Parkinson, A. L., Korzyukov, O., Larson, C. R., Litvak, V., & Robin, D. A. (2013). Modulation of effective connectivity during vocalization with perturbed auditory feedback. Neuropsychologia51(8), 1471-1480.

The integration of auditory feedback with vocal motor output is important for the control of voice fundamental frequency (F0). We used a pitch-shift paradigm where subjects respond to an alteration, or shift, of voice pitch auditory feedback with a reflexive change in F0. We presented varying magnitudes of pitch shifted auditory feedback to subjects during vocalization and passive listening and measured event related potentials (ERPs) to the feedback shifts. Shifts were delivered at +100 and +400 cents (200 ms duration). The ERP data were modeled with dynamic causal modeling (DCM) techniques where the effective connectivity between the superior temporal gyrus (STG), inferior frontal gyrus and premotor areas were tested. We compared three main factors: the effect of intrinsic STG connectivity, STG modulation across hemispheres and the specific effect of hemisphere. A Bayesian model selection procedure was used to make inference about model families. Results suggest that both intrinsic STG and left to right STG connections are important in the identification of self-voice error and sensory motor integration. We identified differences in left-to-right STG connections between 100 cent and 400 cent shift conditions suggesting that self- and non-self-voice error are processed differently in the left and right hemisphere. These results also highlight the potential of DCM modeling of ERP responses to characterize specific network properties of forward models of voice control.

 

Behroozmand, R., Korzyukov, O., & Larson, C. R. (2012). ERP correlates of pitch error detection in complex tone and voice auditory feedback with missing fundamental. Brain research1448, 89-100.

 The integration of auditory feedback with vocal motor output is important for the control of voice fundamental frequency (F0). We used a pitch-shift paradigm where subjects respond to an alteration, or shift, of voice pitch auditory feedback with a reflexive change in F0. We presented varying magnitudes of pitch shifted auditory feedback to subjects during vocalization and passive listening and measured event related potentials (ERP’s) to the feedback shifts. Shifts were delivered at +100 and +400 cents (200 ms duration). The ERP data were modeled with Dynamic Causal Modeling (DCM) techniques where the effective connectivity between the superior temporal gyrus (STG), inferior frontal gyrus and premotor areas were tested. We compared three main factors; the effect of intrinsic STG connectivity, STG modulation across hemispheres and the specific effect of hemisphere. A Bayesian model selection procedure was used to make inference about model families. Results suggest that both intrinsic STG and left to right STG connections are important in the identification of self-voice error and sensory motor integration. We identified differences in left to right STG connections between 100 cent and 400 cent shift conditions suggesting that self and non-self voice error are processed differently in the left and right hemisphere. These results also highlight the potential of DCM modeling of ERP responses to characterize specific network properties of forward models of voice control.

 

Liu, H., Wang, E. Q., Metman, L. V., & Larson, C. R. (2012). Vocal responses to perturbations in voice auditory feedback in individuals with Parkinson’s disease. PloS one7(3), e33629.

Background
One of the most common symptoms of speech deficits in individuals with Parkinson’s disease (PD) is significantly reduced vocal loudness and pitch range. The present study investigated whether abnormal vocalizations in individuals with PD are related to sensory processing of voice auditory feedback. Perturbations in loudness or pitch of voice auditory feedback are known to elicit short latency, compensatory responses in voice amplitude or fundamental frequency.

Methodology/Principle Findings
Twelve individuals with Parkinson’s disease and 13 age- and sex- matched healthy control subjects sustained a vowel sound (/ɑ/) and received unexpected, brief (200 ms) perturbations in voice loudness (±3 or 6 dB) or pitch (±100 cents) auditory feedback. Results showed that, while all subjects produced compensatory responses in their voice amplitude or fundamental frequency, individuals with PD exhibited larger response magnitudes than the control subjects. Furthermore, for loudness-shifted feedback, upward stimuli resulted in shorter response latencies than downward stimuli in the control subjects but not in individuals with PD.

Conclusions/Significance
The larger response magnitudes in individuals with PD compared with the control subjects suggest that processing of voice auditory feedback is abnormal in PD. Although the precise mechanisms of the voice feedback processing are unknown, results of this study suggest that abnormal voice control in individuals with PD may be related to dysfunctional mechanisms of error detection or correction in sensory feedback processing.

 

Behroozmand, R., Korzyukov, O., & Larson, C. R. (2011). Effects of voice harmonic complexity on ERP responses to pitch-shifted auditory feedback. Clinical Neurophysiology122(12), 2408-2417.

Objective
The present study investigated the neural mechanisms of voice pitch control for different levels of harmonic complexity in the auditory feedback.

Methods
Event-related potentials (ERPs) were recorded in response to +200 cents pitch perturbations in the auditory feedback of self-produced natural human vocalizations, complex and pure tone stimuli during active vocalization and passive listening conditions.

Results
During active vocal production, ERP amplitudes were largest in response to pitch shifts in the natural voice, moderately large for non-voice complex stimuli and smallest for the pure tones. However, during passive listening, neural responses were equally large for pitch shifts in voice and non-voice complex stimuli but still larger than that for pure tones.

Conclusions
These findings suggest that pitch change detection is facilitated for spectrally rich sounds such as natural human voice and non-voice complex stimuli compared with pure tones. Vocalization-induced increase in neural responses for voice feedback suggests that sensory processing of naturally-produced complex sounds such as human voice is enhanced by means of motor-driven mechanisms (e.g. efference copies) during vocal production.

Significance
This enhancement may enable the audio-vocal system to more effectively detect and correct for vocal errors in the feedback of natural human vocalizations to maintain an intended vocal output for speaking.

 

Greenlee, J. D., Jackson, A. W., Chen, F., Larson, C. R., Oya, H., Kawasaki, H., & Howard III, M. A. (2011). Human auditory cortical activation during self-vocalization. PloS one6(3), e14744.

During speaking, auditory feedback is used to adjust vocalizations. The brain systems mediating this integrative ability have been investigated using a wide range of experimental strategies. In this report we examined how vocalization alters speech- sound processing within auditory cortex by directly recording evoked responses to vocalizations and playback stimuli using intracranial electrodes implanted in neurosurgery patients. Several new findings resulted from these high-resolution invasive recordings in human subjects. Suppressive effects of vocalization were found to occur only within circumscribed areas of auditory cortex. In addition, at a smaller number of sites, the opposite pattern was seen; cortical responses were enhanced during vocalization. This increase in activity was reflected in high gamma power changes, but was not evident in the averaged evoked potential waveforms. These new findings support forward models for vocal control in which efference copies of premotor cortex activity modulate sub-regions of auditory cortex.

 

Behroozmand, R., & Larson, C. R. (2011). Error-dependent modulation of speech-induced auditory suppression for pitch-shifted voice feedback. BMC neuroscience12(1), 54.

Background
The motor-driven predictions about expected sensory feedback (efference copies) have been proposed to play an important role in recognition of sensory consequences of self-produced motor actions. In the auditory system, this effect was suggested to result in suppression of sensory neural responses to self-produced voices that are predicted by the efference copies during vocal production in comparison with passive listening to the playback of the identical self-vocalizations. In the present study, event-related potentials (ERPs) were recorded in response to upward pitch shift stimuli (PSS) with five different magnitudes (0, +50, +100, +200 and +400 cents) at voice onset during active vocal production and passive listening to the playback.

Results
Results indicated that the suppression of the N1 component during vocal production was largest for unaltered voice feedback (PSS: 0 cents), became smaller as the magnitude of PSS increased to 200 cents, and was almost completely eliminated in response to 400 cents stimuli.

Conclusions
Findings of the present study suggest that the brain utilizes the motor predictions (efference copies) to determine the source of incoming stimuli and maximally suppresses the auditory responses to unaltered feedback of self-vocalizations. The reduction of suppression for 50, 100 and 200 cents and its elimination for 400 cents  pitch-shifted voice auditory feedback support the idea that motor-driven suppression of voice feedback leads to distinctly different sensory neural processing of self vs. non-self vocalizations. This characteristic may enable the audio-vocal system to more effectively detect and correct for unexpected errors in the feedback of self-produced voice pitch compared with externally-generated sounds.

 

Liu, H., Meshman, M., Behroozmand, R., & Larson, C. R. (2011). Differential effects of perturbation direction and magnitude on the neural processing of voice pitch feedback. Clinical Neurophysiology122(5), 951-957.

Objective
The present study examined the neural representations of voice pitch feedback perturbations during vocalization.

Methods
N1-P2 complex event-related potentials (ERPs) were recorded from twelve right-handed speakers when they sustained a vowel phonation and their voice pitch feedback was randomly shifted ±100, ±200, and ± 500 cents with 200 ms duration.

Results
The results showed that larger pitch-shifted stimuli led to greater N1-P2 peak-to-peak magnitudes when voice pitch feedback was shifted downward. Downward stimuli generated larger auditory ERP amplitudes than upward stimuli for 200 cents and 500 cents pitch-shifted stimuli. Shorter N1 and P2 latencies were associated with larger magnitudes of pitch feedback perturbations.

Conclusion
N1-P2 complex ERPs can be used to reflect the neural processing of voice pitch feedback perturbations during vocalization as reflected by their sensitivity to the magnitude and direction of pitch-shifted stimuli.

Significance
The findings of the effects of the interaction between stimulus magnitude and stimulus direction on the N1-P2 complex suggest that neural representations of pitch feedback perturbations may be highly depended on the stimulus features.

 

Behroozmand, R., Liu, H., & Larson, C. R. (2011). Time-dependent neural processing of auditory feedback during voice pitch error detection. Journal of Cognitive Neuroscience23(5), 1205-1217.

The neural responses to sensory consequences of a self-produced motor act are suppressed compared with those in response to a similar but externally-generated stimulus. Previous studies in the somatosensory and auditory systems have shown that the motor-induced suppression of the sensory mechanisms is sensitive to delays between the motor act and the onset of the stimulus. The present study investigated time-dependent neural processing of auditory feedback in response to self-produced vocalizations. Event related potentials (ERPs) were recorded in response to normal and pitch-shifted voice auditory feedback during active vocalization and passive listening to the playback of the same vocalizations. The pitch-shifted stimulus was delivered to the subjects’ auditory feedback after a randomly chosen time delay between the vocal onset and the stimulus. Results showed the neural responses to delayed feedback perturbations were significantly larger than those in response to pitch-shifted stimulus occurring at vocal onset. Active vocalization was shown to enhance neural responsiveness to feedback alterations only for non-zero delays compared with passive listening to the playback. These findings indicated that the neural mechanisms of auditory feedback processing are sensitive to timing between the vocal motor commands and their incoming auditory feedback. Time-dependent neural processing of auditory feedback may be an important feature of the audio-vocal integration system that helps to improve the feedback-based monitoring and control of voice structure through vocal error detection and correction.

 

Liu, H., Behroozmand, R., & Larson, C. R. (2010). Enhanced neural responses to self-triggered voice pitch feedback perturbations. Neuroreport21(7), 527.

The present study investigated the effect of self-triggered voice fundamental frequency (F0) feedback perturbation on auditory event-related potentials (ERPs) during vocalization and listening. Auditory ERPs were examined in response to self- and computer-triggered -200 cents pitch-shift stimuli while subjects vocalized or listened to the playback of their self-vocalizations. The stimuli were either presented with a delay between 500-1000 ms after subjects pressed a button or delivered by a computer with an inter-stimulus interval between 500-1000 ms. Results showed that self-triggered stimuli elicited larger ERPs compared with computer-triggered stimuli during both vocalization and listening conditions. These findings suggest that self-triggered perturbation of self-vocalization auditory feedback may enhance auditory responses to voice feedback pitch perturbation during vocalization and listening.

 

Behroozmand, R., Karvelis, L., Liu, H., & Larson, C. R. (2009). Vocalization-induced enhancement of the auditory cortex responsiveness during voice F 0 feedback perturbation. Clinical neurophysiology120(7), 1303-1312.

Auditory neural responses to self-produced sounds have been shown to be suppressed during active vocalization compared to passive listening to the playback. A recent study in primates showed that the vocalization-induced suppression of auditory neurons enhances their sensitivity to feedback perturbation suggesting that the co-occurrence of vocalization and feedback perturbation onsets can elicit neural responses that reflect the simultaneous effect of two phenomena: 1) suppression due to vocalization and 2) suppression-induced enhancement of the neural responsiveness during feedback perturbation. We tested the hypothesis that self-vocalization enhances auditory responsiveness to voice pitch feedback perturbation by temporal separation of a pitch-shifted stimulus (PSS) and vocalization onset on neural responses to feedback perturbation.  We also investigated the effect of voice pitch-shifted feedback magnitude on neural responsiveness. Event related potentials (ERPs) were recorded in 15 subjects in response to +100, +200 and +500 cents pitch-shifted voice feedback during active vocalization and passive listening to the playback signal. Results revealed significantly larger P1 and P2 ERP components during vocalization than passive listening. The vocalization-induced increase in neural responsiveness was significantly larger for +100 than +500 cents pitch-shifted feedback suggesting that although auditory cortex is more responsive to voice F0 feedback perturbation during vocalization, the vocalization-induced enhancement of the neural responsiveness is greater during smaller compared with larger voice F0 feedback deviations.