Temporally structured motor and auditory representations in covert syllable production

Abstract

Inner speaking—the deliberate generation of speech through covert production mechanisms—is a common human experience. Current accounts propose that it engages sensorimotor processes similar to those underlying overt speech. Here, we asked whether motor and auditory representations during inner speaking maintain the granularity and temporal structure observed in overt speech. Using magnetoencephalography and time-resolved decoding, we examined neural dynamics across two experiments. Participants covertly produced consonant–vowel syllables designed to emphasize either articulatory or acoustic phonetic components through contrasts in the consonants or vowels, respectively. Across experiments, neural activity closely paralleled stages for overt speech. Consonants (articulatory contrasts) were more strongly decoded from speech motor cortex before the expected syllable onset, whereas vowels (acoustic contrasts) were more strongly decoded from auditory cortex immediately afterward, consistent with the onset of internally generated percepts. Vowel discriminability in auditory regions was further graded according to separation along a perceptually relevant acoustic dimension in formant space approximated by the F2–F1 projection, indicating specificity in auditory representations. These findings reveal temporally structured, phoneme-level content-specific sensorimotor representations during inner speaking, consistent with production-based accounts involving internal forward models.