Control of oral closure in lingual stop consonant production

Abstract

Previous work has shown that the lips are moving at a high velocity when the oral closure occurs for bilabial stop consonants, resulting in tissue compression and mechanical interactions between the lips. The present experiment recorded tongue movements in four subjects during the production of velar and alveolar stop consonants to examine kinematic events before, during, and after the stop closure. The results show that, similar to the lips, the tongue is often moving at a high velocity at the onset of closure. The tongue movements were more complex, with both horizontal and vertical components. Movement velocity at closure and release were influenced by both the preceding and the following vowel. During the period of oral closure, the tongue moved through a trajectory of usually less than 1 cm; again, the magnitude of the movement was context dependent. Overall, the tongue moved in forward-backward curved paths. The results are compatible with the idea that the tongue is free to move during the closure as long as an airtight seal is maintained. A new interpretation of the curved movement paths of the tongue in speech is also proposed. This interpretation is based on the principle of cost minimization that has been successfully applied in the study of hand movements in reaching.

FIG. 1

Acoustic and movement signals recorded during the production of the utterance “Say agu again” by subject LK. The labels in the audio signal correspond to the onset and release of the oral closure for the consonant, and the onset of the second vowel in /agu/. The vertical lines labeled V1 and V2 were defined in the speed signal of the tongue body to identify the onset and offset of the tongue movement from the first to the second vowel in /agu/. The right panel shows the receiver trajectories from the first to the second vowel and also the part of the trajectory made during the oral closure for the consonant.

FIG. 2

Plots of receiver trajectories during single productions of sequences with a voiceless velar stop /k/ for subjects LK and DR. The trajectory from the first to the second vowel is shown and also the part of the trajectory that occurred during the oral closure for the consonant.

FIG. 3

Plots of receiver trajectories during single productions of sequences with a voiceless alveolar stop /t/ for subjects LK and DR. The trajectory from the first to the second vowel is shown and also the part of the trajectory that occurred during the oral closure for the consonant.

FIG. 4

Percentile plots of tongue body curvature for the productions with a velar stop consonant shown in Fig. 2. The box encloses 90% of the data with the bottom representing 5% and the top 95% of the data. The solid line inside the box is the median value, while the lower and upper two dashed lines in the box represent 25% and 75% of the data, respectively. The numbers below each box show the median curvature for the interval. The arrows above or in each box show the change in curvature for the interval. Two or more arrows indicate several changes occurring in the order from the left to the right arrows.

FIG. 5

Percentile plots of tongue tip curvature for the productions with an alveolar stop consonant shown in Fig. 3. The box encloses 90% of the data with the bottom representing 5% and the top 95% of the data. The solid line inside the box is the median value, while the lower and upper two dashed lines in the box represent 25% and 75% of the data, respectively. The numbers below each box show the median curvature for the interval. The arrows above or in each box show the change in curvature for the interval. Two or more arrows indicate several changes occurring in the order from the left to the right arrows.

FIG. 6

Receiver positions at onset and release of oral closure for velar stops.

FIG. 7

Average tongue body velocity at the onset and offset of the oral closure in sequences where the first vowel is (a) /a/; (b) /i/; and (c) /u/.

FIG. 7

Average tongue body velocity at the onset and offset of the oral closure in sequences where the first vowel is (a) /a/; (b) /i/; and (c) /u/.

FIG. 8

Average movement path of the tongue body receiver during the period of oral closure; the error bars show the standard deviation.

FIG. 9

Receiver positions at onset and release of oral closure for alveolar stops.

FIG. 10

Average tongue tip velocity at the onset and offset of the oral closure in sequences where the first vowel is (a) /a/; (b) /i/; and (c) /u/.

FIG. 10

Average tongue tip velocity at the onset and offset of the oral closure in sequences where the first vowel is (a) /a/; (b) /i/; and (c) /u/.

FIG. 11

Average movement path of the tongue tip receiver during the period of oral closure; the error bars show the standard deviation.