Faces under continuous flash suppression capture attention faster than objects, but without a face evoked steady-state visual potential: Is curvilinearity responsible for the behavioral effect?

Abstract

Highlights 1• Faces presented outside of awareness do not evoke a steady-state visually evoked 2 potential. 3• This is true for both neutral and fearful faces. 4• However, faces do breakthrough interocular suppression faster than objects. 5• Curvilinear objects breakthrough interocular suppression faster than rectilinear objects. 6• The breakthrough time advantage for faces over objects is due to their curvilinearity. 7 8 Nonconscious face perception and curvilinearity 3 Abstract 1 Face perception is a vital part of human social interactions. The social value of faces makes their 2 efficient detection evolutionarily advantageous. It has been suggested that this might occur 3 nonconsciously, but experimental results are equivocal thus far. Here, we probe nonconscious 4 face perception using a novel combination of binocular rivalry with continuous flash 5 suppression, and steady-state visually evoked potentials. In the first two experiments, 6 participants viewed either non-face objects, neutral faces (Study 1), or fearful faces (Study 2). 7Consistent with the hypothesis that faces are processed nonconsciously, we found that faces 8 broke through suppression faster than objects. We did not, however, observe a concomitant face-9 selective SSVEP. Study 3 was run to reconcile this paradox. We hypothesized that the faster 10 breakthrough time was due to a mid-level visual feature, curvilinearity, rather than high-level 11 category membership, which would explain the behavioral difference without neural evidence of 12 face-selective processing. We tested this hypothesis by presenting participants with four different 13 groups of stimuli outside of conscious awareness: rectilinear objects (e.g., chessboard), 14 curvilinear objects (e.g., dartboard), faces, and objects that were not dominantly curvilinear or 15 rectilinear. We found that faces and curvilinear objects broke through suppression faster than 16 objects and rectilinear objects. Moreover, there was no difference between faces and curvilinear 17 objects. These results support our hypothesis that the observed behavioral advantage for faces is 18 due to their curvilinearity, rather than category membership. 19 20 Nonconscious face perception and curvilinearity 4