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1
Perceptual compensation for /u/-fronting in
American English KATAOKA, Reiko
(kataoka_at_berkeley.edu)Department of Linguistics,
University of California at Berkeley, 1203
Dwinelle Hall, Berkeley, California 94720-2650
Summary and Discussion
Materials and Methods (cont.)
Results Experiment 2
Introduction
Materials and Methods (cont.)

• Listeners heard an ambiguous stimulus more often
  as /u/ in Alveolar than in Bilabial or Zero
  context, and did so both in Acoustic and Restored
  phoneme conditions (Experiment 1). Also, the /u/
  identification function shifted as a function of
  consonantal context (Experiment 3). These
  results confirm listeners ability to
  perceptually compensate for coarticulatory
  fronting of /u/ in alveolar contexts by shifting
  the category boundary. It also seems to show
  listeners ability to utilize mentally stored
  acoustic images of linguistic contexts to perform
  compensation.
• Alveolar context shortens the RT for
  /u/-identification (Experiment 1 2). This
  suggests that the perceptual system not only
  shifts the perceptual category boundary but also
  to facilitate perceptual processing for a
  category that is contrastive to the context.
• Speech rate of precursor influenced vowel
  identification in Bilabial and Zero context
  (Experiment 2), suggesting the listeners ability
  to perform not only categorical but also gradient
  compensation. The effect was absent in Alveolar
  context. This could be due to ceiling effect in
  this particular experimental setting. This
  effect needs to be re-examined by using an
  improved method.
• Mild correlation was found between /u/
  identification in perception and F2 measured from
  /u/ production (Experiment 3). Among those who
  produced /u/ with relatively low F2 (back /u/),
  many also accepted fronted /u/s as category
  members in perceptual vowel categorization task.
  Although previous studies (e.g. Harrington et.
  al., 2008) demonstrated robust link between
  production and perception, language users seem to
  be much more tolerant to speech variation (e.g.
  dialects, sociolects, style shifts, etc.) that
  differs from their own production patterns.

Listener's identification of speech sounds are
influenced by both perceived and expected
characteristics due to the influence of
surrounding sounds. For example, a vowel
ambiguous between /i/ and /e/ is heard more often
as /e/ when the precursor sentence has low F1 but
it is heard as /i/ when the precursor has high F1
(Ladefoged Broadbent 1957), and a greater
degree of vowel undershoot is perceptually
accepted in fast speech than in slow speech
(Lindblom Studdert-Kennedy 1967). Later,
Ohala and Feder (1994) showed that American
listeners judge a vowel stimulus which is
ambiguous between /i/ and /u/ more frequently as
/u/ in alveolar context than in bilabial context,
and do so both when the context is heard and when
it is restored. The current study is an
attempt to extend Ohala Feders study with
additional measures to reveal the locus of
perceptual compensation in the human speech
processing system.

• Presentation
• A stimulus was played after a precursor I guess
  the word is.
• Each stimulus was tested 5 times.
• Fillers (CiC, C?C, CuC, and C?C, each
  three times) were mixed in the trials to create
  genuine vowel quality variation.
• Test stimulus and fillers were presented at
  random order.
• During a trial, the two alternative words (/CiC/
  and /CuC/ forms) appear on the screen. (See Table
  1.) The words on the screen will make subjects
  to restore the onset and coda phoneme even when
  hearing the stimulus with white noise.
• Task Two-alternative forced-choice. The
  subjects determined which of the two words on the
  screen the word just heard was.
• Subjects 31 native speakers of American English
  (10-M, 21-F)
• Factors
• Consonantal context (3 conditions Alveolar,
  Bilabial, Zero)
• Status of context (2 conditions Acoustic or
  Restored)
• Table 1. Factors tested, stimuli presented (e.g.
  dyt), and two alternatives shown on the screen
  for each stimulus.

Table 3. of responses by Context and
Condition (5 repetition X 31 listeners 155 cell
total)

• Stimuli 3 continua of 10 syllables each,
  varying by vowel backness (i.e., /dit/ - /dut/,
  /bip/ - /bup/, and /i/ - /u/ continuum) were
  created by the following process
• Create 10 equal-step /i/ - /u/ continuum. The
  voice source was extracted from a sustained
  vowel, which was produced by the speaker of a
  precursor sentence, by applying an inverse
  filtering of LPC object of the vowel so that the
  voice of the stimuli matches to the voice of the
  precursor. All 10 vowels have identical formant
  structures except for F2 value, which varied from
  2,300 Hz (step 1) to 860 Hz (step 10). See Fig.
  2.
• Add amplitude contour and F0 contour as in Exp.1.
• Add onset and coda consonant bursts as in Exp.1.
• Presentation and Task Same as Experiment 1
  except that each stimulus was tested 4 times.
• Subjects Same as Experiment 1.
• Factor Consonantal context (3 conditions
  Alveolar, Bilabial, Zero).

Objectives

• To replicate Ohala Feders findings and further
  investigate the context effect on Reaction Time
  (RT) (Experiment 1)
• To test the effect of speech rate on the degree
  of perceptual compensation (Experiment 2)
• To investigate the relationship between speech
  production and perceptual compensation
  (Experiment 3)

Results Experiment 1
Effect of Context Fast F6.0 (2, 48),
plt0.05 Med F9.3 (2, 52), plt0.001 Slow
F10.2 (2, 60), plt0.001
Table 2. of responses by Context and
Condition (5 repetition X 31 listeners 155 cell
total) Chi-Square test for association
of /u/-response and Contexts Acoustic Condition
?23.429 (2), p0.180 Restored Condition
?20.612 (2), p0.736
Figure 4. Reaction Time for /u/ response.
Materials and Methods
Results Experiment 3

• EXPERIMENT 1
• Stimuli Re-synthesized syllables dyt, byp,
  and y (to be used in Acoustic condition) and
  another set where white noise replaced the
  consonants (to be used in Restored condition)
  were created by
• Iterating single vowel period in the CV
  transition of dude to obtain a steady vowel
  (i.e. no formant transition) of 100 ms
• Adding amplitude contour for the first and last
  15 ms of the vowel
• Adding F0 contour 130 at onset ? 90 Hz at offset
• Adding excised natural stop burst (/b/ or /d/) at
  vowel onset and another (/p/ or /t/) 70 ms after
  the vowel offset, or (Fig. 1, a)
• Adding white noise in the place of natural stop
  burst (Fig. 1, b)

Citation
Harrington, J., Kleber, F., and Reubold, U.
(2008). Compensation for coarticulation,
/u/-fronting, and sound change in standard
southern British An acoustic and perceptual
study, J. Acoust. Soc. Am. 123,
2825-2835. Ladefoged, P., and Broadbent, D. E.
(1957). Information conveyed by vowels, J.
Acoust. Soc. Am. 29, 98-104. Lindblom, B., and
Studdert-Kennedy, M. (1967). On the role of
formant transitions in vowel recognition, J.
Acoust Soc. Am. 42, 830-843. Ohala, J. J., and
Feder, D. (1994). Listeners identification of
speech sounds is influenced by adjacent
restored phonemes, Phonetica 51, 111-118.
Figure 5. /u/-response as a function of
stimulus number, in three different consonant
conditions.
Figure 6. Scatter plot of the perceptual /u/
space against normalized F2 of /u/.
Effect of Contexts Restored F4.5 (1.5, 43.3),
plt0.05 Acoustic F3.0 (1.8, 52.9), p0.06
(a)
Figure 7. Metric for obtaining the perceptual
space for the vowel /u/. The space is defined as
an area under the /u/-response function.
(b)
Figure 1. Waveforms of a /dVt/ stimulus used in
Acoustic Context condition (a) and Restored
Context condition (b).
Figure 2. Spectrograms of 10-step /i/ - /u/
continuum. Formant frequency (Hz) for the vowels
are F1375, F2 variable, F3 2500, F4 3500,
and F5 4500.
Figure 3. Reaction Time for /u/ response.