Response Profile of the Face-Sensitive N170 Component: A Rapid Adaptation Study

Abstract

To study the response profile of the face-selective N170 component, an adaptation procedure was employed where adaptor and test stimuli were presented in rapid succession. Test stimuli came from 4 different face categories (upright, inverted, and eyeless faces and eyes-only images). The same face stimuli, as well as upright and inverted houses, served as adaptors. Strong N170 amplitude reductions indicative of adaptation were found for all types of face test stimuli preceded by face adaptors relative to house adaptors, demonstrating that at a generic level, the N170 reflects the activation of face-selective neurons by full faces and by face parts. The highly specific pattern of N170 adaptation effects for different combinations of adaptor and test stimulus categories suggests additional distinct contributions of eye-selective neurons and of face-sensitive neurons that are tuned to deviations from canonical stimulus orientations to the N170 component. Results demonstrate that the N170 is generated by multiple neural sources at both early and later stages of configural face processing and that rapid adaptation techniques provide a powerful tool to dissociate these sources.

Species sensitivity of early face and eye processing

“…The N170 response to eyeless faces would also reflect the sole response of face neurons which seems optimal when eyes are present as reflected by shorter latency to faces than eyeless faces. This model, and in particular the idea that eye neurons are inhibited in response to upright but not inverted faces, was recently supported by an adaptation study (Eimer et al, 2010).…”

The early development of face processing — What makes faces special?

“…Several studies using priming or habituation paradigms have shown reduced N170 amplitude (or M170 amplitude in MEG studies) in response to faces that were preceded by faces compared to non-face stimuli [74,[77][78][79][80][81] . These repetition suppression or adaptation effects are typically taken as evidence that the preceding stimulus and following stimulus activate a common neuronal representation at Inversion Enhanced amplitude and/or delayed latency [87,[99][100][101] Reduced amplitude [98] Delayed repetition effects [95] Contrast-reversal Enhanced amplitude [99] Repetition effects spread over longer time-window [95] Eye removal Similar amplitude for complete faces and faces with -eyes removed [86] No effects of inversion or contrast-reversal for faces -with eyes removed [103] Isolated eyes Similar or enhanced amplitude compared to intact faces [87] Holistic processing Shorter latency for repeated face halves in aligned faces [110] Longer latency for aligned compared to misaligned face halves [110] Less repetition suppression to aligned face stimuli for -half-identical or completely new faces compared to identical faces [111] Second-order relational processing Conflicting evidence on the effects of thatcherization on -processing of upright and inverted faces [114][115][116] Larger amplitude for configurally than featurally altered faces over the right hemisphere [117] Stimulus repetition Repetition suppression.…”

“…Reduced amplitude for repetition Repetition enhancement. Enhanced amplitude for repetition of different [74,77,80,81] or same faces [94] of same faces [88,91,92] Fig and profile-view faces has been taken as evidence that a view-invariant representation of faces is accessed in both cases [82] .…”

“…To sum up, the adult N170 seems to reflect the activity of neurons sensitive to eyes as well as neurons sensitive to facial configuration whose activation relies on a view-invariant neural representation of human faces that can also be accessed if eyes are not visible in the face and if isolated eyes are presented [80,82,86,99] . Even though often stated in the literature, it is not entirely clear to what extent the N170 reflects holistic and second-order relational processing of faces and more studies on this topic are clearly needed.…”

Early sensitivity for eyes within faces: A new neuronal account of holistic and featural processing

“…The amplitude increase with inversion, also termed the N170 "face inversion effect" (FIE), is thus believed to reflect the disruption of early holistic processing stages specific to human faces and has been used as a hallmark of face specificity. At the neuronal level, this increase has been explained by the recruitment, in addition to face-sensitive neurons, of object-sensitive neurons (Itier & Taylor, 2002;Rossion et al, 1999;Sadeh & Yovel, 2010;Yovel & Kanwisher, 2005), other facesensitive neurons tuned to the inverted orientation (Eimer et al, 2010), or eye-sensitive neurons (Itier et al, 2007). Itier et al (2007) showed that, in contrast to intact faces, inversion of eyeless faces elicited a much reduced N170 FIE and thus proposed that eyes played an important role in this early face specific phenomenon, an idea reinforced by the replication of this finding in later studies Kloth et al, 2013;Nemrodov & Itier, 2011).…”