THE
JOURNAL
OF THE
ACOUSTICAL
SOCIETY
OF AMERICA
VOLUME
29, NUMBER
5
MAY,
1957
Perception of Vowels Heard in Noises of Various Spectra*
J. M. PICKETT
OperationalApplicationsLaboratory,Air ForceCambridgeResearchCenter,Bolling Air ForceBase25, D.C.
(ReceivedDecember3, 1956)
The perceptionof vowelsheard in noisesof variousspectrais analyzedby meansof stimulus-response
matrices.The stimulusvowelswere spokenin PB-word lists and in syllablelists in which the vowelswere
equally probable.The matricesshowshiftsin vowel confusions
dependingon how differentnoisespectra
mask the vowel formants. Vowel duration and intensity are measuredand related to vowel perception.
Vowel guessingis related to past training.
HISpaper
presents
ananalysis
oftheintelligibilityreplacementand spokenin a short carrier phrase.The
and confusionof vowelsheardat low signallevels bVb tests were presented through earphonesand the
noises. The data are of interest for two
PB-word tests were presentedwith the earphonesfor
reasons'first, they provide a basisfor selectingvowels sometests, and over loudspeakersfor other tests. The
for use in noise, and, second,they are relevant to the speechwas recordedfor the tests with bVb syllables;
the PB wordswere read into a microphone,amplified,
formant theory o[ vowel perception.
The roleof the formantsin vowelperceptionhasbeen and presentedto listeners.
Four noisesignalswere obtained by RC filtering of
studied largely with synthesizedvowels rather than
spokenvowelsin order that formant frequenciesmay the output of a random noise sourceproviding white
be preciselymanipulatedJ Spokenformants may be noiserestrictedto the range0-20 000 cy. These signals
studiedby maskingthem with noiseand constructing had spectrawith very nearly linear slopesof +6, 0, --6,
stimulus-response
matricesas did Miller and Nicely in and --10 db/octave between 200 and 7000 cy as
analyzingthe perceivedfeaturesof consonants.
2 in our measuredper cyclewith a wave analyzer;the respective
caselisteners'vowel responseswill be groupedin the acousticreproductionsof these noiseswill be referred
matricesaccordingto the typical frequencyregionsof to belowashighfrequency,flat, low frequency,and very
their formants. Spokenvowels also differ perceivably low frequency. These terms are descriptive of the
in durationand intensitya and the contributionof these frequencyregionof speechwhich the noiseswill mask,
cuesto vowelperceptionmay be isolatedwhenpatterns sincethe speechand noisesignalswere reproducedby
the sametransducer.The noiseand speechsignalswere
of formant frequencyare maskedby noise.
mixed electrically, power-amplified,and then applied
PROCEDURES
to the earphonesor loudspeakers.The earphoneshad
a
real ear responsewhich was flat 4-3 db from 200 to
Two setsof test syllableswereused:one artificial set
7000
cy. The loudspeakers'responsecurve, varying
in which the vowelsoccurredwith equalprobability and
4-5
db,
wasflat from 100 to 1200cy, then fell 4 db from
anothersetin which the vowelsoccurredapproximately
as they do in English.The artificialsyllableswereof the 1200 to 3000 cy and 8 db from 3000 to 7000 cy. The
form bVb; lists of 60 syllableswere formed by using soundpressurelevel of the noisesat 2000 cy was 45 to
50 db per cyclere 0.0002dyne/cm•'.The soundpressure
five of each of the twelve American vowels. 4 The set of
level
of speech,dependingon test material and noise
English syllablesconsistedof the Harvard PB words,
1000 syllablesphonetically balanced in lists of 50 spectrum,rangedfrom 50 db to 83 db, over all longrms.
ratio) was measuredwith a VU
to match approximatelythe frequencyof occurrence
of SIN (signal-to-noise
meter
at
the
output
of
the power amplifier.The microthe speechsoundsin English.In both setsof tests,the
phone,
recorder,
and
amplifiers
introduced negligible
syllableswere drawn randomlyfrom the lists without
distortionand had flat responsecurves4-« db from 50
* This is AFCRC Technical Note 56-12 of the Operational to 15 000 cy.
ApplicationsLaboratory, Air Force CambridgeResearchCenter,
The talkers were college-educated
men 23 to 33 years
in broad-band
Bolling Air Force Base 25, D.C.
ASTIA Document No.: AD
old. Three talkers were used for the bVb tests and four
110057.
• Delattre, Liberman, Cooper, and Gerstman, Word 8, 195
(1952); R. K. Potter and J. C. Steinberg,J. Acoust.Soc.Am. 22,
807 (1950); G. E. Petersonand H. L. Barney, J. Acoust. Soc.
Am. 24, 175 (1952); R. L. Miller, J. Acoust.Soc.Am. 25, 114-121
with
(1953).
the monitored
2 G. A. Miller and P. E. Nicely, J. Acoust.Soc.Am. 27, 338
PB
words.
Two
talkers
were
common
to both
crews.They were trained to monitor their speechso
that the averageintensity of the carrier phrasefell at
level and the test words fell at their own
natural levels. The listeners were made thoroughly
0955).
aW. R. Tiffany, J. SpeechandHearingDisorders18, 289 (1953). familiar with the syllablesand other conditionsby pre4The vowelsusedare referredto belowby their symbolsin the
InternationalPhoneticAlphabet and a key word for pronuncia- liminary tests affordingpractice at all rangesof inteltion follows each:
u (boob); u (book), o (boat), o (bought), a (Bob), A (bud),
, (Bert), ae (bat), e (bet), e (babe), I (bib), i (beet).
ligibility. Five listenerswrote the wordsthey heardin
the PB word tests. For the bVb tests, six listeners
613
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614
j.M.
PICKETT
recordedthe vowelsthey heard by a simplephonetic
code.Theselistenersknew that the vowelswere equally
probable,but they did not consciously
keep countsof
vowels during a test list. Listeners respondedto all
probable.The vowelsof the matricesare arrangedin
three groupsaccordingto whether they have generally
low, medium,or high frequencyof the secondformant.
Within thesegroupsthe vowelsare arrangedin order
stimuli.
of increasingfrequencyof the first formant.5 To make
The vowel or diphthongof eachresponsewas tabu- it easierto seethe salient features of the matrices, the
lated in a stimulus-response
matrix witk rows for the confusionswere systematicallydegradedto give only
spokenvowel stimuli and columnsfor the response four gradesof confusionfrequency:2 to 5%, 5 to 10%,
vowels of the listeners. The entries in the final matrix
10 to 20%, and greater than 20% of all responses
to
gave the numberof timesthat eachresponse
occurred each stimulus vowel. These were entered in new matrices
to each stimulus. Results with different talkers, noise usingdots gradedin four sizesand eliminatingcorrect
Larger sizeof dot representsmoreconfusion.
spectra,andS/N's weretabulatedin separatematrices. responses.
Reference to the "Formant Key" of Fig. 2 will
These werethen pooledto showthe main effectof noise
spectrumon confusion
patterns.Effectsdueto different illustrate the following interpretations of confusion
talkers were relatively minor.
patterns' (1) Confusionswhich fall near the main
diagonal indicate correct perceptionof the frequency
RESULTS WITH VOWELS EQUALLY PROBABLE
region of the secondformant. Large rectanglesare
Table I showsthe pooledmatricesresultingfrom the formedby groupingthe vowelsinto our second-formant
;bVb tests where the stimulus vowels were equally categoriesand theseare shadedso that one can easily
TABLe.I. Vowelsheard in variousnoisespectrawhen stimulusvowelsare equally probable.
Part A' low-frequency noise,SIN =-
20 db.•'
Responsevowel
u
u
o
202
34
12
225
10
34
6
2
9
33
5
6
9
7
115
11
16
34
16
6
12
3
20
242
4
8
341
26
5
3
13
1
8
10
4
8
4
71
12
14
8
29
11
2
7
28
6
286
18
1
6
268
2
5
13
379
14
5
1
8
16
6
6
7
3
1
2
4
2
4
28
5
9
17
4
7
7
10
3
30
4
8
1
1
4
11
279
18
44
7
5
18
257
10
16
1
292
20
10
283
25
2
2
51
14
13
4
4
5
51
2
6
o
•r
A
a
Part B' Flat noise,S/N=-
i
I
3
7
3
8
11
3
10
2
5
2
3
2
15
3
31
1
5
16
8
11
19
11
5
5
3
24
309
11 and --15 db.b
Responsevowel
u
U
o
244
12
5
12
318
8
2
16
285
19
1
56
6
13
9
5
64
1
7
o
,
A
a
i
1
1
1
18
33
9
1
3
206
4
2
428
1
7
18
2
17
30
3
349
9
4
353
1
2
4
475
15
1
1
22
3
3
3
2
6
1
5
414
6
15
6
2
7
24
19
5
Each vowel spoken 405 times; vowel intelligibility,
Each vowel spoken 495 times; vowel intelligibility,
1
10
4
2
4
50
4
2
1
33
1
13
10
106
4
7
6
1
141
1
10
5
32
6
5
2
35
1
4
14
67
6
15
7
388
2
13
1
5
427
4
2
2
16
1
395
3
9
!
8
424
69.3%.
75.7%.
5R. K. Potter and J. C. Steinberg,J. Acoust.Soc.Am. 22, 807 (1950); G. E. Petersonand H. L. Barney,J. Acoust.Soc.Am. 24,
175 (1952).
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PERCEPTION
OF
VOWELS
IN
NOISE
615
TABLe. I.--Continued.
Part C' High-frequencynoise,S/N---
30 db.e
Responsevowel
o
U
u
o
132
1
2
162
1
12
5
El'
o
,
2
3
A
2
2
179
1
2
252
22
16
2
23
177
1
i
a
I
e
124
1
6
80
12
7
65
3
5
3
195
1
1
8
1
19
5
62
1
266
31
2
4
2
239
51
218
1
1
13
1
11
1
1
34
1
1
250
227
23
Part D. High-frequencynoise,S/N----40
2
234
db.d
Responsevowel
u
u
u
o
•
•
o
u
8
113
o
o
88
12
5
1
•
12
16
A
a
'• i
2
2
36
2
o
2
6
87
3
,
1
145
48
26
9
1
21
9
2
1
I
4
60
7
2
e
16
3
26
1
e
1
7
4
16
m
1
1
3
42
Each vowel spoken 270 times; vowel intelligibility.
Each vowel spoken 270 times; vowel intelligibility,
A
3
12
17
6
17
2
16
81
4
7
123
i
a
5
3
45
6
e
g
a•
1
20
148
6
7
3
7
85
3
2
12
5
139
4
1
11
4
18
1
3
2
52
5
4
4
2
19
5
36
5
14
72
2
23
3
1
6
2
19
2O3
7
19
3
8
6
163
1
11
9
5
4
187
3
9
5
7
3
155
15
4
1
0
15
130
229
1
9
9
2
4
i
5
1
2
8
42
78.1%.
52.6%.
see the generalextent to which the secondformant is frequencyrange rather than in the middle. This may
correctlyheard.(2) Whenconfusions
fall in the unshaded be partially due to the more frequent occurrenceof
rectangles,the secondformant is not heard correctly. low and high secondformantsin English.
(3) When confusions
fall alongthe parallel diagonalof
When the confusionsin high- and low-frequency
an unshadedrectangle,the first formant is correctly noiseare compared,the effectsof different amountsof
heard, since within these categories,the vowels are maskingof the first and secondformants can be seen.
arrangedin orderof increasingfirst formant frequency. First, with high-frequencyand flat noisethere is more
For the testswith syllableshaving equal vowelprob- tendencyto confusethe secondformants,as shownby
abilities, the simplified confusionmatrices are shown the greaternumberof confusions
in the unshadedrecin Fig. 1. There is a strongtendencyfor the confusions
tangles. With low-frequencynoise many more conto fall alongthe diagonalwithin categoriesof secondfusions occur within the shaded rectangles showing
formant frequency. This is particularly so with the
greaterhigh-frequency
maskingprovidedby the high- grosslycorrectperceptionof the frequencyregionof
the second formant and confusion of the first formant. ø
frequency and flat noises. Thus, when the second
formant is masked, confusionsoccur between vowels
6The effectsseenwith different masking spectraare analagous
mainly distinguished
by differences
in this feature,and to resultsobtainedby Delattre et al.• with identificationof synthe response
vowelsas heard tend rather closelyto be thetic vowels having but one formant. When low formant frequencieswere presentedback vowelswith corresponding
first
given the correctfirst formant. Confusionof the two formant
frequencieswereheard.When the formant wasincreased
extreme values of the second formant
is much more
commonthan confusionwith a middle frequencyposi-
in frequencyfront vowelswere assignedand accordingto their
secondformant frequencies.In the present study, however, it
appearsthat the presence
of the maskedsecondformantis always
detected or assumedby the listener and hence assignmentsto
tion. Apparently,whenthe second
formantis not heard,
the listener tends to assignit at the extremesof its front vowelsare always present.
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616
j.M.
LOW-FREQUENGY NOISE
PICKETT
FLAT NOISE
,
ß
u
u
'u'
o
o
o
A
0
i
i
e
e
Fro. 1. Simplified patterns of
confusion among vowels heard
in noisesof various spectra. The
stimulus vowels (rows) occurred
with equal frequency. Original
data
HIGH-FREOUENOY
NOISE.S/N - -30
#
HIGH-FREQUENCY
NOISE,S/N ß- 40
ß
i
are shown
in Table
I.
The
formant key of Fig. 2 showshow
the vowelswere groupedaccording
to the typical frequencyregionsof
B
u
their
formants.
Amount
of
con-
fusion is indicated in four grades
by the size of dot entered in the
confusion
cells.
When
the
dots
fall heavily in the shadedsquares,
the first formant is masked by the
noise and the second is heard;
when they fall on the diagonalsof
the large, unshadedrectangles,the
o
D
A
first formant
is heard
second is masked.
and
the
i
I
VOWELS
EQUALLY
PROBABLE
the confusedpairs i-u, I-U, e-o, e-a, and ae-Aform a
series having rising frequency of the first formant,
whereeachpair has a first formant frequencywhich is
There is a rather remarkable
constriction of the
commonto the pair but differentfrom the next pair.
vowel confusionsto the diagonals of the confusion However, in the utteranceof averagetalkers there is
categories.
This is probablydue to the joint operation overlapof formant frequenciesin this series.Therefore,
of cuesof duration and formant frequency.Particularly, cuesof vowel duration must also be a factor in forcing
confusions
into the diagonalcells.8 The two rather long
pairs i-u and e-o are separatedby a short pair, I-U.
TA]rr.•. II. Intensities of vowels and their
intelligibility in noise.
Thesethree pairs showthe neatestconfusionrelations.
The next pairs, ae-Aand e-a are respectivelylong-short
Intelligibility, % correct
and short-longand hencethey are mutually confused
Mean relative
--6/oct.
Flat
+6/oct.
but not often with members of the first three pairs
Vowel
intensity, db
noise
noise
nome
The very commonconfusionof the vowel pairs i-u,
I-U, and e-o was first demonstratedwith white noiseby
Moser and I)reher 7 and is confirmedby our results.
93.6
96.0
91.6
--0.1
0.0
84.2
86.5
73.5
--0.6
66.2
71.3
58.8
--0.8
--0.9
-- 1.0
-- 1.2
70.6
55.6
59.8
69.9
70.5
64.2
57.6
79.8
47.7
50.9
49.2
70.7
--1.3
-- 1.7
--2.1
76.3
63.5
72.1
85.7
78.4
86.3
67.3
70.5
80.9
--3.3
49.9
49.3
40.7
--4.9
68.9
83.6
81.8
which have lower first formants.
In order to see what effect the natural intensity
differencesof different vowels might have on their
intelligibility in noise, the intensitiesof all of the
8 Measurements
of the duration
of five of each stimulus vowel
of eachof the three talkersgave the followingmeandurationsin
seconds:
•e, 0.328; a, 0.323; o, 0.322; e, 0.319; o, 0.298;•, 0.288;
u, 0.285; i, 0.284; e, 0.238; 3_,0.227; u, 0.227; I, 0.207ßThese
durations were surprisinglyinvariable among utterancesand
talkers. The evidence that duration is used as a cue can be seen
by collapsingconfusions
into smallermatricesand lookingfor a
long-short"axis"acrossthe matrixßThe threedurationcategories
?H. M. MoserandJ. J. Dreher,"Phonemic
confusion
vectors," of long vowels•e, a, o, e, medium vowelso, •, u, i, and short
Air Force CambridgeResearchCenter, Report TR 54-84, 1954. vowels,I, e, 3_,U, showthe effect especiallywell.
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PERCEPTION
OF
VOWELS
IN
NOISE
617
stimuls vowelsin bVb syllableswere measuredwith a the vowelsu and u are least intelligible.This result is
VU meter. Table II showsthe mean relative intensity grosslyconsistentwith differencesamong vowels in
of eachvowelalongwith its intelligibility in eachnoise. thresholdof detectabilityin quiet asfound by Tiffany?
The relationsbetweenmeanintensityand intelligibility
were evaluated by rank correlations.The relation is
RESULTS
WITH
VOWELS
OF PB WORDS
statistically significant only in low-frequencynoise
(p=0.05). Apparentlyvowelsof highnaturalintensity
are more intelligible only when both formants are
heard in some degree. When the secondformant is
maskedby flat or high-frequencynoise,high intensity
of the remaining first formant cannot increaseintelligibility.
Insofar as general resistanceto noise is concerned,
the vowelsa, •, and e are most intelligiblein noiseand
In order to extendthe principleseento hold for the
maskingof vowelformantsin bVb syllables,we undertook an identicalanalysisfor the vowelsand diphthongs
of PB words.Ourtalkersmighthaveemphasized]the
formantsto better distinguishamongthe bVbsyllables?
Also the variety of consonantmovementsin the PB
syllablesmight changevowel formantsin ways that
TA..•. III. Vowelresponses
to PB wordsheardin variousnoisespectra.
Part A' Very low frequencynoise,S/N--
16 and --18 dbP
Responsevowel
o
36
25
1
21
9
7
8
9
6
o
,
2
2
58
27
10
53
4
14
11
1
3
8
A
1
1
4
23
5
1
4
1
!
4
2
15
1
3
4
4
ai
1
3
'
2
a
4
2
3
6
5
129
22
i
1
83
15
1
7
6
7
7
1
4
m
3
2
1
1
3
1
18
2
3
5
3
8
2
23
8
22
7
2
21
146
9
19
7
95
10
10
7
20
10
119
24
7
6
6
3
77
1
!
1
4
2
1
2
1
e
1
1
4
5
e
5
5
5
1
2
4
1
I
1
1
2
au
1
1
1
1
2
10
2
4
2
4
1
14
5
8
3
4
3
14
205
1
1
2
2
8
11
2
118
1
iu
1
1
Part B- Low-frequencynoise,S/N--
ai
2
1
1
2
3
4
3
2
1
2
46
1
5
au
iu
1
5
1
2
7
1
12 db.b
Responsevowel
o
43
4
13
2
g .
o
A
a
• i
'•
m
4
3
1
7
I
9
e
2
e
2
ae
2
ai
au
iu
•r
A
a
i
I
e
17
5
2
1
1
2
1
3
2
1
5
3
9
1
4
2
81
11
3
58
5
1
10
4
10
3
1
1
3
3
1
4
3
25
14
1
ae
ai
1
4
2
1
3
2
13
7
1
4
2
3
134
6
4
11
3
5
3
7
1
8
91
1
7
2
3
4
9
1
2
1
3
2
2
3
1
7
5
5
1
5
7
85
9
13
3
3
28
139
13
22
9
17
17
99
16
6
4
17
3
94
12
2
2
1
6
214
9
2
1
2
1
2
4
1
4
3
2
6
4
3
1
1
2
7
2
2
2
1
2
1
e
9
4
4
1
2
o
5
3
12
5
1
1
2
1
3
3
3
142
1
1
1
1
1
1
1
4
34
Total stimuli, 1983; vowel intelligibility, 61.2%.
Total stimuli, 1953; vowel intelligibility, 63.8%.
9 W. R. Tiffany, J. SpeechandHearingDisorders18, 379 (1953).
x0SeePotterand Steinberg's
paper(reference
3) wherevowelsspokenrepeatedlyby a trainedphoneticJan
are shownto have
remarkably distinct and invariableformant frequencies.
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618
J.
M.
TABLE
PICKETT
III.--Continued.
Part C' Flat noise,S/N=-
10 and --12 db.c
Responsevowel
•
u
A
a
59
1
2
3
9
5
5
21
2
1
2
149
10
4
80
7
2
1
4
1
3
2
17
8
69
2
6
90
1
2
1
9
e
ai
2
8
i
I
41
3
1
5
16
11
3
1
1
7
4
1
11
114
lO
11
4
1
5
198
5
15
2
1
8
151
19
12
ai
e
28
7
5
19
1
6
13
1
5
6
lOO
lO
6
5
2
14
204
1
au
iu
1
4
in
an
1
3
12
12
1
5
117
14
8
56
3
2
1
14
Part D' High-frequency noise,SIN =--33 db.d
Responsevowel
•
u
A
a
1
u
11
2
1
2
35
1
6
4
38
6
3
6
a•
10
1
2
2
1
3
ai
9
4
3
5
2
e
au
i
1
3
8
I
e
ai
14
4
6
1
2
6
4
1
13
3
1
8
1
4
10
1
4
2
2O
10
6
1
12
17
27
14
14
9
7
7
28
13
10
1
1
2
2
2
15
1
1
lO
11
2
3
2
24
11
1
2
2
4
36
12
3
2
au
4
13
11
27
5
9
11
iu
Part E' High-frequencynoise,S/N---
22 db.e
Responsevowel
u
U
o
o
o'
A
a
i
I
e
au
in
13
u
69
2
7
37
3
9
2
17
lO
4
e
83
64
49
124
3
5
2
ai
au
1
3
71
1
4
4
2
54
6
1
2
131
2
78
1
22
iu
Total stimuli, 2055; vowel intelligibility, 69.6 %.
Total stimuli, 747; vowel intelligibility, 32.8 %.
Total stimuli, 986; vowel intelligibility, 84.3 %.
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PERCEPTION
OF
VOWELS
IN
NOISE
VERY LOW FREQUENGYNOISE
SECOND
FORMANT
• LOW
619
LOW-FREQUENCY
NOISE
-'HIGH
foFIrst
.-•Hiah
Low
'---,' High
rmon! . --Law
'-- LoveHigh
I
LOW
LOW
LOw
High ,
HIGH
FORMANT
FLAT
NOISE
KEY
HIGH-FREQUENOY
NOISE
f,S/Nß-33
,HIGH-FREQUENGY
NOISE
f S/N--E2
Fro. 2. Simplifiedpatterns of confusionamongthe vowelsand diphthongsin PB wordsheard in noisesof variousspectra.The
stimuli are the rows. The frequencyof occurrenceof each stimulusdependedon the PB-word lists used. Original data are shown
in Table III. The formant key showshow the vowelswere groupedaccordingto the typical frequencyregionsof their formants.
Amount of confusionis indicated in four gradesby the size of dot entered in the confusioncells. When the dots fall heavily in the
shadedsquares,the first formant is maskedby the noiseand the secondis heard; when they fall on the diagonalsof the large,
unshadedrectangles,the first formant is heard and the secondis masked.
complicatetheir relationswith vowel perception.
n The
data from PB wordsalsoofferedan opportunityto see
whetherthe vowelfrequencydistributionof the stimulus
set had a marked effecton confusionpatterns.
The stimulus-response
matricesfor the vowelsof the
PB-word testsare shownin Table III and the simplified
confusionmatrices appear in Fig. 2. In interpreting
thesematrices,it shouldbe kept in mind that the different stimulus vowels and diphthongshave different
probabilitiesof occurrence.Vowelswith relatively high
values of the secondformant frequency occur about
2 timesmoreoften per vowel than thosewith low values
main differencesbetweenconfusions
amongthe syllables
where the vowelsoccurredwith equal probability, and
among the vowels of the P B words. The shift in confusion patterns with progressivelylower masking frequenciesis very striking.
An analysiswas made of the effectof stimulusprobability on the frequencyof occurrenceof eachvowel as
an
error
under
the
different
noise
conditions.
The
question was whether the listeners assigneduncertain
vowel responsesat random or accordingto their frequencyof occurrencein the stimulusset, or, in the case
of equalvowelprobability, accordingto their frequency
and 1.5 times more often than the three middle vowels.
of occurrencein past experience.The rank-order correSince the listenerswere made quite familiar with the lation betweendifferent vowel frequencydistributions
wordswhich might occur,we expectedto seea greater was usedas a meansof comparingthem. These correconcentrationof "guesses"fall amongthe vowelswith lations are shown in Table IV.
The correlation between the stimulus distribution and
high secondformants.Essentially,this accountsfor the
the error distributionfor PB wordsis significantin flat
n See Moser, Dreher, and Harbold, "Three magnitudes of
inter-phonemictransitionalinfluence," AF Cambridge Research and high-frequencynoise,showingthat listenersdo not
Center, Report TN 55-74, 1955. This investigationshowsthat assign uncertain responsesat random but tend to
listeners isolate and, to some extent, respondto the amount of match the stimulus set. For the equally probable
formant frequency shift which occurs when the articulatory
apparatus movesfrom consonantconstrictionto vowel position vowelsthe vowel error distributionsin high-frequency
and v.v.
noisealso correlatehighly with the distributionof the
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 192.87.79.51 On: Tue, 21 Oct 2014 10:32:57
620
J.
M.
PICKETT
TABLE IV. Rank-order correlations between frequency distributions of vowels as errors and as stimuli.
Vowel
Vowel errors
to PB words
Noise spectnlm
with PB-word
stimulus
vowels
Very low frequency
40.47
errors
to equally
Vowel
errors
to equally
probable vowels probable vowels
with PB-word
stimulus
vowels
-..
about 1.4 timesmoreoften per vowelin the PB lists
than thosewith low first formants,i, I, u, u, e, and o.
Perhapsthisrangeof stimulus
probabilities
is not large
enoughto havemucheffecton uncertainresponses.
with vowel
errors to PB
words
SUMMARY
The perceptionof vowelsspokenin syllablesand
--0.09
--'•.•}4
40.42
heard in noisesof various spectrawas analyzedby
meansof confusionmatrices.The followingconclusions
+0.56 •
+0.82 b
were reached:
Low
frequency +0.48
Flat
+0.61 a
--0.40
High frequency
+0.69 a
(1) Significant
shiftsin vowelconfusions
occurwith
Significantly different from zero at the $ % level.
Significantly different from zero at the 1% level.
changesin noisespectrum.
(2) The shiftsin vowelconfusions
areconsistent
with
stimulus vowels in the PB words and with the distribution of vowel errors to PB words heard in the same
type of noise.Three of the six listenersin thesetests
had had extensiveprior test experience
with PB-word
lists. Apparently a listener,when guessingat equally
probablevowels,is still constrained
to a distributionof
guesses
about the secondformant which conformsto
somedegreewith pasttraining.On the otherhand,with
low-frequency
and flat noisewherethe secondformant
is better heard but the first formant is masked,there is
no consistent relation
between
vowel distribution
in
a formanttheoryof vowelperception.
(3) When noisemasksprimarilyone formant,the
resulting
confusions
showthat theunmasked
formantis
correctlyperceived.
(4) Whenonlyoneformantis perceived,
differences
in durationamongthe vowelsare a strongfactor in
restrictingthe listener'sresponse.
(5) Vowelsspokenwith highernaturalintensityare
significantly
moreintelligiblein low-frequency
noise,
but not in high-frequency
and flat noise.
(6) Vowel-guessing
produces
frequency
distributions
whichconformin somedegreewith
the stimulussetand that in errorresponses.
The vowels of vowelresponses
distribution
of thevowels
in pasttraining.
with high first formants,ee,A, a, •, e, and• occuronly thefrequency
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