PTLC2005 Geoffrey Schwartz Phonetics-phonology interface – implications 1 The phonetics-phonology interface – implications for teaching L2 pronunciation Geoffrey Schwartz Adam Mickiewicz University, Poznań, Poland 1 Introduction The phonetics-phonology interface (see e.g. Hume and Johnson, 2001), examining the role of acoustic and perceptual phenomena in the shaping and maintenance of phonological contrasts, is a “hot” topic in current linguistic research. At the core of this interface lies the fundamental issue of how continuous phenomena found in the acoustic speech signal are represented in speakers’ discrete mental representations of linguistic units. At present, this area represents largely uncharted waters in the field of foreign language pedagogy. Pronunciation teachers and textbooks tend to rely on static phonological labels, symbols of “phonetic” transcription that provide useful reference points, but make it easy for teachers and students to overlook the dynamic aspects of speech that are so crucial to comprehension. This paper reports on three experiments investigating how pronunciation teachers might benefit by approaching their jobs from the point of view of speech perception - concentrating on the dynamic nature of the acoustic speech signal. Each experiment was carried out with Polish students of English, and deals with the long/short contrast in English high vowels (e.g. infamous pairs such as ship and sheep), a problematic area for many foreign learners. Before reporting on the individual experiments, it is worth providing a quick illustration of some acoustic phenomena associated with this contrast. 2 The phonetic anatomy of a binary contrast The vowel contrast in the pair of English words seat and sit is generally considered a binary phonological opposition, characterized as either long v. short or tense v. lax. Although for the purposes of phonemic analysis seat and sit represent a minimal pair, an acoustical investigation may reveal differences in several phonetic parameters between the two vowels. 5000 1 3 0 1 .5 4 2 6 3 2 400 4 100 0 1 .5 4 2 6 3 T im e ( s ) Figure 1 – Spectrogram and pitch track for English seat (left) and sit. Arrows point to various acoustic parameters discussed in Section 2. PTLC2005 Geoffrey Schwartz Phonetics-phonology interface – implications 2 Figure 1 presents a spectrogram and pitch track of the words seat and sit as produced by a native speaker of English. The two tokens were recorded in carrier sentences to control for phonetic and prosodic context effects. The numbers on the spectrograms point to four different acoustic phenomena by which the two vowels differ. The first arrows (numbered 1) point to the first and second formants, which at first glance show a more peripheral articulation target (higher, more fronted tongue position) for the seat vowel. However, a closer look at reveals an important dynamic phenomenon associated with the contrast. We can notice in the seat vowel that there is much more formant movement, betraying it’s diphthongal nature. Arrow number two indicates the longer duration of the seat vowel. The third arrow points to the area of the spectrum between the first and second formants. Notice that in the sit vowel, there is significant harmonic energy in this frequency range, while in the seat vowel there is almost none. This is a reflection of a difference in voice quality between the two vowels – the seat vowel is characterized by more breathy phonation while the sit vowel is produced with a creakier voice quality. Finally, arrow 4 pointing to the pitch track indicates that despite the fact that these tokens were produced in identical prosodic positions, the seat vowel is marked by more dramatic movement in pitch than the sit vowel. Table 1 summarises these and other acoustic phenomena that were measured for these tokens, showing that the binary long/short vowel contrast is realized on the basis of several phonetic parameters. Parameter Overall amplitude seat 70dB sit 75dB Duration 160ms 120ms Average F1-F2 295 Hz-2498 Hz 438 – 2059 Hz Range of movement F1 275-304 Hz in F1 and F2. F2 2362-2645 Hz F1 386-449 Hz F2 1979-2123 Hz Relative amplitude of 49.6 dB H1 first two harmonics 36.3 dB H2 41.4 dB 51.2 dB Overall amplitude of 49.8 dB 3rd – 9th harmonics2 combined 68.6 dB Pitch range 209-199 Hz. 226-186 Hz comments more closed vowel generally lower in amplitude A “standard” parameter of the associated with the contrast Difference in articulatory target. More peripheral for seat very large (and slow)1 F2 movement for seat, showing vowel’s diphthongal quality Strong fundamental associated with breathier phonation in seat Energy in higher harmonics typical of creakier phonation for sit greater pitch movement on long vowel Figure 2 – Summary of acoustic differences between the vowels in the tokens of seat and sit shown in Figure 1. 3 Experimental Studies To investigate the benefits of such an approach to second language pronunciation teaching, this paper reports on three experiments dealing 1 The approach to the F2 target took 100 ms, more than half of the duration of the vowel, perhaps the most telling statistic of the diphthongality of the seat vowel. 2 This measurement was taken after band-pass filtering the signal in the range that corresponded to the harmonics between F1 and F2. PTLC2005 Geoffrey Schwartz Phonetics-phonology interface – implications 3 with Polish students’ production of the long/short (tense/lax) contrast in English high vowels. 3.1. Experiment 1: This experiment (written up in Schwartz, 2004) investigates the role of voice quality in native speakers’ perception of the contrast as produced by foreign learners. Eight native speakers of American English were asked to rate 5 different Polish students’ productions of the minimal pairs seat and sit. At the same time, measurements were taken of the same productions to rate each student’s contrast acoustically in three parameters: Tongue position (F1F2), Duration, and Voice Quality. These acoustic ratings aimed to describe the distinctiveness of students’ contrasts for each acoustic parameter. They were calculated by taking the difference in the relevant acoustic parameters between the two vowels (F2/F1 for tongue position, amp f0 – amp H2 for voice quality, and duration). These results are summarized in Table 2 below, showing acoustic contrast measures for the three parameters, as well as for a native speaker. The ranking according to listeners’ ratings is presented in Table 3. Speaker Tongue position Voice Quality Duration Alicja 4.9 11.2 1.37 Anna 3.1 14.5 1.39 Ewa 3.2 8.1 1.13 Ola 3.0 7.2 1.07 Julia 2.2 3.2 1.12 Native 4.8 17.6 1.10 Table 2 - Contrast measures for the five students’ productions and one native production of the English tense-lax contrast Listeners' Ranking Speaker name 1 Anna 2 Alicja 3 Ewa 4 Ola 5 Julia Table 3 – Native listeners’ ranking of students based on average ratings for all listeners. 3.2 Experiment 2: This experiment (written up in Schwartz and Glogowska, 2004) was designed to test the teachability of the non-distinctive features of voice quality, amplitude, and pitch movement. Four Polish students of English were recorded before and after a 90-minute instructional session devoted to the three features in maintaining the long/short contrast. The recordings were then presented to 18 teachers of English. The teacher-listeners (half of them native speakers) heard improvements in 48.6 % of the tokens. The student subjects also reacted positively, and were all in agreement that these features made it easier to perceive and produce this difficult contrast. 3.3 Experiment 3: This experiment (see Schwartz, to appear) tested the role of pitch movement in students’ production of English long high vowels. The pitch contours of productions of these vowels were manipulated to native-like norms for utterance PTLC2005 Geoffrey Schwartz Phonetics-phonology interface – implications 4 prominent syllables, and presented to 21 teacher-listeners with a forced-choice task. The results are presented in Table 4, showing that the manipulated tokens were heard as improved at a higher than chance level. Word Set “Greetings” Manipulated has better total # (%) 8 (38,1%) token vowel- Original token has better vowel- total # (%) 1 (4,8%) Neither has better vowel- total # (%) 12 (57,1%) “Luke” 10 (47,6%) 2 (9,5%) 9 (42,9%) “Leave” 9 (42,9%) 6 (28,6%) 6 (28,6%) “cheeks” 8 (38,1%) 7 (33,3%) 6 (28,6%) “Luke” 8 (38,1%) 2 (9,5%) 11 (52,4%) “deed” 10 (47,6%) 6 (28,6%) 5 (23,8%) “Luke” 8 (38,1%) 4 (19,0%) 9 (42,9%) “cheeks” 12 (57,1%) 5 (23,8%) 4 (19,0%) Overall 73 (43,5%); 33 (19,6%) 62 (36,9%) t=4.13, p<0.005 t=3.63, p<0.005 t=0.72, p>0.1 Table 4 – Results of Experiment 3. 4 Discussion These experiments seek to address two primary questions: 1) do “subfeatural” parameters associated with the contrast play a role in the listeners’ perception of L2 speech as being “native-like”? 2) From the pedagogical perspective is it possible to teach such parameters? The results of Experiments 1 and 3 indicate that subfeatural phonetic phenomena such as voice quality and pitch movement may be specified in speakers’ representations of segments, underlying the importance of such features in “native-like” production. At the same time such findings lend support to a usage-based model of phonology (Bybee, 2001). Assuming a usage-based model might have significant implications for SLA in that it would promote the role of variation in the language learning process, a notion that may prove troublesome for proponents of proposals that try to simplify the task of learning English pronunciation (Jenkins, 2000). At the same time, Experiment 2, while limited in scope, did have one important pedagogical finding: features such as pitch movement and voice quality, because they are concrete acoustic phenomena that students may imitate, are in principle quite teachable. References Bybee, J. (2001) Phonology and Language Use. Cambridge: Cambridge University Press. Hume, E and Johnson, K (2001) The role of speech perception in phonology. San Diego: Academic Press. Schwartz, G (To appear) Pitch movement and the realization of English vowels. Schwartz, G. (2004) Voice quality in students’ production of the English tense/lax contrast. In Sobkowiak, W, Waniek-Klimczak, E (eds.) Dydaktyka fonetyki języka obcego. Zeszyty Naukowy PWSZ w Koninie 1(4), 75-79. Schwartz, G and Głogowska, M (2004) Acoustic tools for students’ production of English long (tense) vowels. In Sobkowiak, W, Waniek-Klimczak, E (eds.) Dydaktyka fonetyki języka obcego. Zeszyty Naukowy PWSZ w Koninie 1(4), 80-85.