LETTERS
TO THE EDITOR
ThisLetterssectionis forpublishing(a) briefacousticalresearchor appliedacousticalreports,and (b) commentson articlesor letterspreviouslypublishedin thisJournal.Extensivereportsshouldbe submittedas articles,not in a letter series.Lettersarepeer-reviewed on the same basisas articles,but usuallyrequirelessreviewtimebefore acceptance.Letterscannotexceed fourprintedpages (approximately3000-4000 words)includingl•7ures,tables,references,and a requiredabstractof about 100 words.
Effect of intensity slopeson the perception of vowel duration Yukihiro NishinumaandSerge Santi InstitutdePhon•tique,Universit•deProvence, CNRS R. U.A.261, 29AvenueRobert$chuman, 13621Aix-en-Provence, France
(Received2 January1992;revised17June1992;accepted13August1992)
Thediscrimination of durationwasinvestigated usingsynthetic vowelswithnegative intensity changes (0, - 6, - 12,and - 18dB). Teststimulus durations rangedfrom 100to 300msin stepsof 20 msandthestandard stimulus was200msin durationandhada uniformintensity. Stimulus pairswerepresented to 20 subjects whosetaskwasto statewhichvowelin thepair sounded longer(forcedchoice;methodof constant stimuli).The dataindicatethata dropin intensityof morethan 12dB resultsin a significant decrease in discriminability of duration differences.
PACS numbers:43.71.Hw, 43.66.Mk, 43.66.Fe
(the observedaveragewas -- 16 dB in our prior speech data) wouldmakeit difficultto correctlyperceivethat syllaTheprosodic analysis of speech, whichconsists of interpretingacoustic parameters suchasduration,fundamental ble'sduration.An experimentcarried out to verify this hypothesisis reportedbelow. frequency, andintensity,isnotaneasytask.Two reasons for thisarethat thesefactorsare not independentin humanperceptionandtheyvary asthe speechsignalevolvesin time; I. EXPERIMENT i.e., withina syllable,word,clause,etc.It is knownthat the Klatt's formantsynthesizer wasusedto generatestimuli perception of pitchvariationsdepends uponthedurationof voicedsounds(Rossi, 1971;Beckman,1986). Furthermore, for theperception test(Klatt, 1980).The goalwasto obtain themelodiccontoursof segments with negativeandpositive speech-like stimulithat variedin bothdurationandintensiintensityglides(i.e., overallintensitychanges appliedto the ty. Negativeintensitychanges(overallintensitydecreases) source)are perceiveddifferently(Rossi, 1978; Beckman, were usedto approximatethe final syllableof declarative 1986). However, we know little about the interaction besentences.The material was designedto be usedin a psychoacoustic test based on the method of constant stimuli. tweendurationand intensityin speech.In particular,the a duration of influenceof intensityvariationsontheabilityto discriminate The standard stimulus was the vowel/a/with the durationof speechsoundshasnot beenexperimentally 200 ms and a uniform intensity contour of 80 dB at the to the averagelength of documented.This problem arosein our previousstudy, source.This durationcorresponds stressed syllablesin a normalspeechrate in French.The test whichinvestigated the differentialthresholdof syllableduration in a sentencecontext in French (Nishinuma, 1990). stimuli weresynthesizedwith durationsrangingfrom 100to Here the term differential threshold is used to refer to the 300 msin 20-mssteps(for a total of 11 differentdurations). differentiallimen (DL) or just-noticeabledifference(jnd). Four linear intensityslopeswereutilized:0, - 6, - 12, and Duration discriminationwas found to be significantlyless -- 18 dB (Fig. 1). The fundamentalfrequencycontourwas accurateon the final syllable (stressed,thereforelonger) the samefor all stimuli. A slightloweringof overall pitch from 140 to 130 Hz made the stimuli sound natural. The than on precedingsyllables.The sametendencywas obstandardstimuluswas paired with eachof the test stimuli servedin Klatt and Cooper'sdata (1975), whichshoweda (thus, a stimulus pair might sound like two successive higherthresholdfor the durationof fricativesat the endof sentences than in other locations.This raisedthe questionof monosyllabicwords). The two vowelsin eachpair weresepwhethera dropin intensityon thefinalsyllableof a sentence aratedby a silentperiodof 600 ms. The intervalseparating INTRODUCTION
3425
J. Acoust.Soc.Am.92 (6), December1992
0001-4966/92/123425-03500.80
@ 1992Acoustical Societyof America
3425
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.59.222.12 On: Fri, 28 Nov 2014 07:14:26
40 T !
20•IB
•
T In•en•itLj i
•
l
o da -•
- 6; dB _ 18dB
Duration
FIG.1.Intensity envelopes used forstimulus generation. Toavoid clicking,
a 20-Blineardropinintensity for10mswasadded atsegment onset and offset.
10
i 0 dB
I -6 dB
I -12
I dB
,
-11• dB
Intensity slopes
onepairfromthenextwasthreeseconds. Bothwithin-pair orders were used, standard/test stimulus and vice versa.
Each pair occurredfour times. Stimuli were generatedin random order by a computer and recordedon a digital audiotape.A trial seriesof 22 pairswasaddedto the beginning of the test sequence.A shortbeepfollowedby a five second silent interval was insertedafter every 22 pairs. The perceptiontestswere carried out in a soundproof room. Twenty subjectswere tested individually, each in a singletrial lasting20 min. The listeninglevelof the standard stimulusleavingthe headphones wassetat approximately70 dB. The subjectswereinstructedto mark which vowelin the pair waslongerby checkingon a forced-choiceanswersheet. II. RESULTS
AND DISCUSSION
A two-way repeated-measures analysisof variancewas performed.The dependentvariablewas the duration of the stimulusuponwhichthe subjectchangedanswersfrom "the first is longer" to "the secondis longer" or vice versa,for each repeat.The two independentvariableswere stimulus order and intensityslope.As expected,variationsin the intensity factor produced significantly different results [F(3,152) = 10.464,p < 0.001]. Stimulusorderalsoyielded a significanteffect[F(1,152) = 4.971,p < 0.05]. There was a significnatinteractionbetweenstimulusorder and intensity slope[F( 3,152) = 5.089,p < 0.01]. We observedlessaccurate reactionsamongsubjectsto the stimuluspairs presented in "test/standard order" for the steeperintensity slopes. Assuminga psychometricfunction with a cumulative normal distribution,the threshold (jnd in duration) wasinterpolatedat the 75% correctlevel.As isshownin Fig. 2, the thresholdin millisecondsfor durationwas proportionalto the magnitudeof the intensityslope.In other words,as the intensityslopebecamesteeper,the detectionof durationdifferences became less and less accurate. This effect on the
discriminationof durationis clearly shownby the progressiveincreasein the means.Interestingly,thepost-hocteston the data for the firsttwo intensityslopes(0 and -- 6 dB) did not yield any significantdifferences.Apparently, a 6-dB drop in intensitydoesnot leadto difficultyin detectingthe correct duration. In contrast, the stable versus -- 12-dB dif-
ference was statistically significant [F(1,152) = 3.113, p • 0.01], and thereforethe opposition"stableand -- 6 dB" 3426
J. Acoust. Soc. Am., Vol. 92, No. 6, December 1992
FIG. 2. Durationthreshold asa functionof intensity slopefora standard duration of 200ms.Durationthreshold in milliseconds isplottedonthey axisandtheintensity slopes applied to theteststimuliareplottedonthex axis.Eachpointrepresents themeanof the20 subjects ( 160judgments) interpolated at the 75% levelof the psychometric function.The standard
deviation isindicated bya verticallineacross themeanpoint.
vs "-- 12and -- 18dB" wassignificant[F(1,152) = 3.738, p • 0.01 ]. It is noteworthythat our resultsindirectlysupport thoseobtainedby Rossi (1978), who estimatedthe intensity glidethresholdto be approximately11dB for a vowellasting 200 ms. The observedchangein the way intensityinformation is processedseemsto dependon whether or not the intensitydecreasesbeyondthat critical value. In comparisonto the resultspublishedin psychoacoustic studiesusingspeechsounds,our thresholdvalue at 200 msis closeto the minimumvalueof thosepreviouslyreported. For a standard stimulus duration of about 200 ms, the
reportedjust-noticeabledifferencein duration,with uniform intensity,generallyrangesfrom 8% to 30% with a representative valuewhich appearsto be approximately20% (Huggins, 1971a,b;Nooteboom, 1973; Klatt and Cooper, 1975; Bovet and Rossi, 1977; Rossi, 1972; Eilers et al., 1984; Bochneret al., 1988). Theseexperimentsusedseveralstandard stimulusdurationsrangingfrom someten milliseconds to severalhundredmilliseconds.In our experiment,all stimulus pairshad a 200-msvowel (the only standardduration used), with a level intensityin first or secondposition.The fact that a stimulus of this constant duration
was available
on all trials for comparisonmay have reducedtask uncertainty and thus led to better performance.The duration thresholddefinedhere (i.e., asa functionof intensityslope) shouldthereforenot be viewed as comparableto thoseobtained under normal, stableintensityconditions. III. CONCLUSIONS
The resultsof our perceptiontestsdemonstratedthat the discriminationthresholdsfor duration may be significantly increasedby a progressivedecreasein intensityof morethan ten decibels.This findingmay havesomeimplicationsfor the interpretationof prosodicdata at the sentence level.
Y. Nishinuma and S. Santi: Letters to the Editor
3426
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.59.222.12 On: Fri, 28 Nov 2014 07:14:26
Beckman, M. E. (1986). Stressand Non-StressAccent (Foris, Dordrecht, The Netherlands). Bochner,J. H., Snell, K. B., and MacKenzie, D. J. (1988). "Duration dis-
criminationof speechandtonalcomplexstimuliby normalhearingand hearing-impaired listeners,"J. Acoust.Soc.Am. 84, 493-500. Bovet,P., andRossi,M. (1977). "Etudecompar6e dela sensibilit6 diff6rentielle•tla dur6eavecun sonpur et avecunevoyelle,"Du tempsbiologique au tempspsychologique, PUF, Paris,289-306. Eilers, R. E., Bull, D. H., Oller, D. K., and Lewis, D.C. (1984). "The discriminationof vowel duration by infants," J. Acoust. Soc. Am. 75, 1213-1218.
Huggins,A. W. F. (1971a). "Justnoticabledifferences for segmentduration in naturalspeech,"J. Acoust.Soc.Am. 51, 1270-1278. Huggins,A. W. F. (1971b). "On theperceptionof temporalphenomena in speech,"J. Acoust.Soc.Am. 51, 1279-1290. Klatt, D. H. (1980). "Softwarefor a cascade/parallel formantsynthesiz-
3427
J.Acoust. Soc.Am.,Vol.92,No.6, December 1992
er," J. Acoust. Soc. Am. 67, 971-995.
Klatt, D. H., and Cooper,W. E. (1975). "Perceptionof segmentduration in sentence contests,"in Structureand Process in SpeechPerception, editedby A. CohenandS. G. Nooteboom(Springer-Verlag,New York), pp. 69-89.
Nishinuma,Y. (1990). "Discriminationof syllabledurationin Englishand Frenchshortsentences," J. Acoust.Soc.Am. Suppl. 1 87, S72. Nooteboom,S. G. (1973). "The perceptualrealityof someprosodicdurations," J. Phon. 1, 2546.
Rossi,M. (1971). "Le seuildeglissando ouseuildeperceptiondesvariation tonalespourlessonsde la parole,"Phonetica23, 1-33. Rossi,M. (1972). "Le seuildiff6rentielde dur6e,"Papersin Linguisticsand Phoneticsto theMemory of PierreDelattre, editedby A. Valdman ( Mouton, The Hague), pp. 435450. Rossi,M. (1978). "The perceptionof non-repetitiveintensityglideson vowels," J. Phon. 6, 9-18.
Y. Nishinuma andS.Santi: Letters totheEditor
3427
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.59.222.12 On: Fri, 28 Nov 2014 07:14:26
TO THE EDITOR
ThisLetterssectionis forpublishing(a) briefacousticalresearchor appliedacousticalreports,and (b) commentson articlesor letterspreviouslypublishedin thisJournal.Extensivereportsshouldbe submittedas articles,not in a letter series.Lettersarepeer-reviewed on the same basisas articles,but usuallyrequirelessreviewtimebefore acceptance.Letterscannotexceed fourprintedpages (approximately3000-4000 words)includingl•7ures,tables,references,and a requiredabstractof about 100 words.
Effect of intensity slopeson the perception of vowel duration Yukihiro NishinumaandSerge Santi InstitutdePhon•tique,Universit•deProvence, CNRS R. U.A.261, 29AvenueRobert$chuman, 13621Aix-en-Provence, France
(Received2 January1992;revised17June1992;accepted13August1992)
Thediscrimination of durationwasinvestigated usingsynthetic vowelswithnegative intensity changes (0, - 6, - 12,and - 18dB). Teststimulus durations rangedfrom 100to 300msin stepsof 20 msandthestandard stimulus was200msin durationandhada uniformintensity. Stimulus pairswerepresented to 20 subjects whosetaskwasto statewhichvowelin thepair sounded longer(forcedchoice;methodof constant stimuli).The dataindicatethata dropin intensityof morethan 12dB resultsin a significant decrease in discriminability of duration differences.
PACS numbers:43.71.Hw, 43.66.Mk, 43.66.Fe
(the observedaveragewas -- 16 dB in our prior speech data) wouldmakeit difficultto correctlyperceivethat syllaTheprosodic analysis of speech, whichconsists of interpretingacoustic parameters suchasduration,fundamental ble'sduration.An experimentcarried out to verify this hypothesisis reportedbelow. frequency, andintensity,isnotaneasytask.Two reasons for thisarethat thesefactorsare not independentin humanperceptionandtheyvary asthe speechsignalevolvesin time; I. EXPERIMENT i.e., withina syllable,word,clause,etc.It is knownthat the Klatt's formantsynthesizer wasusedto generatestimuli perception of pitchvariationsdepends uponthedurationof voicedsounds(Rossi, 1971;Beckman,1986). Furthermore, for theperception test(Klatt, 1980).The goalwasto obtain themelodiccontoursof segments with negativeandpositive speech-like stimulithat variedin bothdurationandintensiintensityglides(i.e., overallintensitychanges appliedto the ty. Negativeintensitychanges(overallintensitydecreases) source)are perceiveddifferently(Rossi, 1978; Beckman, were usedto approximatethe final syllableof declarative 1986). However, we know little about the interaction besentences.The material was designedto be usedin a psychoacoustic test based on the method of constant stimuli. tweendurationand intensityin speech.In particular,the a duration of influenceof intensityvariationsontheabilityto discriminate The standard stimulus was the vowel/a/with the durationof speechsoundshasnot beenexperimentally 200 ms and a uniform intensity contour of 80 dB at the to the averagelength of documented.This problem arosein our previousstudy, source.This durationcorresponds stressed syllablesin a normalspeechrate in French.The test whichinvestigated the differentialthresholdof syllableduration in a sentencecontext in French (Nishinuma, 1990). stimuli weresynthesizedwith durationsrangingfrom 100to Here the term differential threshold is used to refer to the 300 msin 20-mssteps(for a total of 11 differentdurations). differentiallimen (DL) or just-noticeabledifference(jnd). Four linear intensityslopeswereutilized:0, - 6, - 12, and Duration discriminationwas found to be significantlyless -- 18 dB (Fig. 1). The fundamentalfrequencycontourwas accurateon the final syllable (stressed,thereforelonger) the samefor all stimuli. A slightloweringof overall pitch from 140 to 130 Hz made the stimuli sound natural. The than on precedingsyllables.The sametendencywas obstandardstimuluswas paired with eachof the test stimuli servedin Klatt and Cooper'sdata (1975), whichshoweda (thus, a stimulus pair might sound like two successive higherthresholdfor the durationof fricativesat the endof sentences than in other locations.This raisedthe questionof monosyllabicwords). The two vowelsin eachpair weresepwhethera dropin intensityon thefinalsyllableof a sentence aratedby a silentperiodof 600 ms. The intervalseparating INTRODUCTION
3425
J. Acoust.Soc.Am.92 (6), December1992
0001-4966/92/123425-03500.80
@ 1992Acoustical Societyof America
3425
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.59.222.12 On: Fri, 28 Nov 2014 07:14:26
40 T !
20•IB
•
T In•en•itLj i
•
l
o da -•
- 6; dB _ 18dB
Duration
FIG.1.Intensity envelopes used forstimulus generation. Toavoid clicking,
a 20-Blineardropinintensity for10mswasadded atsegment onset and offset.
10
i 0 dB
I -6 dB
I -12
I dB
,
-11• dB
Intensity slopes
onepairfromthenextwasthreeseconds. Bothwithin-pair orders were used, standard/test stimulus and vice versa.
Each pair occurredfour times. Stimuli were generatedin random order by a computer and recordedon a digital audiotape.A trial seriesof 22 pairswasaddedto the beginning of the test sequence.A shortbeepfollowedby a five second silent interval was insertedafter every 22 pairs. The perceptiontestswere carried out in a soundproof room. Twenty subjectswere tested individually, each in a singletrial lasting20 min. The listeninglevelof the standard stimulusleavingthe headphones wassetat approximately70 dB. The subjectswereinstructedto mark which vowelin the pair waslongerby checkingon a forced-choiceanswersheet. II. RESULTS
AND DISCUSSION
A two-way repeated-measures analysisof variancewas performed.The dependentvariablewas the duration of the stimulusuponwhichthe subjectchangedanswersfrom "the first is longer" to "the secondis longer" or vice versa,for each repeat.The two independentvariableswere stimulus order and intensityslope.As expected,variationsin the intensity factor produced significantly different results [F(3,152) = 10.464,p < 0.001]. Stimulusorderalsoyielded a significanteffect[F(1,152) = 4.971,p < 0.05]. There was a significnatinteractionbetweenstimulusorder and intensity slope[F( 3,152) = 5.089,p < 0.01]. We observedlessaccurate reactionsamongsubjectsto the stimuluspairs presented in "test/standard order" for the steeperintensity slopes. Assuminga psychometricfunction with a cumulative normal distribution,the threshold (jnd in duration) wasinterpolatedat the 75% correctlevel.As isshownin Fig. 2, the thresholdin millisecondsfor durationwas proportionalto the magnitudeof the intensityslope.In other words,as the intensityslopebecamesteeper,the detectionof durationdifferences became less and less accurate. This effect on the
discriminationof durationis clearly shownby the progressiveincreasein the means.Interestingly,thepost-hocteston the data for the firsttwo intensityslopes(0 and -- 6 dB) did not yield any significantdifferences.Apparently, a 6-dB drop in intensitydoesnot leadto difficultyin detectingthe correct duration. In contrast, the stable versus -- 12-dB dif-
ference was statistically significant [F(1,152) = 3.113, p • 0.01], and thereforethe opposition"stableand -- 6 dB" 3426
J. Acoust. Soc. Am., Vol. 92, No. 6, December 1992
FIG. 2. Durationthreshold asa functionof intensity slopefora standard duration of 200ms.Durationthreshold in milliseconds isplottedonthey axisandtheintensity slopes applied to theteststimuliareplottedonthex axis.Eachpointrepresents themeanof the20 subjects ( 160judgments) interpolated at the 75% levelof the psychometric function.The standard
deviation isindicated bya verticallineacross themeanpoint.
vs "-- 12and -- 18dB" wassignificant[F(1,152) = 3.738, p • 0.01 ]. It is noteworthythat our resultsindirectlysupport thoseobtainedby Rossi (1978), who estimatedthe intensity glidethresholdto be approximately11dB for a vowellasting 200 ms. The observedchangein the way intensityinformation is processedseemsto dependon whether or not the intensitydecreasesbeyondthat critical value. In comparisonto the resultspublishedin psychoacoustic studiesusingspeechsounds,our thresholdvalue at 200 msis closeto the minimumvalueof thosepreviouslyreported. For a standard stimulus duration of about 200 ms, the
reportedjust-noticeabledifferencein duration,with uniform intensity,generallyrangesfrom 8% to 30% with a representative valuewhich appearsto be approximately20% (Huggins, 1971a,b;Nooteboom, 1973; Klatt and Cooper, 1975; Bovet and Rossi, 1977; Rossi, 1972; Eilers et al., 1984; Bochneret al., 1988). Theseexperimentsusedseveralstandard stimulusdurationsrangingfrom someten milliseconds to severalhundredmilliseconds.In our experiment,all stimulus pairshad a 200-msvowel (the only standardduration used), with a level intensityin first or secondposition.The fact that a stimulus of this constant duration
was available
on all trials for comparisonmay have reducedtask uncertainty and thus led to better performance.The duration thresholddefinedhere (i.e., asa functionof intensityslope) shouldthereforenot be viewed as comparableto thoseobtained under normal, stableintensityconditions. III. CONCLUSIONS
The resultsof our perceptiontestsdemonstratedthat the discriminationthresholdsfor duration may be significantly increasedby a progressivedecreasein intensityof morethan ten decibels.This findingmay havesomeimplicationsfor the interpretationof prosodicdata at the sentence level.
Y. Nishinuma and S. Santi: Letters to the Editor
3426
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.59.222.12 On: Fri, 28 Nov 2014 07:14:26
Beckman, M. E. (1986). Stressand Non-StressAccent (Foris, Dordrecht, The Netherlands). Bochner,J. H., Snell, K. B., and MacKenzie, D. J. (1988). "Duration dis-
criminationof speechandtonalcomplexstimuliby normalhearingand hearing-impaired listeners,"J. Acoust.Soc.Am. 84, 493-500. Bovet,P., andRossi,M. (1977). "Etudecompar6e dela sensibilit6 diff6rentielle•tla dur6eavecun sonpur et avecunevoyelle,"Du tempsbiologique au tempspsychologique, PUF, Paris,289-306. Eilers, R. E., Bull, D. H., Oller, D. K., and Lewis, D.C. (1984). "The discriminationof vowel duration by infants," J. Acoust. Soc. Am. 75, 1213-1218.
Huggins,A. W. F. (1971a). "Justnoticabledifferences for segmentduration in naturalspeech,"J. Acoust.Soc.Am. 51, 1270-1278. Huggins,A. W. F. (1971b). "On theperceptionof temporalphenomena in speech,"J. Acoust.Soc.Am. 51, 1279-1290. Klatt, D. H. (1980). "Softwarefor a cascade/parallel formantsynthesiz-
3427
J.Acoust. Soc.Am.,Vol.92,No.6, December 1992
er," J. Acoust. Soc. Am. 67, 971-995.
Klatt, D. H., and Cooper,W. E. (1975). "Perceptionof segmentduration in sentence contests,"in Structureand Process in SpeechPerception, editedby A. CohenandS. G. Nooteboom(Springer-Verlag,New York), pp. 69-89.
Nishinuma,Y. (1990). "Discriminationof syllabledurationin Englishand Frenchshortsentences," J. Acoust.Soc.Am. Suppl. 1 87, S72. Nooteboom,S. G. (1973). "The perceptualrealityof someprosodicdurations," J. Phon. 1, 2546.
Rossi,M. (1971). "Le seuildeglissando ouseuildeperceptiondesvariation tonalespourlessonsde la parole,"Phonetica23, 1-33. Rossi,M. (1972). "Le seuildiff6rentielde dur6e,"Papersin Linguisticsand Phoneticsto theMemory of PierreDelattre, editedby A. Valdman ( Mouton, The Hague), pp. 435450. Rossi,M. (1978). "The perceptionof non-repetitiveintensityglideson vowels," J. Phon. 6, 9-18.
Y. Nishinuma andS.Santi: Letters totheEditor
3427
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 128.59.222.12 On: Fri, 28 Nov 2014 07:14:26
