Cortical processes of speech illusions in the general population

Abstract

BackgroundThere is evidence that experimentally elicited auditory illusions in the general population index risk for psychotic symptoms. As little is known about underlying cortical mechanisms of auditory illusions, an experiment was conducted to analyze processing of auditory illusions in a general population sample. In a follow-up design with two measurement moments (baseline and 6 months), participants (n = 83) underwent the White Noise task under simultaneous recording with a 14-lead EEG. An auditory illusion was defined as hearing any speech in a sound fragment containing white noise.ResultsA total number of 256 speech illusions (SI) were observed over the two measurements, with a high degree of stability of SI over time. There were 7 main effects of speech illusion on the EEG alpha band—the most significant indicating a decrease in activity at T3 (t = −4.05). Other EEG frequency bands (slow beta, fast beta, gamma, delta, theta) showed no significant associations with SI.ConclusionSIs are characterized by reduced alpha activity in non-clinical populations. Given the association of SIs with psychosis, follow-up research is required to examine the possibility of reduced alpha activity mediating SIs in high risk and symptomatic populations.

Similar EEG Activity Patterns During Experimentally-Induced Auditory Illusions and Veridical Perceptions

“…Alpha power modulations in association with certain forms of task-elicited illusions in different sensory modalities have been observed in previous studies ( Lange et al, 2014 ; Leske et al, 2014 ; Schepers et al, 2016 ). Additionally, studies mainly in the visual domain demonstrated that reduced prestimulus alpha power increases the likelihood of perceiving an illusory visual stimulus, however, it has been proposed that alpha has a more general effect on perceptual decisions across sensory modalities by modulating the neural excitability and therefore the sensory bias (rather than sensitivity) ( Samaha et al, 2020 ).…”

“…Pre-stimulus alpha and to a lesser extent beta frequency bands have been implicated in the formation of illusions in previous studies, therefore, we also examined the ERSP for alpha and beta frequency bands ( Lange et al, 2014 ; Leske et al, 2014 ; Schepers et al, 2016 ). The ERSPs in the 7–30 Hz frequency range were calculated and the spectral power values in the activation vs. baseline intervals were statistically compared.…”

“…In previous studies, different experimental paradigms have been utilized to induce different forms of auditory illusions, however, the number of studies investigating the neural correlates of speech in noise auditory illusions are relatively sparse ( Schepers et al, 2016 ). The goal of our experiment was to induce task-elicited auditory illusions in our group of participants in order to study their corresponding neural underpinnings.…”

“…Alpha oscillations have been shown to play an important role in the formation of illusions in different sensory modalities including auditory domain (for a review see Lange et al, 2014 ). Reduced alpha power has been found during experimentally-induced auditory illusions, most prominently over temporal regions in a speech in noise signal detection task ( Schepers et al, 2016 ). A relative increase in upper alpha power with respect to baseline was observed during the Zwicker tone illusion along with a linearly decreasing alpha power trend with increasing levels of perceived loudness of the tone ( Leske et al, 2014 ).…”