Diagnostic Features of Emotional Expressions Are Processed Preferentially

Citation: Scheller E, Bu chel C, Gamer M ( Diagnostic Features of Emotional Expressions Are Processed Preferentially Elisa Scheller 0 Christian Bu chel 0 Matthias Gamer 0 David Whitney, University of California, Berkeley, United States of America 0 1 Department of Psychiatry and Psychotherapy, University Medical Center Freiburg , Freiburg, Germany , 2 Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf , Hamburg , Germany Diagnostic features of emotional expressions are differentially distributed across the face. The current study examined whether these diagnostic features are preferentially attended to even when they are irrelevant for the task at hand or when faces appear at different locations in the visual field. To this aim, fearful, happy and neutral faces were presented to healthy individuals in two experiments while measuring eye movements. In Experiment 1, participants had to accomplish an emotion classification, a gender discrimination or a passive viewing task. To differentiate fast, potentially reflexive, eye movements from a more elaborate scanning of faces, stimuli were either presented for 150 or 2000 ms. In Experiment 2, similar faces were presented at different spatial positions to rule out the possibility that eye movements only reflect a general bias for certain visual field locations. In both experiments, participants fixated the eye region much longer than any other region in the face. Furthermore, the eye region was attended to more pronouncedly when fearful or neutral faces were shown whereas more attention was directed toward the mouth of happy facial expressions. Since these results were similar across the other experimental manipulations, they indicate that diagnostic features of emotional expressions are preferentially processed irrespective of task demands and spatial locations. Saliency analyses revealed that a computational model of bottom-up visual attention could not explain these results. Furthermore, as these gaze preferences were evident very early after stimulus onset and occurred even when saccades did not allow for extracting further information from these stimuli, they may reflect a preattentive mechanism that automatically detects relevant facial features in the visual field and facilitates the orientation of attention towards them. This mechanism might crucially depend on amygdala functioning and it is potentially impaired in a number of clinical conditions such as autism or social anxiety disorders. - Funding: The study was supported by a grant from the Bundesministerium fu r Bildung und Forschung (BMBF, Network Social Cognition). C.B. is additionally funded by the German Research Foundation (DFG) SFB TRR 58, project B3. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Human faces are stimuli we are exposed to every day. Throughout our lives, we have probably seen thousands of faces and certainly looked at some of them more closely to discover that they show various expressions. Human communication not only consists of voice messages but is disambiguated by gesture and facial expression. In line with this reasoning, emotionally expressive faces seem to be processed preferentially as compared to neutral ones [1,2]. Thus, as social beings, it is important for us to be able to understand and interpret facially displayed emotions correctly. But how do we analyze faces to determine which expression they show us? The simple answer is that we seem to use diagnostic facial features. Already in 1944, Hanawalt showed that different facial features are important to distinguish between different specific emotions [3]. For example, he suggested the mouth to be most informative for recognizing happy faces and the eyes to be most important for detecting fearful facial expressions. Recently, these findings were confirmed with the help of technically more sophisticated approaches. In 2001, the Bubbles technique was developed [4] and used to reveal that diagnostic features differ as a function of the task at hand [5]. This latter study revealed that the eye and mouth region across a wide range of spatial frequencies were diagnostic in an identity recognition task, which may indicate that the relationship between these features is crucial for the identification of a person. By contrast, the left side of the face around the eye region was most diagnostic for gender discrimination and the mouth region was most relevant for determining whether the depicted face showed a happy or neutral facial expression. Thus, it already appeared that different sets of facial features are diagnostic for different types of task. Using a similar technique, the distribution of diagnostic facial features was determined for each of the six basic emotional expressions [6]. In this study, observers yielded best results when the eye region was visible for fearful, the mouth region for happy and a mixture of these and other facial features for neutral facial stimuli. An extraction of information from different facial features can also be assessed by monitoring eye movements and analyzing fixation patterns. Such a procedure was adopted by a number of studies focusing on clinical populations. For example, the comparison of visual scan paths of persons with autism spectrum disorder and a control group in an emotion classification task revealed a strong bias for primarily scanning the eye region in both groups [7]. Comparable results were reported by Hernandez and colleagues, who found a clear preference for fixating the eye region of sad, happy and neutral faces in autistic as well as in control subjects [8]. Additionally, there seemed to be a trend for spending relatively less time on the eye region and more time on the mouth of happy faces as compared to the other expressions in healthy controls. This may indicate that observers scanning behavior is sensitive to the diagnostic features of different emotional expressions. Although it is still debated whether patients with autism spectrum disorder scan (emotional) faces differently than healthy controls [9,10], these studies reveal that eye tracking can be highly useful for elucidating information extraction processes during face perception. However, a major drawback of these studies is the use of comparably long exposure times (typically longer than 2 s) which only allow for characterizing explicit face perception mechanisms which presumably are under conscious control. Recent evidence suggests that briefly presented faces also trigger very early, potentially reflexive, eye movements that are sensitive to the distribution of diagnostic facial features [11]. In this particular study, fearful, happy, angry and neutral faces were presented briefly (150 ms) so that observers were only able to accomplish a saccade after stimulus offset (...truncated)