Exploring the Mechanisms Underlying the Phenomenon of Inner Speaking-Induced Suppression

Area of Science:

• Neuroscience
• Auditory Perception
• Cognitive Psychology

Background:

• Speaking-induced suppression (SIS) describes reduced auditory cortex activity to self-generated sounds.
• Inner SIS, where inner speech reduces auditory responses to external sounds, is hypothesized to involve corollary discharges.
• An alternative explanation for inner SIS is a priming effect due to expectation.

Purpose of the Study:

• To test if expectancy-based priming, without inner speech, can induce auditory suppression effects similar to inner SIS.
• To differentiate between corollary discharge and priming mechanisms in auditory processing during speech perception.

Main Methods:

• Participants (N=70) performed a task without inner speech.
• On each trial, an on-screen syllable (cue) preceded an audible syllable.
• Conditions varied whether the on-screen syllable matched, mismatched, or was absent compared to the audible syllable.

Main Results:

• No significant differences in auditory electrophysiological responses (N1, P2, pre-stimulus activity, gamma-band power) were found between the primed and misprimed conditions.
• Bayesian analysis confirmed a meaningful difference compared to prior inner speech studies.
• Simple cue-based priming, in the absence of inner speech, did not reproduce inner SIS effects.

Conclusions:

• Expectancy-based priming alone is insufficient to explain the inner SIS phenomenon.
• The findings support the role of corollary discharges, rather than simple priming, in mediating inner SIS.
• This research clarifies the neural mechanisms underlying the interaction between speech production and perception.