Frequency and Duration Discrimination of Short First-Formant Speechlike Transitions Van Wieringen, A.; Pols, L.C.W

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Frequency and duration discrimination of short first-formant speechlike transitions van Wieringen, A.; Pols, L.C.W. DOI 10.1121/1.408344 Publication date 1994

Published in The Journal of the Acoustical Society of America

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Citation for published version (APA): van Wieringen, A., & Pols, L. C. W. (1994). Frequency and duration discrimination of short first-formant speechlike transitions. The Journal of the Acoustical Society of America, 95, 502- 511. https://doi.org/10.1121/1.408344

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Download date:30 Sep 2021 Frequency and duration discrimination of short first-formant speechlike transitions Astdd van Wieringenand LouisC. W. Pols Institute of PhoneticSciences, Universit• of /lmsterdarn,Herengracht 338, 1016 CG /lmsterdarn, The Netherlands

(Received2 $uly 1992;revised 29 April 1993;accepted 30 August1993) Frequencyand duration discriminationthresholds of short rising and falling one-formant speechliketransitions without a steadystate were determined by meansof same/differentpaired comparisontasks in two experiments.When frequencyextent is varied (experiment 1}, just noticeabledifferences decrease with increasingtransition duration. Expressed in Hz, thresholds are, on average,70, 63, and 58 Hz for 20, 30, and 50 ms, respectively.However, when transition durationis variedat a constantfrequency extent (experiment 2 }, differencelimens increase with increasingduration and are, on average,2.7, 4.5, and 4.9 ms for standardtransitions of 20, 30, and 50 ms, respectively.The thresholdsdetermined in the two experimentsindicate that differentpsychoaeoustieal cues are useddepending on whetherfinal frequency(experiment 1 ) or transitionduration (experiment2) are varied. Both experimentswere performedat two differentfrequency regions (between 200 and 700 H2 and between500 and 1000 Hz), but the resultsdid not differper region.In addition,no significantdifferences were found between rising and falling transitions.Particular attention was paid to a methodologicalissue, viz., the extent to which sensitivitychanges as a resultof differentproportions of catchtrials. It wasfound that the listenersmaintained the sameresponse strategies throughout the tests,as their performance is similar, irrespectiveof the numberof catchtrials includedin the testingsessions. PACS numbers: 43.71.Es, 43.66.Fe, 43.66.Mk

INTRODUCTION transitionrate, (end point) frequency,average frequency, duration,bandwidth, or a combinationof suchparameters. Followingan acousticaldescription, speech formant Interpretationof restfitsbecomes even more complicated frequenciescharacterize the time-varyingchanges of the with morespeechlike stimuli, when fundamental frequency vocaltract. Of the continuouslychanging formant frequen- and additional varying resonancesare involved. cies the relatively slowly changingones are perceivedas To avoid some of the complexitiesassociated with vowel-like,whereas relatively rapid changesin frequency speechlikestimuli, many studieshave measuredthe just are importantacoustic cues for the perceptionof conso- noticeabledifferences in frequencyand duration of tone nants. glides(Sergeant and Harris, 1962;Pollack, 1968;Nfib•lek In order to understandthe auditory principlesunder- and Hirsh, 1969; Nfib•lek etal., 1970; Nfib•lek, 1978; lying speechperception it is necessaryto determinethe Tsumura et al., 1973; Fujisaki and Sekimoto, 1975; Ar- sensitivityof the hearingsystem for the relativelyslow, as lingeret al., 1977;Gardner and Wilson, 1979;Collins and well as for the faster transients.The sensitivityto possible Cullen, 1978; Collins, 1984; Cullen and Collins, 1978, cuesfor vowelperception has been closely examined in the 1982;Tyler et aL, 1983;Sehouten, 1985, 1986;Dooley and literature by determiningthe just noticeabledifferences in Moore, 1988a,b; Aslin, 1989; Cullen et al., 1992). Com- frequency,duration, loudness,and timbre of long and parison of these differencelimens with those determined short stationarystimuli, ranging from sinusoids(Moore, from stationarystimuli shouldgive insightinto the percep- 1973; Feth, 1974; Jesteadtand Bilger, 1974; Jesteadtand Sims, 1975; Jesteadtet al., 1977; Wier etaL, 1977; Fastl, tual cuesused in the discriminationof long and short dy- 1978; Fasti and Hesse, 1984; Tyler et al., 1983; Nelson namic stimuli. The issue is more complex, however, as et aL, 1983) to speechformant stimuli (Flanagan, 1955a,b, differencelimens determinedfrom glidesof the sameduration show that transition rate affects discrimination dif- 1957; Fairbanks and Grubb, 1961; Danaher et al., 1973). The discriminabilityof cuesfor consonantperception is a ferently,depending on whetherfrequency extent is varied more complexissue, not only becauseit involvesan addi- at a constantduration (frequencydiscrimination) or du- tional factor, i.e., transition rate, but also because the ration is varied at a constantfrequency extent (duration short,rapid, consonantlikeglides (between 20 and 50 ms) discrimination). In the present study we are interestedin have a broader bandwidth than the longer ones. In addi- the discrimination of short, rapid transitions with more tion to this, as one dimension(e.g., frequency) of a glide speechlikeproperties. This may improveour understand- alwayscoyaries with anotherone (e.g., duration), it is very ing of the perceptionof syntheticspeech, and also that of difficult to isolate the auditory propertieson which a sub- some consonantsin natural speech.In the next two sec- ject's responseis based. Discrimination can be basedon tions,frequency (Sec. A) and duration (Sec. B) discrimi-

502 J. Acoust. Soc. Am. 95 (1), January 1994 0001-4966/94/95(1)/502/10/$6.00 ¸ 1994 AcousticalSociety of Amedca 502 nationof shortand long tone and formantglides will be (Elliott et aL, 1989). This differencebetween stationary reviewed. stimuli and glidesis larger than the one determinedwith A. Rate-of-change discrimination and frequency experimentsusing tone glides (Dooley and Moore, 1988b), discrimination eitheras a resultof the complexityof the stimulusor becausethe 750-ms glidesof Dooley and Moore (1988a) Discriminationof fixed-durationglides changingin were much longer than the 120 ms on,• of Elliott et al. frequencymay depend on variousphysical properties, such (1989). as (center) frequency,frequency extent, glide duration, the Third, a rise/fall effectmay disappe•,rwith more com- presenceor absenceof steadystate(s), transitiondirection, and task. Becauseof the large number of the potential plex stimuli. Schoutenand Pols (1989) performeddiscrim- sourcesof informationinvolved, it is impossibleto draw inationexperiments between exponentia.ly rising and fall- firm conclusionsabout relevant auditory constraints. Fur- ing, rising and level, and falling and level band sweeps thermore,because of the interdependenceof frequency,du- (with and without a steady state) of variousrates and ration, and transition rate, it remains unclear whether dis- durations in 4-IFC paradigms.Contrary to the experi- criminationis basedon the samplingof end points,or on mentswith tone glides(Schouten, 1985), there was much the differencesin rate (samplingof differentpoints in a less tendencyto perceivelevel and slowly rising band glide), or on the differencebetween the initial and final sweeps,centered at 1300 Hz, as falling. When the band frequencies. sweepsstarted or ended at 1300 Hz Iwith or without Although frequencydiscrimination improves with in- steady states) the resultsshow no evidenceof the asym- creaseof duration due to an increasein processingtime roetry betweenfalling and rising sweeps.Discrimination (N•b•lck et aL, 1969,1970; Tsumura et aL, 1973;Dooley improveswith increasein durationfor stimuli movingto and Moore, 1988b;Elliott et aL, 1989, 1991;Porter et al., and from 1300 Hz, and, on the whole, also with increasein 1991), the perceptualcues underlying discrimination may rate. vary with transition duration. Whereasdiscrimination of Despite this difference between tone and formant relativelylong glides, containing "sufficient" spectral infor- glides,the relationshipbetween the complexityof the stim- mation,may be basedon pitch or timbre cues,that of short ulus and the rise/fall effect is not clear (NAb•lek and (<50 ms) glides may rely more on rate of frequency Hirsh, 1978; Collins and Cullen, 1978; Cullen and Collins, change,with differencelimens improvingas rate of fre- 1982; Schouten, 1985, 1986; Pols and Schouten, 1987; quencychange increases (N•b•lek et al., 1969, 1970; Por- ter etaL, 1991). Differencelimens in frequencyof short Moore et al., 1989; Porter et al., 1991;Cullen et al., 1992). formantlikctransitions in which rate of frequencychange No significantdifferences were found by N•b•lek and varies,range between7.5 and 8.5 Hz/ms for 30-ms tran- Hirsh (1969), nor by Arlinger et aL (1977) whenperform- sitions and between 1.0 and 3.75 Hz/ms for 60-ms ones ing experimentswith sinusoids.Neither did Elliott et al. (Elliott et al., 1989, 1991; Porter et aL, 1991). (1989, 1991) find differentthresholds in frequencyfor ris- Several studies have examined the discrimination of ing or failingsecond-formant transitions, with and without complexstimuli to determinewhether, and to what extent, a plateau.Porter et al. (1991), however,obtained smaller psychoacousticalproperties found with toneglides also ap- differencelimens in frequencyfor falling seeond-formant ply to more complexstimuli. Due to the large numberof transitionsthan for risingones. Their data suggestthat the variables, firm conclusionsare difficult to draw. Some find- relatively high-frequencyregion affects,discrimination of ings are discussedbelow. transitions. First, frequencydifference limens of formant transi- In conclusion,discrimination of transitionsvarying in tions (Danaher etal., 1973; Mermclstein, 1978; Horst, frequencyand duration cannot be explainedsolely as a 1982, 1989; Schoutenand Pols, 1989; CosgroveetaL, functionof transitionduration nor of fi'equencyextent. 1989;Elliott etal., 1989, 1991;Porter et aL, 1991) are, in Togetherwith transitionduration, discrimination depends general,similar to thoseof tone glides,i.e., they alsode- on the changingdimension, namely transition duration or crease with increase of transition duration. The modulation frequencyextent, the kind of stimulus,the presenceor discriminationthresholds determined by Horst (1982, absenceof a steady state, and the direction of the transi- 1989) are comparableto thoseof stationarypure tones tions. Although differencelimens increasewith stimulus (1%-3.5%). However, relatively large differencesare complexity,discrimination of tone and formant glidesap- foundfor thosetransitions varying in a multiformantcom- plex: The just noticeabledifferences of the secondformant pearsto be basedon similar psyehoacousticalcues. A key in 250-ms two-formant consonant-vowel combinations question,therefore, concerns the extent t• which discrim- (Danaher, 1973) appearedto be 3%-4% of the reference ination is affectedby the changingdimension, i.e., fre- frequencies(1100 or 2200 Hz), whereasthose determined quency extent, transition duration, and ,speciallytransi- by Mermelstcin (1978) in five formant syntheticstimuli tion rate, as the latter varies in both experiments.In ranged from 9%-14% of the formant frequency. experiment1, discriminationof fixedduration transitions is Second,dynamic cuesinfluence discrimination of for- examined.In the next sectiondiscriminate.on of tone glides mant glides,as the frequencythresholds for 120-mstran- varying in duration at a constantfrequency extent will be sitionswere smallerthan thoseof 300-msstationary sounds reviewed.

503 J. Acoust. Soc. Am.. Vol. 95, No. 1, January 1994 A. van Wieringenand L. C. W. Pols: First-formar,ttransitions 503 B. Rate-of-change discrimination and duration ences for these short transitions will be determined in this discrimination study by varying the frequencyextent, at a constantdura- The ability to discriminatedifferences in the rate of tion (experiment 1), as well as by varying the transition changeof glidesby varyingthe durationof stimuli with a duration,at a constantfrequency extent (experiment2), in constantfrequency extent, (Pollack, 1968; Nfib•lek and two separateexperiments. Hirsh, 1969; Dooley and Moore, 1988a) involvesa cova- Although differencelimens of variousdurations and fiation of rate of changeand duration.As the differencein frequencyextents have alreadybeen determined (see Sec. time requiredfor temporaldiscrimination increases as the A), thoseof short and rapid (plosivelike) formant transi- standardtime increases(Creelman, 1962;Abel, 1972), it is tions not bounded by plateaushave not been examined difficult to determine whether discrimination is based on extensively.Whereas most studiesinclude short and long temporalor on spectralcues, or on a combinationof both. transitions,we focuson short durationsonly (20-50 ms). Different psychoacousficalcues are involved in the dis- In addition to this, differencelimens of short formant tran- criminationtask depending on whetherfrequency extent or sitions, varying in transition duration at a constantfre- transitionduration are variedtogether with transitionrate. Thresholds for this duration condition also increase with quencyextent, have not yet beenreported in the literature. increasingduration. Relatively few studieshave compared In speech,end point frequencytypically signals place of frequency and duration conditions.With infants, Aslin articulation,whereas transition duration signals manner of (1989) foundlarger difference limens for glidesvarying in articulation.However, within a shortdurational range the transitionduration than in frequency.However, the exper- differencelimens in both conditionscan be compared:The imentsdiffer in task and stimulustype (a steadystate was first formanttransition is similarfor stopconsonants. In an added in the duration condition). attemptto get more insightinto the psychoacousticalcues Dooley and Moore (1988a) compareddiscrimination usedin the processingof short transitionswe have used in durationfor relativelylong steadyand glidingsinusolds stimuli that differ from thoseof Dooley and Moore (1988) (standard:750 ms). By askinglisteners to indicatethe in that they are shorter (20-50 ms), and more complex. longeststimulus of a pair, they took advantageof the co- Unlike N•b•lek and Hirsh (1969), Elliott et al. (1989, variation betweenduration and rate of change.Smaller 1991) and Porter et al. ( 1991) we examined the first for- differencelimens were found for dynamicthan for station- mant region.In speech,the firstformant transitions of the ary stimuli,suggesting that gliderate wasused as an extra stop consonantslb/, /d/, and/g/are generallysimilar cue in their experiments. when they precedeor follow the same vowel. Two fre- In order to prevent listenersfrom using the total du- quencyregions were chosen,in one the first formanttran- ration of the transition as a cue, some studies allow the sitionsare typicalof stopconsonants (between 200 and 700 transition to be precededor followed by a steady state (Pollack, 1968; Nfib•lek and Hirsh, 1969; N•b•lek et al., Hz), in the other (between500 and 1000Hz) the pattern 1970;Tsumura et al., 1973;Arlinger et al., 1977;Collins, doesnot correspondto any linguisticcategory. Both fre- 1984; Aslin, 1989; Schoutenand Pols, 1989; Elliott et aL, quencyregions are relativelylow, so that thresholdswould 1989; Porter et al., 1991). However, listenersmay still be not be expectedto differ on the basisof the differencein able to detect differencesin the durationsof the glide, frequency.However, it is possiblethat discriminationis therebymaking use of other cuesthan glide rate. In addi- influencedby a linguisticreference. Also, three different tion to this, the steadystate may also interferewith the frequencyextents (330, 430, and 530 Hz) are examined discriminationof glides.Tsumura et al. (1973) measured per testingregion to determinewhether transition rate af- frequencydiscrimination as a function of transitiondura- fects discrimination of transitions of the same duration. tion and steady-stateduration and found thresholds,espe- Thresholdsof both rising and falling transitionswere de- cially those of short transition durations, to increasewith terminedin our studyto examinewhether the presenceor decreasingplateaus. In experiment2 differencelimens of absence of a rise/fall effect is correlated with transition isolatedsingle formant transitionsare determinedto exam- duration (20, 30, and 50 ms), stimulus complexity, fre- ine psychoacousticcues for glidesvarying in transitiondu- quencyregion, or absenceof a steadystate. ration. In summary,discrimination in frequency(experiment 1) and duration (experiment 2) of relatively short, for- C. Present study mant transitions are examined, of which, unavoidably, either the endpointfrequency or the transitionduration co- The presentexperiments are part of a study dealing with the perceptionof dynamicformant glides,in particu- vary with rate. This should reveal whether similar lar short stop-consonantliketransitions. The first-formant psychoacousticalcues are used in the two conditionsand transitionsof voicedplosives in naturalspeech rise and fall whether thresholdsper conditionare comparablewith re- betweenapproximately 220 and 700 Hz at a relativelyhigh spectto direction,rate of frequencychange, and frequency rate of change.In this study,the perceptualimportance of region. Furthermore,the extent to which sensitivityand transition rate as a cue to the discrimination of transitions responsebias are separated,is examinedby comparingthe is examined. As transition rate always covarieswith fre- subjects'performance for differentproportions of catchtri- quencyextent or transitionduration, just noticeablediffer- als (18.75%-81.25%) includedin the testingsessions.

504 J. Acoust.Soc. Am., Vol. 95, No. 1, January1994 A. van Wieringenand L. C. W. Pols: First-formanttransitions 504 I. GENERAL METHOD TABLE I. Transition rates (in Hz/ms} of standard stimuli in the frequencyand durationconditions for risingand falhngtransitions. The just noticeabledifferences in transitionrate were measuredby varying the frequencyextent at a constant 20 ms 30 ms 50 ms duration (experiment1), and by varying the transition 220-550 Hz 16.5 Hz/ms 11.0 Hz/ms 6.6 Hz/ms duration at a constantfrequency extent (experiment2). 520-850 Hz Thresholdsof risingand fallingtransitions were measured 220-650 Hz 21.5 Hz/ms 14.3 Hz/ms 8.6 Hz/ms as a functionof transitionduration, frequency extent, and 520-950 Hz frequency region. Difference limens were collected by means of the method of constant stimuli in a same/ 220-750 Hz 26.5 Hz/ms 17.6 Hz/ms 10.6 Hz/ms differentprocedure. A same/differenttask does not require 520-1050 Hz the listenerto recognizea specificfeature of the signal, suchas transitiondirection. This would be a very difficult task at very short durations,where listenershardly even eventhough the first periodof all the stimuli startedon a perceivethe glide. In the method of constantstimuli the zero crossing.The stimuli were then addedto the centerof numberof stimuli is predeterminedby the experimenter, 150 ms of low-level white noise (signal-to-noiseratio of and the sequenceof trials doesnot dependon the subjeet's approximately50 dB) to minimizeexternal auditory fac- response.Although time-consuming, this methodyields an tors. Due to the different transition durations the amount accurateestimation of the listener'ssensitivity when taking of noisepreceding and followingthe transitionvaried. The the responsesto catchtrials (physicallyidentical pairs of 16-bit stimuli were transferredfrom the/zVAXII to an stimuli, which are intermixedin the testingsession; ex- IBM-PC. They were presented using an OROS-AU22 pectedresponse is "same") into account.If analyzedby D/A converter(the measuredsignal-to-noise ratio of the the theoryof signaldetectability (TSD, Egan et al., 1966, total systemis 92 dB). 1975), the subjeet'sbias (which is presentin all psycho- physicalprocedures) can be separatedfrom his sensitivity. B. Stimulus characteristics In order for bias and sensitivityto be separated,two as- sumptionshave to be met, i.e., that the data are normally I. Frequency condition: Varying transition rate by distributedand of equal variance.The extent to which end point frequency these assumptionsare satisfiedis exanfinedby including In experiment1 discriminabilityin transitionrate of varyingproportions of catchtrials in eachtesting series. risingand fallingtransitions was determined by varyingthe A. Stimuli frequencyextent (at a fixedinitial frequency).The transi- One-formantlinear risingand falling transitionswere tions were not bounded by plateaus. We investigated generatedby a digital formant synthesizeron a/zVAX II whether detectionof differencesin rate of frequencytran- (KLINKERS, Weenink, 1988). The glottal function (a sitionswas frequencydependent by determiningdifference pulse train) was held constant at a (fundamental) fre- limens in two different frequencyregionts. Transitions in quency of 110 Hz. The formant bandwidth was always the lower frequencyregion are similar to the first-formant 10% of the changingformant frequency.Two frequency transitionsof voicedplosives (Liberman et aL, 1956), be- regionswere examined. The onsetfrequency of the rising tween 220 and 750 Hz, whereasthose in the higher fre- transitions(or the offsetfrequency of the fallingones) was quencyregion, between 520 and 1050Hz, haveno linguis- either 220 or 520 Hz. tic reference.Frequency extents and rates of frequency Six differentstandard trajectories, three per frequency changewere identical across series. Each series consisted of region (extentsof 330, 430, and 530 Hz), and three differ- 18 standard transitions, i.e., fixed transitions, which were ent transition durations, 20, 30, and 50 ms were tested. comparedto comparisontransitions of the sameduration, These transitiondurations are typical of stop-consonant but varying frequencyextent. Figure I illustratessome of transitionsin speech.Depending on the condition,either the stimuli in one of the transition durations, i.e., 30 ms, the frequencyor the transition duration of the standard for both series,schematically. trajectorywas changed.The rates of frequencychange of Although the rate of frequencychange is faster for risingand falling standardtransitions is givenin Hz/ms in shorterthan for longer transitions,the differencein step Table I. Comparedto Porter et al. (1991), whoserates of size in Hz/ms is the samefor each of the three frequency frequencychange were 10, 5, and 2.5 Hz/ms for 30, 60, and 120ms, respectively, our ratesof frequencychange are deliberatelysomewhat higher, becauseof the shorter transition durations. To ensurea precisegeneration of theseformant transitions,the formant frequencyvalues were updatedevery 1 ms at a sample frequencyof 1.2 MHz. After low-passfil- 220Hzo•$20 Hz • • • 30 ms 30 nt• 30 ms •0 ms 30 ms 30 ms tering, they were downsampledto 20 kHz (at a 16-bit resolution).A 2-ms Hamming window at both end points FIG. 1. Illustration of stimuli in the frequencycondition for a standard (1 ms for the 20-ms transitions) was used to avoid clicks, transitionof 30 ms (dashed)with a yawing final ficquency.

505 J. Acoust. Soc. Am., VoL 95, No. 1, January 1994 A. van Wieringen and L. C. W. Pols: First-formanttransitions 505 extentsper transitionduration. Each standardtransition Rising 10or20 Failing msec in lm• 750 Hz o• 1050 Hz was comparedto stimuli of a higher and lower rate of step• 650 Hz m'950 Hz frequencychange. 550 Hzor g50 Hz Randomizedsets of discretestimuli coveringa range of 200 Hz belowand abovethe standardtransition in steps of 10 Hz, servedas test blocks.A 200-Hz frequencyrange (40 stimuli in total) was chosen to include a number of readily discriminablestimuli in the testingsessions. Testing FIG. 2. Illustration of stimuli in the duration condition for a standard sessionscontaining the longest transitions were usually transition of 30 ms (dashed) at either 550 or 850 Hz. consideredmore difficult,presumably because the differencein rate is much smallerwith the longerthan with the 10-ms above and below the standard transition for the shortertransitions. Every block of randomizedstimuli was 20-ms stimuli, and 20 ms for the 30- and 50-ms transitions. balancedin that each stimuluswas presentedtwice, once Some of the stimuli used in this condition are illustrated beforeand onceafter the standardtransition, resulting, in total, in 80 responsesper standardstimulus per testing schematicallyin Fig. 2. The testingprocedure was exactly session. the sameas in the frequencycondition. Transition dura- All the transition duration and direction conditions tions were testedseparately: Two differentstandard tran- were testedseparately. However, to avoid listenersfocus- sitions,differing only in transitionduration, not in final ing on one standardtransition only, two standardtransi- frequency,were includedin one testingsession. Catch tri- tions,differing only in frequencyextent, were includedin als were addedand intermixedwith the physicallydifferent one testingsession. This was possibleas somestandard pairs of stimuli, but the number of physicallyidentical transitionshad similartesting ranges. For instance,a 220- pairs of stimuli was not varied systematically.One fixed 550 Hz and 220-650 Hz were testedtogether, with a test- percentage,i.e., 37.5%, was usedthroughout the test. ing rangevarying from 220-350 Hz to 220-850 Hz. Each The numberof trials varied per testingsession, de- testingsession included a new order of randomization. pendingon the testingrange. As in the frequencycondi- At least20 responseswere collected for eachstandard- tion, at least 20 responseswere collected for each trial comparisonpair of transitions.When the comparisontran- havinghigher and lower ratesof frequencychange than the sitionshigher and lower than the standardtransition are standard transition. Once again these were collectedfor added together, there are at least 40 responsesfor each three frequencyextents, three transitionsdurations, and two directions. frequencydeviation, i.e., for each differencebetween the end pointfrequencies of the standardand comparisontran- As glide rate doesnot remain constant,but decreases sitions.These were collectedfor three frequencyextents, with increasingduration, and temporalproperties strongly three transition durations, and two transition directions, influence discrimination, we also determined duration dif- from eachof four subjects.In total, nearly 3000 responses ference limens of 50-ms stationary one-formant stimuli were collectedfor each standard-comparisonpair in the (whose frequencywas endpointfrequency of the transi- 200-Hz range (40 responsesX 3 frequencyextents X 3 tran- tion). If gliderate is usedas a perceptualcue, thresholds of sitiondurations X 2 transitiondirections X 4 subjects). the dynamic stimuli should be smaller than those of the In addition to this, the sets of randomized stimuli in- stationaryones. As the differencesin glide rate, decrease cludeda proportionof catch trials. The numberof these with increasingtransition duration, 50-ms thresholds were physicallyidentical pairs of stimuli, which were added to comparedto stationaryones. These stationarythresholds the standard-comparisonpairs, varied per testingsession. were collectedfrom three subjects(who also participated With regard to the total numberof physicallydifferent in the frequencycondition). They were determinedin the trials, there were five differentpercentages of catchtrials, sameway as the differencelimens of the dynamicstimuli. i.e., 18.75%, 25.0%, 37.5%, 50%, and 81.25%. These were randomlyinterspersed in the testingsession. C. Procedure

2. Duration condition: Varying transition rate by Blocksof trials were presentedreal time on a PC (16- duration bit resolution) in two or three 10-min sessionsa day with Transition rate was also varied by changing the tran- short breaks in between. Subjectswere seated in front of a sition durationfor a constantfrequency extent. As in the terminaland heard two formant glidesin noisesuccessively frequencycondition, thresholds in experiment2 were once at a comfortablelistening level. By pressingthe appropri- againdetermined as a functionof direction,fixed frequency ate mousekey they were requiredto indicatefor eachpair extent, frequencyrange, and transitionduration (20, 30, whetherit wasthe sameor different.Following a response, and 50 ms). two new stimuli were offeredimmediately. There was no The same final frequencieswere examinedas in the feedback.Before the testingsession they weretold the pro- frequencycondition, i.e., 550, 650, and 750 Hz in the first portion of catch trials, so that they could adjust their eri- series, and 850, 950, and 1050 Hz in the second series. teflon accordingly. While the frequencyextent remainedthe same,transitions The P(C)max (Egan, 1965) was calculatedfor each now differedin stepsof 1 ms each. The testingrange was frequencyextent. l Thresholds correspond to frequency de-

506 d. Acoust.Soc. Am., Vol. 05, No. 1, January1994 A. van Wieringenand L. C. W. Pols:First-formant transitions 506 (a) Frequencycondition (b) Frequencycondition Frequencytltltlditittt!

I0 20 30 40 50 10 20 30 40 50 60

Transitionduration (ms) Transitionduration (ms )

FIG. 3. Differencelimens and standarddeviations in the frequencycon- ditionexpressed in transitionrate (left panel) and final frequency(fight panel). Data are averagedover four subjects,two frequencyregions, two lB 20 3O directions,and threefrequency extents. Transilion rate (Hz/ms viationsyielding a P(C)m• of at least0.75. All conditions FIG. 4. Differencelimens and standarddeviation:• in the frequencycon- were analyzedseparately. dition in termsof transitionrate. The threepoints per transitionduration reflectthe three frequencyextents (three transitionrates, see Table I). Data are averagedover subjects,frequency regions, and transitiondirec- D. Subjects tion, but the three differentfrequency extents per transitionduration are Thresholdsof four normal hearing subjectswere de- displayedseparately. termined,two in the first and two in the secondfrequency region.All four subjects(aged between22 and 34 years) sured transitionswithout a steadystate. The thresholdsof participatedin both the frequencyand the transitiondura- the shortest transitions are lower than those of Elliott et al. tion conditions.They receivedabout 2 h of practicebefore ( 1989:110 Hz, on average),possibly because we variedthe data collectionbegan. The subjectshave absolutethresh- final frequencyand Elliott etal. (198!)) the initial fre- olds lessthan 10 dB HL at all audiometricfrequencies. quency.Difference limens of 20-ms transitionscould be Two subjectswere paid for their participation. determinedreliably, despite their short durations. The thresholdsare alsoin agreementwith the differencelimens in onset frequencies(Porter et al., 1991), although not E. Results with respectto the rise/fall and higherjqowerrate effects Thresholdsand standarddeviations of risingand fall- reportedin that study (for the transitionslonger than 45 ing transitionsof the frequencyand duration conditions ms). The resultsof the experimentare generallyin agree- (averagedover four subjects,two frequencyregions, and ment with a samplingtheory of glideperception (Pollack, transitiondurations) are plottedin Figs. 3-6. Thresholds 1968;Dooley and Moore, 1988b), which statesthat if sam- in the frequencycondition are plotted•n transitionrate as pling the end pointsunderlies perception of glidediscrim- a functionof transitionduration [Fig. 3 {a)], in termsof the ination, the thresholdsshould become Foorer as stimulus differencein final frequency(Hz) as a functionof transi- duration decreases.However, if transitionduration is very tion duration[Fig. 3(b)], and in transitionrate (Hz/ms) short, listenersmay not be samplingend points.Discrim- as a functionof transitionrate as specifiedin Table I (Fig. ination might be based on the differencesin bandwidth, 4). which is directly related to transition duration. In Fig. 3 (a), differencelimens in transitionrate are, on To examinethe perceptualimporutnce of transition average,3.4, 2.2, and 1.2 Hz/ms, and in Fig. 3(b) differ- rate, thresholds of the 20-, 30-, and 50-ms transitions are encelimens in final frequencyare 70, 63, and 58 Hz for 20, plottedas a functionof their transitionrates in Fig. 4. As 30, and 50 ms, respectively.A split-plotfactorial ANOVA one can seefrom the three pointsper transitionduration (Kirk, 1982} with frequencyregion (between blocks), (indicatingthree different transition rates, see Table I) the subjects,transition duration, transition direction, fre- differencesin transitionrate per transitionduration did not quency extent, and higher or lower rate of frequency influence discrimination. If discrimination were solely change(within blocks)was conducted on the thresholdsin based on transition rate, difference limens of the 30-ms final frequency (Hz} and transition rate (Hz/ms). The transitionwith the smallestfrequency extent would be sim- subjectsfactor was random, the others were fixed. There ilar to a 50-msone with the largestfreq Jencyextent (see was a significantmain effectof transitionduration, for the transitionrates of 11.0 and 10.6 Hz/ms, respectively,in transition rate thresholdsexpressed in Hz/ms [F(2,4) Table I). Also, it is expectedthat if discriminationwere =98.3 p <0.001] and the final frequencythresholds in Hz based on transition rate, lower rate transitionswould yield [F(2,4) = 8.85, p < 0.005]. None of the other factorsnor smallerdifference limens than higherrate onesper transi- anyof the interactionswere statistically significant. 2 Ex- tion duration. If discriminationwere basedon frequency ceptfor the 20-mscondition, thresholds in final frequency extent only, differencelimens would incn.•asewith increase are comparablewith Elliott et al. (1989), who also mea- of frequencyextent per transitionduration. If discrimina-

507 J. Acoust.Soc. Am., Vol. 95. No. 1, January1994 A. van Wieringenand L. C. W. Pols:First-formaat transitions 507 Transition duration condition Transition duration condition

o 4

ß [] 20 ms I ß ¸ 3ores at- •i' 50ms I 0 • I • I 10 20 30 0 10 20 30 40 50 60 Transition rate (Hz/ms ) Transitionduration (ms )

FIG. 6. Thresholds determined in the transition duration condition, ex- FIG. 5. Difference limens and standard deviations in the transition du- pressedin transition rate, for transitionsshorter (untilled symbols) and ration condition, averagedover frequencyregion, direction, and fie- longer (filled symbols)than the standard.Data are averagedover sub- quencyextent. The differencelimen of the 50-ms stationarystimuli is jects,direction, and frequencyregion, yet plottedseparately for the three marked by a solid line. differentfrequency extents (or transitionrates) per transitionduration. tion were basedon final frequency,difference limens would The most strikingfinding, however, was that the difference be similar for the three frequencyextents per transition limens are larger in the dynamic conditionthan in the duration (as the difference limen is defined as the differ- stationary one. Difference limens of stationary complex eneebetween the end pointsof the standardand compar- stimuli were measuredat three frequencies(the end point ison stimuli). For most of the transition durations, thresh- frequenciesof the transitions)for 50-msstandard stimuli. olds are nearly identical,suggesting that discriminationis On average,thresholds were 3 ms in all conditions(Fig. basedon the differencebetween the end pointsof the stan- 5). dard and comparisonsignals, rather than on transition To determinethe perceptualimportance of transition rate, rate differencelimens are expressedin transitionrate of the By analogywith Weber'slaw, the ability to discrimi- comparisontransitions as a functionof the transitionrate nate temporal changesbetween intervals should decrease of the standardtransitions in Fig. 6 (to be comparedwith with increasingduration (experiment2). Contrary to the Fig. 4 in the frequencycondition). Data are averagedover differencelimens in the frequencycondition, thresholds in four subjects,direction, and frequencyregion. Following the transitionduration condition (Fig. 5) increasewith the differencelimens in the frequencycondition, sensitivity increaseof transitionduration. Averaged over the two fre- increaseswith increaseof transitionduration. Compare the quencyregions and three frequencyextents, thresholds are differencelimens of 20-ms (squares),30-ms (circles), and 2.7, 4.5, and 4.9 ms for the 20-, 30-, and 50-ms standard 50-ms (stars) transitions.However, interpretationof the transitions,respectively (Fig. 5). A split-plot faetorial resultsin this conditionis more complicatedand therefore ANOVA with frequencyregion (between blocks) and sub- hardly comparableto thoseof the frequencycondition, as ject, transition direction, transition duration, and fre- the differencein slope doesnot remain constantper tran- quencyextent (within blocks) was conductedon the dif- sition duration, but decreasesas the transition becomes ference limens in milliseconds. Transition duration was a longer, In other words,20- vs 22-ms stimuli will be more significantmain effect, i.e., for the averagedifference li- difficult to discriminatethan 18- vs 20-ms ones, not only mens[F(2,4) = 113.3,p < 0.001],for thoseshorter than the becausethe temporaldifference limen is larger (also for standard[F(2,4)----22.3, p<0.001], and for thoselonger steadystates), but also becausethe relative differencein than the standard [F(2,4} = 163.5, p<0.001]. There were slope is smaller. Therefore, the differencelimens of the no other significantfactors nor significantinteractions. transitions shorter (untilled symbols) and longer (filled Although the differencelimens vary with transition symbols)than the standard,were analyzedseparately. The duration, it remains unclear whether discrimination is differencebetween the thresholdsof the transitionslonger basedon temporalor spectralproperties. Due to the tem- and shorter than the standard increases with decrease of poral propertiesinvolved in this conditionwe also mea- transition duration, due to the increase of transition rate sured differencelimens of stationary 50-ms stimuli, of three and, subsequently,the increasingdifference in the asym- subjects,to comparepsychoaeoustical cues in both condi- merry of the slope (Fig. 6). It is difficult to determinethe tions. It is expectedthat if discriminationbenefits from extent to which discriminationis basedon temporal or on transitionrate, differencelimens of dynamicstimuli would spectralproperties in this condition.Transition rate may be smaller.If not, one would expectthem to be the same. be an importantpsyehoaeoustieal cue, as differencelimens

508 J. Acoust.Soc. Am., VoL 95, No. 1, January1994 A. van Wiefingenand L. C. W. Pols:First-formant transitions 508 Transitiota duraticm ctmdition enceswere found statisticallyfor transition direction, frequencyextent or frequencyregion. Also, thresholdsfor stimuli havinghigher rates of frequencychange than the standardare comparableto those having lower rates of frequencychange than the standard(despite some individual differences)in the frequencyconditian. Discrimination o experimentswith formant transitionsfollowed by a steady s state (Porter et al., 1991) have shown difference limens to improveas rate of frequencychange increases, possibly as a result of the relativelylarge extentsof frequencychange. By contrast,increasing or decreasingthe extent of frequencychange in our experimentsaffected discrimination similarly.

F. Discussion 10 20 30 40 50 60

Transition duration (ms ) The thresholdsdetermined in the two experimentsindicate that different psychoacousticalcues are used de-

FIG. 7. Thresholds determined in the transition duration condition, ex- pending on whether final frequency (experiment 1) or pressedin transitionduration, for transitionsshorter (untilled symbols) transitionduration (experiment2) are varied.The thresh- and longer (filled symbols) than the standard. Data are averagedover olds determinedfor formant sweepsin our frequencycon- subjects,direction, and frequencyregion. dition are in agreementwith Elliott et al., (1989,1991), and Porter et al. (1991) and for tone glidesin agreement increasewith increaseof transition rate. Also, somethresh- with Sergeantand Harris (1962), Pollack (1968), and Ar- olds, for which the standards have similar transition rates linger et al. (1977). Discriminationof tone and formant but differentdurations (see Table I), are very similar (due glidesclearly benefits from an increaseof processingtime, to the temporal thresholds,these differencelimens will i.e., when the transitions become longer (Dooley and neverbe identicalacross transition durations). Compare, Moore, 1988a,b;Elliott etal., 1989, 1991; Porter etal. for instance, the thresholds of the 20- and 30-ms transi- 1991). With shorter transition durations, between 20 and tions,with transitionrates of 16.5 and 14.3 Hz/ms, respec- 50 ms, discriminationmay be basedon rate of frequency tively. On average,their differencelimens are 2 Hz/ms. In change(Porter et al., 1991). However,no supportfor rate comparisonwith the thresholdsdetermined in the fre- cueswas found in our experiments,where similar thresh- quencycondition, the differencelimens of the 50-ms tran- oldswere determinedfor transitionsincrementing and dec- sitionsare very small, i.e., on average,I Hz/ms. This cor- rementingin transitionrate. respondsto a temporaldifference of, on average,5 ms (see Apart from transitionrate, discriminationcan alsobe Figs. 5 and 7), due to the small differencesin transition basedon frequencyor bandwidthcues. Consider the spec- rate for the longertransitions. It is not very surprisingthat trum of a signal,which is a functionof duration.The signal difference limens increase with increase of transition rate, bandwidthincreases with decreasingtransition duration, because the difference in transition rate increases with in- and thiscan be an importantfactor limiting frequency dis- creaseof frequencyextent for the samestandard duration. crimination in short duration stimuli. It, other words, the Comparethe thresholdsof the 30-ms transitionwith the spectralbandwidth of a 20-mssignal is approximately50 smallestfrequency extent and the 50-msone with the larg- Hz. The formant bandwidthof the varying formant was est frequencyextent. They are relatively close to each always 10% of the formant frequency.With short transi- other,between 1.0 and 1.5 Hz/ms, suggestingthat spectral tion durations,it is unlikelythat initial or final frequencies, propertiesinfluence discrimination. However, as the differ- for falling and risingtransitions, respectively, serve as per- ence limen in transition rate of the 30-ms transition is ceptualcues. The 20-mstransitions hardly seem to be per- much smaller than the 30-ms difference limens in final fre- ceivedas glides.Discrimination is morelikely to be based quency (Fig. 4), it is more likely that discriminationis on the differencesbetween initial and final frequenciesof governedby temporal cues.It must be kept in mind that the two stimuli or on the differencesin bandwidth, both of the temporal,as well the spectraldifferences are small,and which are related to each other. that the frequencyextent factor was not significant. When transitionsvary in transition duration, as in ex- Figure 7 illustratesthe differencelimens in transition periment 2, temporal, as well as spectralproperties are duration for transitionsshorter and longer than the stan- used. The shorter the transition, the better the temporal dard. Thresholds of the transitions shorter than the stan- resolutionof the auditory system,as differencelimens in- dard (untilled symbols)are smallerthan thoselonger than creasewith increasingtransition duration (Fig. 7). Dis- the standard (filled symbols),especially at 30 and 50 ms. crimination is, to some extent, also based on transition In temporal differences,thresholds for the three frequency rate, as some transitions having similar rates but different extentsappear to be fairly similar (see Fig. 6). No differ- durationsyield similar thresholds(Fig. 6). However, it is enceswere found betweenrising and falling transitions. unlikely that spectraldifferences of lesslhan 1 Hz/ms are Apart from transition duration, no significantdiffer- perceivedat 50 ms. In our study it seemsas if spectral

509 J. Acoust.Soc. Am., Vol. 95, No. 1, January1994 A. van Wieringenand L. C. W. Pols:First-formant transitions 509 propertieshamper discrimination, as the thresholdsfor the formationof the d' associatedwith the stimulus-responsematrix (Mac- stationary stimuli are smaller than the dynamic ones. millanand Creelman,1991 ). This bias-freemeasure of sensitivityis pre- ferred to d', as small differencesin probability values are easier to Differencelimens were similar for the three frequency comparethan small differencesin d'. extentsper transitionduration, the two frequencyregions, 2Thesame/different psychephysical procedure isanalyzed directly within and for rising and falling transitions.Results of N•b•lek the contextof a decision-theorymodel. It is assumedthat the listener's and Hirsh (1969) indicate that the extent of frequency criterion to determinewhether a pair is the sameor differentremains constantduring a test,but maybe changedby informingthe listeneron change influencesdiscriminability. Best thresholdsare the proportionof catch trials includedin the testingseries. We have achievedat small glide rates for small frequencydiffer- explicitlyelsmined the extentto whichdiscrimination and responsebias ences,and at high rates for large frequencydifferences. are separatedby comparingthe valuesof P(C)m,• of the differentpro- Frequencyextent did not influencediscrimination in our portionsof catchtrials per testingsession. The listener'sbehavior con- sistsof two aspects,sensitivity and response bias. As the samestimuli are tests,possibly because all our glide rates were high (see used, sensitivityshould not change.If listenersadjust their criterion Table I), and differencesamong frequencyextents and accordingto the proportionof catchtrials, the criterionwill shiftbut the transitionrates were relatively small. This may alsoexplain differencebetween the two distributions,i.e., sensitivity,should remain why the differentfrequency extents in the transitiondura- the same. Five different proportionsof catch trials were included and systematicallytested in the testingseries of the frequencycondition, i.e., tion condition do not influence discrimination. For a small 18.75%, 25.0%, 37.5%, 50%, and 81.25%. The P(C)max'sfor the five frequencyinterval N•b•lek et al. (1969) found discrim- differentproportions of catch trials (in differenttesting sessions), aver- inability to be better at 30 than at 10 ms. In terms of agedover the threefrequency extents and three transitiondurations, are milliseconds, our data show smaller thresholds at the nearlythe same,indicating the proportionof catchtrials doesnot influ- encethe sensitivity.It is concludedthat the listenersmaintained the same shorterdurations (but this involvesa relativelylarge step responsestrategies throughout the tests,as their performanceis similar, in transition rate). irrespectiveof the proportionof catchtrials includedin the testingses- The lack of a consistent difference in results between sions. rising and failing transitionsagrees with N•b•lek and Hirsh ( 1969}, Arlinger et aL (1977), Dooley and Moore (1988), Elliott et al. ( 1989, 1991), and Schoutenand Pols Abel, S. M. (1972). "Duration discriminationof noise and tone bursts," J. Acoust. Soc. Am. 51, 1219--1224. (1989) who alsofailed to find differencesbetween rising Arlinger,S. D., Jerlvall,L. B., Ahren,L. B., andHolmgren, E. C. (1977). and falling frequencychanges. Porter et al. ( 1991) argue "Thresholdsfor linear frequencyramps of a continuouspure tone," that that the rise/fall effect is due to the difference in rel- Acta Otolaryngol.83, 317-327. ative temporal sensitivityof critical bandsin the lower or Aslin, R. N. (1989). "Discriminationof frequencytransitions by human infants," J. Aconst. Soc. Am. 86, 582-590. higherfrequency regions. Critical band units in the higher Collins,M. J., andCullen, I. K. Jr. (1978). "Temporalintegration of tone frequencyregion (above2000 Hz) have better temporal glides,"J. Acoust. Soc. Am. 63, 469473. resolutionthan thosein the lower frequencyregion. In this Collins,M. J. (1984). "Tone-glidediscrimination: normal and hesxing- line of thought,a rise/fall effectwould not be expectedin impairedlisteners," $. SpeechHear. Res. 27, 403-412. Cosgrove,P., Wilson, J.P., and Patterson,R. D. {1989). "Formant our study:The frequenciesof our transitionsare wellbelow transition detection in isolated vowels with transitions in initial and final 2000 Hz. Discriminationis similar in both frequencyre- position,"Proc. IEEE ICASSP, 278-281. gions,although the transitionsin the lower regioncorre- Creelman,C. D. (1962). "Human discriminationof auditoryduration," spondto the first-formanttransitions of voicedpiesives and J. Acoust. Soc. Am. 34, 582-593. Cullen, J. K. Jr., and Collins,M. J. (1978). "Temporalintegration of thosein the higher frequencyregion have no linguistic two-componenttone glides,"J. Acoust.Soc. Am. 64, 1526-1527. reference. Cullen, I. K., and Collins, M. I. (1982). "Audibility of short-duration The durationsused in the presentexperiments resem- tone glidesas a functionof rate of frequencychange," Hear. Res.7, 115-125. ble stopconsonants in speech.Assuming that our data are Cullen, L K., Jr., Houtsma, A. J. M., and Collier, R. (1992). "iserirn- correctand that thereare no rise/fall, or higherrate/lower ination of brief tone-glideswith high rate of frequency-change,"Ab- rate effectsat very short durations,then the perceptionof stractsof the FifteenthMidwinter Meeting of the Associationfor Re- stopconsonants rising to and fallingfrom targetsshould be searchin Otolaryngology,67. Danaher,E. M., Osberger,M. J., and Pickett, J. M. (1973). "Discrimi- similar. The discrepancybetween CV and VC transitions nationof formantfrequency transitions in syntheticvowels," $. Speech (Collins, 1984} couldbe broughtabout by (maskingof) Hear. Res. 16, 439-451. the surroundingvowel context, not by the transitionitself. Dooley, G. J., and Moore, B.C. J. (1988a). "Duration discriminationof Our futureresearch will focuson the perceptualrelevance steadyand glidingtones: A newmethod for estimatingsensitivity to rate of change,"J. Acoast.Soc. Am. 84, 1332-1337. of physicalproperties of one-formanttransitions in a su- Dooley, O. J., and Moore, B.C. J. (1988b). "ctection of linear fre- prathresholdparadigm. Subsequently, more complex stim- quencyglides as a functionof frequencyand duration,"J. Aconst.So:. uli, i.e., those involving two or more formant transitions, Am. 84, 2045-2057. will be testedin psycheacousticaland speech-perceptual Egan, $. P. (1965). "asking-level differencesas a functionof interaural disparitiesin intensityof signaland of noise,"J. Acoust. Sec. Am. experiments. 1043-1049. Egan,J.P., and Clarke, F. R. (1966). "Psychephysicsand signaldetec- ACKNOWLEDGMENTS tion," in ExperimentalMethods and Instrumentationin Psychology,edited by J. B. Sidowski(McGraw-Hill, New York), pp. 211-246. We are gratefulto Bert Schoutenfor helpfulcriticisms Egan, $. P. (1975). Signal DetectionTheory and ROC ,4nalysis(Aea- on an earlier draft of this paper.This researchwas sup- derrdc,New York). ported by the University of Amsterdam. Elliott, L. L., Hammer, M. A., Schell, M. E., Carrell, T. D., and Wa- sowicz,J. M. (1989). "Discriminationof risingand falling simulated single-formantfrequency transitions: Practice and durationeffects," J. •Themaximum proportion correct, P(C}•, isobtained through a trans- Acoust. Sec. Am. 86, 945-953.

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511 J. Acoust.Soc. Am., Vol. 95, No. 1, January1994 A. van Wieringenand L. C. W. Pols: Fimt-formanttransitions 511