Acoustic feature analysis in the perception of voicing contrasts

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Perceptin & Psychphysics 1977, Vl. 21 (5),418-422 Acustic feature analysis in the perceptin f vicing cntrasts RANDY L. DIEHL and DEBORAH M.

1 Perceptin & Psychphysics 1977, Vl. 21 (5), Acustic feature analysis in the perceptin f vicing cntrasts RANDY L. DIEHL and DEBORAH M. ROSENBERG University ftexas at Austin, Austin, Texas Varius types f acustic cues have been shwn t signal vicing cntrasts in initial prestressed stp cnsnants. Tw f the mst imprtant f these cues are the time interval between the release burst and the nset f vicing (vice nset time) and the duratin f viced transitins. In the present experiment, a selective adaptatin prcedure was used t investigate pssible feature extractin mechanisms which underlie the perceptin f vicing. Subjects first identified either f tw series ftest stimuli, [ba-pba] r [ga-kha]. Next they listened t repeated presentatins f an adapting stimulus and then again identified the riginal test series. Adapting stimuli having the same value f vice nset time but different viced transitin duratins prduced differential (and smetimes ppsite) effects n the identificatin f the test stimuli. In every case, the adapting stimulus with the greater duratin f viced transitins led t larger reductin in viced respnses r t a smaller increase in viceless respnses. These results are incmpatible with mdels f vicing perceptin based strictly n detectrs fr vice nset time. The results als suggest that the adaptatin effect ccurs at a pint in the system prir t the actual phnetic decisin. Much research has been aimed at discvering the articulatry and acustical basis fr the, vicedviceless distinctin in initial prestressed cnsnants. In a spectrgraphic study f naturally prduced wrds, Lisker & Abramsn (1964) fund that an imprtant crrelate f phnemic distinctins alng the vicing dimensin is variatin in vice nset time (VOT), the interval between the release burst and the nset f peridicity that reflects glttal pulsing. Experiments with synthetic speech (Abramsn & Lisker, 1970, 1973; Lisker & Abramsn, 1970) appeared t cnfirm the rle f VOT as a perceptual cue fr vicing distinctins. Stimuli with small VOT values were perceived by English speakers as viced ([b d g)), whereas stimuli with greater VOT values (ver 40 msec) were perceived as viceless ([phthkh)). In the series f synthetic test syllables used by Lisker and Abramsn, increases in VOT ver a certain critical range were accmpanied by decreases in the duratin f viced frmat transitins. It is cnceivable, therefre, that the perative cue fr the viced-viceless distinctin is nt VOT per se but rather the presence r absence f significant frmant transitins fllwing vicing nset. T test this hypthesis, Stevens and Klatt (1974) cnstructed a stimulus set in which VOT and viced transitin duratin (VTD) varied rthgnally. When subjects identified these stimuli, the VOT value f the vicedviceless bundary was fund t vary as a functin This research was supprted by a Bimedical Sciences Research Grant frm the University f Texas at Austin. Requests fr reprints shuld be sent t Randy L. Diehl, Department f Psychlgy, 330 Mezes, University f Texas, Austin, Texas f VTD, thus indicating the perceptual significance f the latter cue. The rle f viced transitins (particularly the first-frmant transitin) in the perceptin f vicing cntrasts was als demnstrated in studies by Summerfield and Haggard (1974, Nte 1). It shuld be nted, hwever, that in nne f these experiments was VOT actually ruled ut as a vicing cue. T the cntrary, Stevens and Klatt (1974) fund that the VTD crrespnding t the viced-viceless bundary tended t increase as VOT increased, and Summerfield and Haggard (1974) shwed that VOT is an especially imprtant vicing cue fr stimuli lacking first-frmant transitins. A recent study by Lisker et al. (Nte 2) replicated the results f Stevens and Klatt (1974), underscring further the fact that neither VOT nr VTD is alne sufficient t accunt fr the perceptin f vicing cntrasts. In view f the abve findings, it is apprpriate t recnsider the prblem f hw the auditry system extracts vicing infrmatin frm the speech signal. In particular, what is the nature f the feature detectin mechanisms which underlie the perceptin f the viced-viceless distinctin in initial stps? Cper (1974) perfrmed a selective adaptatin experiment designed t address this questin. The selective adaptatin paradigm rests n the assumptin that repeated presentatin f a stimulus having a given set f features will reduce the sensitivity f neural detectr mechanisms which nrmally respnd t thse features. Thus, perceptin shuld be distrted in a predictable manner fllwing adaptatin (Eimas, Cper, & Crbit, 1973; Eimas & Crbit, 1973). Cper first had subjects identify a series f synthetic syllables which varied in VOT (as 418

ACOUSTIC FEATURE ANALYSIS IN PERCEPTION OF VOICING 419 well as VTD thrugh part f the stimulus range). These syllables were perceived as either [ba] r [pha].

Bth f the adapting stimuli had the same value f VOT, but ne had a VTO f 10 msec ([da]-shrt) while the ther had a VTO f 40 msec (jdal-lng), Interestingly, these tw adapting stimuli prduced

2 ACOUSTIC FEATURE ANALYSIS IN PERCEPTION OF VOICING 419 well as VTD thrugh part f the stimulus range). These syllables were perceived as either [ba] r [pha]. After this initial identificatin test, the subjects listened t the repeated presentatin f either f tw different adapting stimuli and then again identified the riginal test series. Bth f the adapting stimuli had the same value f VOT, but ne had a VTO f 10 msec ([da]-shrt) while the ther had a VTO f 40 msec (jdal-lng), Interestingly, these tw adapting stimuli prduced differential effects n the identificatin f the test series. The [daj-lng stimulus caused the bundary between the perceived viced and viceless stps t shift significantly tward the viced end f the test series. On the ther hand, the [da]-shrt stimulus prduced a nnsignificant shift f the phnetic bundary tward the viceless end. Cper nted that these results culd bviusly nt be explained by the adaptatin f detectrs sensitive nly t VOT infrmatin. He als argued that an accunt based slely n the adaptatin f VTO detectrs is inadequate, since the tw adapting stimuli prduced differential effects even n the identificatin f stimuli entirely lacking viced transitins. Instead, Cper favred the ntin f an integrative analyzer which either respnds t different vicing cues disjunctively r else respnds t sme weighted cmbinatin f vicing cues. The present experiment was intended t replicate and extend the findings f Cper (1974). One ptential difficulty in interpreting Cper's results arises frm the fact that the synthetic test stimuli which he used had frmant transitins f nly 20 msec duratin, less than half the average fr naturally prduced initial bilabial stps (Lehiste & Petersn, 1961). It is pssible that subjects adpted an unusual perceptual strategy in identifying these smewhat abnrmal stimuli. If this were indeed the case, then the generality f Cper's findings may be questined. We therefre decided t use test stimuli having transitin duratins mre nearly apprximating thse f natural utterances. Our primary questin was whether adaptatin with tw stimuli having the same VOT value but different values f VTO wuld prduce differential effects n the perceptin f the viced-viceless dimensin. initial velar stp ((g) r [k h )). The fllwing vwel in each case was [a). The parameter values f the stimuli were the same as thse used by Lisker and Abramsn (1970).' Each series ranged in VOT frm 0 t + 70 msec in steps f 10 msec, The ttal transitin duratin fr each stimulus was SO msec fr the bilabial series and 70 msec fr the velar series. Thus, increased VOT resulted in decreased VTO acrss mst f the range f the bilabial series and acrss the entire range f the velar series. Lisker and Abramsn (1970) fund that English speakers wh identify these stimuli generally place the phnetic bundary at abut 22 msec VOT fr the bilabial series and at abut 42 msec VOT fr the velar series. Fr each f these bundary values, the crrespnding VTO is rughly 28 msec. Fr these particular stimuli, therefre, the phnetic bundary appears t be invariantly specified by VTO, nt VOT. Tw pairs f adapting stimuli were selected. Each pair cnsisted f a bilabial and a velar adapting stimulus having the same VOT, but different values f VTO. One such pair had VOT values f 30 msec, and the ther f 35 msec, The VTO values fr the 30-msec VOT pair were 20 msec fr the bilabial stimulus and 40 msec fr the velar stimulus. The crrespnding VTO values fr the 35-msec VOT pair were 15 msec and 35 msec. Apart frm VOT and VTO, these adapting stimuli had exactly the same parameter values as either the bilabial r velar test stimuli. Ntice that, given the abve-mentined phnetic bundary values btained by Lisker and Abramsn (1970), the bilabial adapting stimulus f each pair shuld be perceived as viceless (i.e., [pha]), whereas the velar stimulus shuld be perceived as viced (i.e., [ga)). Hereafter each adapting stimulus will be referred t by subscripting the VOT value after the phnetic representatins f the stimulus (e.g., [phah). Figure 1 displays spectrgrams f tw f the adapting stimuli, [phah and [gah' Prcedure In every experimental sessin, subjects first identified ne f the tw test series. The tape cntained 10 instances f each f the eight stimuli, with all items cmpletely randmized. The interval separating the items was 2 sec, with an additinal 2-sec delay after every eighth item. The subjects were instructed t label each stimulus as "8" r "P" ("G" r "K") n an answer sheet prvided. A secnd identificatin test was given after selective adaptatin. An adapting stimulus was presented repeatedly fr perids f I min, and after each such perid, subjects identified a blck f eight stimuli frm the same test tape as presented earlier. This cntinued until all 80 items n the tape were identified. A.S-sec interval separated each presentatin f the adapting stimulus METHOD Subjedli Thirty-three intrductry psychlgy students at the University f Texas at Austin served as subjects. They received curse credit fr their participatin. All were native speakers f English and reprted having nrmal hearing. Stimuli Tw series f eight synthetic stp-vwel syllables, varying in bth VOT and VTO, were used as test stimuli. In ne series, the directin and extent f the first- and secnd-frmant transitins f each stimulus were apprpriate fr an initial bilabial stp ([b) r [ph]); in the ther, the transitins were apprpriate fr an Figure 1. Wide-band spectrgrams f tw f tbe adapting stimuu. Tbe [phahe bas 20 msec f viced transitins; tbe [ga]30 bas 40 msec f viced transitins. Btb stimuli bave a VOT value f 30 msec.

420 DIEHL AND ROSENBERG (ffset t nset), and there was rughly a 3-sec interval between the end f an adaptatin perid and the beginning f an initial test stimulus.

3 420 DIEHL AND ROSENBERG (ffset t nset), and there was rughly a 3-sec interval between the end f an adaptatin perid and the beginning f an initial test stimulus. The subjects were nt infrmed befrehand what the adapting stimulus wuld be. At least 24 h elapsed between experimental sessins. A ttal f eight cnditins were run (4 adapting stimuli x 2 test series). Of the 33 subjects, 12 served in tw f these cnditins (velar test series: bilabial and velar adaptrs with 30-msec VOT), II served in tw ther cnditins (bilabial test series: bilabial and velar adaptrs with 30-msec VOT), and 10 served in the remaining fur cnditins (bilabial and velar test series: bilabial and velar adaptrs with 3S-msec VOT). The test tape and the adaptatin tape were presented n separate Magnecrd 728 tape recrders. Bth sets f stimuli were channeled thrugh a Dynac ST-80 pwer amplifier and heard binaurally ver Kss K6 earphnes at a cmfrtable listening level. RESULTS The data were analyzed in terms f the net increase r decrease in the number f viced respnses fllwing selective adaptatin. Let us first cnsider the cases in which an adaptr f 30 msec VOT was used. The bilabial and velar adaptrs had significantly different effects n respnses t bth the bilabial test series (p <.02)2 and the velar test series (p <.01). With respect t the bilabial series, the bilabial adaptr ([phah) increased the number f viced respnses relative t preadaptatin perfrmance (p <.05), while the velar adaptr ([gah) reduced the number f viced respnses (p <.05). Fr the velar series, the pattern was smewhat different. Bth the [phah adaptr and the [gah adaptr decreased the number f viced respnses (p <.05 and p <.001, respectively), but the latter stimulus prduced a reliably greater decrement than the frmer as nted. Next we cnsider the effects f adapting with [phahs and [gahs. Again, despite having the same VOT value, these tw stimuli prduced different effects n the identificatin f bth the bilabial series (p <.01) and the velar series (p <.05). The [phahs adaptr increased the number f viced respnses t the bilabial test series (p <.01), but [gahs had n significant effect n the identificatin f the series. Finally, with respect t the velar test series, adapting with [phahs led t an increase in viced respnses (p <.05), whereas [gahs prduced a decrease (p <.05). Figure 2 shws grup identificatin functins, befre and after selective adaptatin, fr each f the eight cnditins described. DISCUSSION The present results flatly discnfirm any mdel f vicing perceptin based slely n detectrs f abslute VOT infrmatin. In every case that we tested, adaptrs having identical VOT values but different duratins f viced transitins prduced differential effects n the identificatin f a viced-viceless stimulus series. These results are thus in full accrd with thse f Cper (1974), despite rather cnsiderable differences between the test stimulus parameters used in the tw experiments. The variable f VTO wuld appear t be respnsible fr differential adaptatin effects prduced by tw stimuli having the same VOT. Fr every such stimulus pair, the member with the greater VTO value led t a larger reductin in viced respnses r t a smaller increase in viceless respnses than did the member with the smaller VTO value. Indeed, fr tw f the stimulus pairs, the adaptatin effects BILABIAL TEST SERIES BILABIAL ADAPTOR (VOT'30MSECl VELAR ADAPTOR (VOT-30MSEC) BILABIAL ADAPTOR (VOT-35MSEC) VELAR ADAPTOR (VOT-35MSECl PRE-ADAPT POST-ADAPT '60 ~ 100 ~ I- 40 Z 1IJ 20 U a:: 1IJ Q.. BILABIAL ADAPTOR (VOT'30MSECl VELAR ADAPTOR (VOT'30MSECl VELAR TEST SERIES TEST STIMULUS BILABIAL ADAPTOR (VOT-35MSECI VOT (MSEC) VELAR ADAPTOR (VOT- 35 MSECI Figure 2. Grup identificatin functins fr each f the eight adaptatin cnditins.

4 ACOUSTIC FEATURE ANALYSIS IN PERCEPTION OF VOICING 421 prduced by each member were in ppsite directins. This lends additinal supprt t the claim f Stevens and Klatt (1974) that VTD has a critical rle in the perceptin f vicing cntrasts. The present results unfrtunately d nt speak t the issue f whether adaptatin ccurs at a cuespecific r an integrative level f analysis. Cper (1974) tentatively ruled ut a cue-specific interpretatin f his data n the grunds that adaptrs with different VTD values had prduced different effects n the identificatin f test stimuli entirely lacking viced frmant transitins. He crrectly nted, hwever, that this argument rests n an unprved assumptin, viz., that the detectr fr lng VTD values des nt respnd when n viced transitins are present. The test stimuli used in the present experiment had much lnger frmant transitins (and hence lnger VTD values) than thse used by Cper, and therefre it is quite pssible that the adaptatin effects we btained ccurred at the site f extractin f VTD infrmatin. On the ther hand, an interpretatin based n an integrative level f analysis bviusly cannt be discunted. 3 One special type f integrative hypthesis wuld hld that adaptatin takes place primarily at r beynd that pint in the system where ultimate phnetic decisins are made. On this view, the directin and magnitude f the present adaptatin effects wuld have depended n whether the adapting stimulus is perceived as viced r viceless and nt n particular acustic prperties f the stimulus such as VOT r VTD. This hypthesis is cmpatible with mst f the present findings. In general, an adaptr perceived as viced reduced the test stimuli identified as viced, whereas just the ppsite ccurred if the adaptr was perceived as viceless. Hwever, there was ne imprtant exceptin t this generalizatin. Fr the velar test series, [phah actually reduced the number f viced respnses. It can be seen frm Figure 2 that this stimulus, when it appeared in the test series, was identified as viceless between 80lJ,10 and 9OlJ,10 f the time. Thus the directin f the adaptatin effect prduced by [phah in this case appears t be incmpatible with the strng phnetic hypthesis under cnsideratin. This result is cnsistent with'a recent finding f Blumstein and Stevens (Nte 3), wh adapted subjects with a stimulus cntaining cnflicting placef-articulatin cues. Thugh the subjects identified the stimulus as having a particular place value, it prduced an adaptatin effect in the directin ppsite t that expected n the basis f phnetic labeling. It shuld be nted, hwever, that several ther experiments (Diehl, 1975; Diehl & Grves, Nte 4) have suggested that under certain cnditins the bundary shift is determined mre by the perceived phnetic quality f adapting stimulus than by its acustic prperties. Sme pssible reasns fr these apparently discrepant results will be explred in detail in a frthcming paper (Diehl & Grves, Nte 4). If adaptatin is indeed ccurring at an integrative level f vicing analysis, as argued by Cper, then the present results suggest that it is a level which precedes the ultimate phnetic decisin. Sme recent mdels f vicing perceptin (Ades, Nte 5; Summerfield, Nte 6) prvide fr a number f intermediate prcessing stages, e.g., rate nrmalizatin and cue reweighting, between the initial extractin f acustic prperties and the phnetic decisin. Selective adaptatin may cnceivably affect any and all such intermediate prcessing stages in additin t the acustic prperty detectrs themselves. Future research must attempt t islate and explre each f these pssibilities. In summary, the results f this experiment clearly exclude any mdel f vicing perceptin based entirely n VOT analyzers. The mst likely site f adaptatin is either at the level f VTD detectin r at an integrative level which receives inputs frm varius prperty detectrs. If an integrative level is invlved, it des nt appear t be lcated at r beynd the prcessing stage where phnetic decisins are made. REFERENCE NOTES 1. Summerfield, A. Q., & Haggard, M. P. Perceptin f stpvicing. A rate-specific transitin detectr? Speech Perceptin, 1972,2.1, (Prgress Reprt f the Department f Psychlgy, Queen's University f Belfast.) 2. Lisker, L., Liberman, A. M., Ericksn, D., & Dechvitz, D. On pushing the vice-nset-time bu1fdary abut. Paper presented at the 89th Meeting f the Acustical Sciety f America, Austin, Texas, April Reprinted in Haskins Labratries: Status Reprt n Speech Research, 1975, SR-42143, Blumstein, S. E., & Stevens, K. N. Prperty detectrs fr bursts and transitins in speech perceptin. Paper presented at the 89th Meeting f the Acustical Sciety f America, Austin, Texas. April Diehl, R. L., & Grves, K. A. Phnetic levels fprcessing in speech perceptin: Evidencefrm selective adaptatin experiments. Frthcming. 5. Ades, A. E. Adapting the prperty detectrs fr speech perceptin. Frthcming. 6. Summerfield, A. Q. Tward a detailed mdelfr the perceptin fvicing cntrasts. Speech Perceptin, 1974, 2.4, (Prgress Reprt f the Department f Psychlgy, Queen's University f Belfast.) REFERENCES ABRAMSON, A. S., & LISKER, L. Discriminability alng the vicing cntinuum: Crss-language tests. In Prceedings f the Sixth Internatinal Cngress f Phnetic Sciences. Prague Prague: Academia, Pp ABRAMSON, A. S., & USKER, L. Vice-timing perceptin in Spanish wrd-initial stps. Jurnal fphnetics, 1973, I, 1-8. COOPER, W. E. Selective adaptatin fr acustic cues f vicing in initial stps. Jurnal fphnetics, 1974, 2,

422 DIEHL AND ROSENBERG DIEHL, R. L. The effect fselective adaptatin n the identificatin f speech sunds. Perceptin & Psychphysics, 1975, 17,48-52. EIMAS, P. D., COOPER, W. E., & CORBIT,J. D. Sme prperties f linguistic feature detectrs.

5 422 DIEHL AND ROSENBERG DIEHL, R. L. The effect fselective adaptatin n the identificatin f speech sunds. Perceptin & Psychphysics, 1975, 17, EIMAS, P. D., COOPER, W. E., & CORBIT,J. D. Sme prperties f linguistic feature detectrs. Perceptin & Psychphysics, 1973, 13, EIMAS, P. D., & CORBIT, J. D. Selective adaptatin f linguistic feature detectrs. Cgnitive Psychlgy, 1973, 4, LEHISTE, I., & PETERSON, G. E. Transitins, glides, and diphthngs. Jurnal fthe AcusticalSciety famerica, 1961, 33, USKER, L., & ABRAMSON, A. S. A crss-language study f vicing in initial stps: Acustical measurements. Wrd, 1964, 20, USKER, L., & ABRAMSON, A. S. The vicing dimensin: Sme experiments in cmparative phnetics. In Prceedings f the Sixth Internatinal Cngress fphnetic Sciences, Prague Prague: Academia, Pp STEVENS, K. N., & KLATT, D. H. The rle f frmant transitins in the viced-viceless distinctin fr stps. Jurnal fthe Acustical Sciety famerica, 1974, 55, SUMMERFIELD, A. Q., & HAGGARD, M. P. Perceptual prcessing f multiple cues and cntexts: Effects f fllwing vwel upn stp cnsnant vicing. Jurnal fphnetics, 1974, 2, NOTES 1. We thank James J. Jenkins, wh prvided us with a tape f these stimuli, which were riginally prduced at Haskins Labratries. 2. In all cases, statistical significance was determined by twtailed t tests fr crrelated bservatins. 3. As Cper (1974) has pinted ut, tw general versins f an integrative acustic analyzer can be distinguished: an ORgate which respnds disjunctively t inputs frm separate cuespecific detectrs, and an AND-gate which respnds t cmbinatins f such inputs. In the latter case, the inputs culd determine the respnse in either an additive r an interactive manner. (Received fr publicatin December 6, 1976; revisin accepted March 14, 1977.)

DIRECTED FORGETIING: SHORT-TERM MEMORY OR CONDITIONED RESPONSE? WENDY S. MILLER and HARVARD L. ARMUS The University of Toledo

The Psychlgical Recrd, 1999, 49, 211-220 DIRECTED FORGETIING: SHORT-TERM MEMORY OR CONDITIONED RESPONSE? WENDY S. MILLER and HARVARD L. ARMUS The University f Tled Previus researchers have interpreted