Audiovisual temporal capture underlies flash fusion.

When sequential visual flashes are accompanied by a lower number of sequential auditory pulses, the perceived number of visual flashes is lower than the actual number, an illusion termed 'flash fusion'. We examined whether temporal capture of flashes by pulses underlay flash fusion. One of the visual flashes was given a luminance increment, and observers reported which flash had the luminance increment. Results showed that the pulse strongly captured the flashes in its temporal vicinity, resulting in flash fusion. Moreover, when one of the successive pulses was given a higher frequency than others, the luminance increment was perceptually paired with the pulse with the higher frequency. The pairing of audiovisual features disappeared when the temporal pattern of the pulse frequency was difficult for the observer to anticipate. These data indicate that flash fusion is caused by temporal capture of flashes by the pulse, and that feature matching between auditory and visual signals also contributes to the modulation of perceived temporal structure of flashes during flash fusion.