  Speech requires programming the sequence of vocal gestures that produce the
sounds of words. Here we explored the timing of this program by asking our
participants to pronounce, as quickly as possible, a sequence of
consonant-consonant-vowel (CCV) structures appearing on screen. We measured the
delay between visual presentation and voice onset. In the case of plosive
consonants, produced by sharp and well defined movements of the vocal tract, we
found that delays are positively correlated with the duration of the transition
between consonants. We then used a battery of statistical tests and
mathematical vocal models to show that delays reflect the motor planning of
CCVs and transitions are proxy indicators of the vocal effort needed to produce
them. These results support that the effort required to produce the sequence of
movements of a vocal gesture modulates the onset of the motor plan.
