Memory for emotional events is usually very good even when tested shortly after study, before it is altered by the influence of emotional arousal on consolidation. Immediate emotion-enhanced memory may stem from the influence of emotion on cognitive processes at encoding and retrieval. Our goal was to test which cognitive factors are necessary and sufficient to account for EEM, with a specific focus on clarifying the contribution of attention to this effect. In two experiments, participants encoded negative-arousing and neutral pictures. In Experiment 1, under divided-attention conditions, negative pictures were better attended and recalled even when they were matched with neutral pictures on semantic relatedness and distinctiveness, and attention at encoding predicted subsequent emotion-enhanced memory. The memory advantage for emotional stimuli was only abolished when attention to emotional and neutral stimuli was also matched, under full-attention in Experiment 1 and under divided-attention in Experiment 2. Emotional memory enhancement was larger in Experiment 1 when the control of organization and distinctiveness was relaxed. These findings suggest that attention, organization and distinctiveness provide a necessary and sufficient account for immediate emotion-enhanced free recall memory.
Memory for moderately arousing emotional stimuli, such as images of violence, is better than memory for neutral stimuli. There is good evidence for emotion-enhanced memory (EEM) in both humans and non-human animals (Cahill and McGaugh, 1998 and Labar and Cabeza, 2006). Evidence from animals shows that the sympathetic emotional arousal response enhances long-term memory by activating the amygdala, which modulates the long-term consolidation of memory traces in the hippocampus, so that after a prolonged delay, memory for emotional events is enhanced (McGaugh, 2004). Although this model can explain a host of data from human participants (Labar & Cabeza, 2006), researchers often overlook the fact that because the modulation mechanism only influences long-term memory consolidation, it does not account for the enhanced memory in immediate long-term memory tests (Cahill & McGaugh, 1998), namely tests that occur shortly after study but following a brief distractor activity, which clears working memory. In the general discussion section we review evidence from animal studies that shows conclusively that the mechanism used by the modulation model to account for delayed EEM does not account for immediate EEM ( Bianchin et al., 1999, Ellis and Kesner, 1983, Frey et al., 2001 and Seidenbecher et al., 1997). A complementary mechanism is therefore required to account for immediate EEM, which humans exhibit readily.
The goal of the current study was to establish a cognitive account of immediate EEM. The cognitive account attributes this effect to altered encoding and retrieval of emotionally arousing events, instead of to their modulated consolidation. The notion that cognitive factors contribute to immediate EEM is not new (Cahill and McGaugh, 1998 and Kensinger and Corkin, 2004), yet it is unknown which factors are necessary and sufficient to account for this effect. Consequently, the cognitive account has had a relatively modest influence on neuroscience research. For example, a recent meta-analysis (Murty, Ritchey, Adcock, & Labar, 2010) highlighted the fact that although many brain regions are consistently associated with EEM, their contribution to EEM is under-investigated. This is likely due to the prominence of the modulation model, as researchers typically focus on brain regions relevant to that model and interpret their findings within its framework even when memory is tested shortly after study (Kensinger and Corkin, 2004, Sommer et al., 2008 and Strange et al., 2003). Moreover, researchers interested in modulated consolidation test memory after a prolonged delay, which complicates the isolation of an independent cognitive contribution (Ritchey, Bessette-Symons, Hayes, & Cabeza, 2011). Understanding the critical psychological determinants of immediate EEM can inspire and inform future research of its underlying brain mechanisms.
Our objective here was to show that the influence of three factors – organization, distinctiveness, and attention – on encoding and retrieval provides a necessary and sufficient account of immediate EEM in free recall. The two experiments reported here support this claim by showing that EEM can only be abolished when these three factors are controlled. Our approach relies on the assumption that to fully understand an empirical phenomenon, such as immediate EEM, we need to know the conditions for its manifestation, and that such understanding is evident in the ability to systematically influence the phenomenon by manipulating its triggering conditions.
The contribution of organization, distinctiveness, and attention to EEM will be reviewed next.
