Vertical larynx actions and intergestural timing stability in Hausa ejectives and implosives

Abstract

The current project undertakes a kinematic examination of vertical larynx actions and intergestural timing stability within multi-gesture complex segments such as ejectives and implosives that may possess specific temporal goals critical to their articulatory realization. Using real-time MRI (rtMRI) speech production data from Hausa non-pulmonic and pulmonic consonants, this study illuminates speech timing between oral constriction and vertical larynx actions within segments and the role this intergestural timing plays in realizing phonological contrasts and processes in varying prosodic contexts. Results suggest that vertical larynx actions have greater magnitude in the production of ejectives compared to their pulmonic counterparts, but implosives and pulmonic consonants are differentiated not by vertical larynx magnitude but by the intergestural timing patterns between their oral and vertical larynx gestures. Moreover, intergestural timing stability/variability between oral and non-oral (vertical larynx) actions differ among ejectives, implosives, and pulmonic consonants, with ejectives having the most stable temporal lags, followed by implosives and pulmonic consonants, respectively. Lastly, the findings show how contrastive linguistic 'molecules' - here, segment-sized phonological complexes with multiple gestures - interact with phrasal context in speech in such a way that it variably shapes temporal organization between participating gestures as well as respecting stability in relative timing between such gestures comprising a segment.

Keywords: non-pulmonic consonant production; real-time MRI; speech timing; timing stability.

Figure 1:

Coupling schema for (a) ejectives, (b) implosives, and (c) voiced plosives.

Figure 2:

Vocal tract mid-sagittal images of three subjects (S1, S2, and S3, respectively).

Figure 3:

Vocal tract mid-line from automatic calculation (left) & ROI overlayed image (images taken from S3; right: image of a speaker producing a vowel /ɑ/, with regions of interest [LABIAL in yellow, CORONAL in pink, and DORSAL in green from left to right]).

Figure 4:

ROI-overlayed images of a speaker producing /b/ (LAB), /d/ (COR), and /k/ (DOR) from left to right (images taken from S3).

Figure 5:

Pre-processing steps for automatic centroid tracking: (a) manually select the rectangular VTR for larynx, (b) select seed to capture only the larynx object, (c) get intensity-weighted centroids based on pixel intensity of three connected components (CC) inside the VTR. The closet centroid from the seed is chosen as the first centroid for larynx (Oh and Lee 2018; images adapted from Oh and Lee 2018).

Figure 6:

The centroid tracking output of the production of a VCV sequence /ɑɠɑ/.

Figure 7:

Temporal landmarks of a schematic gesture (based on pixel intensity for oral [labial, coronal, & dorsal] gestures [cf. 2.4.1] & centroid position for LX gestures [cf. 2.4.2]). The landmarks are defined by velocity thresholds of the gestural movement.

Figure 8:

Larynx raising displacement (left) and larynx extremum (right). (The lower and upper box hinges correspond to the first and the third quartiles [i.e., the inter-quartile range, or IQR], the whiskers extend to the smallest and the largest value within the 1.5 × IQR, and the notches extend 1.58 × IQR/sqrt[n].).

Figure 9:

Larynx raising displacement (left) & extremum (right) for individual speakers.

Figure 10:

Larynx raising displacement (left) & extremum (right) in ejective stops and fricatives.

Figure 11:

Larynx lowering displacement (left) & larynx extremum (right). (See Figure 8 for other details).

Figure 12:

Larynx lowering displacement (left) & extremum (right) for individual speakers.

Figure 13:

Larynx displacement (left) & larynx extremum (right) for individual speakers.

Figure 14:

Sample trajectories for voiced implosives (left) and voiced plosives (right). The boxes in the bottom represent the movement onset to the offset of the LX and the oral LAB gestures. Vertical lines are drawn as reference lines marking the onset of the LX gesture (cf. Figure 7 for temporal landmarks).

Figure 15:

Histogram and distribution of onset lags for ejectives, implosives, and pulmonic consonants (dashed lines indicate median).

Figure 16:

Density distribution for onset lags in pulmonic consonants, ejectives, and implosives (dashed lines indicate median).

Figure 17:

Density distribution for oral target to vertical larynx onset lags in pulmonic consonants, ejectives, and implosives (dashed lines indicate median).

Figure 18:

Correlation graphs for intergestural timing and LX duration (left: onset lags & LX duration; right: LX onset to oral target lags & LX duration).