Spectral resolution has been reported to be closely related to vowel and consonant recognition in cochlear implant (CI) listeners. One measure of spectral resolution is spectral modulation threshold (SMT), which is defined as the smallest detectable spectral contrast in the spectral ripple stimulus. SMT may be determined by the activation pattern associated with electrical stimulation. In the present study, broad activation patterns were simulated using a multi-band vocoder to determine if similar impairments in speech understanding scores could be produced in normal-hearing listeners. Tokens were first decomposed into 15 logarithmically spaced bands and then re-synthesized by multiplying the envelope of each band by matched filtered noise. Various amounts of current spread were simulated by adjusting the drop-off of the noise spectrum away from the peak (40–5dBoctave). The average SMT (0.25 and 0.5cyclesoctave) increased from 6.3 to 22.5dB, while average vowel identification scores dropped from 86% to 19% and consonant identification scores dropped from 93% to 59%. In each condition, the impairments in speech understanding were generally similar to those found in CI listeners with similar SMTs, suggesting that variability in spread of neural activation largely accounts for the variability in speech perception of CI listeners.

1.
Abbas
,
P. J.
,
Hughes
,
M. L.
,
Brown
,
C. J.
,
Miller
,
C. A.
, and
South
,
H.
(
2004
). “
Channel interaction in cochlear implant users evaluated using the electrically evoked compound action potential
,”
Audiol. Neuro-Otol.
9
,
203
213
.
1.
American National Standards Institute (ANSI) (
1996
). “American standard specification for audiometers” (American National Standards Institute, New York).
2.
Bacon
,
S. P.
, and
Viemeister
,
N. F.
(
1985
). “
Temporal-modulation transfer functions in normal-hearing and hearing-impaired listeners
,”
Audiology
24
,
117
134
.
3.
Baer
,
T.
, and
Moore
,
B. C.
(
1994
). “
Effects of spectral smearing on the intelligibility of sentences in the presence of interfering speech
,”
J. Acoust. Soc. Am.
95
,
2277
2280
.
4.
Baer
,
T.
,
Moore
,
B. C.
, and
Gatehouse
,
S.
(
1993
). “
Spectral contrast enhancement of speech in noise for listeners with sensorineural hearing impairment: Effects on intelligibility, quality, and response times
,”
J. Rehabil. Res. Dev.
30
,
49
72
.
5.
Baskent
,
D.
, and
Shannon
,
R. V.
(
2003
). “
Speech recognition under conditions of frequency-place compression and expansion
,”
J. Acoust. Soc. Am.
113
,
2064
2076
.
6.
Bernstein
,
L. R.
, and
Green
,
D. M.
(
1987
). “
Detection of simple and complex changes of spectral shape
,”
J. Acoust. Soc. Am.
82
,
1587
1592
.
7.
Boex
,
C.
,
Kos
,
M. I.
, and
Pelizzone
,
M.
(
2003
). “
Forward masking in different cochlear implant systems
,”
J. Acoust. Soc. Am.
114
,
2058
2065
.
8.
Carney
,
L. H.
(
1994
). “
Spatio-temporal encoding of sound level: Models for normal encoding and recruitment of loudness
,”
Hear. Res.
76
,
31
44
.
9.
Cazals
,
Y.
,
Pelizzone
,
M.
,
Saudan
,
O.
, and
Boex
,
C.
(
1994
). “
Low-pass filtering in amplitude modulation detection associated with vowel and consonant identification in subjects with cochlear implants
,”
J. Acoust. Soc. Am.
96
,
2048
2054
.
10.
Cohen
,
L. T.
,
Lenarz
,
T.
,
Battmer
,
R. D.
,
Bender von Saebelkampf
,
C.
,
Busby
,
P. A.
, and
Cowan
,
R. S.
(
2005
). “
A psychophysical forward masking comparison of longitudinal spread of neural excitation in the contour and straight nucleus electrode arrays
,”
Int. J. Audiol.
44
,
559
566
.
11.
Cohen
,
L. T.
,
Richardson
,
L. M.
,
Saunders
,
E.
, and
Cowan
,
R. S.
(
2003
). “
Spatial spread of neural excitation in cochlear implant recipients: Comparison of improved ECAP method and psychophysical forward masking
,”
Hear. Res.
179
,
72
87
.
12.
Cohen
,
L. T.
,
Saunders
,
E.
, and
Richardson
,
L. M.
(
2004
). “
Spatial spread of neural excitation: Comparison of compound action potential and forward-masking data in cochlear implant recipients
,”
Int. J. Audiol.
43
,
346
355
.
13.
Dorman
,
M. F.
,
Dankowski
,
K.
,
McCandless
,
G.
, and
Smith
,
L.
(
1989
). “
Identification of synthetic vowels by patients using the Symbion multichannel cochlear implant
,”
Ear Hear.
10
,
40
43
.
14.
Dorman
,
M. F.
,
Loizou
,
P. C.
, and
Rainey
,
D.
(
1997
). “
Speech intelligibility as a function of the number of channels of stimulation for signal processors using sine-wave and noise-band outputs
,”
J. Acoust. Soc. Am.
102
,
2403
2411
.
15.
Dubno
,
J. R.
, and
Dorman
,
M. F.
(
1987
). “
Effects of spectral flattening on vowel identification
,”
J. Acoust. Soc. Am.
82
,
1503
1511
.
16.
Dynes
,
S. B.
, and
Delgutte
,
B.
(
1992
). “
Phase-locking of auditory-nerve discharges to sinusoidal electric stimulation of the cochlea
,”
Hear. Res.
58
,
79
90
.
17.
Eddington
,
D.
,
Tierney
,
J.
, and
Long
,
C.
(
1997a
).
Cochlear Implants
(
RLE
, Cambridge, MA).
18.
Eddington
,
D. K.
,
Rabinowitz
,
W. R.
,
Tierney
,
J.
,
Noel
,
V.
, and
Whearty
,
M.
(
1997b
). “
Speech processors for auditory prostheses
,” 8th Quarterly Progress Report, NIH Contract No. N01–DC-6–2100.”
19.
Efron
,
B.
, and
Tibshirani
,
R.
(
1993
).
An Introduction to the Bootstrap
(
Chapman and Hall
, New York).
20.
Ferguson
,
W. D.
,
Collins
,
L. M.
, and
Smith
,
D. W.
(
2003
). “
Psychophysical threshold variability in cochlear implant subjects
,”
Hear. Res.
180
,
101
113
.
21.
Firszt
,
J. B.
,
Holden
,
L. K.
,
Skinner
,
M. W.
,
Tobey
,
E. A.
,
Peterson
,
A.
,
Gaggl
,
W.
,
Runge-Samuelson
,
C. L.
, and
Wackym
,
P. A.
(
2004
). “
Recognition of speech presented at soft to loud levels by adult cochlear implant recipients of three cochlear implant systems
,”
Hear. Res.
25
,
375
387
.
22.
Friesen
,
L. M.
,
Shannon
,
R. V.
,
Baskent
,
D.
, and
Wang
,
X.
(
2001
). “
Speech recognition in noise as a function of the number of spectral channels: Comparison of acoustic hearing and cochlear implants
,”
J. Acoust. Soc. Am.
110
,
1150
1163
.
23.
Fu
,
Q. J.
(
2002
). “
Temporal processing and speech recognition in cochlear implant users
,”
NeuroReport
13
,
1635
1639
.
24.
Fu
,
Q. J.
, and
Nogaki
,
G.
(
2005
). “
Noise susceptibility of cochlear implant users: The role of spectral resolution and smearing
,”
J. Assoc. Res. Otolaryngol.
6
,
19
27
.
25.
Fu
,
Q. J.
,
Shannon
,
R. V.
, and
Galvin
,
J. J.
, III
. (
2002
). “
Perceptual learning following changes in the frequency-to-electrode assignment with the Nucleus-22 cochlear implant
,”
J. Acoust. Soc. Am.
112
,
1664
1674
.
26.
Glasberg
,
B. R.
, and
Moore
,
B. C. J.
(
1986
). “
Auditory filter shapes in subjects with unilateral and bilateral cochlear impairments
,”
J. Acoust. Soc. Am.
79
,
1020
1033
.
27.
Good
,
P. I.
(
1994
).
Permutation Tests: A Practical Guide to Resampling Methods for Testing Hypotheses
(
Springer-Verlag
, New York).
28.
Harnsberger
,
J. D.
,
Svirsky
,
M. A.
,
Kaiser
,
A. R.
,
Pisoni
,
D. B.
,
Wright
,
R.
, and
Meyer
,
T. A.
(
2001
). “
Perceptual ‘vowel spaces’ of cochlear implant users: Implications for the study of auditory adaptation to spectral shift
,”
J. Acoust. Soc. Am.
109
,
2135
2145
.
29.
Henry
,
B. A.
, and
Turner
,
C. W.
(
2003
). “
The resolution of complex spectral patterns by cochlear implant and normal-hearing listeners
,”
J. Acoust. Soc. Am.
113
,
2861
2873
.
30.
Henry
,
B. A.
,
Turner
,
C. W.
, and
Behrens
,
A.
(
2005
). “
Spectral peak resolution and speech recognition in quiet: Normal hearing, hearing impaired, and cochlear implant listeners
,”
J. Acoust. Soc. Am.
118
,
1111
1121
.
31.
Horst
,
J. W.
(
1987
). “
Frequency discrimination of complex signals, frequency selectivity, and speech perception in hearing-impaired subjects
,”
J. Acoust. Soc. Am.
82
,
874
885
.
32.
Irvine
,
D. R. F.
,
Rajan
,
R.
, and
McDermott
,
H. J.
(
2000
). “
Injury-induced reorganization in adult auditory cortex and its perceptual consequences
,”
Hear. Res.
147
,
188
199
.
32.
Klatt
,
D. H.
(
1980
). “
Software for cascade/parallel formant synthesizer
,”
J. Acoust. Soc. Am.
67
,
971
995
.
33.
Levitt
,
H.
(
1971
). “
Transformed up-down methods in psychoacoustics
,”
J. Acoust. Soc. Am.
49
(
2
),
467
477
.
34.
Litvak
,
L. M.
,
Delgutte
,
B.
, and
Eddington
,
D. K.
(
2001
). “
Auditory nerve fiber responses to electric stimulation: Modulated and unmodulated pulse trains
,”
J. Acoust. Soc. Am.
110
,
368
379
.
35.
Loeb
,
G. E.
(
2005
). “
Are cochlear implant patients suffering from perceptual dissonance?
,”
Ear Hear.
26
,
435
450
.
36.
Loeb
,
G. E.
,
White
,
M. W.
, and
Merzenich
,
M. M.
(
1983
). “
Spatial cross-correlation. A proposed mechanism for acoustic pitch perception
,”
Biol. Cybern.
47
,
149
163
.
37.
Miller
,
G.
, and
Nicely
,
P.
(
1955
). “
An analysis of perceptual confusions among some English consonants
,”
J. Acoust. Soc. Am.
27
,
338
352
.
38.
Ohde
,
R. N.
, and
Abou-Khalil
,
R.
(
2001
). “
Age differences for stop consonant and vowel perception in adults
,”
J. Acoust. Soc. Am.
110
,
2156
2166
.
39.
Oppenheim
,
A. V.
, and
Schafer
,
R. W.
(
1975
).
Digital Signal Processing
(
Prentice–Hall
, Englewood Cliffs, N.J.).
40.
Rosen
,
S.
(
1992
). “
Temporal information in speech: Acoustic, auditory and linguistic aspects
,”
Philos. Trans. R. Soc. London, Ser. B
336
,
367
373
.
41.
Rosen
,
S.
,
Faulkner
,
A.
, and
Wilkinson
,
L.
(
1999
). “
Adaptation by normal listeners to upward spectral shifts of speech: Implications for cochlear implants
,”
J. Acoust. Soc. Am.
106
,
3629
3636
.
42.
Saoji
,
A.
,
Litvak
,
L.
,
Emadi
,
G.
, and
Spahr
,
A.
(
2005
). “
Spectral modulation transfer function in cochlear implant listeners
,” in
Conference on Implantable Auditory Prostheses
,
Asilomar
, California.
43.
Shannon
,
R. V.
,
Zeng
,
F. G.
,
Kamath
,
V.
,
Wygonski
,
J.
, and
Ekelid
,
M.
(
1995
). “
Speech recognition with primarily temporal cues
,”
Science
270
,
303
304
.
44.
Shannon
,
R. V.
,
Zeng
,
F. G.
, and
Wygonski
,
J.
(
1998
). “
Speech recognition with altered spectral distribution of envelope cues
,”
J. Acoust. Soc. Am.
104
,
2467
2476
.
45.
Summers
,
V.
, and
Leek
,
M. R.
(
1994
). “
The internal representation of spectral contrast in hearing-impaired listeners
,”
J. Acoust. Soc. Am.
95
,
3518
3528
.
46.
Tyler
,
R. S.
,
Preece
,
J. P.
,
Lansing
,
C. R.
,
Otto
,
S. R.
, and
Gantz
,
B. J.
(
1986
). “
Previous experience as a confounding factor in comparing cochlear-implant processing schemes
,”
J. Speech Hear. Res.
29
,
282
287
.
47.
Xu
,
L.
,
Thompson
,
C. S.
, and
Pfingst
,
B. E.
(
2005
). “
Relative contributions of spectral and temporal cues for phoneme recognition
,”
J. Acoust. Soc. Am.
117
,
3255
3267
.
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