Vowel Space Expansion Sensorimotor Adaptation

The overall study (Establishing the clinical utility of sensorimotor adaptation for speech rehabilitation) aims to understand how cognitive, perceptual, and motor processes are integrated in the control of speech movements. The investigators study how this complex skill is performed in healthy speakers to understand how this system functions, how this skill relates to the perception of speech, and what role different parts of the brain play in this process. Different studies look at how speech motor control is executed, maintained, and changed. Overall, the study will recruit 329 participants over the course of 5 years. Participants can expect to be on study for up to 4 weeks.

The entire study is composed of 8 experiments and 6 interventions. The present record represents Experiments 1-4: 1) Generalization of Vowel Space Expansion to Untrained Words and Vowels; 2) Retention of Vowel Space Expansion After Training in Multiple Sessions; 3) Vowel Space Expansion Training With Connected Speech, and 4)The Relationship Between Acuity, Variability, and Adaptation in Vowels. The paradigms in Experiments 1-3 all involve speech production under conditions of altered auditory feedback, while Experiment 4 is a correlative analysis that compares data from Experiments 1 and 2.

The Experiment 1 paradigm tests how the vowel space expansion induced by sensorimotor adaptation generalizes to untrained items in a single session. Participants will produce four training words (bead, bad, bod, and booed) under a vowel centralization feedback paradigm in which auditory feedback is altered, training them to produce these words with more vowel contrast. In addition to these trained words, eight test items will be produced in pre-training and post-training phases only. We will compare to measure how learning transfers across words that share the same vowel (test words: keep, cap, cop, coop) or whose vowels are intermediate to those of the trained words and which share consonants with the trained words (test words: bid, bud, bade, bode).

The Experiment 2 paradigm tests how the vowel space expansion induced by sensorimotor adaptation is retained over time. Participants will complete eight sessions of the vowel centralization sensorimotor adaptation paradigm over four weeks, producing four training words (bead, bad, bod, and booed) under conditions of altered auditory feedback that train them to produce these words with more vowel contrast. We will measure changes in produced vowels at the start of each session in a baseline phase to assess how much retained across days and weeks.

The Experiment 3 paradigm tests whether vowel space expansion can be evoked by a vowel centralization feedback paradigm applied to running speech (full sentences) rather than single words in healthy speakers. Participants will produce sentences from the Harvard corpus while their speech feedback is altered to centralize vowel feedback. The investigators will measure how working vowel space increases under this paradigm.

Experiment 4 is a correlative analysis which tests whether sensory acuity and speech production variability can predict magnitude of sensorimotor adaptation in interventions 1 and 2. Auditory acuity will be measured through a phoneme discrimination task in which vowel sounds are played to participants over headphones; somatosensory acuity will be measured through a tactile discrimination task in which participants report the orientation (horizontal or vertical) of the gratings on a plastic dome pressed lightly into the tongue. Speech production variability will be measured as the formant variability in the baseline phase of the sensorimotor adaptation experiments in interventions 1 and 2. These measures will be correlated with sensorimotor adaptation magnitude found in the prior interventions.