Preliminary Investigation of a New Concept of Velar Activity During Speech

Abstract

Among the reported results of investigations of the velopharyngeal mechanism are observations that the velum assumes a variety of positions during speech. For example, it has been consistently observed (6', 7', 10, 13, 18) that velar elevation varies with tongue height, being greater on high vowels than on low vowels. In addition, it has been reported that on nasal consonants the velum does not descend completely but assumes a position which is intermediate between rest and complete closure (5, 13). A number of possible explanations for observed variations in velar position during speech might be considered. First, it is possible that the different p0sitions reflect changes in the muscular forces applied to this structure. The speaker may 'adjust' such forces in relation to the speech unit being produced, possibly in relation to the degree of velopharyngeal closure required for a particular unit. For example, high vowels may exhibit greater elevation because a small degree of velopharyngeal opening affects the quality of high vowels more extensively than the quality of low vowels (9). The labeling of the intermediate velar position on nasal consonants as the ready position (5, 13) also implies an adjustment by the speaker: the velum presumably is held ready by muscle activity in anticipation of rising on the subsequent non-nasal sound. Recent studies by Lindblom (11) and by Stevens and House (17) suggest another explanation for variations in velar positions. They propose that the variations in articulatory positions which are observed for productions of the same speech unit in different contexts do not necessarily imply similar variations in activity at higher physiological levels. For example, the neural control signals and/or the muscular forces applied to the artic— ulatory structure may be invariant in magnitude and pattern for all occur— rences of a particular speech unit. At the articulatory level, however, the position assumed by the structure may vary, due to the mechanical con-Dr.