Speakers with cerebellar ataxia do not adapt duration of speech segments

Sensorimotor adaptation (motor learning) is crucial to maintain movement accuracy. This is particularly true for temporal control, as duration and initiation timing are perceived only after the movement, and thus cannot benefit from mid-movement adjustments. The cerebellum is critical for both sensorimotor adaptation and various temporal functions, but its role in temporal adaptation has not been investigated. In this study, we examine the effect of cerebellar damage on temporal adaptation in speech, a natural but complex task that requires millisecond precision. We use an altered auditory feedback paradigm to extend the perceived duration of the vowel /ɛ/ in the word “best”. Neurobiologically healthy controls adaptively shorten their vowels, but temporal adaptation is abolished in speakers with cerebellar damage, who instead lengthen their vowels in response to the lengthening perturbation. This departs from findings in the spatial domain, where cerebellar damage merely reduces sensorimotor adaptation. We also found that perceptual deficits did not drive the lack of adaptation, even though speakers with cerebellar damage as a group have lower perceptual acuity for speech segment durations than controls. We suggest that temporal adaptation in speech is abolished due to cerebellar involvement in three aspects of temporal control: duration representation, temporal coordination, and temporal estimation. As speech motor control is highly complex, future research is needed to determine if the lack of adaptation observed in this study is due to combined demands on multiple cerebellar functions, or critical damage to a single temporal function that is common to all temporal control.