Arrows don't look at you: Qualitatively different attentional mechanisms triggered by gaze and arrows

Eye gaze conveys rich information concerning the states of mind of others, playing a critical role in social interactions, signaling internal states, and guiding others' attention. On the basis of its social significance, some researchers have proposed that eye gaze may represent a unique attentional stimulus. However, contrary to this notion, the majority of the literature has shown indistinguishable attentional effects when eye gaze and arrows have been used as cues. Taking a different approach, in this study we aimed at finding qualitative attentional differences between gazes and arrows when they were used as targets instead of as cues. We used a spatial Stroop task, in which participants were required to identify the direction of eyes or arrows presented to the left or the right of a fixation point. The results showed that the two types of stimuli led to opposite spatial interference effects, with arrows producing faster reaction times when the stimulus direction was congruent with the stimulus position (a typical spatial Stroop effect), and eye gaze producing faster reaction times when it was incongruent (a "reversed" spatial Stroop effect). This reversed Stroop is interpreted as an eye-contact effect, therefore revealing the unique nature of eyes as special social-attention stimuli.