revamping of their medium from the bottom up, changing
it from a chaotic assembly of independent elements into one large, coher-
ent, fully linked structure. If one thinks of the early neural activities as
independent, and of the end result of their many independent firings as
the triggering of a well-defined large "module" of neurons, then the word
"crystallization" seems quite apt.
Another argument for funneling is based on the fact that there are a
myriad distinct scenes which can cause you to feel you have perceived the
same object-for example, your grandmother, who may be smiling or
frowning, wearing a hat or not, in a bright garden or a dark train station,
seen from near or far, from side or front, and so on. All these scenes
produce extremely different signatures on the visual cortex; yet all of them
could prompt you to say "Hello, Granny." So a funneling process must takeBrains and Thoughts 347