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Phonetic Society of Japan

NII-Electronic Library Service

PhoneticSociety of Japan

gp± fiff fi rg lg geg 3 e2015(ilZEk 27) tP l2 fi2436.g.

Joumal ofthe Phonetic Society

ofJapan, Xlo1. 19 No. 3 December 2015, pp. 24-36

msr.gA"Critical Period" in Seeond Language Acquisition Reconsidered:

Production Patterns and Listening/Reading

Proficiencies of Japanese Learners

Michiko MocHizuKi SuDo* and Ikuyo KANEKo*

ag=s- ge. apec:-HtsK\ygotnt/tgtsct6annmeftsxl6->tagash

･ ftashoen.6..hs6-

SUMMARY: The present study investigated the effect of living in the target language country and that ofthe age factor

on the acquisition ofEng]ish by Japanese learners. Three subject groups panicipated in this study: Native speakers of

American English, Japanese returnees who had lived in the U.S., and cQllege students who had never lived overseas. For

measuring listening and reading abilities, we employed orncial TOEICsc scores. We also examined two factors ofdura-

tional control: ISI durations and stressed vowel shortening. The results showed significant difTerences in all parametersexamined between the returnees and general college students, We also observed that the age factor had an effect on the

different degrees of attainment efthe production proficiency and on 1istening ability ofthe returnees, but not on their read-

ing ability.

Key words: second language acquisition, age factor, criticaL period,compensatory vowel shortening, ISI

1. Introduction

A variety of factors have been reported in the lit-erature as having influence on second language (L2)acquisition (Altman 1980, Larsen-Freeman and Long1991, Skehan 1989). The individual learner variablesinclude age, aptitucle, motivation, attitude, personality}cogriitive factors, hemisphere specialization, learningstrategies, memory, awareness, will, proficiency in thefirst language (L1), interest, sex, birth order, and priorexperiences. Among them, age is one of the factorsthat has received the most attention in the field of L2acquisition (Ellis 1994). Age of initiation of languageacquisition can be regarded as a crucial variable to

distinguish between Ll and L2 acquisition. In lan-

guage acquisition, there is a general belief that youngerleamers do better than older learners. This belief isbased on the concept ofa critical period. It refers to a

biologically constrained peried in which language canbe acquired more easily than at any other time, and

beyond which complete mastery of a fbreign language

is no longer possible. This concept of the critical pe-riod was originally introduced by Penfield and Roberts

(1959), positing that children have a specific capacity

fbr language learning due to cerebral fiexibility that

subsides at appreximately age 9, Lenneberg (1967), themost well-known researcher for claiming the CriticalPeriod Hypothesis (CPH), proposed a critical periodstarting from about age 2 and continuing to puberty,He also suggested that language learning may be moTediMcult after puberty because the brain lacks the abil-ity fbr adaptation. The theory that the learner's age isa significant factor in restricting language acquisitionhas also been described as the notion of a

"Sensitive

Period" or "Maturational

Constraints" (Bornstein 1989,Knudsen 2004, Lamendella 1977, Long 1990, Oyama

1976, Snow 1987).

[Itiggered by Lenneberg's writing (1967), the ideaof the critical period was extended to the field of L2acquisition. A number of studies have claimed that theage factor affects L2 acquisition (Asher and Garcia1969, Bornstein 1989, DeKeyser 2000, Long 1990,

Oyama 1976, Scoyel 1981, Singleton 2005, Snow1987, Tahta, Wbod and Loewenthal 1981), supportingthe CPH. Major (2001) claimed that both the leanner7sage of arrival in the L2-speaking country and the age

of Iearning are important variables governing whethegor to what degree, a learner can attain native-like

' School of Health and Sports Science,Juntendo University (MfiKEjltl7Z pt - 7 reptN?gB)

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A "Critical

Period'' in Second Language Acquisition Reconsidered

pronunciation, Several studies have observed the difi

ferences in L2 perception and produetion between

early learners and late leamers. McCarthy, Evans and

Mahon (2013) investigated the production of stops

and vewels of Sylheti (Ll) and English (L2) by adult

speakers who had been residents in the UK fbr similar

lengths of time but had arrived there at different ages.

Analyzing Vbice Onset Time (VOT) of stops and vowel

formants and duration, they reported that the late arriv-

als (speakers who had arriyed in the UK after age 16,

mean age of anival: 21) produced native-iike Sylheti

stops and vowels, but that their English categories were

influenced by their Ll. 1[1ie early arrivals (speakerswho had arrived in the UK before the age of 16, mean

age of arrival: 6) and the second-generation speakers

(those who were bom in the UK) produced native-like

Sylheti vowels but not Sylheti stops, while their Eng-lish production was similar to the Standard SouthernBritish English. Darcy and Kruger (2O12) examined the

early L2 learners and investigated the age at which Ll

vowel categories influence the acquisitien ofL2 vowels

in ten-year-old Turkish children acquiring Gerrnan as

their L2. [Ihey tested 28 children (14 native speakers

of Germari and 14 Turkish-German bilinguals) by both

perception and production experiments. In the percep-tion experiment, they tested the children's ability to

discriminate four German vowel contrasts using an

oddity task while they examined their production of

the same vowels with an un-cued word naming task

in the production experiment. Tlie results showed that

the TurkishGerman bilingual children categorized

perceptually dificult German contrasts difTerentlyfrorn German monolingual children, In contrast to the

perception results, the two groups of children were

globally indistinguishable in production, Several other studies, on the other hand, haye shownthat the production of consonants by 1ate L2 learners

displayed their L1 features (Flege, Munro and MacKay1995, Sundara, Polka and Baum 2006). Likewise,the late L2 learners showed the Ll features in the L2vowel production (Baker and Trofimovich 2005, Flege,MacKay and Meador 1999). Sudo and Kaneke (2012)reported the differences in the production ef English

rhythmic patterns between early L2 learners (whoseage ofarTival was before puberty) and latc L2 leamers

(whose age of arrival was after puberty) by measuring

durations of interstress intervals (ISI), suggesting a

different clurational control of stressed and unstressed

syllables in the ISI by the two subject groups. It shouldbe noted that this previous study does not assume equal

ISIs in English. Quite a few studies have shown that

perfect isochronM on the level of production, does not

exist (Beckman 1992, Ericksson 1991, Laver 1994,Lehiste 1977 for review). On the basis of acoustic

measurements, some researchers have rejected the

dichotomy between stress-timed and syllal)le- or mora-

timed languages (Dauer 1983), Others haye reported a

weak categorical distinction between stress-timed and

syllable-timed languages, based on durational variabil-

ity (Grabe and Low 2002). Evidence fbr the compensa-tory control in ISIs has also been presented in varieusstudies from the viewpoints ofboth production and per-ception (Fowler 1977, Huggins 1975, Mochizuki-Sudo

and Kiritani 1991, Rakerd, Sennett and Fowler 1987).The results of the above-mentioned studies indicatethat ISI is a rhythrnic unit in the production and percep-tion of English. Lending support to this claim, Sudo

and Kaneko (2012) observed that the early L2 learners

shewed a significant amount of approximation to the

production patterns of native speakers of English in

terms of the normalized ISI durations and the incre-ments of increase in the normalized ISI durations,while no statistical differences in the ISI durational

patterns were fbund between the late L2 learners and

Japanese learners of English who had neither livednor studied abroad, This result could be interpreted as

indicating that the factor of age of arriyal has an effect

on different degrees of L2 attainment from the view-

point of the production proficiency. Likewise, early L2learners displayed production patterns that are similar

to that ofnative speakers ofboth languages, L1 and L2

(Baker and liofimovich 2005, Guion 2003). Regarding

production, there are some studies which have shown

that even late L2 learners are successfu1 learners in thatthey have become indistinguishable from monolinguals

(Bongaerts, Planken and Schils 1995, Kinsella 2009,

Neufeld 1977, 1979, 1980). In sum, significant early-

late differences have been reported fbr L2 perception,and diflerent degrees of early-late effects have been

observed for L2 production studies,

In order to account for age effects on speech perfbr-

mance, various explanations have been of:ered in L2

research. The most common, and the biological expla-

nation is the critical period concept, as we have men-

tioned above. Another type of explanation is that age

effects arise from input diffbrences between Ll and L2

(Oyama 1976, Snow and Hoeihagel-Hohle 1977, Sudoand Kaneko 2005). What this explanation indicatesis that the accuracy of L2 pronunciation depends onhew much native-speaker input as opposed to fbreign-accented L2 input is received (Flege and Liu 2001), Inother words, late L2 learners receive less adequate L2

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ffZP. 3t(ResearchArticles)

phonetic input than early learners. The phonetic inter-action between L1 and L2 can be offered as another ac-

count for age effects. The Speech Learning Model pos-ited by Flege (Flege 1995, 1999, 2002, Flege, Schirruand MacKay 2003) suggests that the phonic elementsmaking up the Ll and L2 phonetic sub-systems of a

bilingual exist in a common phonologica] space, rather

than in twe separate phonological systems, and the

two phonetic sub-systems interact each other. Anotherexplanation, the Perceptual Assimilation Model (Best,McRoberts and Goodell 200 1 ) indicates that interactionbetween L1 and L2 perception increases with age.

Whatever the source ofan age factor is, this specificfactor in L2 acquisition seems to be undeniable, Thedifferences in the age effect among various studies

suggest that the degrees of attainment of L2 acquisition

might vary, depending on the aspects of acquisition.

In other words, the age factor has different degreesof effects on various features of L2 production and

perceptlon.

Regarding another aspect of production in English,a cQmpensatory vowel shortening which relates to

the production of English rhythmic patterris has beenreported in various studies (Fant, Kruckenberg and

Nord 1991, Fowler 1977, Huggins I975, Katz 2012,

Munhall, Fowler, Hawkins and Saltzman 1992, Rakerd,Sennett and Fowler 1987, Shaiman 2001). This phe-nomenen refers to a shortening of stressed vowels with

the addition of fbllowing unstressed syllables in theISI, Fowler (1977) reported that the average percent-age ofthe stressed vowels from a one-syllable ISI to atwo-syllable ISI was 12%, ranging from 6 to 18% forsix sentence sets. Mochizuki-Sudo and Kiritani (1991)reported a foet-level shortening for the native speak-

ers of English, observing that the average percentageof stressed vowel shortening from a one-syllable ISIto a twe-syllable ISI was 19%, while Japanese non-

profieient speakers of English displayed very littlefoot-level shortening; an average of 7% shortening.

Sudo, Kaneko and Nishimura (2012, 2013), and Sudoand Kaneko (2013) analyzed the compensatory vowel

shortening by Japanese learners of English and exarn-

ined their English proficiency in terms ofthe durationofstressed vowels in ISIs. The results showed that sig-

nificant difierences were observed in the cornpensatoryvowel shortening between Japanese learners of Englishwho had studied English in Japan and Japanese return-ees who had lived in the U.S.

In order to measure the proficiency of English as L2,the fest of English fbr International Communicatien

(TOEICop) is one ofthe most globally adopted standard-

ized tests. It is reported to provide a valid assessment

of English-language reading and listening proficien-cies (In'nami and Koizumi 2012, Powers 201O), It is amultiple-choice assessment consisting ofListening and

Reading Sections. Vhrious factors related to TOEICscores have been reported in literature. Tb cite a few,Sudo, Mochizuki, Itoh and Kirino (2011) reperted sig-

nificant relationships between the L2 reading proficien-cy and the Ll working memory in addition to the sex

diflerences in L2 acquisition, They also reported that

TOEIC scores and reading rate in English exhibited a

posjtive correlation with the working memory-related

parameters in the female group, but not in the male

greup, Mochizuki, Sudo, Itoh and Kirino (2013) inves-tigated the interrelationships among physical abilityl

social functioning, and L2 proficiency and conducted

correlation analyses fbr physical parameters, capacities

of social cognition, and TOEIC scores together with

English reading rate, as well as vecabulary size. Amongthe results, TOEIC seores showed a strong correlation

with reading rate and some correlation with vocabulary,

Also, vocabulary ability showed a negative correla-

tion with one of the social parameters. Regarding theTOEIC sceres, Sudo and Kaneko (2012) showed that

Japanese general college students and returnees were

significantly different in the total TOEIC scores and

those in both Listening Section and Reading Sectien.Thus, TOEIC can be used as one ofthe indices to mea-sure L2 proficiency. The purpose ofthis study was to investigate the age

factor in the acquisition of English by Japanese learn-ers, SpecificallM we attempted to find out the effbcts of

age of arrival in the target language country together

with length of residence on English proficiency of

Japanese Iearners, We analyzed English profieiencyfrom the viewpoints ofproduction patterns and TOEICscores. We focused on the two factors of productionpatterns: ISI durations and stressed vowel shortening.

Based on the results of our previous studies, ISI dura-tional control and stressed vowel shortening are shown

to be the parameters ofnativelikeness. Using TOEICscores, we measured listening and reading abilities.

We were interested in finding out the efTbcts of an age

factor on production patterns and listeninglreading pro-ficiencies. Since speaking ancl listening abilities were

reported to have high corre]ations (Bozorgian 2012),

we hypothesized that there are relationships between

production patterns and listening proficiencies. We

were also interested in the relationships between theEnglish proficiency measured by TOEIC scores and

the proficiency measured by production patterns. The

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A`LCriticalPeriod" in Secend Language Acquisition Reconsidcred

research questions addressed in the present paper are:

1) Does an age factor have an effect on various degrees

ofL2 attainment, depending on different features of

production and perception?2) Is there a

"critical period" in the acquisition of Eng-

lish by Japanese learners?In this study, we attempted to find out the effects of

an age factor on different aspects of production and

perception, testing the hypothesis ofa "critical

period"

in L2 acquisition.

Thble1 Age ofarrival and length ofresidence for RTN.

Age ofarriyal

Lengthofresidence

RTN3 (n ==11) RTN4(n=13)

RTN] (n=17)

RTN2 (n=7)

101 76

2. Methods

2.1 Subjects

We prepared three subject groups for the produe-tion experiment: 13 adult native speakers ofAmerican

English (AMR: 8 males and 5 females), 24 Japanese

retumees who had lived in the U,S, (RTN: 12 males

and 12 females), and 13 Japanese learners of English

who had neither lived nor studied abroad (JPN: 9 malesand 4 females), All subjects from MN started theirEnglish study when they entered a junior high school.

The Japanese learners were all ¢ ollege students who

belong to either a School ofHealth and Sports Science

or a Scheol ofMedicine, and teok the oMcial TOEIC

test fbr the measurement oftheir English proficiency,

The age of arrival in the U,S. fbr the subjects of

RTN was O to 1 8. We divided RTN into two subgroups

according to the age of arrival in the U.S. The age of ar-

rival fbr RTNI was O to 9; the age of anival for RTN2

was 13 to 18 (RTNI: 17 subjects, RTN2: 7 subjects).

We intentionally excluded the subjects from our analy-

sis whose age of arrival was between 10 to 12, since

the definition of puberty varies frorn study to study,

thus making the age of9 and 13 years cut-off points in

this study. Thus, the subjects of RTNI were supposed

to be the subjects befbre the critical period, and those

of RTTN2, the subjects after the critical period, The sub-

jeets of RTN had been in the U.S. fbr over one year at

least, and 12 years at the longest. We also divided the

same RTN into two subgroups according to the length

of residence in the U.S. The length of residence fbr

RTN3 was six years or more (mean=9.3 years); the

length of residence for RTN4 was one to three years

(mean= 1.5 years). Based on the data collected in this

study and to make two subgroups of short versus long

length of residence, we chose three years of length

ofresidence as the cut-off point(RJI]N3: 11 subjects,

RTN4: 13 subjects), The age of arrival and the length

of residence for the subgroups of RTN are presented in

Table l.

Note, RTN=a Japanese retumee who had lived in the U.S.;

RTN1=a returnee whose age ofarrival was O to 9; RTN2=a

returnee whose age ofaniva] was 13 to 18; RTN3=a returnee

whose length ofresidence was six to 12 years; RTN4=a re-

turnee whese length ofresidence was one to three years,

2.2 Materials

Five English sentences were devised as the linguis-

tic material for the production experiment (Tbble 2),

The sentences differed in the number of nominally

unstressed syllables that intervened between a target

stressed syllable and the next stressed syllable. The

number of unstressed syllables ranged frem one to

three. These sentences contained the ISIs within and

between words (ISII), except fbr the one-syllable ISI"Pete."

While the number ofsyllables in the ISI1 varied

from sentence to sentence; the number of syllables in

the fbllowing ISI (ISI2) was always twe syllables, As

shown in Tlable 2, the five sentences contained a target

stressed vowel [i],

Table2 Lingllistic materials for the production experi-

ment.

Number of syllables

in a target ISI1

1, P/etepl/aysthep1iano.

ISI I ISI 2

2, Ptetecanplfaythep1iano,

ISrl ISI2

3. P!eterpl/cuts thepfiano.

ISI I ISI 2

4. P!etercanpt/aythep1iano.

ISI I ISI 2

5. P/etexsonpl1ays thep/iano,

ISI I ISI 2

1

2

2

3

3

2.3

waProcedures measured the Japanese learners' English profi-

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blnge.x(ResearchArtieles)

Tbble 3TOEIC average scores (JPN & RTN).

Subject group Tbtal (SD) Listening(SD) Reading(SD)

JPN

RTN

MeanRangeMeanRange 422 (61)

]** 241 (24)

]**

335-505

844 (le3)

630 - 985

210-280460

(35)

390-495

iiil:lf,:25iO]

'"

235-490

**p<.Ol

Table 4TOEIC average sce res (RTN1 & RTN2).

Subiectgroup Tota] (SD) Listening(SD) Reading (SD)

RTN1

RTTsl2

MeanRangcMeanRange 867 (90)

710-98S

789(12I)

630-955

319Ill

`

l419cr390 - 465

396 (68)

265 - 490354

(95)

235-490

** p<.Ol

ciency by the oMcial TOEIC test, We also carried out

production experiments to investigate the leamers'

proficiency in production of English sentences. We

held one session fbr each subject, and the subjects were

recorded individually. The utterance list of 25 sen-

tences was arrangecl in a pseudo-random order. Befbre

the recording, they were provided suMcient time forpractice. The subjects were instructed to produce theirbest English-like utterance at a comfbrtable speaking

rate and to read each sentenee through without pausing,wuen they made a mistake, they were asked to repeat

the sentence frorn the very beginning. For each subject,

three repetitions of each sentence were selected fromthe total of five repetitions uttered. Spectrograms andwave forms were made from these recordings. We car-

ried out acoustic analysis of the linguistic materials,

measuring durations oftarget ISIs (ISI1) and fbllewingISIs (ISI2). The duration of ISII was defined as the

interval between the onset of the vowel [i] in "Pete",

"Peter",

and `[Peterson"

and that of the next stressed

vowel in "play", while that of ISI2 was defined as the

interval between the onsets ofthe vowel in "play"

and

the next vowel. For the purpose ofthe normalization of

the speaking rates, the ratio f\S was obtained. Further-more, we measured the durations of the target stressed

vowel, [i], The onset of the vowels was defined as theinstant a sharp rise appeared in the power of the firstfbrmant. Since the target vowel was fbllowed by a stop

[t] or a flap [f], the offSet of the yowel was defined as

the abrupt decrease in power corresponding to the stop

closure or the change in power and formant structurecorresponding to the flap.

3. Results

As shown in Tbble 3, the English proficiencies ofthe

Japanese learners were measured by the oMcial TOEIC

test, The TOEIC average score ofJPN was 422 (Listen-ing Section: 241, Reading Section: 181), The average

score of the Japanese learners who had lived in the U.S.

(RTN) was 844 (Listening Section: 460, Reading Sec-tioni 384). RTN showed rnuch higher scores than JPNin both the total scores and the scores of the Listeningand Reading Sections. Ilie results of analysis of vari-

ance showed that the differences in the total TOEIC

scores (F<1, 35)=181.06,p<.Ol, ij2=,84) and those inboth the Listening Section (F<1, 35)=415.39, p<,Ol,op2=.92)andReadingSection(F<1,35)=75,99,p<.Ol,ny2=,68) between JPN and IU]N were statistically sig-

nificant.

In erder to investigate the effect of the age of arriv-

al-a factor related to the Critical Period Hypothesis

(CPH) in the field of L2 acquisition, we divided iU'Ninto two subgroups according to the age of arrival

in the U,S.: RTNI and RTN2. As shown in Tbble 4,

the TOEIC average score of RTNI was 867 (Listen-ing Section: 471, Reading Section: 396), The aver-

age score of RTN2 was 789 (Listening Sectioni 43S,

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PhoneticSociety ofJapan

A `

℃ritical Period" in Second Language Acquisition Reconsidered

[fable5 TOEICaveragescores(RTN3&RTN4).

Subject group Tbtal (SD) Listening(SD) Reading(SD)

RTN3

RTN4

MeanRangeMeanRange 887 (97)

710-985808

(98)

630-965

474 (31)39S-49S450

(35)390-49S

414 (76)

265-490358

(71)

235-470

Reading Section: 354). RTNI showed higher average

seores in the total scores and the scores ofthe two sec-

tions than R[[:N2. The results of analysis of variance

showed that the differences in the total TOEIC scores

(F<2, 34)=99,98,p<.Ol, op2==.85) and those in both theListening Section (F<2, 34)=252.94, p<,Ol, n2=:,94)and Reading Section (F<2, 34)=39.95,p<.Ol, ij2=.70)among RTN1, RTN2 and JPN were statistically signifi-

cant, Furthermore, in order to find the source ofsignifi-

cant differences in the subject groups, multiple compar-

ison te sts (Tukey-Kramer) were carried out. The results

showed that the differences in the tota1 score and the

score of each section between JPN and RTN1and those

between JPN and RTN2 were statistieally significant

(p<.Ol). The differences in the scores ofthe Listening

Section between RTNI and RTN2 were statistically

signifieant Cp<,05), while the differences in the totalscores and those in the Reading Section between these

subject groups were not.

Next, we divided the sarne RTN subjects into twosubgroups according to the length of residence in thetarget language country. Table 5 shows that the TOEIC

average score of RTN3 was 887 (Listening Section:474, Reading Section: 414). The average score of

RTN4 was 808 (Listening Section: 450, Reading Sec-tion: 358), The ayerage tota1 scores ofRT[N3 in additionto the average scores ofListening and Reading Sectionswere higher than those of RTN4. Concretely, there

were eight RTN3s out of 1 1 subjects who scored higherthan 800, while eight RTN4s out of 13 subjects did so.Although RTN3 showed higher average scores than

RTN4, the results ofmultiple comparison tests (Tukey-Kramer) showed that these differences between RTN3and RTN4 were not statistically significant,

Tuming to the production of English sentences bythe same subjects, we measured the durations of target

ISIs (ISI1) and fbllowing ISIs (ISI2), as explained inProcedures. For the purpose of the normalization of

the speaking rates, we obtained the ratio rsrsil,Figure 1shows the results for values ofthe rsrsi'l within a word

produced by the three subject groups: AMR, RTN, and

150%

At20%gV

90%8E

6o%pn

30%o}t

Number of syllables in ISII

Figure 1 DuratiensofISIwithinaword(JRi,S-)forAMR,

JPN, and RTN.

JPN (Sentences 1, 3, and 5 in [Ibble 2).

In Figure 1 , we could observe a durational tendency

related to each ofthe subject groups. The increment ofincrease in the normalized ISI durations with the ad-

ditional unstressed syllables differed among the three

groups of subjects, RT[N showed closer durational pat-terns to those ofAMR. The normalized ISI durationsincreased by the largest increment for JPN, by a smaller

incrernent fbrAMR, and by the smallest increment for

RTN. The results ofanalysis ofvariance for the ISI du-rations within a word ( fi'I ) showed that the differencesin the normalized ISI durations among JPN, RTN, and

AMR were statistically significant, regardless of the

number of syllables in lSII (l syllable: F(2, 147)=7.40,

p<.Ol, n2==.09; 2 syllables: F(2, 147)==5.85, p<.Ol,e2=.07; 3 syllables: F(2, 147)=5.16,p<,Ol, n2=.07),Theresultsofmultiplecomparisontests(Tukey-Kram-er) fbr the ISI durations within a word (-fi,S-2 ) showedthat the differences in the normalized ISI durationsbetween JPN and AMR were statistically significant,

regardless of the number of syllables in ISII (p<.Ol>,The differences between RTN and AMR were shown

to be statistically significant only when ISII was one

syllable (p<,Ol), but not significant in the case of

two syllables and three syllables. The differences indurational pattems in terms of fff2i between JPN and

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EJffiinsc(ResearchArticles)

150%

120%AS

90%･:ti

60%:a

3o%o%

ijpc,Ol..[.Ol

ijp(,Olitpc,Ol"pc.Ol

'

'1

MRRTNRTrvnN"MRRTNRTNJPN

12L12

11

2

AMRRTNRTNJPN

123

Nllmber ofsyllables in ISII

Fig"re 2 Durations oflSI within aword ( ,rs.'S ) forAMR, JPN, RTNI, and RTN2.

tso%

120%Agv

ge%=･s-E

6oza,=a

30%o%

"*p<,Ol

*ip<,Ol

-p<.Ol e*p<.e]

i#p<.OL

/t

:1/1

4

t

/

[iI'

MRRTNRTTS'JPN

341

MRRTNRTNJ?N

32

MRRTNRTNJPN

343

Number of syllables in ISII

Figllre 3 Durations of ISI within a word ( irs,if ) forAMR,

JPN, RTN3, and RTN4.

RTN were statistically significant when ISI1 was three

syllables Cp<.Q5)･ Regarding the ISIs between words, AMR and RTNshowed similar duratiena] patterns when the ISIs werebetween words. The results of analysis of variance

showed significant difTerences among JPN, RTN, and

AMR in the case oftwo syllables and three syllables

(2 syllables: F(2, 147)=9,46, p<.Ol, ij2=.11; 3 syl-

lables: F(2, 147)=13.07,p<.Ol, n2=.15). The results

of multiple comparison te$t$ (Tukey-Kramer) showed

that the differences between AMR and RTN were not

statistically significant, while the difTerences betweenJPN and IU'N were statistically significant in the caseof two syllables and three syllables (p<,Ol). Also, thedifferences between AMR and JPN were statistically

sigriificant when iSI1 was two syllables and three syl-

lables ip<.O1). In order to investigate the effect ofthe age of arriv-

al-a factor related to the Critical Period Hypothesison the production proficiency, we compared the dura-tional patterns for RTN1 and RTTN2. Figure 2 shows the

durations of ISI within a word ( kYI ) fbr AMR, JPN,

RTN1, and RTN2. In this figure, we could observe that

AMR and RTNI showed similar durational patterns,while the patterns for JPN and RTN2 were shown to

be similar, The results of analysis of variance showed

significant differences in the durations of ISI within

a word (rsrsi'S) among JPN, RTNI, RT:N2, and AMR

(1 syllable: F(3, 143)=-10.26, p<.Ol, n2-.18; 2 syl-

lables: K3, 139)=13,66,p<.Ol, ny2=,23; 3 syllables:I<3, 144)=5.98, p<.Ol, ny2=.11). The results of mul-

tiple comparison tests (Tukey-Kramer) showed that

the differences in -fEfF, between RTN2 and AMR were

statistically significant in the case ofone and two sylla-

bles Ct)<,Ol). The difTerences in i",;ii between JPN and

RTNI were statistically significant when ISII was two

syllables and three syllables (p<.Ol). The differencesbetween JPN and RTN2 were shown to be statistieally

not significant The differences in ,L,S',l between IUrNland RTN2 were statistically significant when ISII wasthree syllables Cp<,O1). The values of

'f:;-, fbr the ISIs

between words showed a similar tendency among the

subject groups, which we observed in the normalizeddurations within words. The results of analysis ofvari-

ance showed significant differences in the durations ofISI between words ( ,rs,I2" ) among these subject groups (2syllables: F(3, 145)=4.54,p<.Ol, ny2=.09; 3 syllables:F<3, 144)=9,Ol, p<.Ol, n2=.16). The results of mul-

tiple comparison tests (Tukey-Kramer) showed signifi-

cant differences in fstSJi between JPN and RT[Nl when

ISII was two syllables and three syllables (p<,Ol). Next, we attempted to observe the effect oflength of

residence in the target lariguage country on production

proficiency, and compared the values of -X,IS-2

for RTN3and RTN4. Figure 3 shows the values of -.2 for ISIwithin a word forAMR, JPN, RTN3, and RTN4, In Fig-ure 3, we observe that AMR and RTN3 showed similar

durationa] patterns, while the patterns fbr RTN4 were

relatively eloser to those ofAMR as compared to these

of JPN. The results of analysis of variance showed

sigtiificant differences among these subject groups(1 syllable: FK3, 143)=12.29, p<.Ol, n2=20; 2 syl-lables: F<3, 138)=13.65, p<.Ol, n2=:.23; 3 syllables:

]F<3, 140)=17,88,p<.Ol, rp2=,28). The results of mul-

tiple comparison tests (Tukey-Kramer) showed that

the differences in k'f2i between RTN4 and AMR were

statistically significant in the case ofone and three syl-

lables (p<.O1), and the differences between RTN3 and

AMR were statistically significant only in the case of

one syllable Cp<.05). The differences in -.z between

JPN and R[[N3 were statistically significant when ISII

was two syllables and three syllables (p<.O1), The difL

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A "Critical

Period" in Second Language Acquisition Reconsidered

[[lable6 Percentages of shortening for the target stressed vowels (vowel shortening from a one-syllable ISI to a two-

syllable ISI and three-syllable ISI).

ISIsBetween words Within a word

1.2 1-3 1.2 1.3Mean

AMRJPNRTNRTNIRTN2RTN3RTN41741715221717 28132826312927 26le2320292521 33223636363834 26122624302725

Notc. 1-2==a one-syllable ISI to a two-syllable ISI; 1-3=a one-syLlable ISI to a three-syllable ISI.

ferences in f,9I between JPN and RTN4 were statisti-

cally significant when ISI1 was two and three syllables

(p<,Ol). Regarding the difference in kSJ'2i betweenRTN3 and RTN4, the statistical differenee was only

fbund when ISI1 was three syllables (p<.Ol). In addition to the chirational patterns related to each

ef the subject groups in terms ofvalues of -fi,fl-i

, we ob-

tained the average increment of increase in the norrnal-ized ISI durations from one-syllable ISIs to two-sylla-ble ISIs. The average increment in the normalized ISIduration per syllable, as estimated from the correlationcurve, shows that normalized ISI durations increasedby a larger increment fbr JPN, rather than RTN and

AMR. The results of analysis of variance showed sig-

nificant differences in the subject groups (ISIs within a

word: F(2, 140)= 8.88, p<.05, ny2=,11; ISIs betweenwords: iF<2, 143)=16.06, p<,Ol, n2=,18). The results

of multiple comparison tests (TUkey-Kramer) showed

sigriificant differences between JPN and RTN (ISIswithin a word: p<.05; ISIs between words: p<.Ol).Regarding RTNI, RTN2, JPN, and AMR, analysis of

variance showed statistieally significant differences

among the subject groups in the increment of increase

both in ISIs within a word (fl[3, 139)=8,78, p<,Ol,q2=,16) and ISIs between words (F<3, 142)=13,14,

p<,Ol, rp2=.22), The results ef multiple comparison

tests (Tukey-Kramer) showed significant differencesbetween JPN and RTNI Cp<.OI). Also, analysis of

variance shQwed that there were significant differences

among AMR, JPN, RTN3, and I(rN4 (ISIs within a

word: F<3, 139)=5,88,p<.Ol, n2=,11; ISIs betweenwords: F(3, 142)=10.82,p<.Ol, op2=.19). RTN3 and

JPN showed the statistically significant differences in

the increment ofincrease both in ISIs within a word and

ISIs between words (p)<,Ol). RTN4 and JPN showed

statistically significant differences in the increment ofincrease both in ISIs within a word (p<,Ol) and ISIsbetween words ip<,05), Turning to the target vowel shortening, Table 6shows the degree of vowel shortening fbr AMR, JPN,and RTN. That is, it shews the percentages of shorten-

ing fbr the target stressed yowels from a one-syllableISI to a two-syllable ISI and three-syllable ISI. Asshown in the table, the stressed vowels were shortened

considerably when unstressed syllables were added

to the ISIs in the case of AMR and RTN, while JPNexhibited a much smaller percentage of shortening. Theaverage percentages ofvowel shortening were 26% for

AMR, 2696 fbr RTN, and 129i6 for JPN. The percentage

of the target vowel shortening was shown to be higherin the case ofISIs within a word, as compared to ISIsbetween words fbr all subject groups, The results of

analysis of variance showed significant differences inthe percentage of shortening among AMR, JPN, andRTN (ISIs within a word: one-syllable ISIs to two-

syllable ISIs, F(2, 47)=623,p<.Ol, rp2 =,21; one-syl-

lable lSIs te three-syllable lSIs, F<2, 47)=7,68,p<.Ol,

rp2=,25; ISIs between words: one-syllable ISIs to two-

syllable ISIs, F(2, 47)=]1.28, p<.Ol, u2=.32; one-

syllable ISIs to a three-syllable ISIs, F(2, 47)=7.33,

p<.05, ny2=.24). The results of multiple eomparison

tests (Tukey-Kramer) showed that the differences in

the percentage of shortening between AMR and JPNwere statistically significant in all cases (p<,Ol), ex-

cept that the vowels from a one-syllable ISI to a three-syllable ISI between words were statistically significant

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fiI2retN (ResearchArticles)

40%uaa:S

30%tsets

20%&sg

lo%ee

o%

Number ofsyl]ables in ISII

Figure 4 Percentage of shortening of stressed veyvels in

the ISIs between words forAMR, JPN, RTNI,

and RTN2.

Cp<.05), The differences between RTN and JPN were

statistically sigriificant in all cases (p<.O1), except for

the vowels from a one-syllable ISI to a two-syllable ISI

within a word being significant (p<.05), while thosebetween AMR and RTN were not significant.

Rega:;ding the effbct of the age of arrival, we com-

pared the target vowel shortening for RTN1 and RTN2.Figure 4 shows the percentage of shortening of stressed

vowels in the ISIs between words fbr AMR, JPN,RTNl, and RTN2. As shown in the figure, we observe

that the subgroups of RTN-RTNI and RTN2-and

AMR showed a similar tendency in the percentage efthe target vowel shortening. The average percentage ofvowel shortening from a one-syllable ISI to a two-syl-

lable ISI was 18% for RTNI (ISIs within a word: 20%,

ISIs between words: 15%). In the case of RTN2, the

average percentage ofvowel shortening was 26% (ISIswithin a word: 29%, ISIs between words: 22%). Theresults of analysis of variance showed significant dififerences among the subject groups (ISIs within a word:

one-syllable ISIs to two-syllable ISIs, F(3, 46)==5,13,

p<.Ol, op2= 25; one-syllable lSIs to three-syllable lSIs,fJ<3, 46)=4,61,p<,05, n2=.23; ISIs between words:one-syllable ISIs to two-syllable ISIs, F<3, 46)=8.97,

p<.Ol, ny2=.37; one-syllable lSIs tQ three-syllable lSIs,F<3, 46)=4.96,p<.05, op2=.24). The results ofmultiple

comparison tests (Tukey-Kramer) showed that the

differences between AMR and RTNI, those betweenAMR and RTN2, and those between RTNI and RTN2were not statistically significant. The difference in the

percentage of vowel shortening between RTNI and

JPN was statistically significant in the one-syllable ISIs

to two-syllable ISIs between words (p<.O1), and those

in the one-syllable ISIs to three-syllable ISIs within a

werd and between words (p<,05), The one-syllable

40%uag.-S

30%tsSts

20%&sg

lo%e

£ o%

Number ofsy}lables in ISII

Figure 5 Percentage ofshortening ofstressed vowels in

the ISIs between words for AMR, JPN, RTN3,

alld Fa]N4.

ISIs to two-syllable JSIs within a word did not show

statistical differences between RTNI and JPN, Also,

the differences in the percentage ef vowel shortening

between RTN2 and JPN were statistically significant

(one-syllable ISIs to two-syllable:p<,O1; one-syllable

ISIs to three-syllable ISIs:p<.05).

Regarding the effect of the length of residence, we

compared the target vowel shortening for RTN3 and

RTN4. Figure 5 shows the percentage of shorten-

ing of stressed vowels in the ISIs between words fbr

AMR, JPN, RI'N3, and IU'N4, As shown in the figure,we observe that the subgroups of RTN-RTN3 and

RTN4and AMR showed a similar tendency in the

percentage ofthe target vowel shortening. The average

percentage ofvewel shortening from a ene-syllable ISI

to a two-syllable ISI was 21% for RTN3 (ISIs within a

word: 25%, ISIs between words: 17%). In the case of

RTN4, the average pereentage ofvowel shortening was

19% (ISIs within a word: 219t5, ISIs between words:17%). The results of analysis of variance showed

significant differences among the subject groups invowel shortening (ISIs within a word: ene-syllable ISIsto two-syllable ISIs, F(3, 46)=4.15, p<,05, ag2;21;one-syllable ISIs to three-syllable ISIs, R3, 46) ==4,80,

p<.Ol, ny2=.24; ISIs between words: one-syllable ISIsto two-syllable ISIs, F(3, 46)=7.23, p<.Ol, op2=.32;one-syllable ISIs to three-syllable ISIs, F<3, 46)= 4,66,

p<,05, op2=.23). The results of multiple comparison

tests (Tukey-Kramer) showed that the differencesbetween AMR and RTN3, those between AMR and

RTTN4, and those between RTN3 and RTN4 were not

statistically significant. The difflerences in the percent-age ofvowel shortening between RTN3 and JPN were

statistically significant in all cases (pJ<,Ol), except inone-syllable ISIs to two-syllable ISIs within a word and

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A "Critical

Period" in Second Language Acquisition Reconsidered

one-syllable ISIs to three-syllable ISIs between words

ip<.05). Also, the differences in the percentage of

vowel shortening between IU]N4 and JPN were statisti-

cally significant in all but one case ip<,05 in all cases

except in one-syllable ISIs to twe-syllable ISIs betweenwerds:p<,Ol).

4. Discussion

In the present study, we examined the L2 productionof Japanese learners in terms of ISI durational control

and stressed vowel shortening, In both parameters of

prociuction, we observed significant differences be-tween the JPN wnhout the experience of living in thetarget language county and RTN with the experience.

The experience ofliving in the target language countrywas shown to be a crucial factor in the acquisitiQn of

production patterns. The quantity and quality of L2input are different between JPN and RTN. Regardingthe quantity of input, Asher (1977) reported that on

average, children, by age 6, haye spent a minimum

of 17, 520 hours (8 hours a day) listening to their L1,while Japanese L2 learners, by age 18, have spent from1,OOO to 2,OOO hours (20 minutes a day) of contact

with English as L2 (Thkefuta 1997). In addition to

significant differences in quantity of input, it is obvi-ous that the quality of input is different when learn-ers are surreunded by native speakers of the target

language, in contrast to when they are not exposed to

native speakers in everyday life. In the present study,the subjects of RTN had lived in the U.S. for over ene

year at least. This suggests that fbr successfu1 acquisi-

tion, a minimum of one-year living might be requiredas the amount of necessary exposure to the target

language, which is in accordance with the results of

our study with junior high school students (Sudo andKaneko 2005). Several studies on short-term studying

abroad programs haye reported positive effects on the

participants such as global awareness, socio-cultural

adaptation, and academic success, but not immediateeffects on speaking and listening abilities ofthe partici-

pants (Antonakopoulou 2013, Kurt, Olitsky and Geis

2013, Xu, DeSilva, Neufeldt and Dane 2013), lending

support to the necessity ofa minimum longer period forthe improvement ofthose abilities.

Regarding an early-late efTect on L2 production,we observed that RTNI, rather than RTN2, showed

a significant amount of approxirnation to the produc-tion pattems ef native speakers. We found significantdifferences in the ISI durational patterns between thesubgroups of RTN which were elassified according to

the age of arrival, RTNI being the subgroup of RTN

whose age of arrival was befbre puberty and RTN2, the

subgroup whese age of anival was after puberty. Thissignificant early-late age effect in the ISI production isin line with the results of the previous studies (Bakerand [I)rofimovich 2005, Darcy and Kruger 2012, Flegeet al, 1999, Guion 2003, McCanhy et al. 2013) whichreported the early-late effect on production. Theseresults confirm that there is a critieal period for the ac-quisition ofthis specific feature ofproduction.

Turning to another parameter ofproduction, stressed

vowel shortening, we found that an early-late age efi

fect was not significant on this parameter ofproduction

patterns. Concretely, we did not observe a significant

difference among the subgroups of RTN, RTNI, 2, 3,and 4, The two factors of age of arrival and Iength ofresidence in the target language country did not result

in significant differences in the production patterns ofstressed vowel shortening. This result suggests that

this specific feature ofproduction can be acquired after

the critical period, supponing the results ofthe studies

(Bongaerts et aL 1995, Neufeld 1977, 1979, 1980),which reported even late learners can acquire a native-

like productien. We have presented a difference in age effect on thetwo production parameters. The results indicate that

the degree of diMculty in acquiring durational control

of stressed vowels is not so high, compared with the

acquisition of the ISI durational control, This suggeststhat the acquisition of unstressed syllables in an ISIis more ehallenging than that ef stressed syllables forJapanese learners of English, ofiering further supportto the results ofour study reporting difficulty in acquir-ing durational control ofunstressed syllables (Sudo andKaneko2005).

In addition to production parameters, we also mea-

sured the English proficiency of Japanese learners bythe TOEIC scores. We observed significant differencesin the total TOEIC scores and those in both the Listen-ing Section and the Reading Section between JPN and

RTN. The results of the TOEIC scQres showed that the

experience ofliving in the target language country was

a factor which can facilitate the acquisition oflistening

and reading proficiencies. Regarding the subgroups

of RTN, which were classified accerding to the ageof arrival, we observed significant differences in theTOEIC scores between the twD subgroups. Concretely,a significant difference between RTN1 and RTN2 was

observed in the Listening Section, but not in the Read-ing Section. The results indicated that the factor of age

can be complemented by other factors of learners in

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bcrfithSc(ResearchArticles)

reading ability, while the age factor is a decisive factorin the case of listening ability. This result of the early-

late age effect on listening ability is in accordance with

the results efprevious studies (Flege et al. 1999),

In this study, we attempted to find out why previous

studies on an age effect reportecl different results about

an early-late factor. We offbred data showing that L2Japanese learners have different degrees of attainment

of L2 skills, depending on which feature of productionis the target of acquisition. Stressed vowel shortening

was shown to be a feature which can be acquired after

puberty, while ISI durational control, especially fbr theunstressed syllables in the ISI, showed an effect of the

early-late dichotomy. Regarding listening and reading

abilities measured by the TOEIC, listening proficiencywas shown to have an eaTly-late age efTbct, while read-

ing proficiency could be acquired after puberty. To sum

up, the results of this study lend partial support to the

existence ofa "critical

period" in L2 acquisition.

The factor of length ofresidence in the target lan-

guage country was shown to have an effect on ISI

durational control, but not on compensatory vowel

shortening, We observed that RTN3 with the length

of residence of six years or more, rather than RTN4,showed a significant arnount of approximation to the

production patterns of native speakers, The factor oflength of residence was shown to be not signifieant

in the TOEIC soores of RTN3 and RTN4, which is

in accordance with the results of r[lahta

et al. (19gl),revealing that length of residence was not identified

as a significant predictor. In other words, we observed

significant difTerences in the TOEIC scores of the

Listening Section between IU]Nl and RTN2, but notbetween RTN3 and RTN4, Although the number of

the subjects in this study was net large, and the ageof arrival and the length of residenee were not quan-titatively matched with each other, the results can still

be interpreted as indicating that the age of anival is a

factor that overrides the length ofresidence in regard to

the English proficiency measured by the TOEIC scores.

Even if the length of residence was not long, some of

the leamers showed proficient listening and reading

abilities. It should be noted that this factor could be

complemented by other factors ofIearners, such as mo-

tivation, aptitude, attitude, personality among others,

provided that the learners have the experience of living

in a target language country, regardless of the length

of time. Here, we should consider some limitations of

this study. There remains a possibility that the different

degrees of significance observed in the age of arrival

and the length of residenee may be attributed to the

combined effects of the twe factors. Further research,

with a larger number of subjects, is needed, especially

to analyze the main factor in different degrees of acqui-

sition attainment.

5. Conclusien

The present study investigated the hypothesis of

an age effect, the Critical Period Hypothesis, on L2

production and listening!reading abilities by Japanese

learners of English, and showed that a critical periodexists fbr some aspects of L2 acquisition, but not fbr

others. Concretely, we fbund a critical period for the

acquisition of listening ability and ISI durational con-

trol, including production of unstressed syllables; we

also found that specific features ofproduction, such as

stressed vowel shortening and reading ability could be

acquired after the critical period.

Acknowledgement

This research was supported by a Grant-in-Aid for

Scientific Research from the Ministry of Education,

Culture, Sperts, Science and Tlechnolegy [#25370700].

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