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Abstract:
Abstract: It is well known that the acoustic cues to the
perception of speech sounds vary as a function of the phonetic
context of their presentation. For example, a rising and falling
second-formant transition both serve as acoustic cues to /d/
depending on whether the following vowel is /i/ or /u/,respectively
(Liberman, 1970). This robust behavioral finding points to the lack
of invariance in the speech signal such that there is no one-to-one
correspondence between an acoustic cue and the speech sound it
represents. The objective of the present study was an
electrophysiological investigation of this phenomenon. To this end,
varying combinations of stop-consonant speech sounds (/ba/, /da/,
/ga/) were presented using an oddball paradigm, to ten normal
adults, under passive listening conditions. We found that the
event-related potentials in response to each speech sound reflected
a pattern of obligatory responses (P1, N1, P2) similar to that
elicited by the sound with which it was paired. More specifically,
the same sound elicited characteristically different waveforms as a
function of its phonetic environment. Surprisingly, this effect was
evident regardless of whether the sound served as a standard or
deviant in the oddball presentation. Implications of these findings
for understanding the neural mechanisms of speech perception
processes will be discussed.
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