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Abstract:
Multimodal (visual auditory) information is combined by weighting unimodal signals by their relative reliabilities. Reliability in real-world stimuli, however, does not remain constant. Here we ask whether the system adjusts the weights online in the McGurk effect. Subjects were presented with an audiovisual recording of an actor‘s face producing a series of syllables. Such syllables were composed either by consistent multimodal information, or by auditory /ba/ and lip movement of /ga/. Subjects‘ task was to continuously report the perceived syllable. We varied the reliability of the visual information by changing the visibility of the face. With inconsistent multimodal information, increased reliability of the visual signal biased perception towards the illusory /da/
percept whereas decreased reliability biased perception towards the auditory /ba/. However, changes in reliability had perceptual consequences only after 3 - 4 s. Therefore, the reliability estimate of the sensory signals is not instantaneous but continuously updated with a time-constant of a few seconds.
