N170

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The N170 designates a component in the group of so-called event- related potentials (EKPs) and reflects the neural processing of faces.

Compared to the processing of other visual stimuli, potentials in the processing of faces show a negation of the signal 130-200 ms after the stimulus was shown. The largest rash is caused by occipito-temporal electrodes. The underlying signal sources are assigned to the fusiform gyrus and the inferior temporal gyrus. This could be confirmed with electrocorticographic measurements. The N170 generally shows a right hemispherical lateralization and is associated with the structural encoding of faces. Using transcranial magnetic stimulation in combination with electroencephalography it could be shown that the N170 can be modulated top-down signals from the prefrontal cortex .

history

In 1996 the N170 was first described by Shlomo Bentin and colleagues. In their study, participants looked at images of faces as well as other objects. The neural response to human faces and facial parts (e.g. eyes) was different compared to other stimuli, including faces of animals, other body parts, and cars.

In earlier work by Bötzel and Grüsser from 1989, an attempt was made to first describe an EKP component that is related to the processing of human faces. They showed the observers sketches (in one experiment) and black and white photographs (in two additional experiments) of faces, trees and chairs. Compared to other stimulus categories, faces caused greater positivity after approximately 150 ms. This reached its maximum via central electrodes. The topography of this effect and the lack of lateralization led to the conclusion that this face-specific potential is not due to activations in face-processing areas in the occipito-temporal cortex, but can be assigned to the limbic system . Subsequent work referred to this component as vertex positive potential (VPP).

To explain the discrepancy between the two previous findings, Joyce and Rossion analyzed EKPs from 53 head electrodes while subjects viewed faces and other stimuli. After recording, they referenced the signal with some commonly used reference electrodes, including the nose and mastoid. As a result, they showed that the N170 and VPP can be assigned to the same dipole and thus go back to the same neural generators. So they are the same neural processes.

Functional sensitivity

The three best-studied characteristics of the N170 are changes in alignment, ethnicity, and emotional expressions of faces.

It could be shown that inverted faces (upside down) are more difficult to perceive (see Thatcher illusion ). In a groundbreaking study, Bentin et al. Report that inverted faces are associated with a longer latency of the N170 component. The time course of the face inversion effect (FIE) was then examined by Jacques and colleagues using an adaptation paradigm. The effect described below is manipulated. When the same stimulus is presented multiple times, the neural response decreases over time; however, if another stimulus is presented, the response recovers. The condition under which a "release of the adaptation" takes place thus represents a possibility of measuring the stimulus similarity. In their experiment, Jacques et al. Report that the release of the adaptation for inverted faces takes place smaller and 30 ms later. This indicates that additional neuronal processing steps are required to detect the equality of inverted faces.

In an experiment to investigate the effects of ethnicity on the amplitude of the N170, it was found that an ethnicity effect occurs in connection with the face inversion effect. Vizioli and colleagues investigated the effect of impaired facial perception while subjects were shown images of faces of the same or a different ethnic group. The research team developed an N170 experiment based on the premise that perceptual experiences play a critical role in the face inversion effect. According to this, viewers with strong visual expertise in viewing faces of the same ethnic group (holistic processing) should show a greater face inversion effect compared to images of faces of other ethnic groups. The authors recorded EEGs from European and Chinese test subjects. Images of faces of European, East Asian, and African American descent were shown in upright and inverted orientations. All facial stimuli were clipped so that external features (i.e. hair, beards, hats, etc.) were not seen. Both groups showed a later N170 with a larger amplitude (over the right hemisphere ) for inverted compared to upright faces of the same ethnicity. No face inversion effect could be detected for faces of other ethnic groups shown upright. In addition, no ethnicity effect with regard to the peak amplitude and latency of the N170 for upright faces could be observed in either group of test persons. In contrast, inverted faces enlarged and delayed the N170 amplitude. This led to the conclusion that the inexperience in viewing inverted faces makes it difficult to process them. This effect occurs regardless of the ethnicity of the faces shown.

In addition to modulation through alignment and ethnicity, emotional expressions are the focus of N170 research. In an EKP study, Righart and de Gelder showed that early stages of facial processing in the categorization of anxious and happy facial expressions are influenced by emotional scenes. In their paradigm, the test subjects looked at color images of happy and fearful faces, which overlapped in the middle with images of natural scenes. In order to control the basic image properties (e.g. color saturation or brightness), the pixel positions in all scene images were mixed. The result of the experiment shows that emotion effects are associated with the N170. This has a larger (more negative) amplitude in faces that appear in a fearful compared to a happy or neutral context. In particular, the left-occipito-temporal portions of the N170 were significantly increased for intact fearful faces when they were shown in fearful scenes. Accordingly, the levels were not that high when a scared face was shown in a happy or neutral scene. Similar effects could be shown on intact happy faces, even if the amplitudes were not as high as for fearful faces or scenes. Righart and de Gelder conclude from this that information from task-irrelevant scenes can be quickly linked with information from facial expressions. This context information becomes relevant in the early stages of processing when distinguishing between facial expressions.

Ghuman and colleagues used electrocorticography to record neural signals directly from the fusiform facial area. They report that although the N170 reacts selectively to faces in comparison to other stimuli, it is not sensitive to the identity of a face. Instead, they show that the specifically perceived face can be decoded from the activity between 250 and 500 ms. This corresponds to the hypothesis that identity processing begins with the N250. This result suggests that the N170 is important for the general detection and processing of faces and represents the foundation for further processing steps in face individualization.

Generators

Because of the speed and reliability with which people are able to recognize faces, great efforts have been made to explain the underlying neural processes. Early research on prosopagnosia ("face blindness") shows that damage to the occipito-temporal region leads to a disturbed or completely lacking ability to recognize faces. Further information on the importance of this region in facial processing was provided by fMRI studies. A region of the fusiform gyrus , the "fusiform face area" reacts selectively to images of faces.

Intracranial recordings of humans using electrocorticography offer clear evidence for the fusiform face area as a generator of the N170. Nevertheless, it can be assumed that other regions of the face processing network are also involved in the N170.

An examination of the N170 used EKP source location techniques to estimate possible locations of N170 generators. The result indicates the posterior part of the superior temporal sulcus . It should be noted, however, that these analysis techniques run the risk of providing inaccurate results due to sources of error, which is why there is an ongoing debate and development to increase their validity.

Faces or interstimulus variance

In 2007, Guillaume, Thierry, and colleagues questioned the face specificity of the N170. In most previous studies, the N170 appeared when frontal views of faces were compared to other objects, which, however, could appear in different orientations and configurations. In their study they introduced a new factor: similarity. Stimuli could be faces or non-faces, and each class could have great or little resemblance. Similarity was reported as the correlation between the pixel values for pairs in the same category. When EKPs were compared for different similarity conditions, they found a typical N170 effect for weakly similar non-faces compared to strongly similar faces. Another finding, however, was that strongly similar non-faces produced a significant N170, while it could not be detected for weakly similar faces. This result led the authors to believe that the N170 is a measure of stimulus similarity rather than facial perception per se.

Rossion and Jacques then ascertained the similarity between objects for some other object categories examined in previous studies of the N170. They show that faces evoke a stronger N170 than other stimulus classes with comparable similarity values ​​(e.g. houses, cars or shoes). While Thierry et al. cannot explain why there is a similarity effect in the N170, Rossion and Jacques speculate that less similarity leads to greater variance in response latency. Since EKP components are calculated by calculating the average of the measurements of many individual trials, a high latency variance leads to a "smear" of the answer. The response amplitude appears to be reduced. Rossion and Jacques also criticize the methodology of the study by Thierry and colleagues. They found that it is difficult or impossible to detect the difference between very similar faces and very similar non-faces with the selected electrode locations.

Web links

  • Bruno Rossion's laboratory provided an overview of research into the N170.

Individual evidence

  1. ↑ a b c Avniel Singh Ghuman, Nicolas M. Brunet, Yuanning Li, Roma O. Konecky, John A. Pyles, Shawn A. Walls, Vincent Destefino, Wei Wang, R. Mark Richardson: Dynamic encoding of face information in the human fusiform gyrus . In: Nature Communications . 5, January 1, 2014, ISSN  2041-1723 , p. 5672. doi : 10.1038 / ncomms6672 . PMID 25482825 . PMC 4339092 (free full text).
  2. ^ A b T. Allison, A. Puce, DD Spencer, G. McCarthy: Electrophysiological studies of human face perception. I: Potentials generated in occipitotemporal cortex by face and non-face stimuli . In: Cerebral Cortex (New York, NY: 1991) . 9, No. 5, August 1, 1999, ISSN  1047-3211 , pp. 415-430. doi : 10.1093 / cercor / 9.5.415 . PMID 10450888 .
  3. ↑ a b Does physical interstimulus variance account for early electrophysiological face sensitive responses in the human brain? Ten lessons on the N170 . In: NeuroImage . tape 39 , no. 4 , February 15, 2008, ISSN  1053-8119 , p. 1959–1979 , doi : 10.1016 / j.neuroimage.2007.10.011 ( sciencedirect.com [accessed December 8, 2018]).
  4. ^ Top-down interference and cortical responsiveness in face processing: A TMS-EEG study . In: NeuroImage . tape 76 , August 1, 2013, ISSN  1053-8119 , p. 24–32 , doi : 10.1016 / j.neuroimage.2013.03.020 ( sciencedirect.com [accessed December 8, 2018]).
  5. ^ A b Shlomo Bentin, Truett Allison, Aina Puce, Erik Perez, Gregory McCarthy: Electrophysiological Studies of Face Perception in Humans . In: Journal of Cognitive Neuroscience . tape 8 , no. 6 , November 1, 1996, ISSN  0898-929X , p. 551-565 , doi : 10.1162 / jocn.1996.8.6.551 , PMID 20740065 , PMC 2927138 (free full text) - ( mitpressjournals.org [accessed December 8, 2018]).
  6. ↑ O.-J. Grüsser, K. Bötzel: Electric brain potentials evoked by pictures of faces and non-faces: a search for “face-specific” EEG potentials . In: Experimental Brain Research . tape 77 , no. 2 , September 1, 1989, ISSN  1432-1106 , pp. 349-360 , doi : 10.1007 / BF00274992 ( springer.com [accessed December 8, 2018]).
  7. ^ DA Jeffreys: A face-responsive potential recorded from the human scalp . In: Experimental Brain Research . tape 78 , no. 1 , November 1, 1989, ISSN  1432-1106 , pp. 193-202 , doi : 10.1007 / BF00230699 ( springer.com [accessed December 8, 2018]).
  8. ↑ Bruno Rossion, Carrie Joyce: The face-sensitive N170 and VPP components manifest the same brain processes: The effect of reference electrode site . In: Clinical Neurophysiology . tape 116 , no. 11 , November 1, 2005, ISSN  1872-8952 , p. 2613–2631 , doi : 10.1016 / j.clinph.2005.07.005 , PMID 16214404 ( clinph-journal.com [accessed December 8, 2018]).
  9. ^ Robert K. Yin: Looking at upside-down faces. In: Journal of Experimental Psychology . tape 81 , no. 1 , 1969, ISSN  0022-1015 , pp. 141–145 , doi : 10.1037 / h0027474 ( apa.org [accessed December 8, 2018]).
  10. ↑ Bruno Rossion, Olivier d'Arripe, Corentin Jacques: The time course of the inversion effect during individual face discrimination . In: Journal of Vision . tape 7 , no. 8 , May 1, 2007, ISSN  1534-7362 , p. 3–3 , doi : 10.1167 / 7.8.3 ( arvojournals.org [accessed December 8, 2018]).
  11. ↑ Roberto Caldara, Guillaume A. Rousselet, Kay Foreman, Luca Vizioli: Inverting faces elicits sensitivity to race on the N170 component: A cross-cultural study . In: Journal of Vision . tape 10 , no. 1 , January 2, 2009, ISSN  1534-7362 , p. 15–15 , doi : 10.1167 / 10.1.15 ( arvojournals.org [accessed December 8, 2018]).
  12. ↑ Beatrice de Gelder, Ruthger Righart: Rapid influence of emotional scenes on encoding of facial expressions: an ERP study . In: Social Cognitive and Affective Neuroscience . tape 3 , no. 3 , September 1, 2008, ISSN  1749-5016 , p. 270–278 , doi : 10.1093 / scan / nsn021 , PMID 19015119 , PMC 2566764 (free full text) - ( oup.com [accessed December 8, 2018]).
  13. ↑ Vera C. Blau, Urs Maurer, Nim Tottenham, Bruce D. McCandliss: The face-specific N170 component is modulated by emotional facial expression . In: Behavioral and Brain Functions . tape 3 , no. 1 , January 23, 2007, ISSN  1744-9081 , p. 7 , doi : 10.1186 / 1744-9081-3-7 , PMID 17244356 , PMC 1794418 (free full text).
  14. ↑ James W. Tanaka, Tim Curran, Albert L. Porterfield, Daniel Collins: Activation of preexisting and acquired face representations: the N250 event-related potential as an index of face familiarity . In: Journal of Cognitive Neuroscience . 18, No. 9, September 1, 2006, ISSN  0898-929X , pp. 1488-1497. doi : 10.1162 / jocn.2006.18.9.1488 . PMID 16989550 .
  15. ^ Roxane J. Itier, Margot J. Taylor: Source analysis of the N170 to faces and objects . In: Neuroreport . tape 15 , no. 8 , June 7, 2004, ISSN  0959-4965 , p. 1261-1265 , PMID 15167545 .
  16. ↑ Luck, Steven J. (Steven John), 1963-: An introduction to the event-related potential technique . Second ed. Cambridge, Massachusetts 2014, ISBN 978-0-262-32405-2 .
  17. ^ Alan J. Pegna, Paul Downing, Clara D. Martin, Guillaume Thierry: Controlling for interstimulus perceptual variance abolishes N170 face selectivity . In: Nature Neuroscience . tape 10 , no. 4 , April 2007, ISSN  1546-1726 , p. 505-511 , doi : 10.1038 / nn1864 ( nature.com [accessed December 8, 2018]).