論文

The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English
vowels produced by Japanese learners
Toru Isono

要旨

本論文では，第二言語音声習得研究において長年議論されてきた，「どうしてある特定の音素が他のものよりも早く習得されるのか」という疑問に答えるため，日本人英語学習者から得た英語母音データを音響分析し，その結果を踏まえて第二言語音声習得プロセスのモデルを提案する。まず，中間言語という概念の説明をしてから，第一言語習得と第二言語習得のプロセスの違いを確認する。次に，英語母音の音響分析の概要を紹介し，その結果を考察する。そして最後に，本論文での全ての議論をもとに第二言語音声習得プロセスのモデルを提案し，その有効性を論じる。

, pronunciation（発キーワード : Second Language Acquisition （第二言語習得）音）, the acquisition model（習得モデル）, acoustic phonetics（音響, interlanguage（中間言語）音声学）

1. Introduction
Nowadays, the acquisition process of Second Language (L2) pronunciation is regarded as acreative process by which L2 learners produce an internalised representation of the regularities theyfind in the linguistic data to which they have been exposed through their interaction with theirenvironment. To put it another way, L2 learners are supposed to be able to construct and develop their

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愛知大学 言語と文化 No. 12

own regular and systematic phonological systems as well as native children. The phonologicalsystems that lie midway between a learner’s First Language (L1) and the L2 are named interlanguage
phonology, and the creative process is called the continuum of interlanguage phonology.
Concerning the nature of the continuum of interlanguage phonology, some pieces of research
conducted in the 80’s (e.g., Flege, 1980; Major, 1987a) clarified the following two points. One is that
L1 interference is dominant in L2 phonological errors, especially at the beginning stage. The other isthat the features of L1 interference are replaced by near-L2 features step by step after a certain periodof learning. Based on these facts, we can probably say that the nature of the continuum ofinterlanguage phonology is a continuum that the origin is a learner’s L1, and the features of the L1
sound system are gradually replaced with those of the L2 sound system. In other words, the acquisition
process of L2 pronunciation is the selection process that decides which L1 features are transferred andwhich are not, and also which L2 features are taken into the systems of interlanguage phonology. The
important thing is that it is still not clear why there are some L1 features more likely to be transferredthan others, and why there are some L2 features more likely to be acquired than others.
In this paper, by examining the acquisition process of English vowels by Japanese learners, we will
clarify a feature which affects the decision of the above L2 learners’ selection process, and propose
the model of the acquisition process of L2 pronunciation.

2. Kiparsky and Menn’s Framework for First Language Acquisition in
Pronunciation
One of the basic concepts of interlanguage is that the process of interlanguage is similar to that ofFirst Language Acquisition (FLA) in some points. Therefore, we start the discussion by referring to
the work which proposes a framework of acquisition of phonetic repertoire by native children.
The cognitive approach triggered by Chomsky claims that children do not only imitate the input
they receive, but they have the ability of establishing their own hypothesises against the input andalso the ability to test these hypothesises. Although this idea was developed in the domains ofgrammatical and morpheme studies, it was also accepted in the acquisition of pronunciation. For
example, Kiparsky and Menn (1987) claim that the process of pronunciation acquisition by native
children is a ‘problem-solving’ activity from the earliest stages, and propose a framework consistingof three stages, which is presented on the next page, for the acquisition model of L1 sounds.
Stage A is constituted by the children’s hypotheses about the underlying representations of theadult language they are acquiring. The underlying representations, which do not appear in actual

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The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

A

underlying representations
hypothesized by child(A⇒B) LEARNED RULES

B

phonetic representations
perceived by child(B⇒C) INVENTED RULES

C

child’s pronunciation(Kiparsky and Menn, 1987: 36)

Figure 1. Kiparsky and Menn’s frameworkspeech, are considered to form the knowledge of the phonological relationships between different
forms of words. Stage B consists of the children’s perceptions of the phonetic representations of theadult language that they are acquiring. The ‘problem-solving’ activity is conducted between this stage
and the next stage, and the children’s intended pronunciations are finally produced at Stage C. Theirproductions could be different in certain ways from the physical output, as when a purely physicallimitation prevents them from producing segments that the children believe they are distinguishing.
According to Kiparsky and Menn (1987), in the early stage of language acquisition, Stages A andB coincide, but Stages B and C are completely distinct. As children master more of the phonetic
repertoires of the adult language after the initial period of rule invention, Stage C approaches StageB, and the system of rules shrinks. The process normally terminates when Stage C becomes identicalwith Stage B. On the other hand, as children continue to discover the phonological relationships ofthe adult language, Stage A becomes increasingly different from Stage B.
When Kiparsky and Menn’s framework is applied to Second Language Acquisition (SLA), somecrucial differences between FLA and SLA should be noted. Firstly, children start acquiring their L1sfrom scratch, whereas L2 learners have already acquired their L1 sound systems. Secondly, children
normally have enormous opportunities for receiving input and feedback, but these opportunities are
relatively limited in the case of SLA. Finally, not all L2 learners succeed in acquiring an L2, although
all children basically do in FLA. Taking these differences into account, we will examine the acoustic
data of the acquisition process of English vowels by Japanese learners, and then propose theacquisition model for L2 pronunciation.

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愛知大学 言語と文化 No. 12

3. The Summary of the Experiments on the Acquisition Process of the English Vowels
Isono (2000, 2003) investigated the acquisition process of the English vowels [ , æ, , i , ]produced by 51 Japanese subjects consisting of three groups (the US, the PS, and the AS groups) andthe native control group (the NS group) made up of 8 native speakers who had been teaching English
in Essex, East Anglia, England. The characteristics of the three Japanese groups are summarised inTable 1 (See details in Isono, 2003).
Table 1. Summary of the US, the PS, and the AS groups
US group

PS group

AS group

The number ofthe subjects

17 subjects(13 females : 4 males)

17 subjects(8 females : 9 males)

17 subjects(12 females : 5 males)

StatusUndergraduates

Postgraduates

Overseas students

Experience ofstudying abroadLess than 1 month(2 of the subjects)

Less than 1 year
(5 of the subjects)

More than 3 years(All of the subjects)

Major

Literature

Linguistics or Literature

Linguistics

Mean age

22

27

30

These Japanese groups were selected to reflect three learning stages of English, and as a result of
the reading-aloud test, it was clarified that they were indeed at different levels in their pronunciation
proficiency, which means, the most advanced Japanese subjects in order were the AS group, then the
PS group, and the US group 1 .
The subjects were asked to produce five English words: but; bat; bit; beat; and bet, whichcontained the vowels [ , æ, , i , ], in the carrier sentence ‘I say

again’, and their speech

productions were recorded using a digital recording machine. Each target word was randomly shownat regular intervals to the subjects in all the groups three times. Therefore, a total of 885 different
vowel productions (3 repetitionsぉ5 vowelsぉ59 subjects [{3 Japanese groupsぉ 17 subjects} + 8English subjects]) were obtained. Each of the 885 productions was characterised by the features ofthe frequencies of the first two formants (F1 and F2) and the vowel duration time by using the SUGI
Speech Analyzer (produced by ANIMO Ltd.). The relationships between the frequencies of F1 andF2 and vowel sound quality are summarised as follows in Table 2.
Table 2. Relationships between frequencies and the characteristics of vowels
F1

F2

High frequency

Low vowel

Front vowel

Low frequency

High vowel

Back vowel─ 4 ─

The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

Although various findings were observed in the experiment, the issue which is relevant to thecurrent topic is that only the English [æ] was approximated to the norm as the Japanese subjects
became more advanced learners. In other words, concerning the other English vowels [ ], [ ], and[ ] 2 , approximations to the norms were not statistically observed regardless of the degree of theJapanese subjects’ learning levels (See details in Isono, 2003).
Isono (2000, 2003) attributed the reason why different degrees of progress of approximation were
found in the four vowels [æ] and [ , , ] to the view that the amount of L2 exposure made it possible
for the advanced learners to produce a ‘new’ vowel (the English [æ] in the case of the study) in anative-like way, but it did not affect the productions of ‘similar’ vowels, such as [ , , ], following
Bohn and Flege (1992) who investigated the English vowels [æ, , , i ] produced by two groups ofadult German learners differing in the period of exposure to English. This view is based on Flege’s(1987) assumption that a similar vowel which has a close counterpart in L1 is often regarded as being
equivalent to the L1 vowel, but a new L2 vowel which does not have a counterpart in L1 can evadethe process of equivalence classification if a sufficient input is provided to L2 learners. We previously
outlined the phenomenon in L2 pronunciation that there are some L1 features more likely to betransferred than others, and noted this is because L2 learners themselves ‘select’ what to transfer andwhat not to transfer. This study should be respected in that it showed how the phonetic distance
between the L2 sound and the corresponding L1 sound affects the selection process.

4. The Characteristics in the Acquisition Process of the English [æ]In this paper, in addition to the above findings, we turn our attention to the accuracy of the English[æ] produced by the Japanese subjects and investigate what differences are found between the groups.
Based on the results, we will find some characteristics in the acquisition process of the English [æ]which are particular to Japanese learners, and will examine one of the tendencies characterising theacquisition continuum of interlanguage phonology.
As previously mentioned, the English [ ] and [æ] produced by the Japanese subjects did not show
the same rate of improvement, despite the fact that both of the English [æ] and the English [ ] aretypically replaced by the Japanese [a]. In most cases, the English [æ] was more improved by theJapanese subjects as they became more advanced learners, but the English [ ] was not. In this respect,
we could say that the first step for Japanese learners in acquiring the English [ ] and [æ] is to becomeaware of the difference between the Japanese [a] and the English [æ], and to make a distinction
between the English [ ] and [æ] in their English productions by improving their English [æ]s, even

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愛知大学 言語と文化 No. 12

though their English [ ]s are still replaced by their Japanese [a]s. Therefore, the first analysis(Analysis 1) deals with how many subjects in each Japanese group were able to distinguish between
the English [ ] and [æ] in their English productions by approximating their English [æ]s to the nativelike English [æ], even though their productions may not be accurate enough.
Table 3 provides the details of Analysis 1, which examined how many subjects in each Japanesegroup met the above requirement 3 .
Table 3. Details of the subjects who were able to distinguish the English [æ] from [ ]Number of
subjects

Minimum
difference

Maximum
difference

Mean groupdifference

US group

2 / 17338 Hz441 Hz389 HzPS group

9 / 17212 Hz703 Hz435 HzAS group

11 / 17239 Hz663 Hz403 HzNote. The minimum and maximum differences in this table are the values of thesubject’s mean differences of the three repetitions.

The Japanese subjects who were regarded as being able to distinguish the English [æ] from [ ] intheir English productions are: 2 subjects from the US group; 9 subjects from the PS group; 11 subjects
from the AS group, as Table 3 indicates 4 . Since there were only 2 subjects in the US group, they were
included in the PS group for the aim of the analysis as their personal scores in the test of readingaloud did not reach the average score of the AS group and they did not have any experience studying
abroad. This group is labelled the US/PS group in the analysis.
In the case of examining the English [æ]s produced by Japanese learners, the relationships between
their intended English [æ, ] productions and their Japanese [a] productions are mainly focused,because the former are typically replaced by the latter. However, in the case of other language
learners, such as Portuguese or German learners, their English [æ]s are usually replaced by their [e]sin L1. Hence, some researchers have been interested in comparing these learners’ intended English[æ] productions with their intended English [ ] productions (e.g., Major, 1987b; Bohn & Flege, 1992).
In fact, the distribution of the English [æ] itself is closer to that of the English [ ] rather than that of
the English [ ] (See details in Isono, 2003). Kent and Read (1992) also note the similarity of theformant patterns between the English [æ] and [ ] from the viewpoint of acoustic analysis. Therefore,
as far as the acquisition process for the English [æ] by Japanese learners is concerned, the next stepfor the Japanese learners who can stop substituting the Japanese [a] for the English [æ] will be tocontrol their articulations of the English [æ]s so that their intended English [æ]s are notmisunderstood as the English [ ]s by native speakers.

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The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

Analysis 2, which is the main analysis in this paper, investigates how accurately the Japanese
subjects who were not eliminated in Analysis 1 produced their English [æ]s, mainly by comparing
their English [æ] productions with their English [ ] productions. This analysis focused on these 30
subjects divided into 3 groups (11 subjects from the US/PS group, 11 subjects from the AS group, and
8 subjects from the NS group), and the 180 vowel productions (30 subjectsぉ 2 vowelsぉ 3
repetitions) elicited from them were characterised by the frequencies of F1 and F2, and then the meanfrequency values were calculated for productions of each subject.
Firstly, we focus on the characteristics in F2 which correspond to the frontness-backness
dimension. Based on the results reported by Isono (2003) who investigated the acoustic differences
between the English tested vowels and the corresponding Japanese vowels, the mean F2 frequencyof the Japanese [a] was 1664 Hz and that of the English [æ] was 1828 Hz. Hence, when Japaneselearners try to produce the English [æ] in a native-like fashion, they face the task of moving the wholeraised shape of the tongue body to a more front position than the position needed for the Japanese [a].
Taking this fact into account, we see Table 4 showing the details of the group differences.
Table 4. Details of the group differences in F2 of the English [æ] and [ ]US/PS group

AS group

NS group

Mean (Hz)SD

Mean (Hz)SD

Mean (Hz)SD

English [æ]2177.4244.4

2017.8160.1

1828.5

53.8

English [ ]2326.9218.92287.4108.42099.0136.7

As the table presents, the Japanese subjects were successful in moving the whole raised shape ofthe tongue body to a more front position, but they exaggerated it too much, as long as the criterion isset on the British accent 5 . Especially, the US/PS group’s English [æ] has much higher frequencies
than the NS group’s English [æ], and it is even higher than the NS group’s English [ ]. According to
one-way ANOVA, the group difference for F2 of the English [æ] was significant, F (2, 27)＝ 8.7, p <.01, and Bonferroni’s Post Hoc Tests reported that the US/PS group’s English [æ]s had significantly
higher frequencies than the NS group’s English [æ]s at the .05 level.
The error bar on the next page shows each group’s mean value for the difference between the
English [ ] and the English [æ] ([ ] value minus [æ] value) and its distribution range (95% ConfidenceInterval for the Mean) in the frequencies of F2.
As the value for the NS group shows, the difference in the F2 frequency between the English [ ]and [æ] is approximately 250 Hz. This means that the F2 frequency of the English [ ] is about 250 Hz
higher than that of the English [æ] and that the English [ ] is a more front vowel than the English [æ].

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愛知大学 言語と文化 No. 12

Figure 2. Differences between the English [æ] and [ ] in F2

Although the distribution range of the values of the AS group is slightly wider than the NS group, no
noticeable difference is found in the mean differences between the two groups. However, when we
pay attention to the US/PS group’s value, we will notice that the mean difference is much smaller andthe distribution range is much wider than the other two groups, although the differences for the meanvalues were not significant according to one-way ANOVA, F (2, 27)＝ 1.4, p >.05. It should be
especially noted that the distribution range for the US/PS group even includes a minus value whichmeans that some of the subjects in the US/PS group produced their English [æ]s more as front vowels
than their English [ ]s. The question is why the subjects in the US/PS group exaggerated the‘frontness’ of the English [æ], and it is a question to be considered later.
We now turn our attention to the F1 frequency which represents the vowel height dimension. The
details for the acoustic data are summarised in Table 5. We can see that the F1 frequency for the
US/PS group’s English [æ] is much lower than that of the other two groups, and it means the US/PS
group’s English [æ] is closer to the English [ ] than the other two groups. One-way ANOVA revealed
that there was a significant group difference for the F1 in the English [æ], F (2, 27)＝4.7, p < .05,
and, according to Bonferroni’s Post Hoc Tests, the US/PS group’s F1 was significantly lower thanthe other two groups, at the .05 level.

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The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

Table 5. Details of the group differences in F1 of the English [æ] and [ ]US/PS group

AS group

NS group

Mean (Hz)SD

Mean (Hz)SD

Mean (Hz)SD

English [æ]

829.2

146.8

924.3

110.9

989.7

43.6

English [ ]

655.9

82.2

647.4

88.3

695.0

57.1

The error bar presented below describes each group’s mean value for the difference in F1
frequencies between the English [æ] and [ ] and its distribution range. For the frequencies in F1, thevalue of the frequency of the English [æ] is normally higher than that of the English [ ], so thedifferences were calculated by subtracting the latter from the former.

Figure 3. Differences between the English [æ] and [ ] in F1

As the figure shows, a similar tendency as was seen in the case of F2 is found. In short, a noticeable
difference is not observed in either the mean difference or the distribution range between the NS and
the AS groups, but the US/PS group’s mean difference value is much smaller and its distribution
range is much wider than the other two groups. According to one-way ANOVA, a significant groupdifference for the mean difference was obtained, F (2, 27)＝3.6, p < .05, but Bonferroni’s Post Hoc
Tests did not reveal a significant group difference at the .05 level. This is because the difference
between the US/PS and the NS group was just not significant (p ＝.07).
We are now able to speculate about the acquisition process of the English [æ] for Japanese learners,
if we regard the AS group as learners in the final stage of learning, the US/PS group as learners in the─ 9 ─

愛知大学 言語と文化 No. 12

intermediate stage, and the US group as learners in the beginning stage. In the early stage oflearning, Japanese learners tend not to be able to distinguish the difference between the English [æ]and the Japanese [a], and directly substitute the Japanese [a] for the English [æ]. This was supportedby the phenomenon that most of the subjects in the US group used the Japanese [a] as a replacement
for their English [æ]s. As Japanese learners become more advanced learners, they stop substituting
the Japanese [a] for the English [æ] as they become aware of the difference and try to produce theirEnglish [æ]s in a more native-like fashion. However, some of the Japanese learners’ articulations are
not accurate enough, and they produce the English [æ]s quite similar to their English [ ]s. Thisphenomenon was observed in both the vowel height and frontness-backness dimensions of the
US/PS group’s productions. This inaccurate pronunciation of the English [æ] will diminish when
Japanese learners have more exposure to real spoken English as most of the subjects in the AS groupdid.
The reason why many subjects of the US/PS group, and actually some of the AS group,
pronounced their English [æ]s similar to their English [ ]s can be attributed to the fact that Japaneselearners are often instructed to produce an intermediate tone between the Japanese [a] and [e] when
pronouncing the English [æ]. For example, Shimaoka (1994) has utilised Katakana for transcribing
English segmental phonemes, and uses the symbol「ェア」(＝[ea]) as the representation of the
English [æ]. The sizes of the letters correspond to the strength of the stress that learners are to use. In
this method of transcribing, it is quite rare to find that a single English phoneme is transcribed byusing two Japanese vowels, but this is due to the fact that Japanese has no counterpart for the English[æ]. Andoh (1984) presents the formula of「(ア＋エ) ÷ 2」(＝( a＋e ) ÷ 2), as a way for pronouncing
the English [æ]. In Japan, this formula is a quite popular method for teaching the pronunciation of the
English [æ], and it can be found not only in Andoh’s book but also in some other textbooks (e.g.,
Ishiguro et al, 1992).
Figure 4 is an example of the US/PS group’s English [æ] which might have been produced byfollowing the above formulas. As the figure shows, the English [æ] completely diphthongises. The
beginning part of the vowel is characterised by the sound which has approximately 2500 Hz in F2
frequency and 700 Hz in F1 frequency. This combination of F2 and F1 is quite similar to that of theJapanese [e], or even higher than that. However, after passing the midpoint of the vowel, thefrequency of F2 decreases to around 2000 Hz, but that of F1 increases to 1000 Hz, which means the
combination of F2 and F1 becomes closer to that of the Japanese [a].
The aim of these scholars’ attempts is clearly to increase Japanese learners’ awareness of thedifference between the Japanese [a] and the English [æ] and to encourage them to stop substituting

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The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

|a

|s

e

|bæ

t |

e

n |

Figure 4. Example of formant patterns of the US/PS group’ English [æ]the Japanese [a] for their English [æ]s by attaching one more vowel to the Japanese [a]. However,when this method of instruction is used, it is quite natural that the attention of Japanese learners isdirected at the existence of the Japanese [e] in these symbols and formulas. The reason is that mixing
the Japanese [e] with the Japanese [a] is a crucial factor in allowing them to make a distinction
between their intended native-like English [æ]s and the typically accented Japanese learners’ English[æ]s which are directly replaced by the Japanese [a]. Therefore, by placing too much emphasis on theJapanese [e], Japanese learners stop the negative transfer of substituting the Japanese [a] for the
English [æ]; however, their intended English [æ]s become quite similar to their Japanese [e]s and also
to their English [ ]s. This would account for the phenomenon which was observed in the English [æ]productions of the US/PS group in this analysis.

5. The Acquisition Model of L2 Pronunciation
Taking the above findings and discussion into account, the framework shown in Figure 5 is
proposed for the model of the acquisition process of L2 pronunciation.

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愛知大学 言語と文化 No. 12A

L2 sound systems hypothesised by
L2 learners based on their L1s

Bphonetic representations perceived by
L2 learners (filtered by their L1s)

Being aware of the differences

Not being aware of
the differencesDphonetic representations
perceived by L2 learners(not filtered by L1s)
Invented rulesC

learners’ pronunciation accented
by their L1s

Elearners’ pronunciation
not accented by their L1s

Figure 5. A framework of SLA in pronunciation

During Stage A, L2 learners only rely on the knowledge they have already acquired, so they
substitute L1 sounds for L2 sounds. In Stage B, L2 learners receive input and feedback from formal
instruction or by exposing themselves to the target language, but they still cannot escape from the L1
sound systems, because they hear the L2 sounds filtered through the L1 sound systems. L2 learners
are not aware of the differences between L1 and L2 sound systems at these stages, as we can see fromthe fact that most of the subjects in the US group could not distinguish the difference the Japanesevowels and the corresponding English vowels, and substituted the former for the latter in theirEnglish productions.
However, as the result of enough input and feedback, some learners may become aware of ‘some’of the differences between the two languages, and they come to perceive input they receive unfilteredby their L1s. This is Stage D. Concerning ‘some’, as previously noted, Bohn and Flege (1992) andIsono (2000, 2003) reported that it becomes easier for L2 learners to establish new phonetic
categories as the phonetic distances between L2 and the corresponding L1 sounds are larger.
After passing Stage D, L2 learners will try to develop their L2 pronunciations so as to be more
native-like, and this effort makes them invent their own rules and carries them forward onto the final
stage, Stage E. As the English [æ]s produced by the US/PS group suggests, Stage D and E may bedifferent especially at the early stage of acquisition because of the tongue’s muscular limitation or─ 12 ─

The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

wrong rules invented by L2 learners. However, as the acquisition stage proceeds, Stage E is assumed
to approach to Stage D as we can see from the English [æ]s produced by the AS group, and theprocess terminates when they are identical. This process characterises the continuum of interlanguage
phonology.
In contrast, L2 learners who do not become aware of the differences between L1 and L2 soundsystems during Stage B will continue to substitute L1 sounds for L2 sounds, and will not proceed tothe above route to Stages D and E. Their L2 pronunciation ends in Stage C, and is fossilised until they
become aware of the differences.
This paper proposes the acquisition model of L2 pronunciation based on the experimental data of
the English vowels produced by Japanese learners. This model may be useful for both of L2 learners
and teachers. For L2 learners, it will provide an answer to the question about what kind of
deviations L2 learners have to correct at the beginning stage. For teachers, it clarifies why L2
learners produce strange sounds named interlanguage sounds at the stage between Stage D andE, which belong to neither the L1 sound systems nor the L2 sound systems. Recognising thismodel, teachers will understand that the existence of interlanguage sounds in L2 learners’
productions is not a bad sign, but it is a good sign, because these sounds become potential sources ofnative-like pronunciation.

Notes１）The test material consisted of two texts taken from MILESTONE: English Course (published by
Keirinkan). It is a reading textbook for first-year high school students. The first text was directly reprinted
from the textbook, but some words in the second text were changed by the researcher in order to meet therequirement that all English phonemes appeared at least twice, except for the English [ ]. The distributionof the English [ ] is quite limited, so it was very difficult to include the English words which include it in
the two texts. The first text consisted of five sentences, and the second text was comprised of four
sentences (See Appendix).
When the speech productions were edited by the researcher, only 3 native speakers’ speech productions
were randomly selected as the representatives of the NS group, and the other 5 native speakers’
productions were removed from this reading-aloud test, in order to save time scoring the task. In addition,
the first text was divided into two parts in order to control the length of the texts. Finally, the speechsamples were blocked so that the same part for all subjects was on the same block. Naturally enough, they
were randomised in each block with the requirement that the subjects in the same group did not occur backto back.
Each group of the 162 different stimuli (3 paragraphsぉ 54 subjects [51 Japanese and 3 English
subjects]) was separately presented through a headphone, to each of 8 English native listeners who hadteaching experience (M = 18 years). The order of the presentation of the blocks was B1, B2, and B3 for─ 13 ─

愛知大学 言語と文化 No. 12

all listeners. Their task was to determine the degree of the speaker’s foreign accent on a 9 point scale from‘heavy foreign accent’ (1 point) to ‘no foreign accent’ (9 points). They were encouraged to use the fullrange of the scale. They were told that they would be listening to the readings of Japanese and English
speakers, but they were not told either the number of groups or that each speaker would be heard morethan once. The timing of scoring was left to the listeners whether they would score after or during listening
to each speech sample.
The foreign accent score for each subject was calculated as the sum of 24 scores (8 listenersぉ 3
paragraphs). The foreign accent score for each group was calculated as the mean of subjects’ scores in eachgroup. The table below shows the results of the foreign accent scores and SDs of the Japanese and English
groups.
Table 6. Foreign accent scores and SDs of the Japanese and English groups
US group

PS group

AS group

NS group

Mean

122.2

150.8

172.8

215.66

SD

6.8

19.1

6.6

0.57

(Minimum Mean = 24, Maximum Mean = 216)
One-way ANOVA revealed that the group difference was significant, F (3, 50) = 78.56, p < .001, andaccording to Bonferroni’s Post Hoc Tests, there was a significant difference in all cases at the .05 level.
２）Statistical results suggest that there is no significant difference in the shapes of the tongue among theEnglish [i ], the Japanese [i], and the Japanese [i ] (See details in Isono, 2003).
３）It was quite a difficult task to establish a criterion for deciding whether Japanese subjects were able todistinguish the difference between the English [ ] and [æ] in their English productions. Consequently, thedecision relied on the data from the NS group which was obtained in Isono (2003). Before outlining thecriterion, some points, which were clarified in Isono (2003), should be noted in order to make the reasonsfor the decision clear. At first, it should be mentioned that there was not a significant difference among theEnglish [ , æ] and the Japanese [a] in the vowel height dimension. Therefore, in this first analysis, ourfocus will be limited to the characteristics of the frontness-backness dimension.
Concerning the distributions of the frequencies of F2 which represents the frontness-backness
dimension, the Japanese [a] is midway between the English [ ] and [æ]. The English [ ] has generally alower frequency, but the English [æ] has a higher frequency, in comparison to the Japanese [a]. Thismeans, the highest frequency in the range for the NS group’s English [ ] and the lowest frequency in therange for the NS group’s English [æ] are the requirements to be met by Japanese learners in order for themto produce each of the English vowels in a native-like fashion. According to the data from the NS groupwhich was elicited in Isono (2003), the highest mean frequency for the English [ ] was 1572 Hz, and thelowest mean frequency for the English [æ] was 1776 Hz, so the difference between them was 204 Hz. The
mean frequency of the Japanese [a] elicited from the Japanese subjects in Isono (2003) was 1664 Hz, so
the difference between the English [ ] and the Japanese [a] (the mean frequency of the Japanese [a] minus
the highest mean frequency of the English [ ]) was 92 Hz. The difference between the English [æ] and theJapanese [a] (the lowest mean frequency of the English [æ] minus the mean frequency of the Japanese [a])was 112 Hz. This argument is summarised in Figure 6.

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The Acquisition Process of L2 Pronunciation—based on the acoustic analysis of English vowels produced by Japanese learners

English [æ]1776 Hz112 HzJapanese [a]1664 Hz
92 Hz
1572 Hz

English [ ]Figure 6. Differences in F2 among the English [æ] and [ ] and the Japanese [a]Hence, when only the difference in the frequency is concerned, the value of 204 Hz is the criterion
which decides whether a Japanese learner can distinguish between the English [ ] and [æ] in a native-likefashion. The values of 92 Hz and 112 Hz will be the criteria for judging whether the Japanese subjects areable to distinguish the Japanese [a] from the English [ ], and the English [æ] from the Japanese [a],respectively. Naturally enough, the frequency of the former vowel should be higher than that of the latter.
To sum up, for the purpose of making a distinction between the English [ ] and [æ], regardless ofwhether the Japanese subjects improve only their English [ ]s, only their English [æ]s, or both of them,
their intended English [æ]s should be at least 92 Hz higher than their intended English [ ]s. Therefore, inthis paper, only the Japanese subjects whose intended English [æ]s were at least 92 Hz higher than theirintended English [ ]s in all three repetitions were regarded as being able to distinguish between the
English [ ] and [æ] in their English productions.
As Table 3 shows, all the subjects whose intended English [æ]s were at least 92 Hz higher than theirintended English [ ]s in all three repetitions necessarily produced their English [æ]s at least 212 Hz higher
than their intended English [ ]s in the mean differences of the three repetitions. The fact that the numberof subjects increases as they become more advanced is also consistent with the phenomena reported in
Isono (2000). However, one thing which should be remembered is that these calculations are not related
to the issue of whether they could produce the English [æ] or [ ] accurately, but are only based on the meandifferences between the frequencies of their intended English [ ]s and [æ]s.
４）It was clarified that the rest who were excluded from the analysis substituted their Japanese [a] for theirintended English [æ, ] productions.
５）Even when we set the criterion on the American accent, their English [æ] still had much higher
frequencies than the norm of American English, and the difference in the frequencies between theirEnglish [æ] and [ ] was quite small.

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愛知大学 言語と文化 No. 12

Appendix
Paragraph 1
Martin Luther King Jr. was a son of a black minister. His mother was a teacher. Young Martin spent a quiet
childhood in Atlanta, Georgia. After high school, he went to college and studied to be a minister, like hisfather. In those days, who could guess he was going to be such a great leader of the black people?
Paragraph 2
Mary stayed at the town in the autumn to do some work. When she rented a cabin near the church, she
asked for a boy to come and chop wood for the fireplace. One late afternoon, she found a boy standing at
the door. His name was Arthur.

References
Andoh, K. 1984. Enshuu Onseigaku (A Practical Course in English Phonetics). Tokyo: Seibidou.
Bohn, O. and Flege, J. 1992. The Production of New and Similar Vowels by Adult German Learners ofEnglish. Studies in Second Language Acquisition, 14(2): 131-158.
Flege, J. 1980. Phonetic Approximation in Second Language Acquisition. Language Learning, 30: 117-134.
Flege, J. 1987. A Critical Period for Learning to Pronounce Foreign Language. Applied Linguistics, 8:
162-177.
Ishiguro, A. et al. 1992. Jitsusen Eigo Onseigaku (Practical Phonetics). Tokyo: Kinseidou.
Isono, T. 2000. Nihon-jin Gakushusha no Eigo Boin Shutoku Jyunjyo ni Kansuru Kenkyu (= The Study of
the Acquisition Order of English Vowels by Japanese Learners). The Bulletin of the Federation of English
Education Society in Chuby-area, 29: 87-94.
Isono, T. 2003. Japanese Learners’ Interlanguage Phonology: with special reference to English vowels andplosives. Unpublished Ph.D. thesis. University of Essex.
Kent, R. and Read, C. 1992. The Acoustic Analysis of Speech. California: Singular Publishing Group, Inc.
Kiparsky, P. and Menn, L. 1987. On the Acquisition of Phonology. In Ioup, G. and Weinberger, S. (eds.),
Interlanguage Phonology: the acquisition of a second language sound system. New York: Newbury
House.
Major, R. 1987a. A Model for Interlanguage Phonology. In Ioup, G. and Weinberger, S. (eds.), Interlanguage
Phonology: the acquisition of a second language sound system. New York: Newbury House.
Major, R. 1987b. Phonological Similarity, Markedness, and Rate of L2 Acquisition. Studies of Second
Language Acquisition, 9: 63-82.
Shimaoka, T. 1994. Chuukangengo no Onseigaku (Phonetic Acquisition of English through Interlanguage).
Tokyo: Shougakukan.

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