Abstract
In interpersonal communication, the listener can often see as well as hear the speaker. Visual stimuli can subtly change a listener’s auditory perception, as in the McGurk illusion, in which perception of a phoneme’s auditory identity is changed by a concurrent video of a mouth articulating a different phoneme. Studies have yet to link visual influences on the neural representation of language with subjective language perception. Here we show that vision influences the electrophysiological representation of phonemes in human auditory cortex prior to the presentation of the auditory stimulus. We used the McGurk effect to dissociate the subjective perception of phonemes from the auditory stimuli. With this paradigm we demonstrate that neural representations in auditory cortex are more closely correlated with the visual stimuli of mouth articulation, which drive the illusory subjective auditory perception, than the actual auditory stimuli. Additionally, information about visual and auditory stimuli transfer in the caudal–rostral direction along the superior temporal gyrus during phoneme perception as would be expected of visual information flowing from the occipital cortex into the ventral auditory processing stream. These results show that visual stimuli influence the neural representation in auditory cortex early in sensory processing and may override the subjective auditory perceptions normally generated by auditory stimuli. These findings depict a marked influence of vision on the neural processing of audition in tertiary auditory cortex and suggest a mechanistic underpinning for the McGurk effect.
Highlights
The McGurk effect is an auditory illusion that occurs when the perception of a phoneme’s auditory identity is changed by a concurrently played video of a mouth articulating a different phoneme [1]
Most subjects will report hearing the phoneme articulated by the mouth in the video and not the different phoneme pronounced in the auditory stimulus [2]
Electrical recordings from the surface of the human brain have determined that local field potentials correlate with subjective phoneme categorization [7] and show topographic coding of specific speech sounds in the superior temporal gyrus (STG) [8,9]
Summary
The McGurk effect is an auditory illusion that occurs when the perception of a phoneme’s auditory identity is changed by a concurrently played video of a mouth articulating a different phoneme [1]. Understanding how, and where, neural representations are changed and perceptual identity is altered will provide important insight into the neural mechanisms of everyday speech perception. The perceptual identity of a sound is thought to be processed hierarchically in the human brain along the superior temporal lobe in a cortical processing stream analogous to the ventral visual processing stream in the inferior temporal lobe [3,4,5,6]. Electrical recordings from the surface of the human brain have determined that local field potentials correlate with subjective phoneme categorization [7] and show topographic coding of specific speech sounds in the superior temporal gyrus (STG) [8,9]
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