Simultaneous acquisition of multiple auditory-motor transformations reveals supra-syllabic motor planning in speech production

Motor planning forms a critical bridge between psycholinguistic and motoric models of word production. While syllables are often considered the core planning unit in speech, growing evidence hints at supra-syllabic planning, but without firm empirical support. Here, we use differential adaptation to altered auditory feedback to provide novel, straightforward evidence for word-level planning. By introducing opposing perturbations to shared segmental content (e.g., raising the first vowel formant of “sev” in “seven” while lowering it in “sever”), we assess whether participants can use the larger word context to separately oppose the two perturbations. Critically, limb control research shows that such differential learning is possible only when the shared movement forms part of separate motor plans. We found differential adaptation in multisyllabic words, but of smaller size relative to monosyllabic words. These results strongly suggest speech relies on an interactive motor planning process encompassing both syllables and words.