Phonological Studies (『音韻研究』), 2001, 4, 119-126.

OCP Effects on Japanese Phonological Processing
Katsuo Tamaoka (Hiroshima University, Japan)
Tadao Murata (Kyushu Institute of Technology, Japan)
Key Words: OCP, Vowel Repetition, Cascaded Dual-route Model, ‘Whack-a-mole’ Phenomenon
The Obligatory Contour Principle (OCP) refers to a linguistic constraint on similar or samephonological elements or features from being repeated (e.g., Fukazawa, 1999, 2000; Itô & Mester,
1986; Kubozono, 1999; Kubozono & Ôta, 1998). Kubozono and Ôta (1998) suggested thepossibility that vowel dissimilation in Japanese may be a result of the OCP. For example, the two
Japanese morphemes /nana/ meaning ‘seven’ and /ka/ meaning ‘day’ combine to form the compound
word /nanoka/ meaning ‘the seventh day’ instead of /nanaka/, which would seem to be the likely
combination. This process of vowel dissimilation occurs so as to avoid vowel repetition of /a/ insequence within the three mora CVCVCV word structure (C referring to ‘consonant’ and V referring to‘vowel’). Thus, it would be expected that naming visually-presented Japanese words and nonwords
violating the OCP (i.e., same vowel repetition in a series of CV strings) would result in slower
processing speeds and higher error rates. To test this hypothesis, two experiments were conducted.
The first experiment examined OCP effects in naming real words with and without same vowel
repetition. The second experiment investigated OCP effects in naming nonwords under bothconditions.
EXPERIMENT 1
NAMING REAL WORDS WITH SAME VOWEL REPETITION
Assuming that the OCP affects phonological processing of words with same vowel repetition, thefirst experiment tested the prediction that CVCVCV-structured words with same vowel repetition
would take longer to be named and result in higher error rates than a counter group of
CVCVCV-structured words with no such repetition.
MethodSubjects Twelve female and six male students (18 in total) at Hiroshima University in Japan
participated in Experiment 1. Average age was 27 years and six months for females and 28 years and3 months for males. All participants were native speakers of Japanese.
Stimuli In order to examine OCP effects, words with same vowel repetition were taken from aJapanese dictionary comprised of 50,000 words (Yamada & Ishiwata, 1983). As shown in Table 1, a
total of 175 words with a CVCVCV structure and same vowel repetition such as /sakana/ (‘fish’),/hibiki/ (‘echo’) and /kokoro/ (‘heart’) were found. Among the five vowels in Japanese, the vowel /a/
was the most frequently-repeated, found in 62 words (58 nouns, 2 adverbs and 2 adjectives). The
vowel /u/ came in second, repeated in 59 words (11 nouns and 48 verbs). Since the dictionary formof Japanese verbs always ends with the inflection /u/, it came as no surprise to find so many verbs withthe vowel /u/ repeated. The vowel /i/ was the third most repeated vowel, found in 39 words (onlynouns) while the vowel /o/ came in fourth, repeated in 15 words (13 nouns and 2 adverbs). The
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vowel /e/ was only seen repeated in the adverb /semete/ (‘at least’) out of all 50,000 words in the
dictionary. Kubozono (1998, 1999) explained that the vowels /a/, /i/ and /u/ occur with the greatest
distance apart from each other within the ‘vowel space’, or space in the mouth where vowels arepronounced. Kubozono (1999) further explained that these three vowels are most frequently foundwithin the various languages of the world. It is therefore reasonable to expect that the vowels of /a/,/i/ and /u/ are found to be repeated more often in a single word in Japanese than the vowels of /e/ and/o/.
TABLE 1
Real Words with a CVCVCV String
and Same Vowel Repetition
Grammatical Categories
Type of Vowel
Total
Noun
Verb
Adverb Adjective
/a/
58
0
2
2
62
/e/
0
0
1
0
1
/i/
39
0
0
0
39
/o/
13
0
2
0
15
/u/
11
48
0
0
59
Total
121
48
5
2
175
Note : Words above were taken from among the 50,000 words
contained in the Practical Japanese Dictionary by Yamada
and Ishiwata (1983).

Fifty-four words of a three mora CVCVCV pattern were used as stimuli and divided up into
eighteen sets, each containing three words. Each of the three words in each set fell under one of three
conditions. The first condition was real words with same vowel repetition as in からだ /karada/
meaning ‘body’. The second condition was real words with no repetition of same vowels as in くら
し /kurasi/ meaning ‘life’. Word frequencies using the index established by the National Language
Research Institute (1973) were matched across the real words in each set under these two conditions.
Real words with same vowel repetition (M=20.56) did not differ from real words with no such
repetition (M=20.83). As for the third condition, nonwords without same vowel repetition werecreated. The words across all three stimulus conditions in each set began with the same consonant so
as to avoid a difference in initial sounds which might have affected naming latency related to thetriggering of the voice-activated key. All stimuli were presented to subjects in the hiragana script.
Procedure Stimuli of real words and nonwords were individually presented to subjects in the centerof a Toshiba J-3100 plasma display at a comfortable distance away in a dimly lit, quiet room. Stimuli
were randomly presented 600 milliseconds after the appearance of an eye fixation point marked by anasterisk ‘*’. Subjects were required to pronounce each string of CVCVCV morae as quickly and as
accurately as possible. Subjects spoke into a table microphone connected to a computer via a
voice-activated relay mechanism which automatically turned off a timer used to measure naming
latency. Pronunciation was judged as being correct or not by the examiner and then entered into thecomputer. The next fixation point was indicated 600 ms after the examiner pressed the space key.
Twenty-four practice trials were given to subjects prior to the commencement of the actual testing tofamiliarize them with the task.
Results
The mean naming latencies and error rates across the three stimulus groups are presented in Table120

2. Before the analysis was performed, reaction times outside of 2.5 standard deviations in both thehigh and low range were replaced by the boundaries indicated by 2.5 standard deviations from theindividual means of subjects. This procedure affected 33 scores (3.4%) including both correct andincorrect responses for stimulus items. A one-way analysis of variance (ANOVA) with repeatedmeasures was conducted on the reaction times of correct responses and error rates across all threestimulus conditions. Statistical tests followed analyses of both subject (Fs) and item (Fi) variability.
TABLE 2
Mean Naming Latencies and Percentage of Errors in the Naming Task of Experiment 1
Stimulus Condition
MeasureReal Words with Same Vowel Repetition

Real Words with No Repetition

501 ms (64)
Error Rates
2.47%
Note ： Figures in parentheses indicate standard deviations.
Naming Latency

500 ms (66)
1.23%

Nonwords

570 ms (110)8.64%

Naming Latency Naming latency was based on correct responses from the groups of real words andnonwords. A one-way ANOVA revealed that there was a significant main effect of stimulus
conditions in subject analysis [Fs(2, 34)=24.76, p<.0001] and item analysis [Fi(2, 34)=19.48, p<.0001].
Further analysis with an orthogonal polynominal comparison was carried out to identify the difference
between the three stimulus conditions. As indicated in Table 2, there was only a 1 ms difference in
response time between the naming of real words with and without same vowel repetition. Thisdifference was not significant [Fs(1, 17)=0.03, p<.86; Fi(1, 17)=0.00, p<.98]. Thus, the repetition ofsame vowels did not affect the naming latency of real words with a CVCVCV structure. In contrast,
significant differences were found between the naming latencies of real words with same vowel
repetition and nonwords [Fs(1, 17)=27.57, p<.0001; Fi(1, 17)=22.50, p<.0005], and between those ofreal words without same vowel repetition and nonwords [Fs(1, 17)=26.48, p<.0001; Fi(1, 17)=22.52,
p<.0005]. Thus, an effect of lexical status was apparent.
Error Rates The same one-way ANOVA used for naming latencies was carried out on error rates.
There was a significant main effect of stimulus conditions in both subject analysis [Fs(2, 34)=6.56,
p<.005] and item analysis [Fi(2, 34)=14.07, p<.0001]. Further analysis with an orthogonal
polynominal comparison was carried out to identify the difference in error rates across three stimulus
groups. As indicated in Table 2, the difference was only 1.24 % between real words with and without
same vowel repetition. This difference was not significant [Fs(1, 17)=1.66, p<.23; Fi(1, 17)=1.56,
p<.23]. Thus, repetition of the same vowel in real words did not affect error rates. In contrast,
significant differences were found between real words with same vowel repetition and nonwords [Fs(1,17)=6.12, p<.05; Fi(1, 17)=12.20, p<.005], and between real words without same vowel repetition andnonwords [Fs(1, 17)=7.56, p<.05; Fi(1, 17)=21.24, p<.0005]. Again, an effect of lexical status wasapparent from these results.
Discussion
Experiment 1 used 18 real words with same vowel repetition taken from among the 121
CVCVCV- structured nouns found in the Japanese dictionary (Yamada & Ishiwata, 1983) as shown in
Table 1. These 18 real words with same vowel repetition were matched with 18 real words with nosuch repetition according to phonological structure, number of morae and word frequency. The
results of Experiment 1 indicated no difference in the means of naming latencies and error rates for121

pronouncing either of these groups of real words. The OCP showed no effect in the naming of realwords with a CVCVCV structure and same vowel repetition. Both conditions of real words with thesame repeated and non-repeated vowels resulted in faster naming latencies and lesser error rates than
did the condition of nonwords. A lexical status effect was clearly observed in Experiment 1.
Consequently, as proposed by the cascaded dual-route model in Figure 1 (Coltheart, 1985; Coltheart &Rastle, K., 1994; Coltheart, Curtis, Atkins & Haller, 1993), it is possible that ‘addressed phonology’(the processing of a word as a whole unit) is involved in the processing of real words regardless ofwhether they have same vowel repetition or not, whereas ‘assembled phonology’ (the processing of anonwords by putting smaller phonological units together) is involved in the processing of nonwords.
Thus, Experiment 2 investigated the phonological processing of nonwords with a CVCVCV string ofsame vowels.
EXPERIMENT 2
NAMING NONWORDS WITH SAME VOWEL REPETITION
The naming task in Experiment 1 did not find effects of same vowel repetition on thephonological processing of real words. However, a lexical status effect was evident by the differencein naming latencies between real words and nonwords. To further investigate the effects of samevowel repetition, Experiment 2 produced two types of nonwords: one where the vowel remained
constant throughout the nonword (e.g., ʻたさまかʼ/ta sa ma ka/) and another where the vowels did not
retain their consistency (e.g., ʻてすもきʼ /te su mo ki/). If the OCP does in fact influencephonological processing, the first type of nonwords with repeated vowels would take longer to be
named and cause higher error rates than the second type with differing vowels.
MethodSubjects Twenty-two female and twenty male students (42 in total) at Matsuyama University inJapan participated in Experiment 2. Average age was 21 years for females and 21 years and 6 months
for males. All participants were native speakers of Japanese.
TABLE 3
Examples of Stimuli Used in Experiment 2
Stimulus Conditions
Nonwords with Same Vowel Repetition
Nonwords without Same Vowel Repetition
Real Words

２ Morae
こほ むる/koho/ /muru/
こは むろ/koha/ /muro/
こじ むき/kozi/ /muki/

Number of Morae
３ Moraeのほろれねけ/nohoro/ /reneke/のふれ れにこ/nohure/ /reniko/のうど れいき/noudo/ /reiki/

４ Morae
ひしみに さなたは/hisimini/ /sanataha/
ひせむの さにてほ/hisemuno/ /saniteho/
ひらまく
さくもつ
/hiramaku/ /sakumotu/

Stimuli Words constructed from two to four morae were used as stimuli. They were divided into
sets according to their number of morae and placed under three conditions (see Table 3). Each set,
therefore, contained three words under three different conditions. All words in each set had the same
initial mora. The first condition was nonwords with same vowel repetition as in こほも /ko ho mo/.
The second condition was nonwords without same vowel repetition but containing the same
consonants as nonwords with same vowel repetition. For example, the stimulus nonword of こはみ/ko ha mi/ was constructed using the three consonants of /k/, /h/ and /m/ taken from the aforementioned
nonword of /ko ho mo/ where the vowel /o/ was repeated. The vowel /o/ of the first mora was kept
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and the second and the third vowels were replaced by /a/ and /i/ respectively. The third condition wasreal words with the same initial mora as nonwords such as こりつ /ko ri tu/ to ascertain thewell-established principle of lexical status effect which suggests that real words are pronounced more
quickly than nonwords. According to this procedure, thirty-six sets of two-mora words, thirty-six setsof three-mora words and thirty-six sets of four-mora words under all three above conditions werecreated; a total of 108 sets or 324 stimuli were used.
Stimuli were divided into three counterbalanced lists with an equal number of nonwords (withand without same vowel repetition) and real words. The 42 subjects were also divided into threegroups of 14. In this manner, assignment of the three stimulus words in each set was given to adifferent subject. For example, こほも /ko ho mo/, こはみ /ko ha mi/ and こりつ /ko ri tu/ (all threewords in the same set) appeared separately on three different lists. Thus, no subject saw any morethan one of these three stimuli during the same task. This method of assigning items to lists avoided
repetition of either rime or onset-nucleus patterns by subjects.
Procedure The naming task of Experiment 2 was conducted in the same way as Experiment 1.
Results
The mean naming latencies and error rates for the words in each set are presented in Table 4.
Before performing an analysis, naming latencies outside of 2.5 standard deviations in both the high andlow range were replaced by the boundaries indicated by 2.5 standard deviations from the individual
means of subjects. This procedure affected 141 scores (3.1%) including both correct and incorrect
responses to stimulus items. A two-way 3 X 3 ANOVA with repeated measures was carried out onnaming latencies and error rates relating to the two factors of stimulus conditions and mora structure.
Statistical tests follow analyses of both subject (Fs) and item (Fi) variability.
TABLE 4
Mean Naming Latencies and Percentage of Errors
for the Naming Task in Experiment 2
Stimulus Conditions

２ Morae
574 ms (115)
Nonwords with Same Vowel Repetition
6.94%
545 ms (90)
Nonwords without Same Vowel Repetition
2.38%
513 ms (73)Real Words
1.39%
Note ： Figures in parentheses indicate standard deviations.

Number of Morae
３ Morae
702 ms (160)
13.69%
663 ms (139)6.75%
586 ms (115)
1.79%

４ Morae
804 ms (172)20.83%
781 ms (169)12.10%
580 ms (108)
1.59%

Naming latency Only correct responses of nonwords and real words were used as data in the analysis
of naming latency. The two-way 3 X 3 ANOVA indicated that a main effect of stimulus conditions
was significant in subject analysis [Fs(2, 82)=135.12, p<.0001] and item analysis [Fi(2, 70)=253.73,
p<.0001]. A main effect of the three types of mora structure was also significant in subject analysis[Fs(2, 82)=186.20, p<.0001] and item analysis [Fi(2, 70)=176.08, p<.0001]. The interaction of bothmain effects was also significant [Fs(4, 164)=60.37, p<.0001; Fi(4, 140)=38.45, p<.0001]. Realwords were named consistently faster than nonwords, from 513 ms for those with two morae to 580
ms for those with four morae. The average naming latency for all real words was 560 ms. The factthat this figure was 133 ms. less than the average for nonwords with the same vowel repeated and 103
ms. less than that for nonwords with no repetition of same vowels confirmed a lexical status effect.
Further analysis with an orthogonal polynominal comparison was carried out to identify the difference123between the stimulus conditions of repeated and non-repeated vowels. Significant differences were
found with respect to the two stimulus conditions of repeated and non-repeated vowels on two mora
[Fs(1, 41)=16.00, p<.0005; Fi(1, 35)=10.63, p<.005], three mora [Fs(1, 41)=15.37, p<.0005; Fi(1,35)=10.63, p<.005] and four mora [Fs(1, 41)=5.00, p<.05; Fi(1, 35)=6.66, p<.05] nonwords. These
results indicate that it took longer to name a nonword when the same vowel was repeated.
Error rates The same ANOVA analysis was conducted on error rates. A main effect of stimulus
conditions was significant in subject analysis [Fs(2, 82)=77.68, p<.0001] and item analysis [Fi(2,70)=43.28, p<.0001]. A main effect of the three types of mora structure was also significant insubject analysis [Fs(2, 82)=32.38, p<.0001] and item analysis [Fi(2, 70)=16.32, p<.0001]. Theinteraction of both main effects was also significant [Fs(4, 164)=9.74, p<.0001; Fi(4, 140)=6.11,
p<.0001]. The average error rate in naming real words was only 1.59%, whereas the average fornonwords was 13.82% with same vowel repetition and 7.08% with no such repetition. The error
rates also supported the presumed effects of lexical status. Further analysis with an orthogonal
polynominal comparison was carried out. Significant differences were found between the two
stimulus conditions of repeated and non-repeated vowels on two mora [Fs(1, 41)=16.00, p<.0005; Fi(1,35)=7.13, p<.05], three mora [Fs(1, 41)=15.37, p<.0005; Fi(1, 35)=8.23, p<.01] and four mora [Fs(1,41)=5.00, p<.05; Fi(1, 35)=8.03, p<.01] nonwords. The results of these error rates also confirm
effects of same vowel repetition on nonwords.
Discussion
As in the first experiment, effects of lexical status were also indicated in Experiment 2, which isshown by the fact that real words were named more quickly than both types of nonwords. The
naming latencies for nonwords with repeated and non-repeated vowels showed that nonwords which
had the same vowel repeated were named more slowly than nonwords which did not have the samevowel repeated. In addition, error rates were higher in naming nonwords with repeated vowels thanfor the non-repeated condition. Both naming latencies and error rates supported OCP effects. Even
though nonwords were presented in kana which represent phonological units of mora, it is a smaller
unit of phonemes (i.e., vowels in Experiment 2) which affected the assembling process of nonwords.
GENERAL DISCUSSION
The present study sought out to reveal how the OCP concerning same vowel repetition affects
phonological processing of Japanese real words and nonwords. The findings can be summarized inthree ways. First, real words proved to be named more quickly and accurately than nonwords in bothExperiments 1 and 2. In other words, a ‘lexical status effect’ (real word superiority over nonwords)
was clearly observed in both experiments. These results suggest that real words may be processed
differently from nonwords. Second, in Experiment 1, real words with same vowel repetition were
processed as fast and as accurately as real words with no such repetition. Thus, as far as the chosen
18 stimuli are concerned (about 15% of the 121 total nouns with a CVCVCV string and same vowel
repetition found in the dictionary used), the OCP effect does not seem to apply to same vowel
repetition in the naming of real words. Third, nonwords with same vowel repetition were namedslower and less accurately than nonwords with no such repetition in Experiment 2. This trend wasobserved in all sets of nonwords containing 2-4 morae in a CV string. Consequently, an effect of the
OCP related to same vowel repetition is apparent in the phonological processing of nonwords. The
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lexical status effect found in Experiments 1 and 2 provides fundamental evidence to support thecascaded dual-route model as shown in Figure 1 (Coltheart, 1985, 1987; Coltheart & Rastle, K., 1994;
Coltheart, Curtis, Atkins & Haller, 1993). In addition to a lexical status effect, the present study
showed a clear distinction between real words and nonwords with regards to the OCP. This contrast
of OCP effects on the phonological processing of real words and nonwords is nicely explained by thecascaded dual-route model. The phonological processing of real words as a whole unit (i.e.,addressed phonology) occurs regardless of same vowel repetition, whereas the processing of nonwords
involves the putting together of smaller phonological units (assembled phonology).
Visually-Presented Real Words and Nonwords

Visual Feature Detector

Kana and Kanji Detector

Addressed Phonology

Assembled Phonology

こほも (nonword)
こはみ (nonword)
Orthographic Representations

からだ ('body')
くらし ('life')

Semantic System

Phonological Conversion System/kohomo/ (nonword)/kohami/ (nonword)
Phonological Representations

Inhibition
Excitation/karada/ ('body')/kurasi/ ('life')

Articulation System

Naming
FIG 1. The dual-route cascaded model applied to the Japanese phonologicalprocessing of real words and nonwords with and without same vowel
repetition

125

The explanation proposed for the putting together of smaller phonological units (i.e., assembled
phonology) when processing nonwords is the ‘whack-a-mole’ phenomenon. The vowel in the first
CV mora continues to have a high activation level even when following CV morae are activated.
When the same vowel is repeated throughout the CV morae, as in some of the nonwords used in thisstudy, all the CV morae are simultaneously excited to reach the activation level. For example, since
the three morae of こほも /kohomo/ share the same vowel of /o/, the first vowel /o/ will be activated to
combine with the first consonant /k/ to form the first mora /ko/. However, since the vowel /o/ mustalso be combined with the second and third consonants /h/ and /m/, it creates a high activation levels of
the subsequent morae /ho/ and /mo/. To avoid confusing the sequential order of morae in a CV string,
subsequent morae must be inhibited so as not to be activated to the same degree as the previous CV
mora. This pattern of activation (or excitation) and inhibition results in the decreased speed ofphonological processing of nonwords with same vowel repetition and in the increased rate ofpronunciation errors. In contrary, as for naming nonwords with no repeated vowels, phonologicalassembly of morae in sequential order within a CV string is not affected by the activation of othermorae. For example, the nonword こはみ /kohami/ does not share the same vowel throughout theCV string so assembling its sequential order of phonological structure is not affected by same vowel
repetition. Thus, nonwords with varying vowels are named more quickly than nonwords withrepeated vowels and, concomitantly, fewer errors are observed.
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