Is the Articulatory Trajectory of Changing Syllables Important for Achieving Higher Syllable Rates Compared to Repeated Syllables?

The production of speech-like sequences composed of varying syllables has been reported to achieve higher syllable rates than the production of repeated syllables (commonly designed as sequential motion rate [SMR] and alternating motion rate [AMR] tasks, respectively). The faster rate for SMR relative to AMR sequences is explained by different interpretative hypotheses, which remain empirically unexplored. In the present study, we aimed to investigate whether the high syllable rates of SMR sequences are due to the specific sequences used in most studies that involve front-to-back articulatory movements. Syllable rates of SMR sequences composed of different articulatory trajectories (i.e., labial-alveolar-velar [/pateko/], alveolar-velar-labial [/tekopa/], and velar-labial-alveolar [/kopate/]) were compared with those of the AMR sequences /papapa/, /tetete/, and /kokoko/ in 20 participants. The results show higher syllable rates for each of the three SMR sequences as compared to AMR, suggesting that the trajectory of the articulatory movements in the sequential sequences is not the key to achieving higher syllable rates. The syllable rate advantage for SMR over AMR sequences is not explained by the articulatory trajectories included in the former task, indicating that the front-to-back movements generally included in SMR sequences (i.e., /pataka/) are not decisive in achieving a higher syllable rate.