Language Experience and the Perception of a Voicing Contrast in Fricatives: Infant and Adult Data

Laura Bosch and Núria Sebastián-Gallés Departament de Psicologia Básica, Universitat de Barcelona Passeig Vall d’Hebron, 171, 08035 Barcelona (Spain) e-mail: [email protected], [email protected]

ABSTRACT More critical to the present research are data concerning the perception of voicing contrasts between fricative sounds. Literature on young infants’ discrimination abilities for Only the [s] – [z] contrast has been studied and again some fricative consonants is controversial. The voicing controversy is present. Syllabic position appeared as a distinction between /s/ and /z/, a phonemic contrast present crucial variable in the first report on this issue: [as]-[az] but in Catalan but not in Spanish, was selected to analyze early not [sa]-[za] were discriminated by 3-month-olds using the discrimination capacities and the effect of language HAS procedure [5]. In a second study, using the head- experience in Catalan monolingual, Spanish monolingual turning paradigm, 6-month-olds reached discrimination for and Catalan-Spanish bilingual populations. By 4 months of [sa]-[za] and it was suggested that longer experience with age discrimination could only be reached in syllable initial the language was required to develop sensitivity to this position and for monosyllabic stimuli. By 12 months of age, contrast [3]. This interpretation has been challenged and it initial sensitivities had been modified and only infants has been argued that failure to observe discrimination at an exposed to Catalan showed discrimination. Bilinguals’ early age might be attributed to the testing procedures and results are in conflict with a language-experience account methods of analysis used in that experiment [6]. However, and they suggest specific perceptual reorganization more recent results from two groups of American infants, processes in simultaneous bilingual exposure. Adult data 6- to 8-month-olds and 10- to 12-month-olds, tested on the revealed significant differences in discrimination between native [s]-[z] fricative voicing contrast, indicated that individuals exposed early in life to Catalan and those only although discrimination was observed in both age groups, exposed to Spanish, while Catalan-Spanish bilingual older infants showed marginally lower discrimination participants did not differ from the Catalan group in the results than the younger ones [7]. Taken together, all these perception of this contrast. data from pre-linguistic infants suggest that while some capacity to discriminate fricative contrasts seems to be 1. INTRODUCTION present early on, it may not be as robust as the capacity to discriminate stop contrasts and/or it may be related to It is a well attested fact that young infants are capable of slightly different perceptual cues. speech sound discrimination well before they begin to speak. Voicing and place of articulation distinctions Developmental changes in speech perception capacities between stop consonants have been most extensively observed by the end of the first year of life have been studied (for a review, see [1]). Research indicates that attributed to the effects of specific language experience. As infants show sensitivity to voice and place differences shown in the seminal paper by Werker and Tees [8], shortly after birth and that discrimination is mainly selective declines in sensitivity to a pair of nonnative stop categorical. In the domain of fricative consonants, however, consonant contrasts were observed between 8 and 12 infants’ sensitivities to both voicing and place of months of age. This developmental pattern of decline in the articulation contrasts have also been analyzed, but more discriminative capacity for nonnative consonantal contrasts controversial results have been obtained. remains unquestioned, although some exceptions have been identified, as it is the case of the Zulu lateral vs. Early studies on place of articulation contrasts analyzed medial click contrast, or an Ethiopian ejective-stop place of [sa]-[a] and [fa]-[a] contrasts. While positive evidence of articulation distinction (for a review, see [7]). More discrimination was found for the former at different age relevant for our present research, a Zulu lateral fricative levels, the latter was found to be more difficult to voicing distinction was also tested for discrimination in 6- distinguish, even in 12-month-old infants [2, 3]. More to 8-month-old and 10- to 12-month-old American infants, recent work has shown [fa]-[a] and also [va]-[a] but unexpectedly in this case (the Zulu contrast could have discrimination in 2-month-olds using both synthetic and been assimilated to the native [s]-[z] contrast and be easily natural speech tokens [4]. It is now generally accepted that distinguished), discrimination was found to be just young infants’ capacity to discriminate place of articulation marginal in both age groups. It was argued that this fricative contrasts between fricative consonants is probably in place distinction might be more difficult than other nonnative at an early age and that methodological problems were stop contrasts and that perhaps some of the categories in the probably behind the conflicting results obtained in the early native language may not be completely organized by the studies. end of the first year of life, as the above mentioned data from the [s]-[z] English distinction seemed to indicate [7]. 2.1.2. Material In order to assess phonetic category discrimination rather Long term consequences of early language experience can than a merely acoustic differentiation, several tokens from be explored in adults. Data on the Catalan fricative voicing six different female speakers were selected. The contrast contrast [sa]-[za] obtained in our laboratory showed under study was initially placed within a disyllabic differences between Catalan-dominant and Spanish- non-word, ([dizi] vs. [disi]). Alternative material with the dominant adult participants in a gating task. Those who had contrast in word initial position was also recorded ([zii] vs. Spanish as L1 performed significantly worse than those [si i]), and a monosyllabic version of exactly the same with Catalan as L1 [9]. Thus, even though the contrast  material was also obtained ([zit] vs. [sit]). could be perceived by the Spanish-dominant participants (who could be considered bilingual, but who had not been 2.1.3. Procedure simultaneously exposed to both languages since birth), for Infants were tested with a version of the familiarization- them, the non-native status of this contrast determined their lower performance in the gating task, a result which is more preference procedure [11]. After two minutes’ compatible with the notion of an early shaping of the familiarization to 12 different tokens of the same stimulus type, infants were tested on four test trials, two “same” perceptual system through linguistic exposure. (new tokens of the same type) and two “switch” (novel tokens with the contrastive consonant). Discrimination is In the present research involving Catalan and Spanish, the obtained from differential attention time to same and switch voicing fricative contrast [s]-[z] is present only in Catalan. trials in the test phase, with longer listening time to novel The voiceless fricative [s] is much more frequent than [z] materials being expected. (15.27% vs. 1.34%, from the total number of consonantal units, [10]). The voiced [z] appears most frequently in 2.2. RESULTS medial position and in word final position before a vowel, but it can also be found in word initial position. In Spanish, 2.2.1. Contrast in word-medial position, [dizi] – [disi] [z] can be pronounced as an allophonic variation of [s] in Data from a single group of 12 infants from monolingual final syllable position before a voiced consonant, but has no and bilingual families did not show discrimination. No contrastive value. significant differences were obtained between mean attention time to same (13992ms) and switch (13275ms) The aims of the present research are threefold and they can trials (t<1). be summarized in the following questions: 2.2.2. Contrast in word-initial position, [zii] – [sii] a) Are young infants, below 6 months of age, capable of Data from two groups of 12 infants from Catalan distinguishing the [s]-[z] voicing contrast, and are their monolingual (MC) and Catalan-Spanish (BL) bilingual initial sensitivities restricted to certain word positions? families did not show discrimination. Non significant differences in attention time to same and switch trials were b) Can changes in sensitivity be observed as a consequence obtained (MC: same 13986ms, switch 15630ms; BL: same of differences in linguistic experience? 15045ms, switch 14808ms; all F<1). c) Will long term effects on the discrimination of this 2.2.3. Contrast in word-initial position, [zit] – [sit] contrast be observed in adults from different linguistic environments? Data from 3 groups of 12 infants from Catalan monolingual (MC), Spanish monolingual (ME) and bilingual (BL) 2. YOUNG INFANTS’ DATA families were analyzed. Mean attention times were: MC same 10803ms, switch 13573ms; ME: same 10843ms, A first series of experiments were run with 4 ½ -month-old switch 15836ms; BL: same 13408ms, switch 17859ms. All infants, tested with disyllabic and monosyllabic stimuli that groups reached discrimination. There were no significant had the contrast in word-medial or word-initial position. If differences between them [F(2,33)=1.68, p<0.2], no discrimination could be observed, no differences for infants significant interaction and the main effect of voicing from different linguistic environments were expected, as contrast was highly significant [F(1,33)=22.32, p<0.0001]. perceptual reorganization processes take place during the 2.3. DISCUSSION second semester of life, but not earlier. Young infants’ data confirm previous reports in that 2.1. METHOD evidence of discrimination for a fricative voicing contrast is 2.1.1. Participants not always easily observed. In spite of clear acoustic differences in sonority as well as in duration, our results Different groups of healthy, full-term 4 ½ -month-old suggest that word position can affect discrimination: the infants from Catalan monolingual, Spanish monolingual fricative contrast in medial position and in a non-stressed and Catalan/Spanish bilingual families (n=12). A detailed syllable cannot be easily detected at an early age. questionnaire assessed the linguistic environment and Moreover, length of the stimuli seems to play a role, with offered an estimate of the amount of exposure to each sensitivity to the contrast in initial position limited to short, language. monosyllabic items.

3. EFFECTS OF LINGUISTIC EXPOSURE similar developmental trend, but at an earlier age, has also been found for a vowel contrast [12], thus suggesting that Next series of experiments were aimed at analyzing a specific perceptual reorganization processes are taking possible decline in sensitivity to this contrast, as a function place in pre-linguistic bilingual infants and that the time of linguistic experience, by the end of the first year of life. course of bilingual phonetic representation is different in this case. 3.1. METHOD 4. ADULT DATA 3.1.1. Participants Finally, long-term effects of linguistic experience were Three groups of 12-month-old infants from Catalan assessed in adults, all proficient in Catalan, but with monolingual (MC), Spanish monolingual (ME) and differences in the age of initial exposure to this language bilingual (BL) families were tested, each to be compared to and differences in their linguistic early environment. the younger infants’ group. 3.1.2. Material and procedure 4.1. METHOD The same monosyllabic tokens, ([zit] vs. [sit]), used in the 4.1.1. Participants third experiment with younger infants, and the same Twelve adults raised in Catalan monolingual (MC), 12 in procedure were employed. Spanish monolingual (ME) and 12 in bilingual (Catalan/ 3.2. RESULTS Spanish) families (BL). Subjects in the ME group have been exposed to Catalan outside the family, starting around 3.2.1. Infants from monolingual families school age. They were undergraduate Psychology students A different developmental pattern of discrimination was at the University of Barcelona (where about 60% of the expected between infants exposed to Catalan, where the courses are taught in Catalan) who participated in exchange contrast is present, and infants exposed to Spanish where it of course credits. is inexistent. Results were as predicted. MC infants’ mean 4.1.2. Material attention times were: same 10628ms, switch 13487ms. The ANOVA with younger and older MC data yielded a Several [zit]–[sit] tokens, contrastive only in Catalan, and significant main effect of voicing contrast [F(1,22)= 11.95, [doi]-[dui] ones, a vowel contrast common to both p< 0.002], with no differences between groups and no languages, were selected. interaction (all F<1). On the other hand, ME infants’ mean 4.1.3. Procedure attention times were: same 9016ms, switch 9407ms. The ANOVA with younger and older ME data showed A short-term memory paradigm, originally developed to significant group differences [F(1,22)= 7.02, p< 0.01], and uncover differences in stress perception between Spanish both the main effect of contrast and the interaction were and French natives, was used [13]. In this task, participants significant [F(1,22)= 5.68, p< 0.02; F(1,22)=4.15, p=0.05]. listen to increasingly long sequences of stimuli and they are Results are compatible with the notion of a decline in asked to reproduce them by pressing previously associated sensitivity. Only the younger group listened longer during keys. Sequences increasing from 2 to 6 tokens were used. switch trials and older infants seem to have lost interest: to There were 40 trials (8 per each sequence length) for each them, all the items would belong to a single category. contrast under study. Participants were tested individually in sound-attenuated booths. 3.2.2. Infants from Catalan-Spanish bilingual families 4.2. RESULTS AND DISCUSSION In spite of exposure to Catalan, 12-month-olds did not give evidence of discrimination. Mean attention times to same An ANOVA on the difference scores (common contrast and switch trials were: same 16711ms, switch 15809ms; minus language-specific contrast) was performed. The The ANOVA with younger and older infants’ data showed analysis showed an effect of language group [F(2,33)= 19.9, no significant differences between groups (F<1), a non p<0.0001]. The difference scores for the MC was of –2.417, significant effect of contrast [F(1,22)=2.9, p<0.1], but a for the ME was of –17.083 and for the BL group of –5.167. significant interaction [F(1,22)=6.8, p<0.01]. A Sheffé multiple-comparison test showed no statistical differences between the MC and BL groups, while both 3.3. DISCUSSION groups differed from the ME one (in both cases, p<.0001). By 12 months of age infants from monolingual families These results showed that both MC and BL participants perceive this contrast in accordance with its contrastive performed equally well in the common contrast and value in the language of exposure (at least when it is language-specific ones, but that ME performed presented in word initial position in a short, CVC stimulus). significantly worse in the language-specific contrast than in Bilingual data, however, are somehow unexpected if one the common one. The results of the present experiment are considers that they have been exposed to these sounds. in agreement of previous research in that individuals highly Differences between monolingual and bilingual competent in their L2 but who have been exposed to this environments in terms of the total amount of exposure to language in early childhood have perceptual difficulties each of the languages may play a role, but also, the fact that with some L2 contrasts. in bilingual language acquisition the infant has to deal with a more complex and variable linguistic input, may be a determinant factor in the pattern we have observed. A 5. CONCLUSIONS Journal of the Acoustical Society of America, vol. 61, pp. 1321-1336, 1977. The discrimination of a fricative voicing contrast in very young infants seems to be constrained by its position within a word and by the length of the stimuli. Effects of exposure [6] P.W. Jusczyk, The discovery of spoken language, during the first year of life modify early sensitivities: Cambridge, MA: MIT Press, 1997. monolingual data conform to the predicted pattern of discrimination, with infants from Spanish-speaking [7] C.T. Best, "The emergence of native-language environments showing a decline in sensitivity for an phonological influence in infants: A perceptual inexistent contrast in their familiar language. In assimilation model," in The Development of Speech simultaneous bilingual exposure the pattern obtained Perception: The Transition from Speech Sounds to suggests that linguistic experience alone is not enough to Spoken Words, J.C. Goodman and H.C. Nusbaum, maintain discrimination. The time course of language- Eds., pp. 167-224. Cambridge, MA: MIT Press, 1994. specific category formation processes in bilinguals seems to differ from that of monolinguals. It can be hypothesized [8] J.F. Werker, and R.C. 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