ocular dominance and input

[Brian MacWhinney]

Dear Gary, Ping, and Info-CHILDES,

  The Hubener and Bonhoeffer article from Nature Neuroscience that you cite
is the commentary article that interprets the Crowley and Katz article that
appears later in the issue.  The Crowley and Katz works does indeed show that
the ocular dominance columns can form in an almost normal way without visual
input.  Gary says that this work shows that "Learning must play some role in
fine-tuning things, but the basic structure seems to be available prior to
(womb-external) experience."  I would not interpret either Crowley and Katz
or Hubener or Bonhoeffer as saying this.  This is not a debate about
learning.  It was about whether the wiring of V1 is triggered by mere
connectivity or by connectivity plus activation.  In both scenarios, the
foromation of ocular dominance columns is not the responsibility of genetic
mechanisms, but of the topography of connections between V1 and the LGN.

  Hubener and Bonhoeffer state that, "Because so many experiments
demonstrated that visual experience can influence the layout of cortical
maps, it became widely accepted that vision might actually be instrumental in
their establishment." (p. 1043)   What this gloss leaves out is the role of
the interesting neural network simulations of Miller, Stryker and their
students which show that the emergence of the ocular dominance columns can
arise through competition between the two ocular pathways for projection to
uncommitted neural territory in V1.

  So the real question is not about learning vs maturation, but about whether
competition is grounded on connection (Crowley and Katz) or requires
connection and activation (Stryker & Harris and others).  It seems to me that
the Miller and Stryker analysis goes through just fine even with the Hubener
and Bonhoeffer result.  However, it is certainly interesting to know that
mere connectivity alone is enough to organize ocular dominance columns.
Eventually, this work could tell us something about the molecular basis of
competition for connectivity.

  So, like Ping, I take this Crowley and Katz work as a further elaboration
on Chuck Nelson's point.

  Now, for the real question, what does all of this have to do with language
development?

--Brian MacWhinney