Theta oscillations reflect conflict processing in the perception of the McGurk illusion

Abstract

The McGurk illusion is one of the most famous illustrations of cross-modal integration in human perception. It has been often used as a proxy of audiovisual (AV) integration and to infer the properties of the integration process in natural (congruent) AV conditions. Nonetheless, a blatant difference between McGurk stimuli and natural, congruent, AV speech is the conflict between the auditory and the visual information in the former. Here, we hypothesized that McGurk stimuli (and any AV incongruency) engage brain responses similar to those found in more general cases of perceptual conflict (e.g., Stroop), and propose that the McGurk illusion arises as a result of the resolution of such conflict. We used electroencephalography to measure variations in the power of theta, a well-known marker of the brain response to conflict. The results showed that perception of AV McGurk stimuli, just like AV incongruence in general, induces an increase in activity in the theta band. This response was similar to that evoked by Stroop stimuli, as measured in the same participants. This finding suggests that the McGurk illusion is mediated by general-purpose conflict mechanisms, and calls for caution in generalizing findings obtained using the McGurk illusion, to the general case of multisensory integration.

Neural Oscillations Orchestrate Multisensory Processing

“…In other words, increased theta-band power indexed perceived audiovisual incongruence. Morís Fernández and others (2017b) recently showed increased central theta-band power following the McGurk illusion, as well as incongruent audiovisual stimuli compared with congruent audiovisual stimuli. The authors argue that theta-band power is linked to a general-purpose conflict detection mechanism.…”

From cognitive control to visual incongruity: Conflict detection in surrealistic images

“…We extracted the maximum Theta peak amplitude for each participant and condition in the time window between 50 ms and 600 ms post-stimulus from the average activity from electrodes Fz, FCz and Cz. This is the typical time window used for frontal-medial Theta analysis in the typical laboratory protocol [27][28][29] and it minimizes possible evoked effects due to image onset (< 50 ms). We then calculated the average amplitude within an 80 ms window centered on the peak (from -40 to +40 ms) for each participant and condition.…”

Orchestration of brain oscillations: principles and functions

“…On the other hand, the study by Moris Fernandez et al . () observed a synchronization of theta activity modulated by the conflict (i.e. incongruency) of auditory‐visual speech inputs during the famous McGurk illusion (McGurk & MacDonald, ).…”