When talking, speakers continuously monitor and use the auditory feedback of their own voice to control and inform speech production processes. Auditory feedback processing has been studied using perturbed auditory feedback. When speakers are provided with auditory feedback that is perturbed in real time, most of them compensate for this by opposing the feedback perturbation. For example, when speakers hear themselves at a higher pitch than intended, they would compensate by lowering their pitch. However, sometimes speakers follow the perturbation instead (i.e., raising their pitch in response to higher-than-expected pitch). Although most past studies observe some following responses, current theoretical frameworks cannot account for following responses. In addition, recent experimental work has suggested that following responses may be more common than has been assumed to date.
In the current study, we performed two experiments (N = 39 and N = 24) to investigate whether the state of the speech production system at perturbation onset may determine what type of response (opposing or following) is given. Participants vocalized while they tried to match a target pitch level. Meanwhile, the pitch in their auditory feedback was briefly (500 ms) perturbed in half of the vocalizations, increasing or decreasing pitch by 25 cents. None of the participants were aware of these manipulations. Subsequently, we analyzed the pitch contour of the participants’ vocalizations.
The results suggest that whether a perturbation-related response is opposing or following unexpected feedback depends on ongoing fluctuations of the production system: It initially responds by doing the opposite of what it was doing. In addition, the results show that all speakers show both following and opposing responses, although the distribution of response types varies across individuals.
Both the interaction with ongoing fluctuations of the speech system and the non-trivial proportion of following responses suggest that current production models are inadequate: They need to account for why responses to unexpected sensory feedback depend on the production-system’s state at the time of perturbation. More generally, the current study indicates that looking beyond the average response can lead to a more complete view on the nature of feedback processing in motor control. Future work should explore whether the direction of feedback-based control in domains outside of speech production will also be conditional on the state of the motor system at the time of the perturbation.