How do cognitive processes influence speaking? We used a novel variant of the Stroop test to measure whether cognitiveinhibition could modulate acoustic properties of speech. Participants named the color of words in three categories: 1)congruent (e.g. red written in red), 2) color-incongruent (e.g. green written in red), and 3) vowel-incongruent, withphonetic properties that partially matched the text color (e.g. rid written in red). We hypothesized that the cognitive effortof inhibiting reading in this third conditionsaying red, not ridcould affect the acoustics of the spoken response. A classicStroop effect was evident: congruent trials were faster than color-incongruent trials. Interestingly, vowel-incongruent trialsdid not show this reaction time difference, but spoken vowels from these trials were systematically biased away from thevisually-presented text. Thus, the inhibition of a competing target is manifest in an accentuation of the acoustic contrastbetween the spoken and inhibited words.

How precisely does the brain predict the sensory consequences of our actions? Efference copy is thought to reflect the predicted sensation of self-produced motor acts, such as the auditory feedback heard while speaking. Here, we use magnetoencephalographic imaging (MEG-I) in human speakers to demonstrate that efference copy prediction does not track movement variability across repetitions of the same motor task. Specifically, spoken vowels were less accurately predicted when they were less similar to a speaker's median production, even though the prediction is thought to be based on the very motor commands that generate each vowel. Auditory cortical responses to less prototypical speech productions were less suppressed, resembling responses to speech errors, and were correlated with later corrective movement, suggesting that the suppression may be functionally significant for error correction. The failure of the motor system to accurately predict less prototypical speech productions suggests that the efferent-driven suppression does not reflect a sensory prediction, but a sensory goal.

The control of vocalization is critically dependent on auditory feedback. Here, we determined the human peri-Sylvian speech network that mediates feedback control of pitch using direct cortical recordings. Subjects phonated while a real-time signal processor briefly perturbed their output pitch (speak condition). Subjects later heard the same recordings of their auditory feedback (listen condition). In posterior superior temporal gyrus, a proportion of sites had suppressed responses to normal feedback, whereas other spatially independent sites had enhanced responses to altered feedback. Behaviorally, speakers compensated for perturbations by changing their pitch. Single-trial analyses revealed that compensatory vocal changes were predicted by the magnitude of both auditory and subsequent ventral premotor responses to perturbations. Furthermore, sites whose responses to perturbation were enhanced in the speaking condition exhibited stronger correlations with behavior. This sensorimotor cortical network appears to underlie auditory feedback-based control of vocal pitch in humans.