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Native and foreign vowel discrimination as indexed by the mismatch negativity (MMN) response
Neuroscience Letters 352 (2003) 25–28 www.elsevier.com/locate/neulet
Native and foreign vowel discrimination as indexed by the mismatch negativity (MMN) response Maija S. Peltolaa,b,*, Teija Kujalac,d, Jyrki Tuomainena,e, Maria Ekb, Olli Aaltonena, Risto Na¨a¨ta¨nenc,f a
Department of Phonetics, University of Turku, FIN-20014 Turku, Finland Centre for Cognitive Neuroscience, University of Turku, FIN-20014 Turku, Finland c Cognitive Brain Research Unit, University of Helsinki, Helsinki, Finland d Helsinki Collegium for Advanced Studies, Helsinki, Finland e Laboratory of Computational Engineering, University of Helsinki, Helsinki, Finland f Helsinki Brain Research Center, Helsinki, Finland b
Received 17 January 2003; received in revised form 13 August 2003; accepted 13 August 2003
Abstract The development of a new vowel category was studied by measuring both automatic mismatch negativity and conscious behavioural target discrimination. Three groups, naı¨ve Finns, advanced Finnish students of English, and native speakers of English, were presented with one pair of Finnish and three pairs of English synthetic vowels. The aim was to determine whether the advanced student group would show native-like responses to the unfamiliar vowel contrasts of the target language. The results suggest that learning in classroom environment may not lead to the formation of new long-term native-like memory traces. q 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Discrimination; Language learning; Memory trace; Mismatch negativity (MMN); Reaction time; Vowel perception
Traditionally, second language acquisition research has relied on phonetic tests [6,14] to determine the proficiency in the target language. However, these results may be partly affected by the fact that subjects may resort to overt knowledge of the language and to various conscious strategies [7]. The role of this overt knowledge, i.e. metalanguage [5], is problematic if the purpose is to determine whether the learners of the target language have internalised the new language system. Automatic decoding may be considered one indicator of language proficiency: if speech is recognised automatically on the basis of newly emerged long-term memory traces for the speech sound categories, the new language system is similarly processed as the mother tongue, i.e. the processing is native-like. In order to study whether native-like high level of proficiency has been obtained, it may be advantageous to use methods, which do not depend on conscious effort. The mismatch negativity (MMN), a component of the *
Corresponding author. Tel.: þ 358-2-333-5078; fax: þ358-2-333-6560. E-mail address: [email protected] (M.S. Peltola).
brain event-related potential (ERP), is automatically evoked even when subjects ignore the stimuli. The MMN peaks at 100 – 200 ms from stimulus onset in response to an infrequent change in a constant stimulus train [11]. The MMN can be used to study second language acquisition, since it reveals whether language-specific phoneme representations have emerged [12]. Accordingly, if the memory representations have developed for the phonemes of the new language, then the responses to the foreign speech stimuli should resemble the ones evoked by the phonemes of the mother tongue. Two separate experiments were carried out during one session. In Experiment 1, the MMN was recorded and in Experiment 2, the reaction time (RT) was measured using the same stimuli as in Experiment 1. Three groups of healthy adult subjects participated. The first group consisted of 11 (mean age 19, range 18 –21; four females) native speakers of Finnish with only a little knowledge of English, the second group of ten (mean age 20.6, range 19 –25; six females) Finnish advanced students of English (majors at the Department of English, University of Turku), and the
0304-3940/03/$ - see front matter q 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/S0304-3940(03)00997-2
26
M.S. Peltola et al. / Neuroscience Letters 352 (2003) 25–28
third group of nine (mean age 20.2, range 20– 21; five females) native speakers of English. In both experiments, subjects were presented with synthetic steady-state vowels rated as good category representatives by native speakers. Four stimulus blocks were used: 1. Finnish /i/ –/e/; 2. English /i/ – /e/; 3. English /i/ – /I/; and 4. English /e/ –/I/. (For details of the categories, see ref. [14].) The Euclidean distances in the formant space of the stimulus pairs were: 185 Mel, 272 Mel, 108 Mel, and 182 Mel, respectively. The smallest acoustic difference thus was between the English /i/ and /I/ and the largest between the English /i/ and /e/ while in the two remaining pairs, the distance was almost identical. The stimuli were synthesized using HLSyn software (v.1.0 Sensimetrics, Inc). The stimuli (duration 350 ms) were presented pseudo-randomly in the oddball paradigm consisting of repetitive ‘standard’ stimuli occasionally replaced by ‘deviant’ stimuli. The interstimulus interval was 400 ms. In Experiment 1, 900 standard and 151 deviant (P ¼ 0:14) stimuli were presented in four blocks, with each block lasting for 15 min. During the session, subjects watched a silent movie, and were asked to ignore the auditory stimuli presented binaurally through headphones. In Experiment 2, each of the four stimulus blocks lasted for 5 min, consisting of 350 standard and 50 deviant (P ¼ 0:125) stimuli. Subjects were instructed to press a response button as soon as they heard a change in the vowel quality of the stimulus train. In Experiment 1, the EEG was recorded from the scalp with Ag-AgCl electrodes at locations Fz, Cz, Pz (10 – 20 System) and from the coronal arcs connecting the left and right mastoids (Lm and Rm, respectively) via Fz (Lm, L1,
L2, (Fz), R1, R2, Rm). The reference electrode was attached to the nose. Horizontal eye movements were monitored with an electrode placed near the outer canthus of the right eye and the vertical movements with Fpz. The electrode impedance was kept under 5 kV. The amplifier bandwidth was 0.5– 70 Hz, and a sampling frequency of 200 Hz was used. The ERP epochs were digitally filtered off-line by a 1 – 30 Hz bandpass filter and automatic artefact rejection (^ 70 mV) was applied prior to the averaging of the trials. Separately averaged waveforms for the standard and deviant stimuli (450 ms window including a 50 ms baseline period) were computed for individual subjects. In the analysis, the dependent variable was the mean amplitude measured from three time windows (120 –160, 160 – 200, and 200– 240 ms) placed around the maximum amplitude determined from the grand-average difference waveform. The mean amplitudes at Fz were statistically analysed using repeated measures analysis of variance (ANOVA). In the behavioural discrimination task (Experiment 2), the button presses occurring within 100 – 2500 ms from target-stimulus onset were regarded as hits and the responses occurring at any other time as false alarms. The individual hit and false alarm rates and the RTs were then subjected to repeated measures ANOVA. Fig. 1 shows the grand-average difference waveforms at Fz for all groups and each stimulus pair in Experiment 1. The mean MMN amplitudes are displayed in Table 1. The overall analysis revealed the main effect of the Time Frame (Fð2; 54Þ ¼ 6:848, P ¼ 0:002) and the interactions between (1) the stimulus pair and the Time Frame (Fð6; 162Þ ¼ 14:793, P , 0:001) and (2) the subject
Fig. 1. The grand-mean difference waves (responses elicited by the standard stimuli subtracted from that elicited by the deviant stimuli) in four different vowel blocks for Naı¨ve Native Finns (thin solid line), Advanced Students of English (thick solid line), and Native English speakers (dotted line).
M.S. Peltola et al. / Neuroscience Letters 352 (2003) 25–28
27
Table 1 The mean MMN amplitudes (and standard errors of mean) for latency windows 120–160, 160–200, and 200–240 ms in Experiment 1 Vowel blocks
Finnish /i–e/ English /i– e/ English /i– I/ English /e –I/
Group 1 Naı¨ve
Group 2 Advanced
Group 3 Native English
120–160
160– 200
200 –240
120 –160
160 –200
200–240
120–160
160–200
200–240
22.686 (0.721) 21.032 (0.640) 20.492 (0.605) 20.059 (0.622)
23.286 (0.756) 21.130 (0.649) 21.697 (0.705) 21.587 (0.678)
22.081 (0.843) 21.147 (0.746) 22.415 (0.720) 22.274 (0.640)
21.633 (0.757) 22.952 (0.671) 20.576 (0.635) 20.803 (0.653)
20.901 (0.793) 22.298 (0.681) 21.404 (0.740) 21.041 (0.711)
0.806 (0.884) 20.502 (0.782) 20.730 (0.755) 20.849 (0.671)
21.879 (0.798) 22.793 (0.707) 21.321 (0.669) 21.116 (0.688)
22.326 (0.836) 23.280 (0.718) 22.907 (0.780) 23.009 (0.750)
0.009 (0.932) 21.170 (0.824) 21.877 (0.796) 22.937 (0.707)
group and the Time Frame (Fð4; 54Þ ¼ 4:583, P ¼ 0:003). Further analysis showed a main effect of Stimulus Type in the first (120 – 160 ms, Fð3; 81Þ ¼ 4:970, P ¼ 0:003) and in the third (200 – 240 ms, Fð3; 81Þ ¼ 4:069, P ¼ 0:010) Time Frames. In Time Frame 1 (120 –160 ms), the native language effect on the MMN was found in naı¨ve Finns: the response to the native language vowels (Finnish /i/ – /e/) was markedly larger (tð10Þ ¼ 2:607, P ¼ 0:026) than that to the English vowels /e/ – /I/ in spite of the same acoustic deviant-standard distance, and when the distance was smaller in English /i/ – /I/ (tð10Þ ¼ 2:283, P ¼ 0:023). In addition, in Time Frame 2, the MMN to the native contrast was larger in amplitude than that to the English pair with the same acoustic distance (English /e/ – /I/, tð10Þ ¼ 3:123, P ¼ 0:011) or with the largest acoustic distance (English / i/ – /e/, tð10Þ ¼ 2:371, P ¼ 0:039). A similar response pattern was also found in the native speakers of English in Time Frame 3 (200 – 240 ms): the MMN was significantly larger for the native than the foreign contrast (English /e/ – /I/ versus Finnish /i/ – /e/, tð8Þ ¼ 2:898, P ¼ 0:020). The non-native-like processing of the foreign vowels by the advanced students was clearly demonstrated in the response to the pair English /e/ –/I/ in Fig. 1: the response is significantly smaller for the non-native than the native speakers of English both in Time Frame 2 (tð17Þ ¼ 3:060, P ¼ 0:007) and Time Frame 3 (tð17Þ ¼ 3:601, P ¼ 0:002). In fact, the amplitude of the MMN appears to depend on the acoustic deviant-standard distance, since the MMN to the English /i/ – /e/ was larger than that evoked by English /e/ – /I/ (in Time Frame 1: (tð9Þ ¼ 3:092, P ¼ 0:014) and English / i/ –/I/ (in Time Frame 2: (tð9Þ ¼ 1:983, P ¼ 0:028). In
addition, Fig. 1 suggests that the MMN responses of the advanced students are small altogether. In Experiment 2, the amount of errors made was very low for each group and for each vowel contrast (mean 1.83%, range 1.1 –2.2%), and no significant differences were found between the subject groups and conditions either in errors or hit rates. The acoustic distance of the stimuli in the vowel pair caused systematic differences in the RTs (Fð3; 87Þ ¼ 10:91, P , 0:001; Table 2). Further pairwise comparisons showed that this was due to the pair English /i/ – /I/: the RTs were significantly slower than those for the other pairs (Finnish /i/ – /e/, P , 0:001; English /i/ – /e/, P ¼ 0:001; English /e/ – /I/, P ¼ 0:001). There were no other significant differences in the RTs. The present study showed that the brain responses to speech stimuli are larger for the native language contrasts in comparison with foreign language ones with the same acoustic distance between the stimuli. This was most evident in the MMN responses of the naı¨ve Finns, but it was also seen in native speakers of English. However, the advanced students of English did not respond to the English vowels in a native-like manner, which was seen in the lower amplitude evoked by the English vowel contrast (/e/ –/I/) when compared with the native speakers of English. Furthermore, we found that the response to the mother tongue contrast by the advanced students was not native-like when compared with the naı¨ve Finns, which suggests that the unfinished learning process affects the access to the native language representations. The acoustic distance between the deviant and the standard appeared to be a significant factor in the MMN amplitude in the advancedstudent group, since the response to the acoustically most
Table 2 Mean reaction times (RT) (and standard errors of mean) for Experiment 1 Vowel blocks
Group 1 Naı¨ve
Group 2 Advanced
Group 3 Native English
Finnish /I–e/ English /I –e/ English /i– I/ English /e –I/
348 (17.8) 340 (17.9) 370 (17.6) 347 (15.8)
311 (18.6) 308 (18.8) 334 (18.5) 311 (16.6)
332 (19.6) 312 (19.8) 348 (19.5) 316 (17.5)
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M.S. Peltola et al. / Neuroscience Letters 352 (2003) 25–28
salient contrast (English /i/ – /e/) was largest. In contrast, the responses of the two monolingual groups depended more on the phonemic status of the sounds in the mother tongue. The acoustic salience appeared to be the main factor also in the RT measurements in all groups and the RTs did not show a similar pattern with the MMN amplitude as in studies by Na¨a¨ta¨nen et al. [13] and Menning et al. [10]. However, in these studies, the subjects were originally unable to discriminate the minute differences in the stimuli, whereas in the present study the stimuli were easily discriminable due to large acoustic distances. The very fast RTs in the present study might in part reflect a ceiling effect. The present data are in accordance with the results obtained by Na¨a¨ta¨nen et al. [12] in showing that the representations revealed by the MMN are partly languagespecific. This was most obvious in the monolingual Finnishspeaking group, but also in the native English group. Our results can also be contrasted with the finding of Winkler et al. [15] which demonstrated that new memory traces emerge in subjects who have spent a considerable time in a foreign country (2 –13 years): this naturally obtained language proficiency is therefore markedly different from that resulting from classroom learning. It seems that authentic input is required before the processing of the foreign speech sounds becomes native-like. As our results suggest, this input is insufficient in the context of classroom education and new native-like long-term memory traces for foreign vowels are not formed in spite of extensive (average 12 years) language studies. Curiously, when the responses to the native vowels of the advanced students were compared with the two native speaker groups we noted that the monolinguals processed speech on the basis of the mother tongue model developed in early infancy [4,9], but in the advanced students the response to native vowel contrast seemed not native-like. This may suggest that – in addition to affecting linguistic skills demanding conscious effort [2,8] – the intensive foreign language learning may also affect the processing of native phonological vowel contrasts at the preattentive level. In addition, the overall small MMN amplitudes in the results of these students (most acutely seen in the response for the new contrasts /e/ – /I/) could tentatively be seen as a further indicator of the incompleteness of the learning process: it might be that, when the process of acquisition is unfinished, the small MMN amplitude indexes the ongoing nature of the process. Therefore, the small MMN responses (both to the foreign and native contrasts) could be a neural correlate for the ‘confusion hypothesis’ [1,3], which refers
to a stage in the learning process where the two systems are intertwined.
Acknowledgements The study was supported by the Finnish Cultural Foundation.
References [1] M.L. Albert, L.K. Obler, The Bilingual Brain, Academic Press, New York, 1978. [2] M. Anisfeld, E. Anisfeld, R. Semogas, Cross-influence between the phonological systems of Lithuanian-English bilinguals, J. Verbal Learn. Verbal Behav. 8 (1969) 257 –261. [3] A. Caramazza, G. Yeni-Komshian, E. Zurif, E. Carbone, The acquisition of a new phonological contrast: The case of stop consonants in French-English bilinguals, J. Acoust. Soc. Am. 54 (1973) 421 –428. [4] M. Cheour, R. Ceponiene, A. Lehtokoski, A. Luuk, J. Allik, K. Alho, R. Na¨a¨ta¨nen, Development of language-specific phoneme representations in the infant brain, Nat. Neurosci. 1 (1998) 351 –353. [5] S.P. Corder, Error Analysis and Interlanguage, Oxford University Press, Oxford, 1981. [6] J.E. Flege, The production of ‘new’ and ‘similar’ phones in a foreign language: evidence of speech perception, J. Phon. 15 (1987) 47–65. [7] J. Hillenbrand, G.J. Canter, B.L. Smith, Perception of intraphonemic differences by phoneticians, musicians, and inexperienced listeners, J. Acoust. Soc. Am. 88 (1990) 655– 662. [8] I. Kecskes, T. Papp, Foreign Language and Mother Tongue, Lawrence Erlbaum Associates, Hillsdale, NJ, 2000. [9] P.K. Kuhl, K.A. Williams, W.F. Lacerda, K.N. Stevens, B. Lindblom, Linguistic experiences alter phonetic perception in infants by 6 months of age, Science 255 (1992) 606– 608. [10] H. Menning, S. Imaizumi, P. Zwitserlood, C. Pantev, Plasticity of the human auditory cortex induced by discrimination learning of nonnative, mora-timed contrasts of the Japanese language, Learn. Mem. 9 (2002) 253 –267. [11] R. Na¨a¨ta¨nen, Attention and Brain Function, Lawrence Erlbaum Associates, Hillsdale, NJ, 1992. [12] R. Na¨a¨ta¨nen, A. Lehtokoski, M. Lennes, M. Cheour, M. Huotilainen, A. Iivonen, M. Vainio, P. Alku, R.J. Ilmoniemi, A. Luuk, J. Allik, J. Sinkkonen, K. Alho, Language-specific phoneme representations revealed by electric and magnetic brain responses, Nature 385 (1997) 432 –434. [13] R. Na¨a¨ta¨nen, E. Schro¨ger, S. Karakas, M. Tervaniemi, P. Paavilainen, Development of a memory trace for a complex sound in the human brain, NeuroReport 4 (1993) 503–506. [14] K. Wiik, Finnish and English Vowels, Univ. of Turku, Turku, 1965. [15] I. Winkler, T. Kujala, H. Tiitinen, P. Sivonen, P. Alku, A. Lehtokoski, I. Czigler, V. Cse´pe, R. Na¨a¨ta¨nen, Brain responses reveal the learning of foreign language phonemes, Psychophysiology 36 (1999) 638 –642.
Native and foreign vowel discrimination as indexed by the mismatch negativity (MMN) response Maija S. Peltolaa,b,*, Teija Kujalac,d, Jyrki Tuomainena,e, Maria Ekb, Olli Aaltonena, Risto Na¨a¨ta¨nenc,f a
Department of Phonetics, University of Turku, FIN-20014 Turku, Finland Centre for Cognitive Neuroscience, University of Turku, FIN-20014 Turku, Finland c Cognitive Brain Research Unit, University of Helsinki, Helsinki, Finland d Helsinki Collegium for Advanced Studies, Helsinki, Finland e Laboratory of Computational Engineering, University of Helsinki, Helsinki, Finland f Helsinki Brain Research Center, Helsinki, Finland b
Received 17 January 2003; received in revised form 13 August 2003; accepted 13 August 2003
Abstract The development of a new vowel category was studied by measuring both automatic mismatch negativity and conscious behavioural target discrimination. Three groups, naı¨ve Finns, advanced Finnish students of English, and native speakers of English, were presented with one pair of Finnish and three pairs of English synthetic vowels. The aim was to determine whether the advanced student group would show native-like responses to the unfamiliar vowel contrasts of the target language. The results suggest that learning in classroom environment may not lead to the formation of new long-term native-like memory traces. q 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Discrimination; Language learning; Memory trace; Mismatch negativity (MMN); Reaction time; Vowel perception
Traditionally, second language acquisition research has relied on phonetic tests [6,14] to determine the proficiency in the target language. However, these results may be partly affected by the fact that subjects may resort to overt knowledge of the language and to various conscious strategies [7]. The role of this overt knowledge, i.e. metalanguage [5], is problematic if the purpose is to determine whether the learners of the target language have internalised the new language system. Automatic decoding may be considered one indicator of language proficiency: if speech is recognised automatically on the basis of newly emerged long-term memory traces for the speech sound categories, the new language system is similarly processed as the mother tongue, i.e. the processing is native-like. In order to study whether native-like high level of proficiency has been obtained, it may be advantageous to use methods, which do not depend on conscious effort. The mismatch negativity (MMN), a component of the *
Corresponding author. Tel.: þ 358-2-333-5078; fax: þ358-2-333-6560. E-mail address: [email protected] (M.S. Peltola).
brain event-related potential (ERP), is automatically evoked even when subjects ignore the stimuli. The MMN peaks at 100 – 200 ms from stimulus onset in response to an infrequent change in a constant stimulus train [11]. The MMN can be used to study second language acquisition, since it reveals whether language-specific phoneme representations have emerged [12]. Accordingly, if the memory representations have developed for the phonemes of the new language, then the responses to the foreign speech stimuli should resemble the ones evoked by the phonemes of the mother tongue. Two separate experiments were carried out during one session. In Experiment 1, the MMN was recorded and in Experiment 2, the reaction time (RT) was measured using the same stimuli as in Experiment 1. Three groups of healthy adult subjects participated. The first group consisted of 11 (mean age 19, range 18 –21; four females) native speakers of Finnish with only a little knowledge of English, the second group of ten (mean age 20.6, range 19 –25; six females) Finnish advanced students of English (majors at the Department of English, University of Turku), and the
0304-3940/03/$ - see front matter q 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/S0304-3940(03)00997-2
26
M.S. Peltola et al. / Neuroscience Letters 352 (2003) 25–28
third group of nine (mean age 20.2, range 20– 21; five females) native speakers of English. In both experiments, subjects were presented with synthetic steady-state vowels rated as good category representatives by native speakers. Four stimulus blocks were used: 1. Finnish /i/ –/e/; 2. English /i/ – /e/; 3. English /i/ – /I/; and 4. English /e/ –/I/. (For details of the categories, see ref. [14].) The Euclidean distances in the formant space of the stimulus pairs were: 185 Mel, 272 Mel, 108 Mel, and 182 Mel, respectively. The smallest acoustic difference thus was between the English /i/ and /I/ and the largest between the English /i/ and /e/ while in the two remaining pairs, the distance was almost identical. The stimuli were synthesized using HLSyn software (v.1.0 Sensimetrics, Inc). The stimuli (duration 350 ms) were presented pseudo-randomly in the oddball paradigm consisting of repetitive ‘standard’ stimuli occasionally replaced by ‘deviant’ stimuli. The interstimulus interval was 400 ms. In Experiment 1, 900 standard and 151 deviant (P ¼ 0:14) stimuli were presented in four blocks, with each block lasting for 15 min. During the session, subjects watched a silent movie, and were asked to ignore the auditory stimuli presented binaurally through headphones. In Experiment 2, each of the four stimulus blocks lasted for 5 min, consisting of 350 standard and 50 deviant (P ¼ 0:125) stimuli. Subjects were instructed to press a response button as soon as they heard a change in the vowel quality of the stimulus train. In Experiment 1, the EEG was recorded from the scalp with Ag-AgCl electrodes at locations Fz, Cz, Pz (10 – 20 System) and from the coronal arcs connecting the left and right mastoids (Lm and Rm, respectively) via Fz (Lm, L1,
L2, (Fz), R1, R2, Rm). The reference electrode was attached to the nose. Horizontal eye movements were monitored with an electrode placed near the outer canthus of the right eye and the vertical movements with Fpz. The electrode impedance was kept under 5 kV. The amplifier bandwidth was 0.5– 70 Hz, and a sampling frequency of 200 Hz was used. The ERP epochs were digitally filtered off-line by a 1 – 30 Hz bandpass filter and automatic artefact rejection (^ 70 mV) was applied prior to the averaging of the trials. Separately averaged waveforms for the standard and deviant stimuli (450 ms window including a 50 ms baseline period) were computed for individual subjects. In the analysis, the dependent variable was the mean amplitude measured from three time windows (120 –160, 160 – 200, and 200– 240 ms) placed around the maximum amplitude determined from the grand-average difference waveform. The mean amplitudes at Fz were statistically analysed using repeated measures analysis of variance (ANOVA). In the behavioural discrimination task (Experiment 2), the button presses occurring within 100 – 2500 ms from target-stimulus onset were regarded as hits and the responses occurring at any other time as false alarms. The individual hit and false alarm rates and the RTs were then subjected to repeated measures ANOVA. Fig. 1 shows the grand-average difference waveforms at Fz for all groups and each stimulus pair in Experiment 1. The mean MMN amplitudes are displayed in Table 1. The overall analysis revealed the main effect of the Time Frame (Fð2; 54Þ ¼ 6:848, P ¼ 0:002) and the interactions between (1) the stimulus pair and the Time Frame (Fð6; 162Þ ¼ 14:793, P , 0:001) and (2) the subject
Fig. 1. The grand-mean difference waves (responses elicited by the standard stimuli subtracted from that elicited by the deviant stimuli) in four different vowel blocks for Naı¨ve Native Finns (thin solid line), Advanced Students of English (thick solid line), and Native English speakers (dotted line).
M.S. Peltola et al. / Neuroscience Letters 352 (2003) 25–28
27
Table 1 The mean MMN amplitudes (and standard errors of mean) for latency windows 120–160, 160–200, and 200–240 ms in Experiment 1 Vowel blocks
Finnish /i–e/ English /i– e/ English /i– I/ English /e –I/
Group 1 Naı¨ve
Group 2 Advanced
Group 3 Native English
120–160
160– 200
200 –240
120 –160
160 –200
200–240
120–160
160–200
200–240
22.686 (0.721) 21.032 (0.640) 20.492 (0.605) 20.059 (0.622)
23.286 (0.756) 21.130 (0.649) 21.697 (0.705) 21.587 (0.678)
22.081 (0.843) 21.147 (0.746) 22.415 (0.720) 22.274 (0.640)
21.633 (0.757) 22.952 (0.671) 20.576 (0.635) 20.803 (0.653)
20.901 (0.793) 22.298 (0.681) 21.404 (0.740) 21.041 (0.711)
0.806 (0.884) 20.502 (0.782) 20.730 (0.755) 20.849 (0.671)
21.879 (0.798) 22.793 (0.707) 21.321 (0.669) 21.116 (0.688)
22.326 (0.836) 23.280 (0.718) 22.907 (0.780) 23.009 (0.750)
0.009 (0.932) 21.170 (0.824) 21.877 (0.796) 22.937 (0.707)
group and the Time Frame (Fð4; 54Þ ¼ 4:583, P ¼ 0:003). Further analysis showed a main effect of Stimulus Type in the first (120 – 160 ms, Fð3; 81Þ ¼ 4:970, P ¼ 0:003) and in the third (200 – 240 ms, Fð3; 81Þ ¼ 4:069, P ¼ 0:010) Time Frames. In Time Frame 1 (120 –160 ms), the native language effect on the MMN was found in naı¨ve Finns: the response to the native language vowels (Finnish /i/ – /e/) was markedly larger (tð10Þ ¼ 2:607, P ¼ 0:026) than that to the English vowels /e/ – /I/ in spite of the same acoustic deviant-standard distance, and when the distance was smaller in English /i/ – /I/ (tð10Þ ¼ 2:283, P ¼ 0:023). In addition, in Time Frame 2, the MMN to the native contrast was larger in amplitude than that to the English pair with the same acoustic distance (English /e/ – /I/, tð10Þ ¼ 3:123, P ¼ 0:011) or with the largest acoustic distance (English / i/ – /e/, tð10Þ ¼ 2:371, P ¼ 0:039). A similar response pattern was also found in the native speakers of English in Time Frame 3 (200 – 240 ms): the MMN was significantly larger for the native than the foreign contrast (English /e/ – /I/ versus Finnish /i/ – /e/, tð8Þ ¼ 2:898, P ¼ 0:020). The non-native-like processing of the foreign vowels by the advanced students was clearly demonstrated in the response to the pair English /e/ –/I/ in Fig. 1: the response is significantly smaller for the non-native than the native speakers of English both in Time Frame 2 (tð17Þ ¼ 3:060, P ¼ 0:007) and Time Frame 3 (tð17Þ ¼ 3:601, P ¼ 0:002). In fact, the amplitude of the MMN appears to depend on the acoustic deviant-standard distance, since the MMN to the English /i/ – /e/ was larger than that evoked by English /e/ – /I/ (in Time Frame 1: (tð9Þ ¼ 3:092, P ¼ 0:014) and English / i/ –/I/ (in Time Frame 2: (tð9Þ ¼ 1:983, P ¼ 0:028). In
addition, Fig. 1 suggests that the MMN responses of the advanced students are small altogether. In Experiment 2, the amount of errors made was very low for each group and for each vowel contrast (mean 1.83%, range 1.1 –2.2%), and no significant differences were found between the subject groups and conditions either in errors or hit rates. The acoustic distance of the stimuli in the vowel pair caused systematic differences in the RTs (Fð3; 87Þ ¼ 10:91, P , 0:001; Table 2). Further pairwise comparisons showed that this was due to the pair English /i/ – /I/: the RTs were significantly slower than those for the other pairs (Finnish /i/ – /e/, P , 0:001; English /i/ – /e/, P ¼ 0:001; English /e/ – /I/, P ¼ 0:001). There were no other significant differences in the RTs. The present study showed that the brain responses to speech stimuli are larger for the native language contrasts in comparison with foreign language ones with the same acoustic distance between the stimuli. This was most evident in the MMN responses of the naı¨ve Finns, but it was also seen in native speakers of English. However, the advanced students of English did not respond to the English vowels in a native-like manner, which was seen in the lower amplitude evoked by the English vowel contrast (/e/ –/I/) when compared with the native speakers of English. Furthermore, we found that the response to the mother tongue contrast by the advanced students was not native-like when compared with the naı¨ve Finns, which suggests that the unfinished learning process affects the access to the native language representations. The acoustic distance between the deviant and the standard appeared to be a significant factor in the MMN amplitude in the advancedstudent group, since the response to the acoustically most
Table 2 Mean reaction times (RT) (and standard errors of mean) for Experiment 1 Vowel blocks
Group 1 Naı¨ve
Group 2 Advanced
Group 3 Native English
Finnish /I–e/ English /I –e/ English /i– I/ English /e –I/
348 (17.8) 340 (17.9) 370 (17.6) 347 (15.8)
311 (18.6) 308 (18.8) 334 (18.5) 311 (16.6)
332 (19.6) 312 (19.8) 348 (19.5) 316 (17.5)
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salient contrast (English /i/ – /e/) was largest. In contrast, the responses of the two monolingual groups depended more on the phonemic status of the sounds in the mother tongue. The acoustic salience appeared to be the main factor also in the RT measurements in all groups and the RTs did not show a similar pattern with the MMN amplitude as in studies by Na¨a¨ta¨nen et al. [13] and Menning et al. [10]. However, in these studies, the subjects were originally unable to discriminate the minute differences in the stimuli, whereas in the present study the stimuli were easily discriminable due to large acoustic distances. The very fast RTs in the present study might in part reflect a ceiling effect. The present data are in accordance with the results obtained by Na¨a¨ta¨nen et al. [12] in showing that the representations revealed by the MMN are partly languagespecific. This was most obvious in the monolingual Finnishspeaking group, but also in the native English group. Our results can also be contrasted with the finding of Winkler et al. [15] which demonstrated that new memory traces emerge in subjects who have spent a considerable time in a foreign country (2 –13 years): this naturally obtained language proficiency is therefore markedly different from that resulting from classroom learning. It seems that authentic input is required before the processing of the foreign speech sounds becomes native-like. As our results suggest, this input is insufficient in the context of classroom education and new native-like long-term memory traces for foreign vowels are not formed in spite of extensive (average 12 years) language studies. Curiously, when the responses to the native vowels of the advanced students were compared with the two native speaker groups we noted that the monolinguals processed speech on the basis of the mother tongue model developed in early infancy [4,9], but in the advanced students the response to native vowel contrast seemed not native-like. This may suggest that – in addition to affecting linguistic skills demanding conscious effort [2,8] – the intensive foreign language learning may also affect the processing of native phonological vowel contrasts at the preattentive level. In addition, the overall small MMN amplitudes in the results of these students (most acutely seen in the response for the new contrasts /e/ – /I/) could tentatively be seen as a further indicator of the incompleteness of the learning process: it might be that, when the process of acquisition is unfinished, the small MMN amplitude indexes the ongoing nature of the process. Therefore, the small MMN responses (both to the foreign and native contrasts) could be a neural correlate for the ‘confusion hypothesis’ [1,3], which refers
to a stage in the learning process where the two systems are intertwined.
Acknowledgements The study was supported by the Finnish Cultural Foundation.
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