Sensorimotor adaptation as a window to speech movement planning

Speaking is normally thought of as a two-part process. First, a language planning system transforms ideas, concepts, and/or words into a series of smaller units, such as syllables or speech sounds. These basic linguistic units are then thought to be “read out” into articulatory movements by a separate motor planning system.

However, this divided planning process cannot explain speech production in the real world, because it is possible to learn changes to speech movements that are dependent on language context. For example, if you move from California to Wisconsin, you may learn a new accent: you may unconsciously start saying “bag” with the vowel sound in “say” instead of the vowel sound in “sat”.

If the same change occurred in all words with this sound (“snag”, “dragon”, “agriculture”), it would suggest you learned a change to the smaller unit (“ag”). However, you might change the way you say “bag” while keeping your old pronunciation of “bagpipe”, suggesting learning that is dependent on word context. The purpose of this research is to understand when linguistic context influences learning and when it does not and to use those results to determine the span of speech motor planning in different contexts.

A more accurate characterization of speech motor planning is critical for understanding how we typically speak and how this process breaks down in neurological disorders that impair the way we plan speech movements, such as aphasia and apraxia of speech. The investigators are involved with Frontiers for Young Minds, a journal that aims to engage the next generation of scientists (kids ages 8-15) by involving them in the peer review process.

They will host live demonstrations at the yearly Wisconsin Science Festival, and will provide hands-on science experiences as a part of summer and afterschool programming for Madison-area kids.

To investigate how speech movements are planned, the investigators will use a speech learning task that causes an unconscious change to pronunciation. Participants will talk into a microphone while hearing playback of their voice with certain frequencies shifted, making one vowel sound like another (for example, “bed” could be shifted to sound like “bad”).

Over time, this causes participants to unknowingly shift their vowel pronunciation in the opposite direction. Importantly, participants can simultaneously learn to shift a single vowel sound in different ways based on the word in which it appears (for example, pronouncing “bed” and “head” differently, even though they share the same vowel sound).

This shows that the word context can differentiate planning of this vowel sound. The investigators will test other linguistic contexts that might allow participants to learn different pronunciations for the “same” speech sound, contexts such as word meaning, phrase structure, pitch or intonation, and gesturing while speaking (for example, pointing).

If this learning is possible, it suggests that these contexts are part of the movement plans for speaking, together forming a cohesive unit that can scaffold learning. The work will establish how speech motor planning integrates linguistic representation and other communicative movements such as pitch and gesture.

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