Downstep and high tone raising: interacting factors in Yoruba tone production

This study examines interacting factors in tone production in Yoruba, a tone language with three tone levels, H (high), M (mid), and L (low). Its primary goals are to confirm the existence of downstep, a principle which causes successive H tones separated by L tones to step down in pitch, and to examine the interaction between downstep and H tone raising, a principle which raises H tones to extra-high values before L tones. Controlled comparisons of data from four speakers reveal that both of these principles apply to H tones satisfying their conditions. As a result of H raising, the first H tone in downstepping sequences of the form HLHLH... is raised well above its expected value, while following downstepped H tones are kept from descending into the frequency band reserved for M tones. This study also examines the strategies used for economizing pitch space in longer downstepping sequences. The main strategy used by all speakers is H tone resetting; however, some speakers are also found to raise initial H tones to extra-high values in anticipation of downsteps occurring four syllables away. Other interacting factors in Yoruba tone production include tone-specific declination ("downdrift") operating in the background and local carryover assimilation from a H tone to a following L tone. These various observations support a compo¬sitional model of tone production in which competing factors culminate on individual tones to produce functionally-motivated "compromise" f0 patterns.