MCGURK ILLUSION TO BILATERAL ADMINISTRATION OF SENSORY STIMULI IN PATIENTS WITH HEMISPATIAL NEGLECT

The illusion of McGurk (Nature 264, 746-748, 1976) refers to the blend ing of conflicting audio-visual messages. By taking advantage of this phenomenon the study explored whether visual cues (i.e. manner of arti culation) in ipsilesional (right) space would help a patient with audi tory neglect to mentally reconstruct syllabic sounds voiced in contral esional (left) space. We examined seven patients with clinically detec table visual neglect following right hemisphere damage. All had signs of auditory neglect as documented by the inferior identification of sy llables delivered through a loudspeaker on the left side. In contrast, syllabic sounds delivered contralesionally together with visual stimu li in the ipsilesional space significantly increased identification of ''neglected'' syllabic sounds. Of the increased responses, 23% were c lassified as illusory blends, thereby suggesting that manner of articu lation provides a valuable clue as to the possible ''best fit'' for a consonant. The susceptibility to the blend illusion was identical in p atients and controls. Results indicate that neglected auditory stimuli are retrieved in patients with right hemisphere lesion by the mechani sm of the ventriloquist illusion in the presence of a carefully timed sequence of comparisons of auditory signals in the neglected space wit h visual signals in the attended space. The possibility that neuronal mechanisms that serve audio-visual merger in spatial localization are also utilized for processing speech distinctions is discussed.