Abstract
The current study examined the time course of implicit processing of distinct facial features and the associate event-related potential (ERP) components. To this end, we used a masked priming paradigm to investigate implicit processing of the eyes and mouth in upright and inverted faces, using a prime duration of 33 ms. Two types of prime-target pairs were used: 1. congruent (e.g., open eyes only in both prime and target or open mouth only in both prime and target); 2. incongruent (e.g., open mouth only in prime and open eyes only in target or open eyes only in prime and open mouth only in target). The identity of the faces changed between prime and target. Participants pressed a button when the target face had the eyes open and another button when the target face had the mouth open. The behavioral results showed faster RTs for the eyes in upright faces than the eyes in inverted faces, the mouth in upright and inverted faces. Moreover they also revealed a congruent priming effect for the mouth in upright faces. The ERP findings showed a face orientation effect across all ERP components studied (P1, N1, N170, P2, N2, P3) starting at about 80 ms, and a congruency/priming effect on late components (P2, N2, P3), starting at about 150 ms. Crucially, the results showed that the orientation effect was driven by the eye region (N170, P2) and that the congruency effect started earlier (P2) for the eyes than for the mouth (N2). These findings mark the time course of the processing of internal facial features and provide further evidence that the eyes are automatically processed and that they are very salient facial features that strongly affect the amplitude, latency, and distribution of neural responses to faces.
Highlights
The human face is the most important visual object we process everyday, providing information such as gender, race, age, emotional state, and identity
Open eyes: The analyses revealed a marginally significant orientation effect [F(1,13) = 4.01, p < .06, ηp2 = .24, observed power = .46], with faster response times (RTs) for upright than inverted faces
In particular we explored face-sensitive event-related potential (ERP) components and their time course by comparing ERPs elicited by distinct internal facial features, such as eyes and mouth, of upright and inverted faces
Summary
The human face is the most important visual object we process everyday, providing information such as gender, race, age, emotional state, and identity. The ability to identify a face refers to the ability to discriminate among different exemplars of the face category, recognizing a face as familiar. This sophisticated competence is the result of the analysis of subtle differences between faces, which have a similar structure, where features (i.e., eyes, nose, mouth) are in a PLOS ONE | DOI:10.1371/journal.pone.0147415. Implicit Processing of the Eyes and Mouth similar arrangement (i.e., two eyes above a nose, which is above a mouth) This ability is attributed to enhanced sensitivity to configural information in faces, as opposed to the analytic processing involved in object recognition (e.g., [1]). Some studies on adaption effects in relation to face perception seem to suggest that inverted faces may not be processed configurally, they should share some processing mechanisms with upright faces (e.g., [2])
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