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Abstract:
Abstract: Medicine, 1300 Morris Park Avenue, Bronx, NY 10461
Medicine, 1300 Morris Park Avenue, Bronx, NY 10461 Medicine, 1300
Morris Park Avenue, Bronx, NY 10461 Detection of a rare deviant
sound within a sequence of repetitive standard sounds can be
performed sub-consciously and is indexed by occurrence of the
event-related potential (ERP) mismatch-negativity (MMN) component,
obtained while ignoring the sounds. However, the MMN to ignored
speech contrasts is typically small and variable, possibly
indicating diminished ability to passively discriminate speech
sounds. We tested whether passive speech discrimination, as indexed
by the MMN, improved when subjects listened to the sounds. Cortical
ERP elicited by trains of 7 vowels consisting of a repeated [e] and
a deviant [I] in position 5 or 6, were recorded from eight
normal-hearing adults. The subjects either mentally counted a small
number of target tones occasionally occurring among the vowels
('listen' condition) or read or watched a silenced movie ('ignore'
condition). Specific enhancement of the deviance-related negativity
(DRN) was noted in the 'listen' condition. Earlier components of
the deviant response and the standard response were not enhanced.
Topographic analysis suggested that the DRN enhancement was due to
differential activation of auditory cortex generators in or near
the MMN source, rather than to temporal summation of the
non-specific N2b component associated with conscious target
detection. This indicates enhancement of passive vowel
discrimination when listening to the sounds rather than ignoring
them.
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