Supratemporal Dissociations

by Eric Frye

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The utility of entrainment is thought to be the organization of transient excitability states within neuronal
populations
68

72
. Discrete high excitability periods constitute “windows of opportunity” for
input in
to
sensory
cortex,
as
evidenced by peri
-
threshold detection studies in somatosensory
73
, visual
33,74,75
, and auditory
46,60,76
regions.
During listening,
such
windows might
serve to
segment speech to facilitate comprehension
77
. More
generally, the temporal organization of high excitability periods could serve to minimize temporal uncertai
nty in
stimulus processing and detection
7,78

80
. This view was corroborated by
a
behavioral
study of
responses to the
same white noise
stimulus used in these experiments
that
revealed a striking relationship between detection
accuracy and the preceding rhythmic stimulus
81
. With direct intracranial recordings, we found
that
low
-
frequency phase reset
anticipates
the first “missing” acoustic edge.
These results constitute
strong evidence for neural mechanism
s
in early auditory cortex supporting
entrainment and prediction,
both
fundamental computational element
s
in models of speech perception
4,8,9,22
.
T
he characteristics of these mechanisms
contrast with the
presumption
of “a principled relation between the
time scales present in speech and the time constants underlying neuronal cortical oscillations that is both a
reflection of and the means by which the brain converts speech rhythms into linguistic segments”
4
supported
by “cascaded cortical oscillations”
8
or a “hierarchy of nested oscillations”
9
.
O
ur results
are
instead consistent
with
the predictive encoding of “when” by a bandlimited complex of discrete
computational channels
, each
arising from distinct patterns of hi
erarchical cortical connectivity
22
.

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released January 6, 2019

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