Experiment I found that consonant length contrasts were more difficult to discriminate when the consonants were spectrally continuous with surrounding segments, replicating previous research. Experiment II then directly compared conditions with different amplitude drops and found that length contrasts were more difficult to discriminate for consonant intervals with a smaller amplitude drop. This suggests that both spectral discontinuity and greater amplitude drop help listeners perceive segmental boundaries and discriminate consonant length. Amplitude drop may account for the effects of both spectral discontinuity and drop magnitude, as spectral discontinuity represents an extreme case of high amplitude change. Future research could examine consonants involving spectral discontinuity but little amplitude change, like fricatives.

1. Perceiving Length Contrasts: The Role of Amplitude Drop
Audrey Krum & Lara Martin
with Kelly Garvey, Dr. Shigeto Kawahara, Sarah Korostoff, Michelle Marron, and Melanie Pangilinan
Aresty Symposium, April 29th 2011
Introduction
Experiment II
Discussion
Experiment I: In the first experiment, we replicated
Kawahara et al.’s (2011) result: length contrasts of
consonants that are spectrally continuous with
surrounding segments are more difficult to
discriminate.
Experiment II: Given two spectrally-continuous
conditions, the length consonants of consonant
intervals that involve less amplitude drop are more
difficult to discriminate.
Answer: Both spectral discontinuity and amplitude
drop facilitates the perception of segmental
boundaries.
Amplitude drop accounts for both results; spectral
discontinuity may be an extreme case of high
amplitude change.
Future Research: What about a consonant that
involves spectrally discontinuity but involves little
amplitude change (fricatives)?
References
Kato, Hiroaki, Minoru Tsuzaki, and Yoshinori Sagisaka. "Acceptability for Temporal
Modification of Consecutive Segments in Isolated Words." Acoustical Society of America
101.4 (1997): 2311-322. Print.
Kawahara, Shigeto, Melanie Pangilinan, and Kelly Garvey (2011) Spectral continuity and the
perception of duration: Implications for phonological patterns of sonorant geminates.
Submitted.
Some languages contrast short consonants and long
consonants (a geminate contrast). Geminates are
characterized by long consonantal duration.
Experiment I
Results
The task: Same-different discrimination task.
Stimuli pairs: SS, LL, SL, LS. Short=80ms with 10 ms
transitions; Long=145ms with 10ms transitions.
Experiment I compared the silence condition and the 6dB
drop condition (22 participants). Experiment II compared the
18dB drop condition and 6dB condition (21 participants).
Analysis: d′(detectability index)
Stimuli consist of sine waves that mimic speech sounds
in VCV structure. Vowels=70dB.
Method
Consonant I=Silence;
(0dB; 70dB drop)
Discontinuous
Consonant II=64dB
(6dB drop)
Continuous
Consonant III=52dB
(18dB drop)
Continuous
In order to perceive duration of consonants, a
listener has to detect the segmental boundaries
between the consonants and surrounding vowels.
Question: How do human listeners detect
segmental boundaries, which is necessary to
perceptually calculate the duration of segments?
- Kato et al (1997) suggest that listeners use
amplitude drop to locate segmental boundaries.
- Kawahara et al (2011) showed that spectral
discontinuity makes the perception of duration
easier.
Objective: The study tested how spectral
discontinuity and amplitude drop contribute to the
perceptibility of geminates.
Arabic short [t] and long [tt]
0 1 2 3 4 5
012345
Detectability index (d’)
Silence
Continuous(6dBdrop)
0 1 2 3 4 5
012345
Detectability index (d’)
18dB drop
6dBdrop