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Closure duration of stop consonants
Journal of Phonetics (198 3) 11 , 395 -400
Closure duration of stop consonants Elaine T. Stathopoulos Department of Communicative Disorders and Sciences, State University of New York at Buffalo , Buffalo, New York 14226, U.S.A.
and Gary W eismer Speech Motor Control Laboratories, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A . Received 9th June 1983
Abstract:
The present research was designed to provide additional data on stop closure durations as a function of (1) voicing, (2) stress, (3) position, and (4) place-of-articulation. Six subjects, three males and three females, produced a series of nonsense disyllables of the form CVCVC in a carrier phrase. The test consonant was systematically varied with respect to voicing, stress and position-in-disyllable. Results indicated that: (1) stress effects on stop closure duration vary as a function of stop voicing, (2) the effects on stop closure duration of position-in-word vary according to place of articulation, (3) stop voicing effects on duration are greatest for final stops, and that at least one case (initial stressed) shows voiced stops to have greater duration than voiceless stops, and ( 4) bilabials have longer closure durations than lingua-alveolars or dorsals in all conditions, although the magnitude of the effect varies with other factors.
Introduction It is well known that the duration of a stop consonant in the intervocalic, poststressed position may serve as a cue to that stop's voicing characteristic (Lisker, 1957). A more recent report (Lisker, 1972) on a single speaker has suggested that when stop-closure durations are examined in a variety of positions the voiceless stops have greater duration than the voiced stops only in the intervocalic poststressed position. Examination of other literature bearing on this issue, however, shows that experimental findings are diverse and often inconsistent. Certainly much of the data suggests that closure durations are longer for the voiceless as compared to the voiced stops. Not infrequently, though, acoustic, and physiologic results demonstrate that voiced stops have longer closure durations than voiceless stops, under certain conditions. For example, in Umeda's (1977) data for one speaker there appears to be some tendency for voiced lingua-alveolar and dorsal stops to be of greater duration than their voiceless cognates in the intervocalic, prestressed position. These differences depend on whether or not a word boundary precedes the stop in question. Fischer-J0rgensen (1954) reported close durations for the Danish stops /b/, /d/ and /g/ to be consistently longer than /p/, /t/ and /k/. Ma!ecot (1970), in a study of intraoral air pressures for stops, observed one inconsistency in the durations of the pressure events: 0095-4470/83/040395 + 06$03.00/0
© 1983 Academic Press Inc . (London) Ltd.
396
E. T. Stathopoulos and G. Weismer
initial /b/ was of greater duration than initial /p/, whereas medial and final /p/ were longer than medial and final /b/. In a previous study, Malecot (1968) reported data to the effect that voiceless stops had greater duration than voiced stops in several positions. Crystal & House (1982) reported hold portions of stops from a read script; the mean durations of the voiced stops were slightly longer (2 ms) than the voiceless stops. The variability in these data may possibly be explained by one or a combination of several factors. Among the many factors which may affect the duration of speech segments are stress (Oller, 1973 ; Klatt, 1976 ; Umeda, 1977; lngrisano & Weismer, 1979), number of syllables in a word (Klatt, 1976), syllable position-in-word and in-utterance (Lindblom & Rapp, 1973 ; Klatt, 1976) and phonetic context (Umeda, 1977). Thus, some of the diverse results obtained across studies may be due to variation in certain of these factors . In addition, several of the relevant studies are based on data from a single subject, so differences in results could be partly a function of inter-speaker variability . The present research was designed to provide additional data from several subjects on stop-closure durations as a function of voicing, stress, sex, position-in-word and place-ofarticulation. Method
Six subjects, three males and three females, produced a series of nonsense disyllables of the form consonant-vowel-consonant-vowel-consonant (CVCVC) in the carrier phrase "Say again". For each disyllable, one consonant was a " test consonant", and the other two were controls (see appendix for test stimuli). The test consonant was systematically varied with respect to voicing, stress, and position-in-disyllable, and place-of-articulation. All subjects produced the disyllables with fee / in the stressed syllables, and the vowel in all unstressed syllables was always produced as schwa. Vowel context was not varied as a pilot study (Stathopoulos & Weismer, 1979) indicated little or no effect on stop closure durations. Subjects produced the speech samples while seated in an lAC booth. Tape recordings were made on a Crown Series 700 recorder in association with a Shure microphone. Each subject produced five lists of 36 randomized sentence stimuli which included every possible combination of stress, position and place-of-articulation . Stop closure durations were measured from storage oscilloscope (Tektronix 51 08B) displays of the speech waveform. Stop closure duration was defined as the interval between the last glottal pulse for the preceding vowel and the burst of the following stop. All measurements were performed by one of the experimenters ; 10% of these data were remeasured by the same experimenter so that reliability of measurement could be determined (Snedecor & Cochran, 1967). No statistically significant differences were found in theremeasured data (t = 0.35); measurement of these data were judged to be reliable. Results and discussion
All data were pooled across sex because no trend was apparent to distinguish male and female productions. Table I shows the effect of stress in the initial, medial and final (stress in final position occurred when stress was placed on the second syllable) positions according to place-of-articulation and voicing characteristics of the stop. The values entered in the table are means and standard deviations in ms . The first obvious feature of these data is that stressed stops are produced with longer closure durations then unstressed stops in initial and medial positions across all places-of-articulation. In the final position, unstressed stops were associated with longer closure durations than stressed stops and this appears to be due mostly to the voiced condition. Also , the stress effect appears to be greater for voiced stops
Table I Stop closure durations (ms) are shown as a function of position, voicing, place-of-articulation, and stress. Difference scores (in ms) for stop closure durations are shown between voiced and voiceless stops in each position and stress condition at the bottom of the table. A positive value indicates that voiceless stop durations were longer than voiced stop durations. A negative value(-) indicates that voiced stop durations are longer than voiceless stop durations
Initial
v
Bilabial
fo
Medial
v
VL
!:::
i::i ......
VL
cs·
;:s
+
+
-
+
122 15
106 16
115 20
106 16
92
10
66 162
96 12
87 11
75 9
86 26
98 23
96 22
+
"'
!:::
(il
~
Final
v
VL
~
+
+
2.,
"' (3" '"'=S r,
0
;:s
L-A
X SD
114 17
80 15
105 18
85 13
76 13
41 15
82 13
44 11
40 11
58 15
58 23
76 24
Dorsal
X SD
107 16
78
103 21
84 16
68 10
56 7
72 11
71 13
64 10
71 15
83 18
82 13
[:3
;:s
§
r;;-
12
Initial + Stress
Initial - Stress
-7
5
Medial + Stress
5
Medial- Stress
13
Final+ Stress
Final - Stress
20
13
V = voiced, VL = voiceless,+ = stressed,-= unstressed.
w \0 -....]
398
E. T. Stathopoulos and G. Weismer
as compared to voiceless stops and seems to be independent of place-of-articulation and position-in-word. The exceptions to this trend are seen for the lingua-alveolar stops in medial and final positions; the effect in the medial position is largely due to similar durations for the unstressed /t/ and /d/ which are both realized as flaps. Voicing effects can be seen by examining Table I (top). First, voiceless stops are generally produced with longer closure durations and are unaffected by place-of-articulation. A second notable trend for voicing occurred as a position and stress effect. In the initial stressed condition, the mean duration of voiced stops across all places-of-articulation are longer than all voiceless stops. The differences in duration between the voiced and voiceless stops in each position and stress condition are shown at the bottom of Table I. The medial stress condition should be considered first , since this is the environment in which voiceless stops consistently have been shown to be of greater duration than voiced stops (Lisker, 1957, 1972; Male cot, 1968). The present data confirms this, although the magnitude of the difference (13 ms) is less than that reported by Lisker (1971, 36 ms) or which is apparent from Malecot's (1968) tables (30-40 ms). In Umeda's (1977) data, the average difference between voiceless and voiced bilabials and dorsals is 9 ms , which is in good agreement with the present data. It seems likely that the large differences obtained by Lisker (1972) and Malecot (1968) are due in part to the use of isolated word production, because Umeda (1977) used connected speech and the present study employed an approximation thereto . Closure durations of stops in the final position are subject to a larger voicing effect (voiceless greater than voiced) for both stressed and unstressed conditions. The syllable-initial stressed condition, as mentioned previously is the only one in which the mean duration of the voiced stop is clearly longer than the voiceless stops; a finding of similar magnitude is shown by Lisker (1972), but Malecot's (1968) data reveal no such effect. Why should voiced stops be longer than voiceless stops only in the word-initial, prestressed position? This does not appear to be a syllable-onset effect because then the same thing should occur in the medial position before stress. Nor is it simply a word-initial effect because it does not occur in the initial-word unstressed condition. The only combination of conditions in which the voicing effect occurs is in the word-initial prestress environment. A possible explanation for the voicing effect lies in the structure of the carrier phrase employed in this study. In the carrier phrase, the initial word "say" is a lexical item and therefore carries word stress (sentence-beginning words typically have at least pitch peaks which makes them intonationally prominent, Stathopoulos & Duchan, 1982). Our speakers were instructed to produce each sentence with normal loudness and pitch with the additional instruction to stress the marked syllables in the target words; the realization of this instruction was that the stressed syllable in the target word became the prominent word within the entire sentence. The speaker now has the problem of making the initial syllable of the target word more prominent than the immediately preceding syllable which already carries initial word-in-sentence stress (i.e . the target word needs extra stress). Since one manifestation of stress is duration , lengthening of VL stops could be achieved by increasing voice onset time (VOT). In the case of V stops, VOT cannot be lengthened, so the stop closure duration is increased. This hypothesis could be tested in a future study by using a carrier phrase with an unstressed function word immediately preceding the target word such as "Say the _ _ again" . Since the immediately preceding syllable is unstressed, there is no need for the extra stress on the target word and the initial-stress position effect found in these data would disappear: the VL stop should again have greater closure durations than V stops and the VL stop VOT should be shorter than those seen in the present study in the initial prestressed condition. The initial prestressed voicing phenomena found in the present
399
Closure duration of stop consonants
Table II Difference scores for stop closure duration (in ms) as a function of place of articulation Initial
v +
Medial
v
VL
+
+
Final
v
VL
+
VL
+
+
A
8
26
10
21
16
26
14
44
35
28
34
20
B
15
27
12
22
24
11
24
16
11
15
15
13
V = voiced , VL = voiceless; ( +) = stressed condition. (-) = unstressed co nditio n; A = bilabial stops minus lingua-alveolar stops, B = bilabial stops minus dorsal stops.
investigation is likely to appear in natural speech as it is not unusual to find two stressed syllables adjacent to each other. Mean closure durations for each place-of-articulation, pooled across sex, can be seen in Table I (top) , data are given at each position-in-word and voicing/stress combination. These results are presented as difference scores in Table II and are consistent with the finding of previous studies (see Smith for a review, 1978) which show the bilabials have longer closure durations than either lingua-alveolars or dorsals. This appears to be true for all positions and voicing/stress combinations. In final position, it appears that the mean durations difference between bilabials and other places is somewhat greater. The effect of position on stop closure duration is reported in Table III. These data entered are means and standard deviations which were averaged across all subjects and placeof-articulation . The most striking effect is that seen for initial-position consonants which were always produced with longer closure durations than median or final stops ; this was true for both conditions of stress and voicing. The same effect for both conditions of stress was not seen when examining these data in medial and final positions. Voiced and voiceless stressed stops were produced with longer closure durations in medial position as compared to the final position, however, final position unstressed stops were produced with longer closure durations than the medial stop for the same condition of voicing. For example, the final voiced unstressed stops had an average closure duration of 71 ms while the medial voiced unstressed stops had a closure duration of 54ms. This final syllable lengthening effect is consistent for the voiced and voiceless unstressed conditions and is in agreement with previous observations of word-final syllable lengthening (Oller, 1973). In summary , the present study has demonstrated that: (1) stress effects on stop closure Table Ill Stop closure duration (ms) means and standard deviations are shown as a function of stress, voicing and position -in-word_ Data was averaged across sex and place-of-articulation
v Stress
Unstress
X SD
X SD
Initial
VL
v
115 17
108 20
87 17
92 18
V = voiced, VL =voiceless .
Medial
Final
VL
v
79 15
84 16
60 18
80 27
54 16
67 23
71 23
85 22
VL
400
E. T. Stathopoulos and G. Weismer
duration vary as a function of stop voicing, (2) the effects on stop closure duration of position-in-word vary according to place of articulation, (3) stop voicing effects on duration are greatest for final stops, and that at least one case (initial stressed) shows voiced stops to have greater duration than voiceless stops, and (4) bilabials have longer closure durations than lingua-alveolars or dorsals in all conditions, although the magnitude of the effect varies with other factors. References Crystal, T. H. & House, A.S . (1982). Segmental durations in connected speech signals: preliminary results. Journal of Acoustical Society of America, 72 , 705-716. Fischer-J0rgensen , E. (1954). Acoustic analysis of stop consonants. Miscellanea Phonetica, II , 42-59. lngrisano, D. & Weismer, G. (1979). s-duratio n: Methodological and linguistic factors. Phonetica, 36, 32-43. Klatt , D. H. (1976) . Linguistic uses of segmental duration in English: Acoustic and perceptual evidence. Journal of Acoustical Society of America, 59,1208-1221. Lindblom, B. & Rapp , K. (1973). Some temporal regularities of spoken Swedish. PILUS Papers , No. 21, Stockholm: Institute of Linguistics. Lisker, L. (1957) . Closure duration and th e intervocalic voiced-voiceless distinction in English. Language, 33,42-49. Lisker , L. (1972). Stop duration and voicing in English. In: Papers in Linguistics and Phonetics to the Memory of Pierre Delattre. (A. Valdman , ed.). pp. 339-343. Paris: Mouton. Malecot, A. (1968). The force of articu lation of American stops and fricatives as a function of position. Phonetica, 18, 95-102. Malecot, A. (1970). The lenis-fortis opposition: Its physiological parameters. Journal of Acoustical So ciety of America, 47,1588-1592. Oller, D. K. (1973). The effect of position in utterance on speech segment duration in English.Journal of Acoustical Society of America, 54, 1235-124 7. Snedecor, G. W. & Cochran, W. G. (1967). Statistical Methods. Ames, Iowa: State University Press . Stathopoulos, E. T. & Weismer , G. (1979). The duration of stop consonants. Acoustical Society of America Speech Communication Preprint, MIT , Cambridge, Massachusetts, June, 201-204. Stathopoulos, E.T., Duchan, J. F., Bruce , N. V. & Sonnenmeier, R . (1983). Intonation and t iming in deaf speech. Journal of Speech and Hearing Disorders. (In press). Smith, B. L. (1978). Temporal aspects of English speech production. Journal of Phonetics, 6, 37-68. Umeda, N. (1977). Co nso nant duration in American English . Journal of Acoustical Society of America , 61, 846-858.
Appendix l. b ;/deed 1 deeb;)d 2. 3. 'deed;>t 4. d;)'deed 5. 'teed;)d ,6. geed;>d 7. d;)'geed 8. t ;)'deed 1 9. p ;) deed 10. d;)'teed 11. d;)'peed 12. d;)'deeb 13. 'deed;)p 14. 'deed.Jd 15. 'deed;)b 16. 'deet;)d 17. g;)'deed 18. 1 heed;)d
19. 20. 21. 22. 23. 24. 25 . 26. 27.
28. 29. 30. 31. 32. 33. 34. 35 . 36.
d ;)'beed d ;)'deeg 'keed;)d d-;)'keed k ;)'deed d;)'deed I peed;)d 'deed;)g 'deebd 'deed;)d d;)'deet d ;)'deek d ;)'deed 'deed;)k 'deed;)d 'deep;)d 'deeg;)d d ;)'deep
Closure duration of stop consonants Elaine T. Stathopoulos Department of Communicative Disorders and Sciences, State University of New York at Buffalo , Buffalo, New York 14226, U.S.A.
and Gary W eismer Speech Motor Control Laboratories, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A . Received 9th June 1983
Abstract:
The present research was designed to provide additional data on stop closure durations as a function of (1) voicing, (2) stress, (3) position, and (4) place-of-articulation. Six subjects, three males and three females, produced a series of nonsense disyllables of the form CVCVC in a carrier phrase. The test consonant was systematically varied with respect to voicing, stress and position-in-disyllable. Results indicated that: (1) stress effects on stop closure duration vary as a function of stop voicing, (2) the effects on stop closure duration of position-in-word vary according to place of articulation, (3) stop voicing effects on duration are greatest for final stops, and that at least one case (initial stressed) shows voiced stops to have greater duration than voiceless stops, and ( 4) bilabials have longer closure durations than lingua-alveolars or dorsals in all conditions, although the magnitude of the effect varies with other factors.
Introduction It is well known that the duration of a stop consonant in the intervocalic, poststressed position may serve as a cue to that stop's voicing characteristic (Lisker, 1957). A more recent report (Lisker, 1972) on a single speaker has suggested that when stop-closure durations are examined in a variety of positions the voiceless stops have greater duration than the voiced stops only in the intervocalic poststressed position. Examination of other literature bearing on this issue, however, shows that experimental findings are diverse and often inconsistent. Certainly much of the data suggests that closure durations are longer for the voiceless as compared to the voiced stops. Not infrequently, though, acoustic, and physiologic results demonstrate that voiced stops have longer closure durations than voiceless stops, under certain conditions. For example, in Umeda's (1977) data for one speaker there appears to be some tendency for voiced lingua-alveolar and dorsal stops to be of greater duration than their voiceless cognates in the intervocalic, prestressed position. These differences depend on whether or not a word boundary precedes the stop in question. Fischer-J0rgensen (1954) reported close durations for the Danish stops /b/, /d/ and /g/ to be consistently longer than /p/, /t/ and /k/. Ma!ecot (1970), in a study of intraoral air pressures for stops, observed one inconsistency in the durations of the pressure events: 0095-4470/83/040395 + 06$03.00/0
© 1983 Academic Press Inc . (London) Ltd.
396
E. T. Stathopoulos and G. Weismer
initial /b/ was of greater duration than initial /p/, whereas medial and final /p/ were longer than medial and final /b/. In a previous study, Malecot (1968) reported data to the effect that voiceless stops had greater duration than voiced stops in several positions. Crystal & House (1982) reported hold portions of stops from a read script; the mean durations of the voiced stops were slightly longer (2 ms) than the voiceless stops. The variability in these data may possibly be explained by one or a combination of several factors. Among the many factors which may affect the duration of speech segments are stress (Oller, 1973 ; Klatt, 1976 ; Umeda, 1977; lngrisano & Weismer, 1979), number of syllables in a word (Klatt, 1976), syllable position-in-word and in-utterance (Lindblom & Rapp, 1973 ; Klatt, 1976) and phonetic context (Umeda, 1977). Thus, some of the diverse results obtained across studies may be due to variation in certain of these factors . In addition, several of the relevant studies are based on data from a single subject, so differences in results could be partly a function of inter-speaker variability . The present research was designed to provide additional data from several subjects on stop-closure durations as a function of voicing, stress, sex, position-in-word and place-ofarticulation. Method
Six subjects, three males and three females, produced a series of nonsense disyllables of the form consonant-vowel-consonant-vowel-consonant (CVCVC) in the carrier phrase "Say again". For each disyllable, one consonant was a " test consonant", and the other two were controls (see appendix for test stimuli). The test consonant was systematically varied with respect to voicing, stress, and position-in-disyllable, and place-of-articulation. All subjects produced the disyllables with fee / in the stressed syllables, and the vowel in all unstressed syllables was always produced as schwa. Vowel context was not varied as a pilot study (Stathopoulos & Weismer, 1979) indicated little or no effect on stop closure durations. Subjects produced the speech samples while seated in an lAC booth. Tape recordings were made on a Crown Series 700 recorder in association with a Shure microphone. Each subject produced five lists of 36 randomized sentence stimuli which included every possible combination of stress, position and place-of-articulation . Stop closure durations were measured from storage oscilloscope (Tektronix 51 08B) displays of the speech waveform. Stop closure duration was defined as the interval between the last glottal pulse for the preceding vowel and the burst of the following stop. All measurements were performed by one of the experimenters ; 10% of these data were remeasured by the same experimenter so that reliability of measurement could be determined (Snedecor & Cochran, 1967). No statistically significant differences were found in theremeasured data (t = 0.35); measurement of these data were judged to be reliable. Results and discussion
All data were pooled across sex because no trend was apparent to distinguish male and female productions. Table I shows the effect of stress in the initial, medial and final (stress in final position occurred when stress was placed on the second syllable) positions according to place-of-articulation and voicing characteristics of the stop. The values entered in the table are means and standard deviations in ms . The first obvious feature of these data is that stressed stops are produced with longer closure durations then unstressed stops in initial and medial positions across all places-of-articulation. In the final position, unstressed stops were associated with longer closure durations than stressed stops and this appears to be due mostly to the voiced condition. Also , the stress effect appears to be greater for voiced stops
Table I Stop closure durations (ms) are shown as a function of position, voicing, place-of-articulation, and stress. Difference scores (in ms) for stop closure durations are shown between voiced and voiceless stops in each position and stress condition at the bottom of the table. A positive value indicates that voiceless stop durations were longer than voiced stop durations. A negative value(-) indicates that voiced stop durations are longer than voiceless stop durations
Initial
v
Bilabial
fo
Medial
v
VL
!:::
i::i ......
VL
cs·
;:s
+
+
-
+
122 15
106 16
115 20
106 16
92
10
66 162
96 12
87 11
75 9
86 26
98 23
96 22
+
"'
!:::
(il
~
Final
v
VL
~
+
+
2.,
"' (3" '"'=S r,
0
;:s
L-A
X SD
114 17
80 15
105 18
85 13
76 13
41 15
82 13
44 11
40 11
58 15
58 23
76 24
Dorsal
X SD
107 16
78
103 21
84 16
68 10
56 7
72 11
71 13
64 10
71 15
83 18
82 13
[:3
;:s
§
r;;-
12
Initial + Stress
Initial - Stress
-7
5
Medial + Stress
5
Medial- Stress
13
Final+ Stress
Final - Stress
20
13
V = voiced, VL = voiceless,+ = stressed,-= unstressed.
w \0 -....]
398
E. T. Stathopoulos and G. Weismer
as compared to voiceless stops and seems to be independent of place-of-articulation and position-in-word. The exceptions to this trend are seen for the lingua-alveolar stops in medial and final positions; the effect in the medial position is largely due to similar durations for the unstressed /t/ and /d/ which are both realized as flaps. Voicing effects can be seen by examining Table I (top). First, voiceless stops are generally produced with longer closure durations and are unaffected by place-of-articulation. A second notable trend for voicing occurred as a position and stress effect. In the initial stressed condition, the mean duration of voiced stops across all places-of-articulation are longer than all voiceless stops. The differences in duration between the voiced and voiceless stops in each position and stress condition are shown at the bottom of Table I. The medial stress condition should be considered first , since this is the environment in which voiceless stops consistently have been shown to be of greater duration than voiced stops (Lisker, 1957, 1972; Male cot, 1968). The present data confirms this, although the magnitude of the difference (13 ms) is less than that reported by Lisker (1971, 36 ms) or which is apparent from Malecot's (1968) tables (30-40 ms). In Umeda's (1977) data, the average difference between voiceless and voiced bilabials and dorsals is 9 ms , which is in good agreement with the present data. It seems likely that the large differences obtained by Lisker (1972) and Malecot (1968) are due in part to the use of isolated word production, because Umeda (1977) used connected speech and the present study employed an approximation thereto . Closure durations of stops in the final position are subject to a larger voicing effect (voiceless greater than voiced) for both stressed and unstressed conditions. The syllable-initial stressed condition, as mentioned previously is the only one in which the mean duration of the voiced stop is clearly longer than the voiceless stops; a finding of similar magnitude is shown by Lisker (1972), but Malecot's (1968) data reveal no such effect. Why should voiced stops be longer than voiceless stops only in the word-initial, prestressed position? This does not appear to be a syllable-onset effect because then the same thing should occur in the medial position before stress. Nor is it simply a word-initial effect because it does not occur in the initial-word unstressed condition. The only combination of conditions in which the voicing effect occurs is in the word-initial prestress environment. A possible explanation for the voicing effect lies in the structure of the carrier phrase employed in this study. In the carrier phrase, the initial word "say" is a lexical item and therefore carries word stress (sentence-beginning words typically have at least pitch peaks which makes them intonationally prominent, Stathopoulos & Duchan, 1982). Our speakers were instructed to produce each sentence with normal loudness and pitch with the additional instruction to stress the marked syllables in the target words; the realization of this instruction was that the stressed syllable in the target word became the prominent word within the entire sentence. The speaker now has the problem of making the initial syllable of the target word more prominent than the immediately preceding syllable which already carries initial word-in-sentence stress (i.e . the target word needs extra stress). Since one manifestation of stress is duration , lengthening of VL stops could be achieved by increasing voice onset time (VOT). In the case of V stops, VOT cannot be lengthened, so the stop closure duration is increased. This hypothesis could be tested in a future study by using a carrier phrase with an unstressed function word immediately preceding the target word such as "Say the _ _ again" . Since the immediately preceding syllable is unstressed, there is no need for the extra stress on the target word and the initial-stress position effect found in these data would disappear: the VL stop should again have greater closure durations than V stops and the VL stop VOT should be shorter than those seen in the present study in the initial prestressed condition. The initial prestressed voicing phenomena found in the present
399
Closure duration of stop consonants
Table II Difference scores for stop closure duration (in ms) as a function of place of articulation Initial
v +
Medial
v
VL
+
+
Final
v
VL
+
VL
+
+
A
8
26
10
21
16
26
14
44
35
28
34
20
B
15
27
12
22
24
11
24
16
11
15
15
13
V = voiced , VL = voiceless; ( +) = stressed condition. (-) = unstressed co nditio n; A = bilabial stops minus lingua-alveolar stops, B = bilabial stops minus dorsal stops.
investigation is likely to appear in natural speech as it is not unusual to find two stressed syllables adjacent to each other. Mean closure durations for each place-of-articulation, pooled across sex, can be seen in Table I (top) , data are given at each position-in-word and voicing/stress combination. These results are presented as difference scores in Table II and are consistent with the finding of previous studies (see Smith for a review, 1978) which show the bilabials have longer closure durations than either lingua-alveolars or dorsals. This appears to be true for all positions and voicing/stress combinations. In final position, it appears that the mean durations difference between bilabials and other places is somewhat greater. The effect of position on stop closure duration is reported in Table III. These data entered are means and standard deviations which were averaged across all subjects and placeof-articulation . The most striking effect is that seen for initial-position consonants which were always produced with longer closure durations than median or final stops ; this was true for both conditions of stress and voicing. The same effect for both conditions of stress was not seen when examining these data in medial and final positions. Voiced and voiceless stressed stops were produced with longer closure durations in medial position as compared to the final position, however, final position unstressed stops were produced with longer closure durations than the medial stop for the same condition of voicing. For example, the final voiced unstressed stops had an average closure duration of 71 ms while the medial voiced unstressed stops had a closure duration of 54ms. This final syllable lengthening effect is consistent for the voiced and voiceless unstressed conditions and is in agreement with previous observations of word-final syllable lengthening (Oller, 1973). In summary , the present study has demonstrated that: (1) stress effects on stop closure Table Ill Stop closure duration (ms) means and standard deviations are shown as a function of stress, voicing and position -in-word_ Data was averaged across sex and place-of-articulation
v Stress
Unstress
X SD
X SD
Initial
VL
v
115 17
108 20
87 17
92 18
V = voiced, VL =voiceless .
Medial
Final
VL
v
79 15
84 16
60 18
80 27
54 16
67 23
71 23
85 22
VL
400
E. T. Stathopoulos and G. Weismer
duration vary as a function of stop voicing, (2) the effects on stop closure duration of position-in-word vary according to place of articulation, (3) stop voicing effects on duration are greatest for final stops, and that at least one case (initial stressed) shows voiced stops to have greater duration than voiceless stops, and (4) bilabials have longer closure durations than lingua-alveolars or dorsals in all conditions, although the magnitude of the effect varies with other factors. References Crystal, T. H. & House, A.S . (1982). Segmental durations in connected speech signals: preliminary results. Journal of Acoustical Society of America, 72 , 705-716. Fischer-J0rgensen , E. (1954). Acoustic analysis of stop consonants. Miscellanea Phonetica, II , 42-59. lngrisano, D. & Weismer, G. (1979). s-duratio n: Methodological and linguistic factors. Phonetica, 36, 32-43. Klatt , D. H. (1976) . Linguistic uses of segmental duration in English: Acoustic and perceptual evidence. Journal of Acoustical Society of America, 59,1208-1221. Lindblom, B. & Rapp , K. (1973). Some temporal regularities of spoken Swedish. PILUS Papers , No. 21, Stockholm: Institute of Linguistics. Lisker, L. (1957) . Closure duration and th e intervocalic voiced-voiceless distinction in English. Language, 33,42-49. Lisker , L. (1972). Stop duration and voicing in English. In: Papers in Linguistics and Phonetics to the Memory of Pierre Delattre. (A. Valdman , ed.). pp. 339-343. Paris: Mouton. Malecot, A. (1968). The force of articu lation of American stops and fricatives as a function of position. Phonetica, 18, 95-102. Malecot, A. (1970). The lenis-fortis opposition: Its physiological parameters. Journal of Acoustical So ciety of America, 47,1588-1592. Oller, D. K. (1973). The effect of position in utterance on speech segment duration in English.Journal of Acoustical Society of America, 54, 1235-124 7. Snedecor, G. W. & Cochran, W. G. (1967). Statistical Methods. Ames, Iowa: State University Press . Stathopoulos, E. T. & Weismer , G. (1979). The duration of stop consonants. Acoustical Society of America Speech Communication Preprint, MIT , Cambridge, Massachusetts, June, 201-204. Stathopoulos, E.T., Duchan, J. F., Bruce , N. V. & Sonnenmeier, R . (1983). Intonation and t iming in deaf speech. Journal of Speech and Hearing Disorders. (In press). Smith, B. L. (1978). Temporal aspects of English speech production. Journal of Phonetics, 6, 37-68. Umeda, N. (1977). Co nso nant duration in American English . Journal of Acoustical Society of America , 61, 846-858.
Appendix l. b ;/deed 1 deeb;)d 2. 3. 'deed;>t 4. d;)'deed 5. 'teed;)d ,6. geed;>d 7. d;)'geed 8. t ;)'deed 1 9. p ;) deed 10. d;)'teed 11. d;)'peed 12. d;)'deeb 13. 'deed;)p 14. 'deed.Jd 15. 'deed;)b 16. 'deet;)d 17. g;)'deed 18. 1 heed;)d
19. 20. 21. 22. 23. 24. 25 . 26. 27.
28. 29. 30. 31. 32. 33. 34. 35 . 36.
d ;)'beed d ;)'deeg 'keed;)d d-;)'keed k ;)'deed d;)'deed I peed;)d 'deed;)g 'deebd 'deed;)d d;)'deet d ;)'deek d ;)'deed 'deed;)k 'deed;)d 'deep;)d 'deeg;)d d ;)'deep