9.5, 9.7 Received 12 November 1065 Distinctive Features and Errors in Short-Term Memory for English Consonants •'AYNE A. •'ICKELGREN Departmentof Psychology,Massach•setts insill,de of Technology,Cambridge, Massachusells 02139 Errorsin short-termrecall of 23 Englishconsonants were tabulated and relatedto threedistinctive-feature systems.The consonantswere always presented in initial positionin a consonant-voweldiagram, and the vowelwas always/a/. Subjectswere instructed to copya list of consonantsasit wasbeing presented, followed by recallof the list. Perceptualerrors were excluded from the recall-errormatrix by scoringfor recallonly correctlycopied consonants. The data were also analyzed in sucha wayas to eliminatedifferences in response biasfor differentconsonants. Having controlled for responsebias, each feature system makes predictions aboutthe rankorder of differentintrusion errors in recall.Each of thethree feature systems was significantly moreaccurate than chancein thesepredictions, but the mostaccurate system was one developed in the presentstudy. This system is a slightlymodified version of the conventionalphonetic analysis of cousonants in termsof voicing,nasalit>', openness of thevocal tract (mannerof articulation),and place of articulation. The resultssuggest that a consonantis codedin short-termmemory, not asa unit, but as a setof distinctive features,each of whichmay be forgottenat leastsemiindependently. INTRODUCTION by a conventionaldistinctive-feature analysis on two dimensions:place of articulation(front, back) and open- NTRUSIONlists are not errorsrandom.in immediateRecent studiesrecall byof Conrad verbal t ness of the vocal tract (narrow,medium, and wide). and Wickelgren2,'• on short-term recall of lists of letters Petersonand Barne? and Miller • hadfound previously and digits have demonstratedthat intrusionstend to that thesame dimensions are involved in theperception have a vowelor consonantphoneme in commonwith of vowels,suggesting that perceptionand STM use thecorrect item. 7his indicatesthat theinternal repre- the samesystem of internalrepresentatives. Although it sentative of a (verbal) item in short-term mentory is not possibleat presentto determinewhether this (STM) is not a singleelement, but a set of internal systemof internalrepresentatives is sensory or motor, representativesof the phonemescomposing the item. no support can be obtainedfrom any of thesestudies The phonemic-codinghypothesis petunits partial for- for the more "abstract" (nonsensoryand nonmotor) gettingof an item and accotintsfor the phonetalcsimi- level of the Chomsky-Hallefeature system.7 larity of intrusions to the correct item. In auditory perceptionof consonantsin noise,Miller If the STM representativeof a letter or digit is a set and Nicel? demonstrated that errors are nonrandom of representativesof phoneroes,it is natural to ask and tend to correlate with their distinctive-feature whetherthe representativeof a phonemeis a set of analysis,described in Table I. The two purposesof the representativesof its distinctive features. A previous presentstudy are to (a) determine if errors in STM for study4 indicated that this was the case for vowel for consonants tend to have features in common with phoneroes,and almostperfect rank-order predictions the correctconsonant, and (b) determinewhat distinc- weremade of the frequencyof differentintrusion errors tive-feature system best predicts these errors. In • R. Conrad, "Acoustic Confusionsin ImmediateMemory," a G. E. Petersonand H. L. Barney, "Control Methods Usedin a Brit. J. Psychol.55, 75-84 (1964). Studyof the Vowels,"J. Acoust.Soc. Am. 24, 175-184 (1952). 2 W. A. Wickelgren,"Acoustic Similarity and Intrusion Erorrs • G. A. Miller, "The Perceptionof Speech,' in For Roman in Short-TermMemory," J. Exptl. Psychol.70, 102-108 (1965). Jakobson,M. Halle, Ed. (Mouton& Co., The Hague,1956), pp. a W. A. Wickelgren,"Similarity and Intrusionsin Short-Term 353-359. Memory for Consonant-VowelDigrams," Quart. J. Exptl. • N. Chomskyand M. Halle, Sound•allern of œnglish(to be Psychoh 17, 241-246 (1965). published). 4 W. A. Wickelgren, "Distinctive Features and Errors in Short- s G. A. Miller and P. E. Nicely, "An Analysisof Perceptual Term Memory for English Vowels," J. Acoust. Soc. Am. 38, Confusionsamong Some English Consonants," J. Acoust.Soc. 583-588 (1965). Am. 27, 338-352 (1955). •88 volume39 number2 1966 DISTINCTIVE FEATURES AN[) SHORT-'I'ERM MEMORV additionto the featuresystem proposed by Miller and TABLEI[. H distinctive-featuresystem. Nicely (MN), a featuresystem proposed by Halle9 (H) - - and Chomskyand Halle? for the parsimoniousdestrip- C,mso-Voic- Nas- Vo- Conso- Contin- St•i- tion cf English sound structure and a feature system nant ing alitv calic nantal uant dent Grave Diffuse proposedby the author (W) are investigated.These P (} 0 0 l 0 0 l 1 featuresystems are describedin Tables II and I[1. 1• l 0 0 1 0 0 1 l MX hasfive dimensions: voicing, nasality, affrication, m 1 l i) 1 0 0 1 l duration, and place of articulation. Place has three t 0 0 0 1 0 0 0 1 values;the rest have two values.MN has only been d 1 o l) 1 o o o 1 definedfor a setof 16 consonants.Within that set,each 1 1 o 1 0 0 0 1 dimensionis definedon every consonant,and all con- 0 0 0 l 0 1 0 0 sonantshave a uniquecharacterization in termsof their' valuesoneach ofthe five dimensions. However, if MN i I 0 0 I 0 1 0 0 wereto be extended toall English consonants, it would k (} 0 o 1 0 o l 0 requiresome additional dimensions or valuesto handle g 1 0 0 1 0 0 1 0 laterals,selnivowels, and the consonants /6', /)'/, and f 0 0 II 1 1 1 l 1 ,;h/. ,' 1 0 0 1 1 1 1 1 H has eight binary dimensionson which consonants 0 0 0 0 1 1 0 0 l are classified.The rather large number of dimensions •5 1 0 0 1 1 0 0 1 resultsfrom the decisionto use only two valuesper s o o o 1 1 l o dimension.Halle gives a moderatelycomplicated articu- z 1 0 0 1 1 1 0 1 latorydescription of the values of thedimensions in the • 0 0 0 1 1 1 0 0 H system,but the system is nnnaturaland inelegant • 1 0 0 l 1 1 0 0 as a descriptionof articulationand no attempt is made 1 0 0 0 l 0 I 1 by Halleto validatethe system on thesegrounds. 9The w featuresshould be consideredto be "abstract," not r 1 0 l l I 0 0 0 necessarilyhaving a simpleacoustic or articulatory I 1 0 i 1 1 0 0 1 description,though recognition and production of speech Y 1 0 o 0 1 0 0 demandthat therebe some,perhaps complex, relation- h 0 0 0 0 1 0 1 0 ship betweenthe abstractfeatures and their acoustic and articulatorycounterparts. The H systemis designed primarily to give a parsimoniousdescription of the ad- lnissiblesound sequences in English,but we are con- TABLE1. MN distinctive-featuresystem. cernedwith how accuratethe H systemis in predicting the rank order of different intrusion errors in short-term recall. Consonant Voicing Nasality Affrication Duration Place '[he W system,like the MN system,is moresimilar p 0 0 0 0 0 to conventionalphonetic analysis of consonantsthan b 1 0 0 0 0 the H system.Only four dimensionsare used,but open- m 1 1 0 0 0 nessof the vocal tract has three valnesfor consonants, t 0 0 0 0 1 and placeof articnlationhas five vaines.Voicing and d 1 0 0 0 1 nasalityare exactlythe sameas in the other two systems. n 1 1 0 0 1 The single dimension of opennessin the W system k 0 0 0 0 2 handles"manner of articulation," which is handled (in g 1 0 0 0 2 a somewhat different manner) by two dimensions f 0 0 l 0 0 (affrication and duration) in the MN system and by v 1 0 1 0 0 four dimensions(vocalic, consonantal, continuant, and strident)in the H system.Place of articulationis coded 0 0 0 1 0 l on a 5-pointscale in the W system,on a slightlyrougher • 1 0 1 0 1 3-point scalein the MX system,and on two binary s 0 0 1 1 1 dimensions(grave and diffuse)in the H system. z I 0 1 I 1 Notice that the opennessof the vocal tract and place • 0 0 l 1 2 of articnlatlon arc the s•tmc two dimensions that were so 2 1 0 I I 2 accuratein predictingthe errorsin STM for English vowels.Of course,the valuesof the opennessdimension for vowels would begin with a value greater than that • M. Halle, "On the Basesof Phonology," in The .5'tructureol' Language,J. A. Fodor and J. J. Katz, Eds. (Prentk'e-Hall, Inc., for the semivowels.Thus, opennessis conceivedto code EnglewoodCliffs, N.J., 19641,pp. 324-333. on a single6-point scale the dil'ferencebetween (1) stop the journalof the AcousticalSociety of America 389 W. A. WICKELGREN digits are not appropriate populations in which to Conso- Voic- Nas- Open- investigateintrusions as a function of feature similarity. nant ing ality hess Place On the other hand, a population of consonants(fol- p 0 0 0 0 lowed by the vowel /a/) has a constant degree of b 1 0 0 0 phonemicsimilarity betweenevery pair of items. rn 1 1 0 0 Sincefeature similarity correlateswith the errors in t 0 0 0 1 auditory recognition,it is important to ensurethat all d 1 0 0 1 intrusionsare errors in short-term recall, not errors in n 1 1 0 1 auditory perception.This can be accomplishedby re- • 0 0 0 3 quiringsubjects to copythe consonantswhile they are • 1 0 0 3 being presented,covering what they have copied,and k 0 0 0 4 then recallingthe consonants.Only the consonantsthat are copiedcorrectly are scoredfor recall.This procedure g 1 0 0 4 T,•BLE III. W distinc- was adoptedin the presentexperiments. f 0 0 1 0 tive-feature system. v 1 0 1 0 I.