Time course of face processing: the N170
The general goal of our research is to clarify the mechanisms of face recognition in the human brain. Event-Related Potentials (ERPs) recorded on the human scalp can be particularly informative for this goal. Because of their excellent time resolution, ERPs can help tracking perceptual face processes as they unfold through time.
The sudden onset (flash) of a face stimulus elicits a particularly large negative component on the adult huma, most prominent onoccipito-temporal sites, peaking at about 170 ms. This component has been named the N170 in the seminal study of Bentin and colleagues (1996), which was the first study to focus on this component and in which several experiments were performed to characterize its response properties. The N170 is clearly related to the conscious perception / interpretation of a visual stimulus as a face, as we argued in this review (Rossion, 2014).
We have been studying this component in the lab for almost 20 years (first papers published in 1999; e.g., Rossion et al., 1999), and have more than 30 publications on this component ( see full list here , and below). In a nutshell, our research has investigated a number of issues with the N170:
- We showed that the N170 and the ealier described Vertex Positive Potential (VPP) by Jeffreys (1989) reflect opposite sides of the same generators, varying inversely in amplitude with the location of the reference electrode on the scalp (Joyce & Rossion, 2005).
- We provided evidence that the N170 onset marks the earliest time-point (on the scalp, and with this approach of flashing stimuli) of face-selectivity that cannot be accounted for by low-level visual cues. In contrast, early sensitivity to faces at the elevel of the P1 component is accounted for by low-level visual cues (Rossion & Caharel, 2011).
- We reported large effects of competition between 2 faces (Jacques & Rossion, 2006) or between faces and objects of expertise (Rossion et al., 2004; Rossion et al., 2007) using an original design in which stimuli are presented concurrently.
- We provided evidence that the N170 amplitude is largely modulated by spatial attention, but that this effect is independent of competition between faces (Jacques & Rossion, 2007).
- We showed that pictures of different kinds of objects also elicit a N170 component, with varying amplitudes Rossion et al., 2000, although the N170 is larger for faces (this is discussed in another review: Rossion & Jacques, 2008).
- We found that the N170 is reduced in amplitude if the same face identity is repeated immediately, an effect that resists changes of size, but not inversion, and is thus not accounted for by low-level visual cues (Jacques et al., 2007). This identity-adaptation effect has been replicated in many studies of our group, showing for instance that it resists changes of viewpoint up to 30 degrees rotation (Caharel et al., 2009; Caharel et al. 2011; Caharel et al., 2015), and is due mainly to shape rather than texture/colour information (Caharel, Jiang et al., 2009).
All these studies are better described in our research program on the N170
see also our review chapter: Rossion, B. & Jacques, C. (2011). The N170 : understanding the time-course of face perception in the human brain. To appear in The Oxford Handbook of ERP Components (2011), Edited by S. Luck and E. Kappenman. Oxford University Press.
Any comment about this text? Please email bruno.rossion@uclo uvain.be.
Caharel, S., Jiang, F., Blanz, V., Rossion, B. (2009). Recognizing an individual face: 3D shape contributes earlier than 2D surface reflectance information. NeuroImage, 47, 1809-1818. [PDF]
- A very clear and interesting finding to me, illustrating nicely the interest of the ERP approach. We used our identity adaptation paradigm, but manipulated the kind of information that conveyed the identity of the face: either 3D shape, or 2D surface reflectance (color/texture), or both simultaneously. Behaviorally, participants discriminated faces better and faster when the two kinds of information were present, as in previous studies. However, ERP data told a different story: at the level of the N170, a significantly larger amplitude than the repeated face identity condition was found only when 3D shape differed between the adapter and target face. When surface reflectance alone was different, there was no significant effect. However, at a later component (P2), shape and reflectance elicited an effect of the same magnitude, while combining the two kinds of diagnostic information elicited the largest effect (in line with behavior). Hence, the early encoding of an individual face percept seems to be based primarily on 3D shape, not surface reflectance.
Jacques, C., Rossion, B. (2009). The initial representation of individual faces in the right occipito-temporal cortex is holistic: electrophysiological evidence from the composite face illusion. Journal of Vision, 9(6):8, 1–16. [PDF]
- Here the identity adaptation paradigm was used to test the hypothesis that as early as the individual face was perceptually encoded (N170 peak, see Jacques et al., 2007, JOV), this encoding is holistic. Observers fixated the top halves of two sequential faces to match. We found that even when the bottom halves only changed identity, eliciting the visual illusion of a change on the fixated top half, the N170 was larger in amplitude than when there was no change of identity. This effect disappeared if the two halves were spatially misaligned. This study therefore demonstrates that the first individual face representation that is perceived is holistic rather than based on independently perceived local part
Rossion, B., Campanella, S., Gomez, C., Delinte, A., Debatisse, D., Liard, L., Dubois, S., Bruyer, R., Crommelinck, M., Guérit, J.-M. (1999). Task Modulation of Brain Activity Related to Familiar and Unfamiliar Face Processing: an ERP Study, Clinical Neurophysiology, 110, 449-462. [PDF]
- One of the first N170 studies that compared the perception of familiar and unfamiliar faces, and failed to find a modulation of the N170 by long-term familiarity of the face.
Rossion, B., Delvenne, J.-F., Debatisse, D., Goffaux, V., Bruyer, R., Crommelinck, M., Guérit, J.-M. (1999). Spatio-temporal brain localization of the face inversion effect, Biological Psychology, 50, 173-189. [PDF]
- One of the first study (with the short paper of Linkenkaer-Hansen et al., 1998) to report a significant increase of the N170 in response to inverted faces. In our discussion, we raised two possible accounts for this paradoxical increase: (1) that the loss of configural processing following inversion could have resulted in a selective amplification of neural activity devoted to faces because of an increase of difficulty of processing; or (2) that the larger amplitude observed for inverted faces might be a result of the recruitment of additional processing resources in object perception systems. I still believe that these two possibilities probably account for part of the effect, even though other authors have proposed alternative explanations.