title: Neural substrates of species-dependent visual processing of faces: use of morphed faces.
abstract: Face identification and categorization are essential for social communication. The N170 event-related potential (ERP) is considered to be a biomarker of face perception. To elucidate the neural basis of species-dependent face processing, we recorded 128-ch high-density ERPs in 14 healthy adults while they viewed the images of morphed faces. The morphed stimuli contained different proportions of human and monkey faces, and the species boundary was shifted away from the center of the morph continuum. Three experiments were performed to determine how task requirement, facial orientation, and spatial frequency (SF) of visual stimuli affected ERPs. In an equal SF condition, the latency, and amplitude of the occipital P100 for upright faces were modulated in a monotonic-like fashion by the level of morphing. In contrast, the N170 latency for upright faces was modulated in a step-like fashion, showing a flexion point that may reflect species discrimination. Although N170 amplitudes for upright faces were not modulated by morph level, they were modulated in a monotonic-like fashion by inverted faces. The late positive (LP) component (350-550 msec) in the parietal region was modulated in a U-shaped function by morph level during a categorization task, but not in a simple reaction task. These results suggest that P100 reflects changes in the physical properties of faces and that N170 is involved in own-species selectivity. The LP component seems to represent species categorization that occurs 350 msec after stimulus onset.
authors.affiliation: Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan yamada@neurophy.med.kyushu-u.ac.jp.
authors.forename: Emi
authors.initials: E
authors.lastname: Yamada
authors.affiliation: Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Ogata
authors.affiliation: Center for Clinical and Translational Research, Kyushu University Hospital, Higashi-ku, Fukuoka, Japan.
authors.forename: Junji
authors.initials: J
authors.lastname: Kishimoto
authors.affiliation: Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Mutsuhide
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Urakawa
authors.affiliation: Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Yamasaki
authors.affiliation: Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Shozo
authors.initials: S
authors.lastname: Tobimatsu
keywords: Categorization; event‐related potentials; face perception; inversion effect; morphing faces