Up Versus Down: The Role of Intersensory Redundancy in the Development of Infants' Sensitivity to the Orientation of Moving Objects.

According to the intersensory redundancy hypothesis (IRH), during early development, perception of nonredundantly specified properties is facilitated in unimodal stimulation as compared with bimodal stimulation. Later in development, attention becomes more flexible and infants can detect nonredundantly specified properties in both unimodal and bimodal stimulation. This study tested these predictions by assessing the development of infants' sensitivity to the orientation of an object striking a surface, information that is nonredundantly specified in visual and in audiovisual stimulation. Infants of 3, 5, and 8 months were habituated to unimodal visual or bimodal, synchronous, audiovisual films of a hammer tapping a rhythm in 1 of 2 orientations (upward vs. downward). Results demonstrated an Age × Condition interaction, where younger infants (3 and 5 months) detected the orientation change in unimodal but not bimodal stimulation, whereas older infants (8 months) detected the change in both types of stimulation. Further, in a control study, 3-month-olds detected the orientation change when bimodal stimulation was asynchronous, demonstrating that temporal synchrony impaired performance in the bimodal condition. These findings converge with those of prior studies and support predictions of the IRH.