Don't blame yourself: Conscious source monitoring modulates feedback control during speech production.

Sensory feedback plays an important role in speech motor control. One of the main sources of evidence for this is studies in which online auditory feedback is perturbed during ongoing speech. In motor control, it is therefore crucial to distinguish between sensory feedback and externally generated sensory events. This is called source monitoring. Previous altered feedback studies have taken non-conscious source monitoring for granted, as automatic responses to altered sensory feedback imply that the feedback changes are processed as self-caused. However, the role of conscious source monitoring is unclear. The current study investigated whether conscious source monitoring modulates responses to unexpected pitch changes in auditory feedback. During the first block, some participants spontaneously attributed the pitch shifts to themselves (self-blamers) while others attributed them to an external source (other-blamers). Before Block 2, all participants were informed that the pitch shifts were experimentally induced. The self-blamers then showed a reduction in response magnitude in Block 2 compared with Block 1, while the other-blamers did not. This suggests that conscious source monitoring modulates responses to altered auditory feedback, such that consciously ascribing feedback to oneself leads to larger compensation responses. These results can be accounted for within the dominant comparator framework, where conscious source monitoring could modulate the gain on sensory feedback. Alternatively, the results can be naturally explained from an inferential framework, where conscious knowledge may bias the priors in a Bayesian process to determine the most likely source of a sensory event.

Towards a somatosensory theory of speech perception.

Speech perception is known to be a multimodal process, relying not only on auditory input but also on the visual system and possibly on the motor system as well. To date there has been little work on the potential involvement of the somatosensory system in speech perception. In the present review, we identify the somatosensory system as another contributor to speech perception. First, we argue that evidence in favor of a motor contribution to speech perception can just as easily be interpreted as showing somatosensory involvement. Second, physiological and neuroanatomical evidence for auditory-somatosensory interactions across the auditory hierarchy indicates the availability of a neural infrastructure that supports somatosensory involvement in auditory processing in general. Third, there is accumulating evidence for somatosensory involvement in the context of speech specifically. In particular, tactile stimulation modifies speech perception, and speech auditory input elicits activity in somatosensory cortical areas. Moreover, speech sounds can be decoded from activity in somatosensory cortex; lesions to this region affect perception, and vowels can be identified based on somatic input alone. We suggest that the somatosensory involvement in speech perception derives from the somatosensory-auditory pairing that occurs during speech production and learning. By bringing together findings from a set of studies that have not been previously linked, the present article identifies the somatosensory system as a presently unrecognized contributor to speech perception.

Drifting pitch awareness after exposure to altered auditory feedback.

Various studies have claimed that the sense of agency is based on a comparison between an internal estimate of an action's outcome and sensory feedback. With respect to speech, this presumes that speakers have a stable prearticulatory representation of their own speech. However, recent research suggests that the sense of agency is flexible and thus in some contexts we may feel like we produced speech that was not actually produced by us. The current study tested whether the estimated pitch of one's articulation (termed pitch awareness) is affected by manipulated auditory feedback. In four experiments, 56 participants produced isolated vowels while being exposed to pitch-shifted auditory feedback. After every vocalization, participants indicated whether they thought the feedback was higher or lower than their actual production. After exposure to a block of high-pitched auditory feedback (+500 cents pitch shift), participants were more likely to label subsequent auditory feedback as "lower than my actual production," suggesting that prolonged exposure to high-pitched auditory feedback led to a drift in participants' pitch awareness. The opposite pattern was found after exposure to a constant -500 cents pitch shift. This suggests that pitch awareness is not solely based on a prearticulatory representation of intended speech or on a sensory prediction, but also on sensory feedback. We propose that this drift in pitch awareness could be indicative of a sense of agency over the pitch-shifted auditory feedback in the exposure block. If so, this suggests that the sense of agency over vocal output is flexible.

Speaking with an alien voice: Flexible sense of agency during vocal production.

Speakers monitor auditory feedback during speech production in order to correct for speech errors. The comparator model proposes that this process is supported by comparing sensory feedback to internal predictions of the sensory consequences of articulation. Additionally, this comparison process is proposed to support the sense of agency over vocal output. The current study tests this hypothesis by asking whether mismatching auditory feedback leads to a decrease in the sense of agency as measured by speakers' responses to pitch-shifted feedback. Participants vocalized while auditory feedback was unexpectedly and briefly pitch-shifted. In addition, in one block, the entire vocalization's pitch was baseline-shifted ("alien voice"), while it was not in the other block ("normal voice"). Participants compensated for the pitch shifts even in the alien voice condition, suggesting that agency was flexible. This is problematic for the classic comparator model, where a mismatching feedback would lead to a loss of agency. Alternative models are discussed in light of these findings, including an adapted comparator model and the inferential account, which suggests that agency is inferred from the joint contribution of several multisensory sources of evidence. Together, these findings suggest that internal representations of one's own voice are more flexible than often assumed. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Consistency influences altered auditory feedback processing.

Previous research on the effect of perturbed auditory feedback in speech production has focused on two types of responses. In the short term, speakers generate compensatory motor commands in response to unexpected perturbations. In the longer term, speakers adapt feedforward motor programmes in response to feedback perturbations, to avoid future errors. The current study investigated the relation between these two types of responses to altered auditory feedback. Specifically, it was hypothesised that consistency in previous feedback perturbations would influence whether speakers adapt their feedforward motor programmes. In an altered auditory feedback paradigm, formant perturbations were applied either across all trials (the consistent condition) or only to some trials, whereas the others remained unperturbed (the inconsistent condition). The results showed that speakers' responses were affected by feedback consistency, with stronger speech changes in the consistent condition compared with the inconsistent condition. Current models of speech-motor control can explain this consistency effect. However, the data also suggest that compensation and adaptation are distinct processes, which are not in line with all current models.

Does passive sound attenuation affect responses to pitch-shifted auditory feedback?

The role of auditory feedback in vocal production has mainly been investigated by altered auditory feedback (AAF) in real time. In response, speakers compensate by shifting their speech output in the opposite direction. Current theory suggests this is caused by a mismatch between expected and observed feedback. A methodological issue is the difficulty to fully isolate the speaker's hearing so that only AAF is presented to their ears. As a result, participants may be presented with two simultaneous signals. If this is true, an alternative explanation is that responses to AAF depend on the contrast between the manipulated and the non-manipulated feedback. This hypothesis was tested by varying the passive sound attenuation (PSA). Participants vocalized while auditory feedback was unexpectedly pitch shifted. The feedback was played through three pairs of headphones with varying amounts of PSA. The participants' responses were not affected by the different levels of PSA. This suggests that across all three headphones, PSA is either good enough to make the manipulated feedback dominant, or differences in PSA are too small to affect the contribution of non-manipulated feedback. Overall, the results suggest that it is important to realize that non-manipulated auditory feedback could affect responses to AAF.

Opposing and following responses in sensorimotor speech control: Why responses go both ways.

When talking, speakers continuously monitor and use the auditory feedback of their own voice to control and inform speech production processes. When speakers are provided with auditory feedback that is perturbed in real time, most of them compensate for this by opposing the feedback perturbation. But some responses follow the perturbation. In the present study, we investigated whether the state of the speech production system at perturbation onset may determine what type of response (opposing or following) is made. The results suggest that whether a perturbation-related response is opposing or following depends on ongoing fluctuations of the production system: The system initially responds by doing the opposite of what it was doing. This effect and the nontrivial 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.

Self-monitoring in the cerebral cortex: Neural responses to small pitch shifts in auditory feedback during speech production.

Speaking is a complex motor skill which requires near instantaneous integration of sensory and motor-related information. Current theory hypothesizes a complex interplay between motor and auditory processes during speech production, involving the online comparison of the speech output with an internally generated forward model. To examine the neural correlates of this intricate interplay between sensory and motor processes, the current study uses altered auditory feedback (AAF) in combination with magnetoencephalography (MEG). Participants vocalized the vowel/e/and heard auditory feedback that was temporarily pitch-shifted by only 25 cents, while neural activity was recorded with MEG. As a control condition, participants also heard the recordings of the same auditory feedback that they heard in the first half of the experiment, now without vocalizing. The participants were not aware of any perturbation of the auditory feedback. We found auditory cortical areas responded more strongly to the pitch shifts during vocalization. In addition, auditory feedback perturbation resulted in spectral power increases in the θ and lower ß bands, predominantly in sensorimotor areas. These results are in line with current models of speech production, suggesting auditory cortical areas are involved in an active comparison between a forward model's prediction and the actual sensory input. Subsequently, these areas interact with motor areas to generate a motor response. Furthermore, the results suggest that θ and ß power increases support auditory-motor interaction, motor error detection and/or sensory prediction processing.

Individual variability as a window on production-perception interactions in speech motor control.

An important part of understanding speech motor control consists of capturing the interaction between speech production and speech perception. This study tests a prediction of theoretical frameworks that have tried to account for these interactions: If speech production targets are specified in auditory terms, individuals with better auditory acuity should have more precise speech targets, evidenced by decreased within-phoneme variability and increased between-phoneme distance. A study was carried out consisting of perception and production tasks in counterbalanced order. Auditory acuity was assessed using an adaptive speech discrimination task, while production variability was determined using a pseudo-word reading task. Analyses of the production data were carried out to quantify average within-phoneme variability, as well as average between-phoneme contrasts. Results show that individuals not only vary in their production and perceptual abilities, but that better discriminators have more distinctive vowel production targets-that is, targets with less within-phoneme variability and greater between-phoneme distances-confirming the initial hypothesis. This association between speech production and perception did not depend on local phoneme density in vowel space. This study suggests that better auditory acuity leads to more precise speech production targets, which may be a consequence of auditory feedback affecting speech production over time.

Modulations of the auditory M100 in an imitation task.

Models of speech production explain event-related suppression of the auditory cortical response as reflecting a comparison between auditory predictions and feedback. The present MEG study was designed to test two predictions from this framework: (1) whether the reduced auditory response varies as a function of the mismatch between prediction and feedback; (2) whether individual variation in this response is predictive of speech-motor adaptation. Participants alternated between online imitation and listening tasks. In the imitation task, participants began each trial producing the same vowel (/e/) and subsequently listened to and imitated auditorily-presented vowels varying in acoustic distance from /e/. Results replicated suppression, with a smaller M100 during speaking than listening. Although we did not find unequivocal support for the first prediction, participants with less M100 suppression were better at the imitation task. These results are consistent with the enhancement of M100 serving as an error signal to drive subsequent speech-motor adaptation.