Abbreviated title: Time course of emotion perception Tracing the time course of emotion perception: The impact of stimulus physics and semantics on gesture processing

2 Numerous ERP-studies reveal the differential processing of emotional and neutral stimuli. Yet, it is an ongoing debate to what extent the ERP-components found in previous research are sensitive to physical stimulus characteristics or emotional meaning. The present study manipulated emotional meaning and stimulus orientation to disentangle the impact of stimulus physics and semantics on emotional stimulus processing. Negative communicative hand gestures of Insult were contrasted with neutral control gestures of Allusion to manipulate emotional meaning. An elementary physical manipulation of visual processing was implemented by presenting these stimuli vertically and horizontally. Results showed dissociable effects of stimulus meaning and orientation on the sequence of ERP-components. Effects of orientation were pronounced in the P1-and N170-time frames and attenuated during later stages. Emotional meaning affected the P1, evincing a distinct topography to orientation effects. While the N170 was not modulated by emotional meaning, the EPN-and LPP-components replicated previous findings with larger potentials elicited by the Insult gestures. These data suggest that the brain processes different attributes of an emotional picture in parallel and that a coarse semantic appreciation may already occur during relatively early stages of emotion perception. Introduction Reacting rapidly and appropriately to threatening or life-sustaining stimuli is imperative for an organism's survival in a complex environment. Thus, motivationally relevant external stimuli may automatically induce a state of natural selective attention (Lang et al., 1997) and effectively guide ensuing perceptual processes. Research utilizing event-related brain potentials (ERP) has determined several indicators of preferential emotion processing along the time scale of visual perception (Flaisch et al., 2008b; Schupp et al., 2006). As emotionally guided perceptual amplification supposedly occurs from very early to relatively late stages of visual processing, the extent to which the observed emotional effects are driven by stimulus differences on a purely physical level or the semantic information associated with such differences is under debate. In the present study, we provide evidence that early indicators of emotion perception conceivably reflect semantic stimulus content and demonstrate that the effects of physical and semantic stimulus attributes can be differentiated along the sequence of emotion perception. Preferential processing of affective pictorial stimuli unfolds in a temporal sequence from relatively early to later stages (Schupp et al., 2006). Studies utilizing ERP-measures identified several electro-cortical components presumably reflecting distinct sub-processes of emotion perception. A large body of research has established the 'early posterior negativity' (EPN) and the 'late positive potential' (LPP) as indices of …