Sign activates the auditory area.

[Robert Ingram]

Actually, Jerison (1973) argued that human language would not have evolved were
it not for the emergence of a highly developed visual system in mammals.

Bob Ingram

Eric Gumpert wrote:

> Alternately, if there were proof that during, say, the performance of spoken
> English, the visual cortex were activated--that would be further proof that
> English is a fully developed linguistic system.