Chapter 17 The Face-Sensitive N 170 Component of the Event-Related Brain Potential

Faces are perhaps the most important object category in visual perception, as faces of conspecifics frequently convey behaviourally, socially, and emotionally relevant information that is critical for the adaptive control of action. Given this undisputed significance of faces, it is not surprising that the study of human face processing has long been one of the most active research areas in visual cognition. In recent years, numerous new insights into the mechanisms and neural processes that underlie our ability to perceive and recognize faces have come from studies that have investigated face processing with neuroscientific methods. Functional brain imaging studies have identified the fusiform face area (FFA; Kanwisher et al., 1997 ), the right lateral occipital face area (OFA; Gauthier et al., 2000b ), and the superior temporal sulcus (Hoffman and Haxby, 2000 ) as regions that are specifically involved in the processing of faces (see Haxby et al., 2000 , for a review of the neural network involved in human face perception; Haxby and Gobbini, Chapter 6, this volume). Electrophysiological evidence for face-specific brain processes has been obtained through intracranial recordings (Allison et al., 1999 ), as well as in many studies using event-related brain potentials (ERPs). These ERP studies have uncovered several components that are linked to different stages in face perception, face recognition, and the processing of emotional facial expression (e.g. Eimer, 2000c ; Eimer and Holmes, 2007 ). The earliest, most prominent, and by far the most widely studied face-sensitive ERP component is the N170. When compared to different categories of non-face objects, human faces consistently elicit a larger negative-going ERP component at occipitotemporal electrodes. The presence of an N170 component in response to faces has been demonstrated in two early ERP investigations of human face perception (Bentin et al., 1996 ; Bötzel et al., 1995 ), and the N170 has since featured prominently in face perception research. There are currently more than 200 published studies that have used this component to investigate different aspects of face processing in the human brain. More recently, an “M170” component with response properties that are very similar but perhaps not identical to the N170 has been identified in experiments that used magnetoencephalographic (MEG) measures to study face processing (e.g. Halgren et al., 2000 ; Harris and Nakayama, 2008 ). The purpose of this chapter is to introduce the N170 component to readers who may not be intimately familiar with the details of ERP methodology and interpretation, and to provide a brief review of some important research questions that have been addressed by employing the N170 as an electrophysiological marker of face processing. The first section will discuss basic properties of the N170 component, its neural basis, as well as some methodological issues that need to be kept in mind when using this component to study face-specific processes, and when evaluating the results from previous N170 experiments. In the next section, a recent methodological challenge to the claim that the N170 reliably reflects face-specific brain processes (Thierry et al., 2007a ) will