Perception of English Plosives by Japanese Learners

論

文Perception of English Plosives
by Japanese Learners

ISONO Toru

要旨

本論文では，日本人学習者の英語破裂音に対する知覚能力を実証的に検証していく。過去の研究においては，日本人が不得意とする ‒  や‒  等の知覚能力を研究対象としたものは比較的多いが，日本語と英語間でレパートリーに差がない破裂音を取り扱ったものは少ないのが現状である。しかしながら，破裂音が語頭におかれた時には，特に無声破裂音において Voice Onset Time (VOT) や帯気音の強さにおいて日本語破裂音と英語破裂音の間には大きな違いが現れ，また語末においては，英語の有声破裂音は無声化されることが多いのに対して，日本語の場合は母音が後続する場合が多い。本研究では，そのような破裂音の日英語間の差と有標性の概念をもとに，日本人学習者が英語破裂音を知覚する時，それらが語頭にきた場合と語末にきた場合，そして無声破裂音と有声破裂音の場合では，正しく聞き取れる比率が異なってくるという仮説をたて，実験の結果を通して検証していく。被験者は英語を専攻している日本人大学生 53 名である。PC 教室において，英語破裂音を語頭と語末に含む英単語を被験者にランダムに計200回与え，毎回どの破裂音と認識したかを答えさせた。
その各英語破裂音に対する正答率が本論文における検証データとなる。
キーワード：perception（音声知覚），plosives（破裂音），Japanese learnersof English（日本人英語学習者），markedness（有標性），
word-initial（語頭），word-final（語末）

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No. 401. Introduction
The main purpose of this paper is to deal with perception of English plosives
by Japanese learners who are at advanced learning stages. Although many studies
have been conducted to clarify the characteristics of acquisition process of English by
Japanese learners, relatively less attention has been paid to their perception ability ofEnglish sounds. In addition to the situation, many of the studies examining Japaneselearners’ perception focused on limited minimal pairs, such as  – ,  – , and –  (ex: MacKain et al., 1981; Iino, 2018). This is because, as Sekiya (1994) reported,
several studies (ex: Scholes, 1968; Miyawaki et al., 1975) have shown that L2 learners’
perception is conditioned by their L1 sound systems, and the above English minimal pairs
are typically difficult for Japanese learners since the sounds of each pair are substituted
by a single Japanese sound. In this sense, it is natural that Japanese learners’ perceptionof English plosives received scant attention, because English and Japanese plosives havethe same repertory which is classified as either voiced or voiceless  – ,  – ,and  – . In addition, the places of articulation are almost identical between the two
languages, except for  –  (the alveolar for the English plosives, but the teeth for theJapanese ones).

2. Research Questions
Despite the above fact, it is also true that there are some crucial differences in
the phonetic basis for the criterion between voiced and voiceless plosives in the two
languages. For example, when the English voiceless plosives , , and  are placedin an initial position of a stressed syllable, these voiceless plosives are attended witha large amount of aspiration. This existence of a strong aspiration is one of the main
ways that English native speakers distinguish the voiceless plosives , , and  fromthe corresponding voiced plosives , , and . Japanese voiceless plosives are also
attended with an aspiration to some degree, but, it is much weaker than that of the English
voiceless plosives. This fact affects the differences in the strength of burst and VOT,
and English voiceless plosives are accompanied by stronger bursts than English voiced
ones and Japanese ones, and the former have much longer VOT values than the latter. In
other words, Japanese voiceless plosives in word-initial position are similar to English

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voiced plosives in word-initial position on these points, so we hypothesize that Japaneselearners might have difficulty with English voiced plosives in their perception as a resultof misperceiving English voiced plosives as voiceless ones.
Some differences are also observed when they are placed in word-final position.
As is widely known, English voiced plosives in word-final position have little voicing.
On the other hand, in the case of Japanese, voiced plosives in word-final position are
voiced as a result of being followed by vowels. Therefore, in production, it is said thatmany learners have difficulty with the voice contrasts of English plosives in word-final
position. This phenomenon can also be explained by the concept of markedness which ismainly approached from the perspective of language typology. Features which are simple
and common in human language are said to be unmarked, but those which are complex
and less common are said to be marked. In language acquisition, marked features are
generally more difficult to acquire than unmarked features, mainly because marked
features require more difficulty in the tongue muscles. English is a language whichallows voice contrasts for all kinds of plosives  – ,  – , and  – , in all
word-initial, -medial, and -final positions. On the other hand, many languages including
Japanese limit the occurrence of voice contrasts in word-final position (Yavas, 1994).
Therefore, concerning the positions where voice contrasts occur, word-final is considered
to be a more marked position than word-initial and -medial. In addition, a voiced plosiveis regarded as more marked than a voiceless plosive, since the occurrence of the formerin natural languages is more limited than that of the latter. For the reason given above,it can be assumed that Japanese learners especially have a difficulty with the productionof English voiced plosives in word-final position, and it was clarified by Isono (2004,
2007). We will examine whether Japanese learners have difficulty with plosives in wordfinal position even in their perception. In past studies, Stevens et al. (1969) and Koike etal. (1978, cited in Sekiya, 1994) noted the effect of markedness on perception of foreign
language sounds. In addition, the latter study reported that difficulty in perception varied
according to positions where target sounds appeared.

3. Experiment
3.1 Subjects
The subjects who participated in the experiment were 17 first-year students (Male =

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No. 405, Female = 12), 16 third-year students (Male = 5, Female = 11), and 20 forth-year students(Male = 4, Female = 16). All of them were students of the department of English at Aichi
University.

3.2 Method
The experiment was conducted in a PC room using English Accent Coach (https://www.englishaccentcoach.com/), which is a free online resource and originally designed
to improve learners’ ability to recognize English sounds. First, learners decide English
sounds to be tested and phonetic contexts, such as the target sounds appear in word-initial
or word-final position. Then, English words including the sounds in a certain condition,spoken by some different native speakers of English, are randomly given for specified
number of times, and learners are asked to identify the English sounds which they heard
by clicking on the phonetic symbols which are shown on the screen. Finally, scores areprovided to learners and they grasp how accurately they can identify the sounds.
In this experiment, the subjects were asked to be enrolled in the following two tasks.
The first task gave them English words having plosives in word-initial position randomly
100 times and asked them to identify the sounds. In the same way, English words having
plosives in word-final position were randomly given to them 100 times in the second task.
In both tests, only plosives were tested, so the subjects were instructed to choose theiranswers from the 6 choices which were , , , , , and .

4. Results
In this experiment, 636 responses (53 subjects × 12 responses showing thepercentages of correct answers for each of the 6 plosives in word-initial and those inword-final position) were obtained.

4.1 Word-initial vs Word-final
The below table presents the mean difference in the percentages of correct answers
between plosives in word-initial position and those in word-final position.

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Perception of English Plosives by Japanese Learners
Table 1. Accuracy in word-initial and word-final position
Accuracy (SD)Word-initial position

Word-final position

95.78% (7.51)

93.88% (10.74)

The accuracy rate on the plosives in word-initial position was higher than that on theplosives in word-final position, although the difference was smaller than expected.
Table 2 shows the breakdown of the above results.
Table 2. Accuracy of the plosives in word-initial and word-final position
Word-initial

Word-final

Difference

98.52% (2.54)

93.92% (6.82)

4.60%



96.71% (3.94)

88.39% (19.7)

8.32%



98.86% (2.27)

94.49% (5.70)

4.37%



95.15% (9.63)

97.52% (2.74)−2.37%

95.41% (5.03)

96.88% (4.72)−1.47%



90.03% (12.1)

92.07% (12.1)−2.04%

As shown in the table, the accuracy rates on plosives in word-initial position weresignificantly higher than those in word-final position in the cases of , , and : t (52)
= 4.517, p < .01; t (52) = 2.928, p < .01; t (52) = 5.024, p < .01, respectively. On the other
hand, differences were not statistically obtained in the cases of , , and : t (52) =−1.693, p > .05; t (52) = −1.627, p > .05; t (52) = −.909, p > .05, respectively. Therefore, inthe cases of , , and , the statistical results are consistent with the hypothesis that
English plosives in word-final position are more difficult to perceive than those in wordinitial position for Japanese learners, but not in the cases of , , and .

4.2 Voiceless plosives vs Voiced plosives
The mean differences in the accuracy rate between voiceless plosives and voiced
plosives are given in the below table.
Table 3. Differences in accuracy between voiceless and voiced plosives
Voiceless plosives

Voiced plosives

Word-initial

97.60% (3.82)

93.96% (9.59)

Word-final

95.10% (5.92)

92.66% (13.9)

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No. 40It can be seen from Table 3 that English voiced plosives were more difficult than English
voiceless plosives for Japanese learners to perceive in both of word-initial and word-final
positions.
The below tables provide the breakdown of Table 3.
Table 4. Difference in accuracy between  and  in word-initial position
Word-initial





Difference

98.52% (2.54)

96.71% (3.94)

1.81%

Table 5. Difference in accuracy between  and in word-initial position
Word-initial





Difference

98.86% (2.27)

95.15% (9.63)

3.71%

Table 6. Difference in accuracy between  and in word-initial position
Word-initial





Difference

95.41% (5.03)

90.03% (12.1)

5.38%

It is clarified from the above tables that all of the English voiced plosives were moredifficult than voiceless plosives for Japanese learners to perceive in word-initial position,and the values were statistically different: t (52) = 2.761, p < .01 for  and ; t (52) =2.718, p < .01 for  and; and t (52) = 3.383, p < .01 for  and . We see that the
English voiced velar plosive  is especially difficult for Japanese learners.
Table 7. Difference in accuracy between  and  in word-final position
Word-final





Difference

93.92% (6.82)

88.39% (19.7)

5.53%

Table 8. Difference in accuracy between  and  in word-final position
Word-final





Difference

94.49% (5.70)

97.52% (2.74)−3.03%

Table 9. Difference in accuracy between  and  in word-final position
Word-final





Difference

96.88% (4.72)

92.07% (12.1)

4.81%

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Perception of English Plosives by Japanese Learners

Concerning the English bilabial plosives  –  and the velar plosives  –  in wordfinal position, the rates on voiced plosives were lower than those on voiceless plosives,
although a statistical difference was obtained only for the latter: t (52) = 1.894, p > .05 forthe difference between  and ; t (52) = 2.665, p < .05 for the difference between 
and . As far as the alveolar plosives in word-final position, the accuracy on the voiced
plosive  was higher than that on the voiceless plosive , t (52) = −3.370, p < .01.
Overall, the above results validate the hypothesis that English voiced plosives are
more difficult than voiceless plosives to perceive for Japanese learners, except the resultsof the alveolar plosives  –  in word-final position.

5. Discussion
The first analysis verified the hypothesis that English plosives in word-final position
are more difficult than those in word-final position for Japanese learners to perceive, andclarified that the results of , , and  were consistent with the hypothesis, but thoseof , , and  were not. Although we cannot say for certain why differences were notobserved in the cases of  and , a reason could be attributed to the low accurate rate
in word-initial position as far as the case of  was concerned. As is generally accepted,
the voiced velar plosive  is regarded as the most difficult sound to produce among
plosives. The phenomenon that the voiced velar plosive is difficult no matter whether it isin word-initial or word-final position suggests that the above characteristic is also true inperception.
The second analysis tested the hypothesis that English voiced plosives are moredifficult than voiceless plosives to perceive for Japanese learners, and it was observed inboth of word-initial and -final positions, except the case of the alveolar plosives  – in word final position. In addition to the low accuracy on the voiced velar plosive which was mentioned earlier, we must pay our attention to the perceptual difficulty withthe bilabial voiced plosive  in word-final position. As a problem concerning it, thephenomenon of mixing up it and the English voiced fricative  has been often reported
in both of production and perception. The corresponding sound of the English  does notexist in the Japanese sound systems, and the Japanese  which is a bilabial plosive tends
to be substituted for the English  because of the similarity in the place of articulation
between the bilabial and the labiodental. Consequently, the Japanese  tends to be

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No. 40substituted for both the English  and . However, the English  was not included in
the current experiment, so there was no chance that the low accuracy rate on the voiced
English plosive  in word-final position was caused by the result of mixing up the twosounds. In this respect, we may say that there is another feature which makes it difficult
for Japanese learners to perceive the voiced English plosive  in word-final position.
In this experiment, we hypothesized that English voiced plosives would be moredifficult than voiceless plosives for Japanese learners to perceive, and the analysis of
those in word-initial position statistically supported it. However, we should notice that theaccuracy rates on the English voiced plosives  and  were sufficiently high, 96.71%
for  and 95.15% for , and a problematic plosive in word-initial position was only thevoiced velar plosive . As far as English plosives in word-final position were concerned,
this experiment suggested that they have difficulty with the voice contrast of the bilabial
plosives  –  and the velar plosives  – . In production, the difference between
English voiced plosives and voiceless ones in this position is the fact that vowels preceding
the former are much longer than the latter, as Roach (1991) explained. Directing learners’
attention to this fact may help them to distinguish English voiced plosives from English
voiceless ones in word-final position in their perception.
The results obtained in this experiment showed high accuracy rates overall, and it
is natural considering the subjects’ learning level and the experimental method that only
plosives were given as the test items. If the subjects had been less advanced learners, theresults showing more significant differences would have been obtained.
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