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Abstract:
Recognition of a word is correlated with its
uniqueness point, i.e., when in a word phonetic input
disambiguates that word from its lexical alternatives.
Recent work in phonetics demonstrates consistent effects of
position in a prosodic domain on the initial portion of a
stressed syllable [1]. In strong positions, vowels are
lengthened, especially for monosyllabic words, and
co-articulation is strongly reduced compared to weak
positions. For cohort pairs such as beaker and beetle,
these changes would be expected to delay the point of
disambiguation, resulting in longer lasting lexical
competition. However, for onset-embedded words such as
doll-dolphin and pen-pencil, prosodic strengthening would
exaggerate differences in vowel duration, making it a stronger
and more reliable cue distinguishing between a monosyllabic word,
such as doll, and a disyllabic competitor, dolphin [2, 3].
An analysis of 8 native speakers confirmed large
and systematic differences in vowel duration for 24 pairs of
embedded words, such as doll and dolphin in weak (medial) and
strong (phrase final) prosodic domains (Put the dolphin/doll
below the triangle and Now, click on the doll/dolphin,
respectively). Vowel differences between monosyllabic and
disyllabic words averaged 30 ms in medial position and 90 ms in
final position, with most of the effect due to large increases in
vowel duration for monosyllabic words in utterance-final
position.
We then monitored eye movements using recordings
from a representative speaker as participants followed
instructions to click on (Now click on the doll/dolphin) or move
(Put the doll/dolphin below the triangle) objects. Displays
contained four pictures: a doll, dolphin, and two unrelated
pictures. Although the phonemic point of disambiguation
occurred 100 ms later in utterance-final position compared to
utterance-medial position, looks to the target and cohort
diverged more than 100 ms earlier, demonstrating that listeners
were using vowel duration information to help disambiguate
between the target and its competitor. This was confirmed
in a second experiment where we used cross-spliced tokens in
strong prosodic domains (e.g., doll from dol/phin and doll+phin
(from dolphin). Misleading vowel information dramatically
increased cohort effects and delayed the point where looks
diverged between targets and cohorts.
The results demonstrate that vowel duration is
used as an on-line cue to help disambiguate between polysyllabic
words and onset-embedded competitors. More importantly, the
results suggest that models of lexical access will need to take
into account information about prosodic domains.
References
[1] Fougeron, C., &P. Keating (1997).
Articulatory strengthening at edges of prosodic domains.
Journal of the Acoustical Society of America, 101,
3728-3740.
[2] Davis, Marslen-Wilson, & Gaskell, (in
press). Leading up the lexical garden-path: Segmentation
and ambiguity in spoken word recognition. Journal of
Experimental Psychology: Human Perception and Performance.
[3] Salverda, A P., Dahan, D., & McQueen, J.
(2001). Effects of vowel duration on the processing of
onset embedded words.
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