Abstract: PURPOSE: Rapid orienting to threat signals within a crowded environment is of great biological significance. Previous research has revealed an attentional bias to threat-related faces, which was most significant when the faces were invisible, especially in clinical and non-clinical high-anxious individuals. In the current study, we investigated whether a fearful face, as a signal of potential threats, can capture attention without awareness, and examined the role of individual trait anxiety in this effect.
METHODS: A fearful face target was embedded in a neutral or a fearful distracting face array, forming a pop-out or a non-pop-out condition. To control for the effect of low-level confounds, we also included two control conditions where the face displays were otherwise the same but inverted. Using the sandwich-masking method, the face displays were rendered invisible, followed by a detection phase where the target face was no longer masked while the other faces remained invisible. Participants were required to indicate the perceived direction of the target face (upright or inverted). After the test, they completed two 2AFC tasks to ensure that they were completely unaware of the suppressed faces. Moreover, participants were divided into high and low trait-anxiety groups according to their scores on the Spielberger State-Trait Anxiety Inventory (STAI).
RESULTS: Despite being totally suppressed, the invisible fearful face popped out of the crowd and speeded up target detection at the pop-out location, yielding faster responses in the pop-out condition relative to the non-pop-out condition. Crucially, such influence was only observed in the upright but eliminated in the inverted condition, with a significant pop-out effect only for the high trait-anxiety group.
CONCLUSIONS: These results demonstrated a non-conscious pop-out effect elicited by threat-related faces. Such effect was strongly modulated by trait-anxiety, pinpointing the intrinsic interaction between fear-driven attentional responses and personality traits.

Key words: Pop-out effect, Attentional Capture, Fearful faces, Visual awareness, Trait-anxiety