Evoked Potentials To Neutral Facial Stimuli, Previously Presented In An Emotionally Negative Context
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We all are familiar with the situation from the practice of criminalistics when a number of people are presented to the witness of crime for identification, among whom there is a criminal. One of the problems of identification is that the witness observed the criminal in a strong emotional state, and the persons proposed for identification are in a neutral state. The question arises whether the witness is able to correctly identify the criminal person under these conditions.
In order to get an answer to this question, we conducted two series of experiments, when the subjects were presented with a video fragment, in which the scene of violence was imprinted [Kanunikov, Pavlova, 2017, Kanunikov, Fomicheva, 2015]. After that, the subjects were presented with photographs of people who are not related to the scene of violence (the so-called fillers), as well as the faces of the criminal and the victims in a calm emotional state. Also, control was carried out when the same faces were presented to subjects who did not watch the film. Evoked potentials (EP) on faces were recorded in all subjects.
It is shown that the EP to the faces have a three-component structure: a positive component with a latent period of about 100 ms (P100), a negative component with a latency of 160 ms (N160), a second positive component with a latent period of 200 ms (P200).
Analysis of the results of two series of experiments revealed a significantly larger amplitude of component P200 in response to the face of the criminal and an unfamiliar person (filler face) in the temporal lobe of the right hemisphere (T6) compared to the left temporal site (T5), with P200 having a large amplitude in response to the face filler. Components P100 and N170 did not reveal differences in response to the criminal face and filler.
In the case of the control group, no significant differences in the EP were found.
In interpreting the above data, it is necessary to take into account the fact that there are two relatively independent systems in the brain: the face recognition system and the system for identifying their emotional states. This is confirmed, in particular, by the data obtained on a patient with prosopagnosia, who was not able to recognize the face of a familiar person, but correctly recognized the emotion on his face (Bruce, Young, 1986). Neurons sensitive to familiar/unfamiliar faces were found in the region of the upper temporal gyrus, and neurons responsible for emotional expressions were found in the region of the lower temporal sulcus [Hasselmo et al., 1989].
Streit et al (2000) concluded that the P2 component (with an average latency of 240 ms peak) reflects the specific processes underlying the recognition of emotional expressions. The large amplitude of the potentials in the temporal retraction of the right hemisphere in comparison with the left hemisphere confirms the hypothesis of its greater participation in the process of facial emotion [Haxby, Hoffman, Gobbini, 2000; Rivolta, 2014].
The fact that differences are observed in the right temporal region (T6) is naturally related to the fact that the right hemisphere is responsible for the perception of negative emotions. Leonard et al. (1985) showed that component P2 reflects a greater degree of activation of the temporal region of the right hemisphere in subjects with a stable negative evaluation of facial images.
Summarizing the above data, one can make the assumption that the neutral face of the criminal is capable of generating a negative emotional image in memory that activates the right temporal region.
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These findings are described in the article entitled Event-Related Potentials to Faces Presented in an Emotional Context, published by Kanunikov I.E., Pavlova V.I., and Fomicheva D.A. (St. Petersburg State University) in the journal Neuroscience and Behavioral Physiology and in the Human Face in Science, Art, and Practice, K. A. Anan’ev, V. A. Barabanshchikov, and Demidov, A. A. (eds.), Cogito-Tsentr, Moscow (2015).