Pupillary responses reveal infants’ discrimination of facial emotions independent of conscious perception Sarah Jessen a,⇑ , Nicole Altvater-Mackensen a , Tobias Grossmann a,b a Research Group Early Social Development, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1A, 04103 Leipzig, Germany b Department of Psychology, University of Virginia, Gilmer Hall, 485 McCormick Rd., Charlottesville, VA, USA article info Article history: Received 9 June 2015 Revised 3 February 2016 Accepted 11 February 2016 Available online 18 February 2016 Keywords: Infants Subliminal processing Pupillometry Emotions Eyetracking abstract Sensitive responding to others’ emotions is essential during social interactions among humans. There is evidence for the existence of subcortically mediated emotion discrimination processes that occur inde- pendent of conscious perception in adults. However, only recently work has begun to examine the devel- opment of automatic emotion processing systems during infancy. In particular, it is unclear whether emotional expressions impact infants’ autonomic nervous system regardless of conscious perception. We examined this question by measuring pupillary responses while subliminally and supraliminally pre- senting 7-month-old infants with happy and fearful faces. Our results show greater pupil dilation, index- ing enhanced autonomic arousal, in response to happy compared to fearful faces regardless of conscious perception. Our findings suggest that, early in ontogeny, emotion discrimination occurs independent of conscious perception and is associated with differential autonomic responses. This provides evidence for the view that automatic emotion processing systems are an early-developing building block of human social functioning. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Emotional communication is an essential aspect of human social encounters (Frith, 2009). Perceiving emotional expressions in others triggers automatic physiological responses in the obser- ver that are regulated by the autonomic nervous system such as changes in heart rate, skin conductance, and pupil dilation (Bradley, Miccoli, Escrig, & Lang, 2008; Ramachandra, Depalma, & Lisiewski, 2009). These responses reflect changes in activation or suppression of the sympathetic and parasympathetic parts of the autonomic nervous system and are thought to facilitate evolution- ary adaptive responding to relevant information (Porges, 2003). Specifically, viewing facial emotional expressions has been shown to elicit changes in pupil dilation that occurred regardless of con- scious perception of the face in adults (see Laeng, Sirois, & Gredeback, 2012, for review). Increased pupil dilation reflects greater activation of the sympathetic nervous system or a suppres- sion of the parasympathetic nervous system, mediated by the locus coeruleus (Bradley et al., 2008; Laeng et al., 2012). The locus coer- uleus has strong connections to other subcortical brain structures such as the amygdala (Van Bockstaele, Colago, & Valentino, 1998) and this is argued to support a close coupling between changes in pupil size and affective processing (Laeng et al., 2012). In partic- ular, one can distinguish between phasic and tonic activation of the locus coeruleus; while the former characterizes responses to speci- fic events, the latter is related to changes in task or a person’s over- all attentional state (Laeng et al., 2012). Measuring pupillary responses to emotional stimuli has become an established method to examine subcortically mediated auto- nomic responses (sympathetic arousal) in adults (Bradley et al., 2008). Increased pupil dilation has typically been observed in response to emotionally arousing stimuli irrespective of valence (Bradley et al., 2008; Partala & Surakka, 2003). However, for facial expressions adults tend to show an increased pupil dilation in response to negative, especially fearful, compared to happy facial expressions (Laeng et al., 2013). The sympathetic arousal (pupil dilation) seen to fearful expressions has been argued to reflect a response that may prepare the body to flee (e.g., Porges, 2003). While most prior work has focused on consciously perceived emo- tions, changes in pupil size have also been observed in response to emotional stimuli that are not perceived consciously but were pre- sented subliminally. As for supraliminal stimuli, an increase in pupil size in adults occurs in response to masked fearful facial expressions, which are not consciously perceived (Laeng et al., 2013). Along these lines, it has been shown that patients suffering from unilateral cortical blindness show a comparable increase in http://dx.doi.org/10.1016/j.cognition.2016.02.010 0010-0277/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: jessen@cbs.mpg.de (S. Jessen), altvater@cbs.mpg.de (N. Altvater-Mackensen), grossmann@virginia.edu (T. Grossmann). Cognition 150 (2016) 163–169 Contents lists available at ScienceDirect Cognition journal homepage: www.elsevier.com/locate/COGNIT