Discriminating between Changes in Bias and Changes in Accuracy for Recognition Memory of Emotional Stimuli

Article excerpt

A debate has emerged as to whether recognition of emotional stimuli is more accurate or more biased than recognition of nonemotional stimuli. Teasing apart changes in accuracy versus changes in bias requires a measurement model. However, different models have been adopted by different researchers, and this has contributed to the current debate. In this article, different measurement models are discussed, and the signal detection model that is most appropriate for recognition is adopted to investigate the effects of valence and arousal on recognition memory performance, using receiver operating characteristic analyses. In addition, complementary two-alternative forced choice experiments were conducted in order to generalize the empirical findings and interpret them under a relatively relaxed set of measurement assumptions. Across all experiments, accuracy was greater for highly valenced stimuli and stimuli with high arousal value. In addition, a bias to endorse positively valenced stimuli was observed. These results are discussed within an adaptive memory framework that assumes that emotion plays an important role in the allocation of attentional resources.

Understanding the interaction between emotion and memory is central to understanding our motivations, our behavior, and our well being. In laboratory research, a study-test procedure is often used that varies the emotional content of studied materials. Such materials usually consist of words or pictures that vary in the responses they provoke in the average individual (Lang, Bradley, & Cuthbert, 1992, 2005). These normatively emotional stimuli vary on two distinct dimensions: valence, or the item's subjective emotional value, ranging from positive to negative; and arousal, or how subjectively intense or exciting it is, ranging from low to high. Although the two variables are positively correlated, a large number of prior findings have shown that both are involved in enhancing memory (e.g., Hamann, Cahill, & Squire, 1997; see Hamann, 2001, for a review).

Enhanced memory of emotional events has been attributed to the activation of the amygdala (Windmann & Kutas, 2001), the capture of attention (Cahill, Babinsky, Markowitsch, & McGaugh, 1995; Cahill & McGaugh, 1998; Estes & Adelman, in press; Hamann, 2001 ; Ochsner, 2000), the binding of emotional stimuli to context (MacKay et al., 2004; Mather & Nesmith, 2008), and stimulus distinctiveness (Ochsner, 2000; reviewed in Christianson, 1992). Even though one might question whether these explanations are mutually exclusive, all of them predict that memory should be better for events that elicit heightened states of emotion or arousal. However, the findings concerning enhanced memory for emotional stimuli have come largely from free recall experiments (e.g., Danion, Kauffmann-Muller, Grange, Zimmermann, & Greth, 1995; Doerksen & Shimamura, 2001 ; Guy & Cahill, 1999; Hertel & Parks, 2002; Kensinger, Brierley, Medford, Growdon, & Corkin, 2002; Kensinger & Corkin, 2003). The findings in the episodic recognition literature are far less consistent in their support of these hypotheses. Some have shown that negative words are recognized better than neutral words (Comblain, D'Argembeau, Van der Linden, & Aldenhoff, 2004; Hamann, 2001; Kensinger & Corkin, 2003; Ochsner, 2000; Pesta, Murphy, & Sanders, 2001), whereas others have shown no difference in accuracy for neutral versus negative words (Doerksen & Shimamura, 2001; Ochsner, 2000). Still others have found decreased accuracy for negative stimuli (Danion et al., 1995; Dougal & Rotello, 2007; Maratos, Allan, & Rugg, 2000). In addition, some have shown that positive stimuli are recognized no better than neutral stimuli (Comblain et al., 2004; Dougal & Rotello, 2007; Ochsner, 2000), whereas others have shown that positive stimuli are recognized worse than neutral stimuli (Dougal & Rotello, 2007). …