McGurk doesn’t work: Individual differences and task demands explain the McGurk illusion

Visual speech cues play an important role in speech recognition, and the McGurk effect is a classic demonstration of this. In the original McGurk and MacDonald (1976) experiment, 98% of participants reported an illusory “fusion” percept of /d/ when listening to the spoken syllable /b/ and watching the visual speech movements for /g/. However, recent work (e.g., Mallick et al., 2015) shows that subject and task differences influence the proportion of fusion responses. In the current study, we varied task (forced-choice versus open-ended), stimuli (synthetic versus naturally produced), design (mixed versus blocked audio-visual and single-modality trials), and data collection environment (lab versus Mechanical Turk) to investigate the robustness of the McGurk effect. Across all conditions, we found a low number of fusion responses. Rather than a robust perceptual illusion, we therefore argue that the McGurk effect is a product of individual differences and task demands.