The effect of preverbal message planning on inhalation depth in narrative speech

Inhalation depth varies with upcoming utterance length, suggesting utterance-level speech motor planning. Yet upcoming syntactic and prosodic structure does not influence inhalation depth when utterance length is controlled, suggesting that the effect is independent of grammatical encoding. This study investigates whether preverbal message planning, via domain-general cognitive demands, might instead influence speech breathing in a manner consistent with the utterance length effect. Fifteen young adults narrated 4 stories each in 36-s bouts of speaking while performing either a serial recall task (cognitive load) or a control task (no load). Speech audio and breathing kinematics were recorded simultaneously. Kinematic waveform segmentation yielded over 4200 speech breathing cycles from which inhalation and exhalation depth were derived. Speech within each cycle was transcribed (= utterance); inhalations were then coded for alignment with elicitation task structure (bout onset vs. within-bout), discourse structure (episode vs. within-episode boundaries), and upcoming utterance length. Analyses validated the cognitive load manipulation before testing for effects on breathing. Linear mixed effect modeling on inhalation depth revealed that speakers took deeper breaths at narrative bout onsets than within bouts, at episode boundaries than within-episode boundaries, and before longer utterances than shorter ones. Critically, cognitive load selectively modulated these effects, amplifying the task structure effect and attenuating the utterance length effect, albeit marginally; the discourse structure effect was unmodulated by cognitive load. The findings support the hypothesis that domain-general cognitive demands influence inhalation depth; physiological arousal and learned optimization of breathing for speech are proposed as linking mechanisms.