What is special about the index finger? The index finger advantage in manipulating reflexive attentional shift

Pointing with the index finger is a universal behavior. However, the functional significance of indexical pointing has not been examined empirically. We examined the efficacy of various pointing gestures in evoking viewer's attentional shifts. After viewing the gesture cue, observers quickly reported the location of a visual target. With a short cue-target delay, reaction times were generally shorter for the target at the location where gesture cues pointed, but not with a long cue-target delay. Moreover, the indexical pointing gesture produced a significantly larger cueing effect than the other gestures. Our control experiments indicated that the index-finger advantage is tightly linked to the proper morphological shape (i.e. length and position of the index finger) of the indexical pointing and is not explained by the directional discriminability of the gesture. The visual system seems to use mechanisms that are partially independent of the directional discrimination of gestures, in order to quickly modulate the viewer's attention.