Lexical processing of emotion words: ERP indexes of an early interaction between emotional valence and arousal

Abstract

Emotion recognition has been characterised according to a two-dimensional structure: valence describes the extent to which an emotion is positive or negative and arousal refers to the intensity of an emotion i.e. how exciting or calming it is. It is known that the emotional content of verbal material influences cognitive processing on a range of experimental tasks testing recollection memory, language comprehension and face processing. More recent work has also shown that emotionally valenced single words (positive or negative) tend to be processed faster than neutral words, as revealed by lexical decision latencies and event-related potentials (ERPs). These results suggest that emotional content affects word recognition (Scott et al., 2009). However, other studies report slower recognition of negative words compared to positive words suggesting an additional effect of automatic vigilance (Algom et al., 2004). These contradictory results are likely due to lack of control over important lexical and semantic features of single words (Larsen et al., 2006). Furthermore, few studies have considered the effects of emotional arousal on word recognition and the relationship between emotional valence and arousal (Kanske & Kotz, 2007; Kissler et al., 2009). This is a critical question given recent brain imaging data showing that valence modulates the increase in activation due to increasing arousal at the neural level (Lewes et al., 2007). The aim of the present study was to disentangle the effects of valence and arousal on word recog-nition and to determine at what stage of processing emotional effects take place; in an ERP experiment both variables were manipulated and a direct measure of lexical access was used, namely lexical decision. Reaction time results showed a significant effect of arousal and a significant interaction between arousal and valence: high arousal words were responded to faster than low arousal words, and this difference was more pronounced for negative words. There was no effect of valence once correlated lexical variables were controlled. ERP data were examined for early posterior negativity (EPN), a component showed to index discrimination between valenced and neutral stimuli. An interaction was observed on this component between 200-300 ms, with higher amplitudes for both negative-low arousal and positive-high arousal words. Although no previous study has tested for interactions between valence and arousal, the present results suggest a higher processing load for emotionally conflicting stimuli which elicit contrasting reactions (Robinson et al., 2004). Specifically, positively valenced and low arousal words both elicit an approach schema (mental set) whereas negatively valenced and high arousal words both elicit an avoidance mental set. More generally, the ERP results suggest that valence and arousal interact at a relatively early stage of lexical access. Our findings highlight the importance of emotional arousal and suggest that accounts of emotion effects on word recognition must integrate both valence and arousal in models of early lexical access. Implications for understanding effects of valence and arousal in affective disorders, neuropsychology and rehabilitation will be outlined. References: Algom, D., Chajut, E. & Lev, S. (2004). A rational look at the emotional Stroop phenomenon: A generic slowdown, not a Stroop effect. Journal of Experimental Psychology, 133, 323-338. Kanske, P. & Kotz, S.A. (2007). Concreteness in emotional words: ERP evidence from a hemifield study. Brain Research, 1148, 138-148. Kissler, J., Herbert, C., Winkler, I. & Junghofer, M. (2009). Emotion and attention in visual word processing ñ An ERP study. Biological Psychology, 80, 75-83. Larsen, R.J., Mercer, K.A. & Balota, D.A. (2006). Lexical characteristics of words used in emotional Stroop experiments, Emotion, 6, 62-72. Lewis, P.A., Critchley, H.D., Rotshtein, P., & Dolan, R.J. (2007). Neural correlates of processing valence and arousal in affective words. Cerebral Cortex, 17, 742-748. Robinson, M.D., Storbeck, J., Meier, B.P. & Kirkeby, B.S. (2004). Watch out! That could be dangerous: Valence-arousal interactions in evaluative processing. Personality and Social Psychology Bulletin, 30, 1472- 1484. Scott, G.G., OíDonnell, P.J., Leuthold, H. & Sereno, S.C. (2009). Early emotion word processing: Evidence from event-related potentials. Biological Psychology, 80, 95-104.