A Corpus-based Analysis of
Simultaneous Interpretation
A. Takagi†, S. Matsubara‡ , N. Kawaguchi‡, and Y. Inagaki††Graduate School of Engineering, Nagoya University‡Information Technology Center/CIAIR, Nagoya University

Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan{atakagi,matu,kawaguti,inagaki}@inagaki.nuie.nagoya-u.ac.jp

Abstract
This paper provides an analysis of
the interpreter’s speeches using analigned simultaneous monologue interpreting corpus.
The following
points have been investigated: (1) theinterpreter’s speaking speed, (2) theinterpreting unit of simultaneous interpretation, and (3) the diﬀerence
between the beginning time of thelecturer’s utterance and that of theinterpreter’s utterance. This paper
also describes characteristic features
about the timing at which professional simultaneous interpreters start
to speak. The analysis will be available for the development of a simultaneous machine interpreting system.

1Introduction

In order to provide an environment supporting
natural dialogues between diﬀerent languages,
simultaneous machine interpretation has beenstudied recently (Amtrup, 1999; Mima, 1998;
Matsubara, 1999). Towards a simultaneous interpreting system, not only the qualityof the interpretation but its output timing isalso important, and it would be eﬀective toinvestigate and analyze the interpreting process of professional simultaneous interpreters.
The Center for Integrated Acoustic Information Research, Nagoya University (CIAIR), isconstructing and maintaining the various typesof speech and language database for the purpose of the advancement of robust speech information processing technologies (Kawaguchi,2001). Moreover, a bilingual database of simultaneous interpretation is also constructed as apart of the project(Matsubara, 2001).

Table 1: Outline of simultaneous interpreting
corpustype of speech
type of interpretation
language
data typetopics
number of interpreters
number ofEnglish lectures
number ofJapanese lecturesmonologue(lecture)
simultaneousJapanese, English
speech, text
computer science,
politics, economy,
history, etc.
2124
(239 min. in total)
15(146 min. in total)

This paper describes an analysis of interpreter’s speeches using the simultaneous interpreting corpus. In the transcript of this corpus, the exact beginning time and ending time
are provided for every utterance. Using thesetime information, we have aligned the interpreter’s utterances with the lecturer’s utterances, and investigated the following points:(1) interpreter’s speaking speed, (2) the interpreting units in simultaneous interpretation,(3) the diﬀerence between the beginning timeof the interpreter’s utterance and that of thelecturer’s utterance, and so on. This paper
also describes the feature about the timing ofsimultaneous interpretation.

2
2.1

CIAIR Simultaneous Interpreting
CorpusOutline of the corpus

The project of multilingual data collection in
CIAIR is collecting speeches of the simultaneous interpretation in both Japanese-English

Table 2: Statistics of the simultaneous interpreting corpus
item
Eng
E-J
Jap
J-E
recoding time (sec) 14359
57300
8767 35078
speaking time (sec) 11458
40473
5690 22289
morphemes
35474 165127 21708 63872
kinds of morpheme
3506
6115
1457
3130
utterance units
5573
20496
4505 12468
utterance sentences
1263
7423
651
3315
ﬁllers
1251
8067
1482
3261

Figure 1: Sample of the transcript (Englishnative speech)

and English-Japanese, and constructing alarge-scale bilingual speech corpus(Aizawa,2000). In 2001, the monologue speeches of English and Japanese and their simultaneous interpretation have been collected. As English
speeches, the lectures about politics, economy,history, etc., and, as Japanese speeches, thoseabout the themes relevant to computer science
have been adopted. Moreover, each monologue
speech is interpreted by four professional interpreters of which the degree of experience differs one another. In a Japanese lecture, since
the lecturer uses the presentation slide, andthe interpreter can also see the slide. Speech
data is transcribed into ASCII text ﬁles according to the transcription criteria of “Corpusof Spoken Japanese(CSJ)”(Maekawa, 2000).
Figure 1 and Figure 2 show the sample of thetranscript. The discourse tags were provided

Figure 2: Sample of the transcript (EnglishJapanese interpreting speech)

for the language phenomena characteristic of
spoken language, such as ﬁllers, corrections,and misstatements. Moreover, the transcript
is segmented into utterance units by the pause
for 200ms or more, or that for 50ms after thesentence break, and the starting time and ending time have been provided for every utterance unit. Table 1 shows the outline of thesimultaneous interpreting corpus.
2.2

Statistics of the Corpus

As fundamental statistics of the simultaneousmonologue interpreting corpus, we have examined the recording time, the number of utterance units, the number of morphemes(words),
the number of diﬀerent morphemes(words),
the speaking time, and the number of discourse
tags. The result is shown in Table 2. Eng, EJ, Jap and J-E in the table mean English lec-Figure 3: Sample of the aligned corpus

ture, English-Japanese simultaneous interpretation, Japanese lecture, and Japanese-English
simultaneous interpretation, respectively. In
this paper, a morpheme in English meansa word, and the number of morphemes inJapanese was calculated on the basis of theresult of a Japanese morphological analyzer
called ChaSen(Matsumoto, 2000). The number of kinds of morphemes in English is thenumber of words whose notations diﬀer, andthat in Japanese is the number of morphemes
whose basic forms diﬀer.

The interpreter’s speaking time is about 4times as much as the lecturer’s time because
the simultaneous interpretations by four interpreters were collected for one lecturer’s speech.
On the other hand, the number of utterance
sentences of English-Japanese interpreters isabout 6 times as much as that of the Englishlecturers and that of Japanese-English interpreters is about 5 times as much as that ofthe Japanese lecturers. This fact substantiates the empirical knowledge supported by aninterpreting theory that a professional interpreter may segment a lecturer’s utterance sentence into 2 or more sentences, and interpretit (Mizuno, 1995).

3

Parallel Corpus Alignment

In order to analyze the process of simultaneous interpretation in detail, it is required toalign utterances by the interpreters with thoseof the lecturers in a possibly small unit. Analignment support tool (Figure 4) which workon the internet have been developed using CGI
script. The users can perform alignment workby carrying out the mouse click on the bilingual text displays. The alignment data can beused for analysis of interpreting units and timing. We have aligned the corpus by this toolaccording to the following conditions:• The smallest unit of alignment is a utterance unit.
• The corpus is aligned as small as possible.
• There is no counterpart for the lecturer’sutterance unit such as a ﬁller, an abbreviation and a supplement, etc.
The alignment data is made by hand for
16 lectures presently in both Japanese-Englishand English-Japanese. Figure 3 shows a part ofan aligned corpus. The left-hand side expresses
Japanese lecturer’s utterance units, and righthand side expresses Japanese-English interpreter’s utterance units. Each line means analignment pair.

18.0

9.2

J-E interpretation
E-J interpretation

9.0

17.5

8.8
17.0

8.6
16.5

8.4
16.0

8.2
15.5

8.0

7.8

02

4

6

8

speaking time(s)

15.0
10

Figure 5: Interpreter’s speaking speed
Figure 4: Alignment support tool4
For each alignment pair in 16 sets of thealigned corpus, we examined the following
items:• The time overlapping with the lecturer’sutterance in the interpreter’s utterance• The diﬀerence between the beginning timeof the lecturer’s utterance and that of theinterpreter’s utterance.
• The speaking time of lecturers and interpreters.
• The numbers of the morphemes of lecturer’s utterances and interpreter’s utterances.
Table 3 shows the result. Sum and Ave in thetable mean the total of the time for 16 lectures
and the average of the time per alignment pair,respectively.

Analysis of SimultaneousInterpreting Corpus

Simultaneous interpretation may overlap withthe corresponding native speech. It is expectedthat an interpreter recognizes a part of a lecturer’s utterance as an interpreting unit, andinterprets it at an early stage. We have investigated the interpreting units of professional
interpreter by analyzing the aligned corpus.
4.1

Analysis of Speaking Speed ofInterpreter

We have investigated the speaking speed of
the interpreter. The speed was calculated with
the number of moras per utterance unit. We
assigned one mora to a short vowel and aconsonant behind vowel, and two moras tolong vowel in English. And we calculated
the number of moras by using the result ofChaSen(Matsumoto, 2000) in Japanese. Figure 5 shows the result.
Although the interpretation begins at an
early stage in order that an interpreter

speaking speed of E-J interpretation(mora/s)

speaking speed of J-E interpretation(mora/s)

Table 3: Statistics of the aligned corps
E-J: 1717 pairs J-E: 1441 pairs
item
Sum
Ave
Sum
Ave
overlapping time (sec)
1845
1.07
1232
0.86
diﬀerence of beginning time (sec)5482
3.195955
4.13
diﬀerence of ending time (sec)
5383
3.13
5829
4.04lecturer’s speaking time (sec)
6593
3.84
5077
3.52
interpreter’s speaking time (sec)6214
3.625388
3.74
lecturer’s morphemes
22360
13.02 18572
12.89
interpreter’s morphemes
25926
15.10 15554
10.79

may raise simultaneity, however, interpreter’sspeaking speed is slow because the role ofthe interpretation is not ﬁxed at the beginning of the utterance. As the lecturer’s utterance is progressing, the interpreter can grasp
a lecturer’s intentions gradually. Therefore, it
is considered that the interpreter makes thespeed gather gradually.
4.2

Japanese-English SimultaneousInterpretation
16 sets of the aligned data are used for the investigation. An interpreting unit may becomea key phrase for determining at which timing
the system starts to generate the result. In order to clarify such a unit, we have analyzed thefeature of each alignment pair. Figure 6 shows
the distribution of the number of morphemesin lecturer’s utterances by the solid line. The
number of the average morphemes is 12.89, andthe range of 20 morphemes occupies 83.1% ofthe whole.
Among these, the utterance consisting of afew morphemes could be regarded as an interpreting unit. Because the system can interpret it immediately when such utterance isdetected.
We have extracted the alignment pairs inwhich lecturer’s utterances consist of four orless morphemes. There exist 231 pairs equivalent to 16.0% of the whole. The main features
are listed below: The frequency is shown in aparenthesis.
• Lecturer’s utterances consisting of a conjunction.(84 pairs)
lecturer: soshite
interpreter: Then
• Lecturer’s utterances consisting of a subject.(42 pairs)
lecturer: yuza-ga
interpreter: the user,• Lecturer’s utterances to be interpreted asa prepositional phrase.(65 pairs)
lecturer: koubunkaiseki-dewa
interpreter: in syntactic parsing,
Next, we have examined the diﬀerence between the beginning time of the interpreter’sutterance and that of the lecturer’s utterance.

frequency
140

J-E interpretation
E-J interpretation

120
100

80
60

40
2000

5

10

15

20

2530

35

40

4550

the number of mophemes of speaker’s utterances

Figure 6: Distribution of the length of the lecturer’s utterance
If lecturer’s utterance can be interpreted bysmall diﬀerence, it is expected that an appropriate reason exists and therefore it may beable to be used as a technique for starting to
make an interpretation at an early timing. The
solid line of Figure 7 shows a distribution of
the diﬀerence between the beginning time of
the interpreter’s utterance and that of the lecturer’s utterance. The average of the diﬀerenceof the beginning time is 4.1 seconds.
We have extracted the factors that the interpreter can follow the lecturer by picking up
30 alignment pairs of smaller diﬀerence of thebeginning time. The main features observed inthese alignment pairs are as follows:• Predicting of the next phrase by referring
the information on the slide of the lecture(6 pairs)
lecturer: haikei-desu-ga
interpreter: This slide shows the background of us.
The lecturer gives a lecture using presentation slides. By seeing this slide, the interpreter canpredict and follow the contents
which the lecturer speaks.
• Conjunction(11 pairs)
lecturer: shitagatteinterpreter: Therefore
When a lecturer generates a conjunction, it can be interpretedfrequency

4.360

J-E interpretation
E-J interpretation

504030201000246810

difference of the beginning time (s)Figure 7: Distribution of diﬀerence between
the beginning time of the interpreter’s utterance and that of the lecturer’s utterance
without waiting for the next utterance.
• Interpolating a subject(4 pairs)
lecturer: bunrui-shi-ta-tokoro
interpreter: we analyzed such patterns
A Japanese lecturer may omit asubject. At this time, an interpreter chooses the general subject “we” or “I” from the context, and generates it at an earlystage.
• Interpreting a subject(3 pairs)
lecturer: yuza-ga
interpreter: the user,
A subject appears at the beginning of a sentence in Japaneseand in English. So the subject
can be interpreted immediately.
• Insertion of a ﬁller(1 pair)

English-Japanese SimultaneousInterpretation
16 sets of the aligned English-Japanese simultaneous interpreting data are used for the investigation. Figure 6 shows the distribution of
the number of morphemes in lecturer’s utterances by the dotted line.
We have extracted the alignment pairs inwhich a lecturer’s utterance consists of four orless morphemes. There exist 170 pairs equivalent to 9.90% of the whole. As a result, thesame features of a Japanese-English interpretation were observed as follows:• Lecturer’s utterances consisting of a conjunction.(36pairs)
lecturer: For example,
interpreter: tatoeba• Lecturer’s utterances consisting of a subject.(32pairs)
lecturer: some of the machinesinterpreter: sonouchi-nokikai-noikutsuka-ga• Lecturer’sutterancesclauses.(48pairs)

ofshortlecturer: Someone once said thatinterpreter: aru hito-ga ii-mashi-ta
Next, we have examined the diﬀerence between the beginning time of the interpreter’sutterance and that of lecturer’s utterances,
The dotted line of Figure 7 shows a distribution of the diﬀerence between the beginning
time of the interpreter’s utterance and of thelecturer’s utterance. The average of diﬀerenceof the beginning time is 3.2 seconds.
The following factors can be observed fromthe investigation of 30 alignment pairs withsmall diﬀerence of the beginning time:• Interpreting a subject(7pairs)

lecturer: ijo-de owari-masu
interpreter: Ah this completes my lecture.

lecturer: I arrived in Japan
interpreter: e watashi nihon-ni tochakushi-mashi-ta-no-ga

While waiting for the next lecturer’s utterance, the interpreter
speaks a ﬁller.

A subject appears at the beginning of a sentence in Japaneseand in English. So the subject
can be interpreted immediately.

• Insertion of a ﬁller(4pairs)
lecturer: these are supporting countries.
interpreter: aa
koyu-yonakuni-gashien-wo shi-te-iru wake-de ari-masu
While waiting for the next lecturer’s utterance, the interpreter
speaks a ﬁller.
• Conjunction(4pairs)
lecturer: but after walking up and downinterpreter: e shikashi ee michi-wo
aruite iru uchi-ni
When a lecturer generates a conjunction, it can be interpreted
without waiting for the next utterance.
• An adverbial phrase and a prepositional
phrase(2pairs)
lecturer: Here in Kansai
interpreter: mm kansai-dewa
The word order of Japanese isﬂexible in comparison with thatof English.
If the adverbial
phrase and prepositional phrase
appear at the beginning of thesentence, the phrase can be interpreted immediately.
4.4 Comparison
The delay of the English-Japanese interpretations is smaller than that of the JapaneseEnglish interpretation about 1.0 seconds. The
following reasons can be considered as the factors: (1)The high simultaneity is attained byinterpreting according to the order of an appearance of an English word because the word
order of Japanese is ﬂexible in comparison withthat of English. (2)It is possible to predict thenext utterance by an interpreter’s backgroundknowledge because the topic of an English lecture was common. (3)Since a verb appears at
the end of sentences in Japanese, the sentence
structure of the interpretation in a JapaneseEnglish at an early stage.

5Conclusion

This paper has described an investigation ofsimultaneous interpreting corpus. The resultsof the investigation are as follows:

1. When a lecturer generates a conjunction,
it can be interpreted immediately without
waiting for the next lecturer’s utterance.
2. Since a subject appears at the beginningof a sentence in both Japanese and English, the subject can be interpreted immediately.
3. While waiting for the next lecturer’s utterance, the interpreter speaks a ﬁller.
4. By controlling the speaking speed basedon the quantity of the input utterance, theinterpreter reduces the diﬀerence between
the beginning time of the interpreter’s utterance and, that of the lecturer’s utterance.
These results will be available for the development of a simultaneous interpreting system.
Acknowledgement:
The collection andtranscription of the speech data have been carried out cooperatively with Inter Group Corporation. The authors with to thank specially Mr. Masafumi Yokoo for his contribution. This work is partially supported by theGrand-in-Aid for COE Research of the Ministry of Education, Science, Sports and Culture, Japan.

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