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SPOKEN WORD ACCESS PROCESSES (SWAP)May 29-31, 2000 |
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SPOKEN WORD ACCESS PROCESSES (SWAP)May 29-31, 2000 |
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A widely held view for many years was that listeners derive an abstract
phonetic representation during speech processing and, in so doing, discard
detailed information about the signal. However, more recent research has
shown that the representations of speech are richer than this emphasis
on abstract categories would suggest, and that listeners retain in memory
a substantial amount of fine-grained information. One line of evidence
for this new view comes from research showing that phonetic categories
are internally structured in a graded fashion, with some members of the
category perceived as better exemplars than others. In this talk I will
briefly review some findings that demonstrate basic characteristics of
such structure and then present results from two new sets of studies that
further examine this structure and its role in processing. In both sets,
we examined the syllable-initial voicing distinction specified by voice-onset
time (VOT), with a specific focus on the voiceless category. The first
set of studies, which used a category-goodness rating task, investigated
how a higher-order linguistic contextual variable, lexical status, affects
the internal structure of the category. We knew from previous work that
acoustic-phonetic contextual factors (e.g., speaking rate) alter not only
perception of stimuli in the category boundary region, but also which stimuli
are perceived as the best category exemplars. The new results showed that
lexical status has a qualitatively different effect: Although a change
in lexical status also altered perception of stimuli in the category boundary
region, the best exemplars of the category remained relatively fixed. Thus
contextual variables that have comparable effects in the boundary region
can in some cases be dissociated with respect to their effects on a category's
best exemplars. The second set of studies, which used a speeded categorization
task, examined how differences in perceived category goodness affect the
speed of phonetic categorization. The results showed that although categorization
time was relatively slow for poor exemplars in the voiced-voiceless boundary
region, poor exemplars with VOT values longer than the best exemplars (and
thus far from the category boundary) were identified as quickly as the
best exemplars themselves. This suggests that categorization time depends
more on an exemplar's location in perceptual space vis-à-vis a boundary
with a competing category than on its perceived category goodness. Taken
together, the new findings underscore the importance of considering both
internal category structure and phonetic category boundaries when developing
models of phonetic categorization.
Bibliographic reference. Miller, Joanne L. (2000): "Mapping from Acoustic Signal to Phonetic Category: Nature and Role of Internal Category Structure", In SWAP-2000, 183-186.