Effects of emotional content on free recall

For memory tested at a delay of 30 minutes overall performance was small. Nevertheless, pleasant adjectives were still remembered better than unpleasant and neutral ones. Superior recall for pleasant adjectives indicates that during encoding some pleasant information could be retained more than momentarily. Previous ERP studies have shown that late positive potentials are associated with better memory consolidation and recall (e.g., Dolcos et al., 2002; Palomba et al., 1997). The memory advantage for pleasant adjectives in contrast to unpleasant adjectives thus agrees with the stronger impact of pleasant adjectives on late positive potentials (LPP) during word presentation. It agrees also with demonstrations of better recall of pleasant events during shallow encoding conditions (e.g., Ferré, 2003; Kiefer et al., in press) as well as with findings reported for short memory retention intervals showing that a memory advantage for pleasant stimuli at immediate recall (e.g., minutes, days) is accompanied with larger cortical positivities to pleasant in contrast to unpleasant stimuli during encoding (e.g., Palomba et al., 1997). In RSVP designs competition from subsequent items leads to forgetting of most of the items. Meaning can be extracted rapidly. However, only that part of information that holds attention will be represented in memory and will be retained more than momentarily (e.g., Potter, 2005 for review). Previous RSVP research has shown that emotional stimuli benefit from rapid extraction of meaning at early levels of perception due to a rapid capture of attention (e.g., Anderson, 2005; Anderson et al., 2001; Junghöfer et al., 2001; Keil et al., 2004). None of the studies reported whether emotional stimuli attracted attention during later time points nor whether emotional stimuli obtained priority in memory processing. Extending this body of research, our results demonstrate that emotional facilitation can be reliably examined within RSVP designs by analyzing early and late brain potentials and testing memory performance.

Even when presented on the fly and no instruction to attend was given, emotional words obtained priority during early and late processing stages and were remembered better than neutral words. Emotional arousal and valence cooperated differently during early and late stages of stimulus processing suggesting that motivational states can change within milliseconds. At early perceptual processing stages, stimulus detection benefited from emotional arousal acting as an unspecific alerting system ensuring rapid orienting to potentially dangerous or attractive stimuli. For faster processing speeds negative valence facilitated perception to assure adaptive survival giving primacy to unpleasant verbal concepts. At a postperceptual level pleasant valence enhanced semantic processing and memory encoding implicating a processing bias for words that match with individual pleasure preferences.

6. Conclusion

The present results complement previous studies on affective processing in important ways. The results demonstrate that emotional facilitation is not restricted to biologically prepared stimuli such as pictures and faces but extends to symbolic verbal stimuli with ontogenetically learned emotional significance. EEG-ERP potentials provide a means of studying emotion effects of different types of stimulus material and provide insight in the time course of emotional meaning processing. Our ERP results show how emotional arousal and valence interact at different levels of processing while subjects passively attend to a stream of incoming words. At early levels of processing the results support the notion that emotional arousal exerts a powerful effect by enhancing perception of stimuli with unpleasant and pleasant significance. Akin to affective picture studies we found that this early processing advantage is reflected in an early negativity potential that is most pronounced over the visual cortex, and occurs at similar latencies as observed for affective picture stimuli. The potential was elicited when participants simply viewed rapidly presented emotional words strengthening the view that emotional stimuli capture attention spontaneously. In support of a negativity bias in emotion perception, unpleasant words captured attention more efficiently than pleasant ones at faster stimulation rates where attention is limited and stimuli have to compete for perceptual awareness.

Interestingly, this detection superiority for unpleasant words was not associated with better recall for unpleasant words. Similarly, Palomba et al. (1997) reported early facilitation of unpleasant and pleasant pictures. However, early facilitation did not correlate with later memory performance. Only in the later time windows of the LPP, enhanced cortical activation elicited by pleasant and unpleasant pictures was associated with better memory recall. Previous RSVP studies have demonstrated that meaning of words and pictures can be extracted much faster than it is represented in memory. At an early level of perceptual processing, semantic processing may be coarse (e.g., Mogg & Bradley, 1998; Potter, 2005) and emotional information is lost when not followed by a more detailed analysis that proceeds after the emotional significance of a stimulus has been identified. Apart from perception, emotional facilitation must include other aspects of cognitive processing to ensure that emotional meaning is integrated in the current context and gets updated in memory. In the literature two brain potentials have been associated with contextual integration of meaning: The N400 potential and late positive potentials (LPP).

Whereas the N400 potential reflects the ease with which meaning can be integrated in the current context, late positive components (LPP) signal the updating process of meaning in memory. To date, a multitude of emotion studies has reported affective modulation of late brain potentials such as the N400 and the LPP. Emotional arousal and valence effects have been

found. With respect to emotional valence some studies have reported stronger activation for pleasant pictures, happy faces or pleasant words than unpleasant or neutral ones. Concerning N400 effects studies using verbal material suggest better integration of mood-congruent pleasant words than for mood-incongruent unpleasant words (e.g., Chung et al., 1996; Kiefer et al., in press; Schirmer et al., 2005). Concerning late positive potentials, pleasant picture stimuli provoke larger P3 potentials than unpleasant pictures when tasks require no explicit emotional stimulus evaluation (Delplanque et al., 2004; Keil et al., 2002). Erotic pictures having the highest rated arousal intensities produce larger late positive potentials than arousing unpleasant pictures (Schupp et al., 2004a). In adults, happy faces compared to angry faces evoke larger P3 potentials (Kestenbaum & Nelson, 1992). Larger P3 and late positive potentials have also been observed for pleasant nouns in contrast to unpleasant and neutral nouns (e.g., Schapkin et al., 2000). Several variables such as the hedonic nature of the stimulus, its emotional intensity, task instructions, attentional demands as well as individual preferences may influence the mobilization of processing resources devoted to affective stimuli at later processing stages.

Using a passive viewing task the current results emphasize findings of a stronger impact of pleasant information on cognitive processing as indexed by the N400 and the LPP suggesting that subjects sustained more engaged in the processing of repeatedly presented pleasant rather than unpleasant or neutral adjectives. In support of the view that deeper engagement during encoding reflects memory updating, pleasant words were also better remembered than unpleasant and neutral adjectives. The beneficial effect of positive emotions/ positive affect on cognitive processing and its practical implications has been reviewed in recent papers (e.g., Isen, 2001; Fredrickson & Branigan, 2005) implicating that pleasant emotions broaden the scope of attention, enhance problem-solving, decision making, memory and well-being. Given that emotional states can change within milliseconds, ERP studies provide a suitable means to study the temporal dynamics and the differential impact of emotion on perception and cognition.

Theoretically, two-stage competition models of attention (Chun et al., 1995) provide a framework helping to explain ERP emotion effects obtained at early and late processing stages.

According to these models, emotion effects reflected in amplitude modulations of the early negativity potential may then be interpreted as reflecting prioritized processing of emotional meaning at the perceptual stage of competition for attention. Emotional meaning can be extracted soon at this level but may be lost. Emotional stimuli that hold attention at a postperceptual level have access to a capacity-limited second processing stage where stimuli become integrated in the current context and get represented in memory. This postperceptual integration may be indexed by the N400 and LPP component.

IV. Chapter 3

Study 3: Brain structures involved in the incidental processing of