FRIDAY MORNING, 20 MAY 2005 REGENCY E, 8:30 A.M. TO 12:00 ...

5aPP8. Perception of combined intensity and frequency contours by
normal-hearing and hearing-impaired listeners. Marjorie R. Leek,
Michelle R. Molis Army Audiol. & Speech Ctr., Walter Reed Army
Medical Ctr., 6900 Georgia Ave, N.W., Washington, DC 20307-5001,
Marjorie.Leek@na.amedd.army.mil, and Jennifer J. Lentz Indiana
Univ., Bloomington, IN 47408
When a speaker utters a consonant-vowel or vowel-consonant syllable,
the frequency transitions are critical to identification of the sound. However,
an intensity contour is also superimposed on the frequency glides, as
the mouth opens or closes. In this study, the interaction of frequency and
intensity contours was explored using a frequency glide discrimination
task. Offset frequency difference limens offset DLs were measured for
upward and downward frequency glides in two frequency regions, and
with three intensity contours, increasing from silence, decreasing to silence,
and steady-state. For both normal-hearing NH and hearingimpaired
HI subjects, larger offset DLs were observed for the high frequency
stimuli than for the lower frequencies, and for upward-gliding
stimuli than for downward frequency glides. Amplitude contour had little
effect on the NH data, but did influence offset DLs for HI subjects. These
findings indicate that for these stimuli, the interaction of frequency and
amplitude contours plays only a small role in the perception of transitionlike
glides for NH listeners, but may affect the perception of frequency
transitions by HI listeners. Work supported by NIDCD.
5aPP9. Processing two stimuli simultaneously: Switching or sharing?
Frederick J. Gallun, Christine R. Mason, and Gerald Kidd, Jr. Hearing
Res. Ctr. and Comm. Disord., Boston Univ., 635 Commonwealth Ave.,
Boston, MA 02215
This study explored whether listeners can perform two auditory tasks
simultaneously or whether they must switch rapidly between tasks. The
stimuli were two simultaneous speech streams sentences processed into
sets of mutually-exclusive narrow frequency bands. One was presented to
each ear and listeners reported either the keywords from the sentences
Task 1, recognition or simply whether or not a sentence had been presented
Task 2, detection. For both sentences and tasks, overlapping
bands of noise were presented at a level that reduced performance to
below 90% correct in a single-stream reference condition. Listeners were
informed of which stream to report either before or after stimulus presentation.
The two tasks were either the same Task 1 at both ears or different
Task 1 on the right, Task 2 on the left. The effect of having the opportunity
to rapidly switch between sentences was examined by presenting
full sentences or only the keywords. Interference occurred primarily when
the tasks were the same in both ears and was greatest when the target ear
was not specified in advance. Presenting only the keywords hurt singlestream
performance but did not increase interference in the different-task
case, arguing against a rapid-switching explanation. Work supported by
NIH/NIDCD.
5aPP10. Explaining two-tone suppression and forward masking data
using a compressive gammachirp auditory filterbank. Toshio Irino
Faculty of Systems Eng., Wakayama Univ., 930 Sakaedani, Wakayama
640-8510, Japan and Roy Patterson Univ. of Cambridge, Cambridge,
CB2 3EG, UK
The gammatone filter was imported from auditory physiology to provide
a time-domain version of the roex auditory filter and enable the
development of a realistic auditory filterbank for models of auditory perception.
The gammachirp auditory filter was developed to extend the domain
of the gammatone auditory filter and simulate the changes in filter
shape that occur with changes in stimulus level. Recently, the gammachirp
was extended to explain the level-independent frequency glide of the impulse
response and a large volume of simultaneous masking data quantitatively.
Although this could be implemented with a static filter, we used a
time-varying filter whose active component is an IIR asymmetric compensation
filter. In this case, it is necessary to estimate the signal level that
controls the level dependency, and explain how the level measurement
produces the time course of threshold observed in forward masking experiments.
In this talk, we propose a new implementation of the timevarying,
compressive gammachirp auditory filterbank to explain two-tone
suppression and forward masking data qualitatively. We will also show
that the system can resynthesize compressed speech sounds and so provide
the basis for a gammachirp analysis/synthesis filterbank. Work supported
by GASRB2 No. 15300061, JSPS.
5aPP11. Behavioral estimates of level-dependent shifts in the
vibration pattern of the apical region of the basilar membrane. Luis
F. Barrios, Enrique A. Lopez-Poveda, and Ana Alves-Pinto Instituto de
Neurociencias de Castilla y Leon, Univ. of Salamanca, Avda. Alfonso X El
Sabio s/n, 37007 Salamanca, Spain
The best frequency of any given site on the BM shifts to a different
value as the stimulus level increases. For basal sites, the shift occurs
towards lower frequencies. For apical sites, however, the direction of the
shift is unclear. Auditory nerve data e.g., Rose et al., J. Neurophysiol. 34,
685–699 1971 suggest that shifts may not occur or may occur toward
higher frequencies. The present work investigates which is the case in
human. To do it, psychophysical tuning curves were measured for three
normal-hearing listeners using forward masking. The level of a masker
tone required to just mask a fixed, low-level probe tone was measured for
different masker-probe time intervals. The duration of the interval was
adjusted as necessary to obtain PTCs for the widest possible range of
masker levels. Probe frequencies of 125, 250, and 500 Hz were considered.
Masker frequencies ranged from 0.5 to 2.0 times the probe frequency.
A clear shift toward lower frequencies occurred for all probe frequencies
for one listener only. For the other two listeners, shifts were not
observed for any probe frequency. No clear shifts toward higher frequencies
were observed. Work supported by Spanish FIS PI020343 and G03/
203.
5aPP12. Modeling the influence of the cochlear nonlinearity on
estimates of psychophysical tuning. Xuedong Zhang and Andrew J.
Oxenham Res. Lab. of Electron., MIT, Cambridge, MA 02139
Most behavioral measures of human frequency selectivity have been
made with simultaneous masking and the notched-noise technique. The
resulting filter shapes may be influenced by the effects of cochlear nonlinearity,
such as suppression. Forward masking may provide a measure
that is more comparable to neural tuning curves, because it does not involve
stimuli that interact with each other along the basilar membrane.
This study investigated the extent to which cochlear nonlinearities can
account for differences in results between forward and simultaneous masking.
The model was constructed using a nonlinear auditory filter, a sliding
temporal integrator, a logarithmic transform and a template mechanism.
The effects of compression and suppression on psychophysical performance
were simulated by varying the relevant parameters of the model
auditory filter. The psychophysical results were simulated for both forward
and simultaneous masking, using the same parameters and tracking procedure
as in the behavioral studies. The results provide a detailed evaluation
of the role of compression and suppression in the models predictions
of psychophysical tuning and assist in the development of the refined
nonlinear cochlear models for human. Work supported by the ASA Hunt
Fellowship and NIH R01DC03909.
5aPP13. Estimating cochlear-filter shapes, temporal-window width
and compression from tone-sweep detection in spectral and temporal
noise gaps. Gaston Hilkhuysen, Tammo Houtgast, and Johannes
Lyzenga Dept. of Otolaryngol., VU Univ. Medical Ctr., de Boelelaan
1117, 1081 HV Amsterdam, The Netherlands, G.Hilkhuysen@vumc.nl
A test, designed for naive listeners, measured tone-sweep detection in
noise with either spectral or temporal gaps. For normal-hearing NH listeners,
detections in spectral gaps depended on level, which can be ex-
2598 J. Acoust. Soc. Am., Vol. 117, No. 4, Pt. 2, April 2005 149th Meeting: Acoustical Society of America 2598