The role of spatial separation on ventriloquism and mcgurk illusions

This study aimed at assessing whether two audiovisual interactions (the McGurk and the ventriloquism effects) are affected by different degrees of spatial separation between the auditory and the visual signals. The materials consisted in trains of three audiovisual monosyllables. They were visually displayed in front of the participants’ head on a TV screen and auditorily played through one of nine hidden loudspeakers (placed every 20°, from straight ahead to 80° to the left or to the right). There were two different conditions in which the speaker’s face was presented either upright or inverted. Each condition included an identification task (to measure the McGurk effect) and a localization task (to estimate the ventriloquism effect). The ventriloquism effect was maximal at 20° and decreased as the loudspeaker location moved away to the left or to the right, but it was not affected by inverted presentation of the speaker’s face. The McGurk effect exhibited the reverse pattern.