Fear in your eyes? The importance of the eyes for rapid discrimination of fearful facial expressions

Abstract

The human face and its profound relevance for social cognition has been a topic of interest in psychology for a long time. Many different aspects of face processing have been investigated and one of these areas of interest is how we perceive and process the facial expressions of other people to recognize their emotions. Another issue that has caused a considerable amount of debate in the past decade is the question of how the eyes are processed and how important a facial feature they are. Hypotheses have been formed about a separate eye processor that coexists in the human brain with a distinct face processor. The present study sought to find out if there is a connection between the above mentioned two issues, and to find answers to the question of whether the eyes are important for the rapid discrimination of fearful and neutral facial expressions as measured with event-related potentials. The participants of this study were healthy volunteer adults (22 participants, mean a!

ge 27 years). The participants viewed fearful and neutral faces in three different conditions regarding the eye region of the stimulus. The conditions were intact full faces, full faces with the eyes covered with sunglasses, and isolated eyes. The participants viewed the stimuli from a computer screen while their EEG activity was recorded. ERP waveforms were then averaged from the data, and peak amplitude and latency of the early P100 and N170 components of the ERP were analysed. Based on prior research, a clear difference was expected to be found between the responses to the fearful and neutral stimuli, and also that the isolated eyes would evoke a distinct response from the full faces. The visibility of the eye region was expected to have an effect on the responses to the facial expressions. The results lent support for the eyes being a special facial feature but conclusive evidence was not found for a critical role of the eyes in the discrimination of fearful and neutral expressions. Specifically, the results of the present study partly replicated results of prior studies in showing enhanced N170 amplitude and delayed N170 latency for isolated eyes as compared to full face stimuli (irrespective of facial expression). The results also showed that fearful stimuli delayed the N170 latency across all three conditions, suggesting that fearful expressions may delay responses due to the involvement of the subcortical route in emotional information processing, or that they may hold the attention of the observer more effectively and thus take longer to process than the neutral faces. The fact that the latency difference was observed when the eye region alone was presented supports the hypothesis that the eye region is important for the discrimination of fearful and neutral facial expressions. The P100 component reflected only the difference between the isolated eyes and the full face stimuli. Contrary to the expectations, no effects of emotional expression were found on the P100 component or the N170 amplitude. There are several possible explanations as to why the results of the present study were inconclusive. One of these includes the possibility that openness of the eyes (i.e., whether the expression fearful or not) could be read from all the stimuli because the eyebrows were in plain sight in all three conditions. Further investigation is needed to find more solid evidence for the importance of the eyes.

KEY WORDS: emotion, fear, facial expressions, eye detector, ERP.