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Using electroencephalography to investigate the neural mechanisms tesponsible for processing self versus externally generated sounds
Poster Session A, Friday, September 12, 11:00 am - 12:30 pm, Field House
Kevin Sitek1, Gabrielle Butler1, Amp Kangsumrith1, Kailyn McFarlane1, Bharath Chandrasekaran1; 1Northwestern University
When we produce sounds ourselves, the brain typically attenuates the neural response through a corollary discharge mechanism (Crapse & Sommer, 2008), allowing us to distinguish between self and external auditory inputs. Prior research has demonstrated clear evidence of suppression at the cortical level, particularly in the auditory cortex as measured by components like the N1 event-related potential (Ford et al., 2013; Sitek et al., 2013). However, it remains unclear whether earlier subcortical processing stages also implement these attenuative mechanisms. One method that has been used to study the early auditory system is the frequency-following response (FFR), an evoked electrophysiological potential that reflects the synchronized neural activity of populations of neurons throughout the auditory pathway in response to periodic acoustic stimuli. While the FFR has multiple neural generators, including auditory cortex, single-electrode scalp-recorded FFRs reflect primarily subcortical sources (Coffey et al., 2016; 2019). This measure has emerged as a powerful tool for understanding the neural encoding of sound with a non-invasive means to assess the fidelity of sound encoding in the early auditory system (Skoe & Kraus, 2010). While most FFRs are collected during passive sound presentation, it is unclear how motor-related signals during active button-pressing affect FFR fidelity. To investigate potential auditory–motor interactions early in the auditory pathway, we recorded FFRs from 32 normal-hearing adults during active (self-initiated) and passive (externally presented) listening conditions using a 170 ms ‘da’ speech syllable presented in positive and negative polarities. FFRs were recorded on a BioSemi ActiveTwo EEG system with a sampling rate 16384 Hz. Stimulus onsets were identified in the stimulus track that was recorded as a separate EEG channel. The electrode placed at Cz was referenced to linked mastoid electrodes and filtered between 65–2000 Hz. After outlier removal (> 75 µV), we averaged responses across positive and negative stimulus polarities within the active (self-initiated) and passive (externally presented) listening conditions. To compare potential differences between active and passive conditions, we conducted analyses in both the time and frequency domains. For the time domain analysis, we computed root mean square (RMS) signal-to-noise ratios (SNR) for each participant's responses. For the frequency domain analysis, we extracted spectral power in the fundamental frequency range of the stimulus (90-110 Hz). Statistical analyses revealed no significant differences between active and passive conditions in RMS SNR (t = 0.232, p = 0.817) or spectral power (t = -1.468, p = 0.147). These findings suggest that motor-induced suppression of self-generated sounds may primarily affect later stages of auditory processing rather than the early subcortical encoding reflected in the FFR. Additionally, the lack of difference between conditions demonstrates that active button pressing does not affect FFR fidelity. This has important implications for understanding auditory-motor integration in speech self-monitoring and could inform future research on clinical populations with altered auditory feedback processing.
Topic Areas: Multisensory or Sensorimotor Integration, Speech Motor Control