Economy of effort in different speaking conditions. II. Kinematic performance spaces for cyclical and speech movements.

This study was designed to test the hypothesis that the kinematic manipulations used by speakers in different speaking conditions are influenced by kinematic performance limits. A range of kinematic parameter values was elicited by having seven subjects produce cyclical CV movements of lips, tongue blade and tongue dorsum (/ba/, /da/, /ga/), at rates ranging from 1 to 6 Hz. The resulting measures were used to establish speaker- and articulator-specific kinematic performance spaces, defined by movement duration, displacement and peak speed. These data were compared with speech movement data produced by the subjects in several different speaking conditions in the companion study (Perkell et al., 2002). The amount of overlap of the speech data and cyclical data varied across speakers, from almost no overlap to complete overlap. Generally, for a given movement duration, speech movements were larger than cyclical movements, indicating that the speech movements were faster and were produced with greater effort, according to the performance space analysis. It was hypothesized that the cyclical movements of the tongue and lips were slower than the speech movements because they were more constrained by (coupled to) the relatively massive mandible. To test this hypothesis, a comparison was made of cyclical movements in maxillary versus mandibular frames of reference. The results indicate that the cyclical movements were not strongly constrained by mandible movements. The overall results generally indicate that the cyclical task did not succeed in defining the upper limits of kinematic performance spaces within which the speech data were confined. Thus, the hypothesis that performance limits influence speech kinematics could not be tested effectively. The differences between the speech and cyclical movements may be due to other factors, such as differences in speakers' "skill" with the two types of movement, or the size of the movements--the speech movements were larger, probably because of a well-defined target for the primary, stressed vowel.