Abstract
The McGurk illusion occurs when listeners hear an illusory percept (i.e., “da”), resulting from mismatched pairings of audiovisual (AV) speech stimuli (i.e., auditory/ba/paired with visual/ga/). Hearing a third percept—distinct from both the auditory and visual input—has been used as evidence of AV fusion. We examined whether the McGurk illusion is instead driven by visual dominance, whereby the third percept, e.g., “da,” represents a default percept for visemes with an ambiguous place of articulation (POA), like/ga/. Participants watched videos of a talker uttering various consonant vowels (CVs) with (AV) and without (V-only) audios of/ba/. Individuals transcribed the CV they saw (V-only) or heard (AV). In the V-only condition, individuals predominantly saw “da”/“ta” when viewing CVs with indiscernible POAs. Likewise, in the AV condition, upon perceiving an illusion, they predominantly heard “da”/“ta” for CVs with indiscernible POAs. The illusion was stronger in individuals who exhibited weak/ba/auditory encoding (examined using a control auditory-only task). In Experiment2, we attempted to replicate these findings using stimuli recorded from a different talker. The V-only results were not replicated, but again individuals predominately heard “da”/“ta”/“tha” as an illusory percept for various AV combinations, and the illusion was stronger in individuals who exhibited weak/ba/auditory encoding. These results demonstrate that when visual CVs with indiscernible POAs are paired with a weakly encoded auditory/ba/, listeners default to hearing “da”/“ta”/“tha”—thus, tempering the AV fusion account, and favoring a default mechanism triggered when both AV stimuli are ambiguous.
Highlights
The classic McGurk illusion (McGurk and MacDonald, 1976) is a perceptual phenomenon whereby watching a person utter the consonant vowel (CV) syllables /ga/ or /ka/ paired with the sounds of /ba/ or /pa/ may induce illusory auditory perception of a third syllable, “da” or “ta,” respectively
Shahin et al (2018) revealed how the visual dominance illusion is manifested in the auditory cortex (AC), by examining the N1-P2 auditory evoked potentials (AEPs) to AV combinations of /ba/ and /fa/
For the AV trials, we hypothesized that upon pairing audio /ba/ with videos of CVs with indiscernible place of articulation (POA), illusory auditory perception should default to “da”/“ta.” If these two hypotheses are realized, the results would provide clear evidence that the McGurk illusion is a case of the visual dominance illusion, rather than being mediated by a fusion process
Summary
The classic McGurk illusion (McGurk and MacDonald, 1976) is a perceptual phenomenon whereby watching a person utter the consonant vowel (CV) syllables /ga/ or /ka/ paired with the sounds of /ba/ or /pa/ may induce illusory auditory perception of a third syllable, “da” or “ta,” respectively. Saalasti et al (2011) showed that individuals, who accurately identified V-only /aka/ as “aka” (i.e., not confused with “ata”), had illusory auditory perception that was dominated by “aka” in response to incongruent AV pairings of audio /ata/ and visual /aka/. For the AV trials, we hypothesized that upon pairing audio /ba/ with videos of CVs with indiscernible POAs, illusory auditory perception should default to “da”/“ta.” If these two hypotheses are realized, the results would provide clear evidence that the McGurk illusion is a case of the visual dominance illusion (i.e., where “da”/“ta” is the dominant V-only percept of visemes with an indiscernible POA), rather than being mediated by a fusion process. This hypothesis is consistent with Alsius et al.’s (2018) assertion that susceptibility to the McGurk illusion is more robust for weak auditory consonants, because the /b/ consonant is confusable with other voice stops
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