The development of pointing perception in infancy: effects of communicative signals on covert shifts of attention.

The present study aims to investigate the interplay of verbal and nonverbal communication with respect to infants' perception of pointing gestures. Infants were presented with still images of pointing hands (cue) in combination with an acoustic stimulus. The communicative content of this acoustic stimulus was varied from being human and communicative to artificial. Saccadic reaction times (SRTs) from the cue to a peripheral target were measured as an indicator of the modulation of covert attention. A significant cueing effect (facilitated SRTs for congruent compared with incongruent trials) was only present in a condition with additional communicative and referential speech. In addition, the size of the cueing effect increased the more human and communicative the acoustic stimulus was. This indicates a beneficial effect of verbal communication on the perception of nonverbal communicative pointing gestures, emphasizing the important role of verbal communication in facilitating social understanding across domains. These findings additionally suggest that human and communicative (ostensive) signals are not qualitatively different from other less social signals but just quantitatively the most attention grabbing among a number of other signals.