Perceived gaze direction in faces and spatial attention: a study in patients with parietal damage and unilateral neglect.

Perceived gaze in faces is an important social signal that may influence orienting of attention in normal observers. Would such effects of gaze still occur in patients with right parietal damage and left neglect who usually fail to attend to contralesional space? Two experiments tested for effects of perceived gaze on visual extinction. Face or shape stimuli were presented in the right, left, or both hemifields, with faces looking either straight ahead or toward the opposite field. On bilateral trials, patients extinguished a left shape much less often when a concurrent right face looked leftward rather than straight ahead. This occurred, even though gaze was not relevant to the task and processing of facial signals implied attention to a competing ipsilesional stimulus. By contrast, rightward gaze in faces presented on the left side had no effect on extinction, suggesting that gaze cues are not extracted without attention. Two other experiments examined effects of perceived gaze on the detection of peripheral targets. Targets appeared at one of four possible locations to the right or left of a central face looking either toward the target location, another location on the same side, the opposite side, or straight ahead. Face and gaze were not relevant to the task and not predictive of target location. Patients responded faster when the face looked toward the target on both the contralesional and ipsilesional sides. In contralesional space, gaze allowed shifting of attention in a specific quadrant direction, but only to the first target along the scan path when there were different possible locations on the same side. By contrast, in intact ipsilesional space, attention was selectively directed to one among different eccentric locations. Control experiments showed that symbolic arrow cues did not produce similar effects. These results indicate that even though parietal damage causes spatial neglect and impairs the representation of location on the contralesional side, perceived gaze in faces can still trigger automatic shifts of attention in the contralesional direction, suggesting the existence of specific and anatomically distinct attentional mechanisms.