The unity hypothesis revisited: can the gender incongruent McGurk effect be disrupted by priming?

The “unity assumption hypothesis” contends that higher-level factors, such as a perceiver’s belief and prior experience, modulate multisensory integration. The McGurk illusion exemplifies such integration. When a visual velar /ga/ is dubbed with an auditory bilabial /ba/, listeners unify the discrepant signals with knowledge that open lips cannot produce /ba/ and a fusion percept /da/ is perceived. Previous research claimed to have falsified this theory by demonstrating the McGurk effect occurs even when a face is dubbed with a gender incongruent voice. But perhaps stronger evidence than just an apparent incongruence between unfamiliar faces and voices is needed to prevent perceptual unity. Here we investigated whether the McGurk illusion with gender incongruent stimuli can be disrupted by priming with appropriate pairing of face and voice. In an online experiment, 89 participants aged 18-62, were randomly allocated to experience experimental trials containing either a male or female face with incongruent gender voice. The number of times participants experienced a McGurk illusion was measured before and after a training block which familiarized them with the true pairings of face and voice. After training and priming, the susceptibility to the McGurk effects decreased significantly on average. The findings support the notion that unity assumptions modulate intersensory bias, and confirm and extend previous studies using gender incongruous McGurk stimuli.