HOW THE BRAIN MAKES POTENTIAL 183I continue to use the notion of “grammars” from time to time in what
follows. For the moment, note again that, induced from experience, they
will vary enormously across individuals and groups. Th ey will also be the
bases of vast individual diff erences in perception, cognition (see chapter 7),
and be hav ior. Th is puts into perspective the idea that, by testing for
highly specifi c expressions of these (as in most intelligence tests), psychol-
ogists are somehow describing individual diff erences in brain power. We
might as well claim that a test of standard En glish can describe individ-
ual diff erences in language ability anywhere around the world.
THE BRAIN GENERALLYAlthough I have concentrated so far on vision, similar princi ples seem to
apply with other sense modes. For example, it is known that receptors in
the cochlea of the ear transform sound into spatiotemporal response pat-
terns sent along the auditory nerve to the brain. Tactile senses, too, are
able to abstract the deeper statistical structure from the sequences of vi-
brations produced by a roving fi n ger tip. Studies with bats and owls show
how they use the spatiotemporal correlations in acoustic patterns to com-
pute the location and distance of prey. Shaowen Bao has reviewed a num-
ber of recent fi ndings on how the “statistical structures of natu ral animal
vocalizations shape auditory cortical acoustic repre sen ta tions.”^17
In fact, direct recordings from auditory neurons confi rm that they are
highly sensitive to correlational structure in inputs. As one report ex-
plained, “Natu ral sounds are complex and highly structured stimuli. A
number of studies carried out on the auditory systems of insects, lower
vertebrates and mammals have yielded evidence for evolutionary adap-
tations which exploit statistical properties of the natu ral acoustic envi-
ronment in order to achieve effi cient neural repre sen ta tions.”^18 As with
vision, the full structure emerges progressively as auditory information
travels through the auditory tract to primary auditory cortex.
Again, however, further clues come from the use of naturalistic audi-
tory inputs. Neuronal responses in auditory cortex are highly context
dependent and “constantly adjust neuronal response properties to the sta-
tistics of the auditory scene.”^19 Somewhat similarly, the study of rhythm,
This content downloaded from 139.184.14.159 on Tue, 17 Oct 2017 13:54:00 UTC