Infants' response to temporally based intersensory equivalence: The effect of synchronous sounds on visual preferences for moving stimuli

Abstract

Four- and 8-month-old infants' responses to temporally based auditory-visual equivalence were investigated in a series of experiments. In the first experiment, infants viewed pairs of computer-generated visual stimuli that moved at different rates while a sound occurred each time one of the stimuli reversed its direction of motion at the bottom of the screen. Contrary to previous reports, infants even as old as 8 months of age did not respond to the auditory-visual correspondence. To determine if this was due to the infants' failure to detect the correspondence per se, or to the pairedpreference method, an habituation-test experiment was conducted. Following habituation to a single moving visual stimulus and a sound that occurred when the visual stimulus reversed its direction of motion, the infants were given one test trial where the sound was no longer synchronized with direction reversal, and one where no sound occurred at all. Four-month-old infants exhibited only limited evidence of discrimination of the change in the temporal relationship between the visual stimulus and the sound, and no evidence of discrimination when the sound was absent. In contrast, 8-month-old infants discriminated both types of changes, indicating that their lack of response to the auditory-visual correspondence in the paired-preference experiments was not due to their inability to respond to it. To find out whether rate differences prevented the infants from responding to auditory-visual synchrony, rate differences were eliminated in a third experiment and the two stimuli were moved at the same velocity but out of phase with one another. Thus, the sound was synchronized with the direction reversal of one of the visual stimuli. Both age groups exhibited intersensory matching in that they looked longer at the stimulus whose direction reversal corresponded to the sound. This was true, however, only when the sound corresponded to the visual stimulus that began to move first.