Complexity of vocal tract shaping in glossectomy patients and typical speakers: A principal component analysis

Abstract

The glossectomy procedure, involving surgical resection of cancerous lingual tissue, has long been observed to affect speech production. This study aims to quantitatively index and compare complexity of vocal tract shaping due to lingual movement in individuals who have undergone glossectomy and typical speakers using real-time magnetic resonance imaging data and Principal Component Analysis. The data reveal that (i) the type of glossectomy undergone largely predicts the patterns in vocal tract shaping observed, (ii) gross forward and backward motion of the tongue body accounts for more change in vocal tract shaping than do subtler movements of the tongue (e.g., tongue tip constrictions) in patient data, and (iii) fewer vocal tract shaping components are required to account for the patients' speech data than typical speech data, suggesting that the patient data at hand exhibit less complex vocal tract shaping in the midsagittal plane than do the data from the typical speakers observed.

FIG. 1.

Real-time MRI images of participants at rest. Top: Typical speakers FT1 and MT1, patient F1 (base of tongue extending into oral tongue), patient M1 (oral tongue). Bottom: patient M2 (base of tongue), patient M3 (base of tongue), patient M4 (base of tongue), patient M5 (unilateral oral and base of tongue). Arrows indicate loci of resection and reconstruction.

FIG. 2.

(Color online) White circles: Manually selected, speaker-specific, labial, palatal, and laryngeal landmarks used to identify vocal tract midline. Yellow: Vocal tract midline used to determine orientation of gridlines.

FIG. 3.

(Color online) Vocal tract cross-distance gridlines, within which air-tissue boundaries are detected based on intensity thresholds, and vocal tract cross-distance measures are calculated.

FIG. 4.

Percentage of variance accounted for by principal components in typical speakers.

FIG. 5.

Percent of variance accounted for by first three principal components in all participants. Overall, patients exhibit higher percentages of variance accounted for by first component and lower percentages of variance accounted for by second and third components than do typical speakers.

FIG. 6.

(Color online) Scaled loadings of principal components 1, 2, and 3 for all speakers. Across speakers, PC 1 values reflect movement in the palatal and pharyngeal regions. PC 2 reflects movement in the velar region for typical speakers FT1 and MT1, and patient M5, movement in both the alveolar/alveopalatal and velar regions for patients M2, M3, and M4, movement in anterior palatal and lower pharyngeal and laryngeal regions with overall low amplitude for patient M1 and does not reflect localized movement at particular regions within the vocal tract for patient F1. PC3 reflects movement in the alveolar/alveopalatal region for typical speakers MT1 and FT1, and patient M5, movement in the alveolar/alveopalatal and pharyngeal regions for patients F1, M2, M3, and M4, and do not reflect localized movement at particular regions within the vocal tract for patient M1.

FIG. 6.

(Color online) Scaled loadings of principal components 1, 2, and 3 for all speakers. Across speakers, PC 1 values reflect movement in the palatal and pharyngeal regions. PC 2 reflects movement in the velar region for typical speakers FT1 and MT1, and patient M5, movement in both the alveolar/alveopalatal and velar regions for patients M2, M3, and M4, movement in anterior palatal and lower pharyngeal and laryngeal regions with overall low amplitude for patient M1 and does not reflect localized movement at particular regions within the vocal tract for patient F1. PC3 reflects movement in the alveolar/alveopalatal region for typical speakers MT1 and FT1, and patient M5, movement in the alveolar/alveopalatal and pharyngeal regions for patients F1, M2, M3, and M4, and do not reflect localized movement at particular regions within the vocal tract for patient M1.