A Japanese trilogy: Segment duration, articulatory kinematics, and interarticulator programming Anders Löfqvist Haskins Laboratories New Haven, CT

Length contrast in Japanese When a speaker of Japanese produces the words “kami” and ‘kammi”, the lips are closed for about 60 ms when the consonant is short, and for about 125 ms when the consonant is long.

In producing long and short consonants, Japanese speakers thus have to close the vocal tract twice as long for a long than for a short consonant. How do they implement this at the articulatory level? Which, if any, kinematic differences occur between long and short consonants? Three issues: A. Lip movements for labial consonants. B. Tongue movements for lingual consonants. C. Interarticulator programming in long and short consonants.

Methods Native (naïve) speakers of Japanese served as subjects, with different subsets of speakers for each experiment. The linguistic material consisted of Japanese words. These words formed minimal pairs, where the only difference between the pairs was the duration of one consonant consonant, which was either long or short. Examples are /napa, nappa, /hata, hatta/, /hosa, hossa/, tagu, taggu, /kami, kammi/. Fifty tokens were recorded for each word type. Articulatory movements were recorded using a magnetometer. A simultaneous acoustic recording was also made. Receiver placements, signal processing, and measurements were tailored to the problem being addressed.

A. Lip kinematics in long and short consonants Hypothesis To make a longer oral closure, speakers change the position of a virtual target for the lower lip, so that it moves to a higher vertical postion during the oral closure. This hypothesis is based on earlier findings of lip and jaw movements in speech, showing that the lips are moving at a high velocity at the moment of oral closure, resulting in mechanical interactions between the lips. Among these are tissue compression and the lower lip moving the upper lip upward. These results are compatible with the idea of a virtual target for the lips that would require them to move beyond each other. Such a control strategy would ensure that the lips form an air tight seal irrespective of variations in the onset positions of their closing movements.

Predictions If the hypothesis that speakers vary the position of a virtual target for the lower lip to produce long and short consonants is correct, the following predictions can be made of the lip movements in long and short consonants: 1. The vertical peak position of the lower lip is higher for a long than for a short consonant. If this is true, the following additional predictions can also be made: 2. There is a positive correlation between the vertical positions of the upper and lower lips at the point in time when the lower lip reaches its highest vertical position. This follows from the previously observed mechanical interactions between the two lips with the lower lip pushing the upper lip upward. Assuming the lower lip reaching a higher vertical position for a long consonant, it would push the upper lip further upward. Hence, the upper lip vertical position at this point in time is higher for a long than for a short consonant.

3. A long consonant is produced with a larger lower lip closing displacement than a short consonant. Furthermore, this is due to a difference in the vertical end position of the lower lip and not to a difference in its starting position. 4. A long consonant is produced with a higher peak closing velocity of the lower lip. This follows from the strong correlation between movement displacement and peak velocity that has been observed in both speech and non-speech movements.

Results I. Is the peak vertical position of the lower lip higher for a long than for a short labial consonant?

Yes!

IIa. Is there a positive correlation between the upper and lower lip vertical positions at the point in time when the lower lip reaches its highest position? Yes, for labial stops and nasals but not for fricatives, which in Japanese are bilabial! IIb. Is the upper lip vertical position at this point higher for a long than for a short consonant?

Yes!

III. Is the lower lip closing displacement larger for a long than for a short consonant? Yes, and it is not due to a difference in starting position!

IV. Is the peak lower lip closing velocity higher for a long than for a short consonant? No!

Conclusion Japanese speakers do not simply vary the position of a virtual target when making a lip closure longer or shorter. What do they do? They change both the magnitude and the timing of the lover lip movement, in particular by modifying the deceleration of the lower lip to keep it in contact with the upper lip for a longer period of time.

Position They thus modulate the muscular activity of the lower lip to make it stay in a high position. This is most clearly seen in the velocity and acceleration signals.

B. Tongue kinematics in long and short consonants Hypothesis A speaker is constrained in producing lingual consonants to maintain the contact between the tongue and the palate. Thus, one can hypothesize that the speed of the tongue movement would be slower during a long than during a short consonant. In addition, the magnitude of the tongue movement will be longer during a long than during a short consonant If the duration of the oral closure for the consonant is increased, a speaker must maintain the contact between the tongue and the palate. To do this, the speaker can in principle use two strategies for controlling the tongue movement, both of which involve modulating the speed of the tongue movement.

One strategy would be to momentarily stop the tongue from moving One strategy would be to momentarily stop the tongue from moving. Alternatively, the speaker could slow down the tongue movement for the long consonant. Of these two possibilities, the second one is the most likely, since a large body of research on tongue movements in speech suggests that the tongue hardly ever stops moving during lingual consonants, with the speed and magnitude of the movement influenced by context.

Results I. Is the average speed of the tongue movement during the consonant slower for a long than for a short consonant?

Yes, for the tongue tip…

…and also for the tongue body!

II. Is the path of the tongue movement during the consonant longer for a long than for a short consonant?

Yes, mostly!

Conclusion Japanese speakers consistently reduce the speed of the tongue movement during a long compared to a short consonant. However, in no case did the tongue come to a complete stop. The path of the tongue during the consonant tends to be longer for long than for short consonants.

C. Interarticulator programming and consonant duration In producing a sequence of vowel-labial consonant-vowel, a speaker has to do two or three things: Close and open the lips for the consonant. Move the tongue from the position for the first vowel to that for the second vowel. If the consonant is voiceless, open and close the glottis If the duration of the labial consonant in such a sequence is changed, how is the tongue movement between the two vowels affected? What happens to the interarticulator programming of lip and tongue movements?

Up Down Front Back Hypothesis If the duration of the oral closure for the consonant is increased, a speaker can in principle use two strategies for the coordination of the tongue and lip movements.

1a. The onset of the tongue movement might be shifted later relative to the oral closure, so that the tongue movement reached its position for the second vowel at the same point in time for the long and short consonant. 1b. Alternatively, the onset of the tongue movement could have the same temporal relationship to the consonant closure. In this case, the interval between the offset of the tongue movement and the release of the oral closure for the labial consonant would thus increase for the long consonant. Another possibility is to shift both the onset and offset of the tongue movement.

2. Modify the tongue movement during the long consonant, so that the relative timing between the tongue movement and the lip movements for the oral closure of the consonant would be more or less the same for the long and short consonants. This would imply making a slower tongue movement trajectory for the long than for the short consonant.

Tongue movement from the first to the second vowel in the word ‘kami/

Tongue movement duration For most subjects and words, the duration of the tongue body movement from the first to the second vowel is longer in the long than in the short consonant. Duration of the of the tongue body movement from the first to the second vowel

Average speed of tongue movement Overall, the average speed of the tongue body movement from the first to the second vowel is slower for the long than for the short consonant. Average speed of the tongue body movement from the first to the second vowel

Magnitude of tongue body movement The magnitude of the path of the tongue body movement from the first to the second vowel did not vary systematically with consonant length within or across speakers. Any difference in movement paths was not related to a consistent change in movement onset or offset position. Path of the tongue body movement from the first to the second vowel.

Conclusion It was hypothesized that a speaker could use one of two possible strategies of interarticulator programming if the duration of the consonant was increased. In one of them, the tongue movement trajectory would be similar for the long and short consonants; thus, the timing between the lip and tongue movements would change. In the second one, the tongue movement would be modified for the long consonant, thus resulting in a similar, but not identical, coordination of lip and tongue movements for both the long and short consonants. The present results clearly support the second strategy. Although all subjects changed the tongue movement between the two vowels, they did not change it in such a way that its duration in the long consonant was about twice the duration of the movement for the short consonant. Thus, the duration of the tongue movement did not correlate closely with the duration of the oral closure

Acknowledgments I am grateful to Mariko Yanagawa for help with the Japanese material and running the experiments. This work was supported by Grant No. DC-00865 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.