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The main goal of this study was to examine behavioral and neural correlates of emotion priming. The function of laughter was of particular interest. That is, whether or not laughter functions as a positive prime and whether laughter-specific effects could be reversed under social anxiety. If so, this finding would provide evidence of flexibility in comprehending the meaning of laughter in different contexts and its effects at the neurocognitive level.

First, we hypothesized that emotionally charged (positive or negative) sounds would prime affectively congruent emotions and emotion representations (Hypothesis 1: Emotion Priming). To test this hypothesis we examined relatedness effects for the control (IADS) stimuli. We expected to see faster or more accurate responses (or both) to affectively related ("congruent") prime–target pairs in comparison with unrelated ("incongruent") stimuli. In addition, we expected to see ERP correlates of emotion priming. Based on previous findings (see Table 3), we expected that priming effects would modulate late ERP components (N400, LPP) that reflect higher cognitive processes. In particular, if the priming effect is due (in whole or in part) to semantic processing (i.e., more symbolic representation of meaning), then we would expect to see N400 effects of emotion priming. By contrast, if the priming effect involves non- semantic processes that contribute to emotion evaluation, then we would expect to see LPP effects.

It is important to note that emotion priming is expected to look different for positive and negative targets. For example, if emotion priming elicits N400 effects, there should be larger N400s (greater negativity over centroparietal regions at approximately 400 ms) in response to positive targets when preceded by negative sounds, because the positive targets are less expected. However, the same positive words should elicit smaller N400s when preceded by

positive sounds, because they are more expected within this context. For this reason, it was important to examine valence-specific effects, to help disentangle effects of priming and effects of target valence (Hypothesis 2).

The second hypothesis addresses whether positive and negative stimuli elicit different behavioral or ERP responses and whether these differences reflect a negativity or a positivity bias (Hypothesis 2: Valence-specific Effects). Furthermore, it is possible that target valence effects alter or obscure emotion priming effects. For this reason, it will be important to look at valence-specific responses to words, and to consider how these may impact behavioral and N400 measures of priming.

Based on previous findings (see Tables 1-2), stimuli of different valence categories show numerous effects on ERP patterns, primarily in the EPN and LPP pattern windows. The different stimulus valence categories compared were usually positive, negative, and neutral and suggest three possible ways valence specific effects could emerge. There could be a negativity bias, a positivity bias, or no bias toward a particular valence in the ERP patterns. It is hypothesized that ERP components such as the EPN and LPP will not differ in latency or amplitude when positive and negative stimuli have been matched on arousal.

Hypotheses 3 and 4 build on these first two questions. Question 3 focused on whether laughter-specific effects were found within the priming paradigm. Hypothesis 4 focused on the possibility that laughter-specific effects might differ under a social anxiety manipulation.

Hypothesis 3 addresses whether there are laughter-specific responses in the ERPs that are differentiated from ERPs evoked by other valenced primes (Hypothesis 3: Laughter-specific Effects).Some researchers have reported that stimuli that are of high evolutionary significance, such as images of mutilation, erotica, and facial expressions, (Schupp et al. 2003; Aeschlimann

et al., 2009; Meyer, Zysset, Von Cramon, & Alter, 2005; Hinojosa et al., 2009) are preferentially processed compared to stimuli that have learned emotional significance, such as words. In addition, there is evidence to suggest that human vocalizations are more effective at conveying affect than other sounds, and that positive sounds are more easily recognized than other environmental sounds (including negative human vocalizations) (Aeschlimann et al., 2008). If laughter primes are "special" in either of these two senses, we might expect to see laughter- specific ERP effects.

Because this is the first study of laughter priming and the first study to examine ERP responses to laughter, we do not have evidence to support a prediction about ERP responses to laughter. However, if laughter elicits qualitatively distinct neurocognitive processes, we expect to see ERP patterns that reflect these differences. If laughter is a qualitatively different (category- specific) positive prime, it is hypothesized that ERP patterns should reflect this difference.

Our last question was whether emotion priming with laughter was different in a context that promotes social anxiety (Hypothesis 4). When the socioemotional context is altered to induce feelings and thoughts about social failure, the ERP patterns related to laughter primed stimuli should differ from those evoked in a neutral context. If the manipulation succeeds, laughs should serve as negative rather than positive affective primes. Therefore, it is hypothesized that laughter priming effects should be reversed following the social context manipulation, whereas effects of other prime sounds should show little or no difference from the neutral context.

3DEVELOPMENT AND VALIDATION OF EXPERIMENT STIMULI

This present investigation involves an emotion priming task utilizing three types of stimuli: (1) short bouts of laughter, which function as primes, (2) positive and negative IADS

sounds, and (3) positive and negative words, which function as targets. Described in this section are the procedures used to develop the set of sound stimuli for the priming task. Priming tasks in many previous studies used SOA lengths of 200-300 ms. This SOA range is often used primarily due to the expectation that the effect of the prime on the target was very short lived, and longer SOAs would not yield priming effects (Hermans, De Houwer, & Eelen, 2001; Hermans, Spruyt, & Eelen, 2003). However, the focus of this investigation is on laughter, which is a sound that unfolds over time. When laughs were truncated to shorter lengths than 500 ms, the resulting sound often ended abruptly and sounded unpleasant. However, when laughs were truncated at 500 ms, it allowed for sufficient vocal energy of the laugh to be transmitted for a laugh to be recognizable. Environmental sounds selected from the IADS were also truncated to 500 ms to control for prime duration.

3.1Sound Stimuli (Primes)