If not chosen carefully, the emotional stimuli in a memory study can be more interrelated and easier to organize semantically than the neutral stimuli (Talmi & Moscovitch, 2004). That is, participants might identify thematic links among the emotional stimuli (e.g., pictures of a shark, bandage, and ambulance) more readily than among the neutral stimuli (e.g., pictures of a dolphin, handkerchief, and bus). This will render the emotional stimuli easier to organize within a given schema, ultimately leading to more elaborative encoding and easier retrieval (Einstein & Hunt, 1980; R. R. Hunt & McDaniel, 1993). Consequently, sets of emotional stimuli that are highly interrelated could result in an immediate EEM effect that would otherwise not be present if the neutral stimuli were also highly interrelated (C. Hunt, Trammel, & Krumrei-Mancuso, 2015; Talmi & Moscovitch, 2004). Indeed, many EEM studies with young adults have used two sets of neutral stimuli: a randomly selected “unrelated-neutral” set, in which item interrelatedness is generally low, and a “related-neutral” set, in which item interrelatedness is high and equal to that of the emotional stimulus set(s). Usually, the young adults remember a greater number of neutral stimuli from the high−than from the−low relatedness sets (Buchanan et al., 2006; Talmi, Luk, et al., 2007; Talmi, Schimmack, et al., 2007), sometimes remembering just as many related-neutral as emotional items (Talmi & Moscovitch, 2004). In older adults, memory for neutral word pairs improves when the pairs are related as compared to when they are unrelated. In fact, semantic relatedness can be so helpful to older adults that this can attenuate the typical age-related memory decreases seen with unrelated-neutral stimuli (Naveh-Benjamin et al., 2005, 2003).
Older adults’ EEM may therefore result in part from their ability to automatically utilize pre-existing semantic associations (Naveh-Benjamin et al., 2005) between emotional stimuli, which would provide an encoding and/or retrieval advantage over unrelated-neutral stimuli. But inherent differences could also exist between the interrelatedness of positive and negative stimulus sets, that when uncontrolled, lead to the positivity bias in older adults. For instance, positive information might be more tightly clustered and interrelated in memory than negative information (Koch et al., 2016; Unkelbach et al., 2008), because of negative information’s greater (Baumeister et al., 2001) – yet more diverse – representation in memory. Older adults could more easily discern the semantic organization of positive stimuli and ultimately remember them better, when the semantic relatedness of the stimulus sets is not controlled. This might affect young adults to a lesser extent because they likely have sufficient resources to organize both types of information and/or to adopt appropriate strategies (Naveh-Benjamin et al., 2007). Consequently, the variability across existing findings on the aging positivity effect in memory might have something to do with differences from study-to-study in stimulus selection across the emotional and neutral item sets. For instance, those articles showing a particularly strong positivity effect in memory might have included positive stimuli that were highly interrelated, or negative stimuli that were slightly less so. Yet, the interrelatedness of emotional and neutral stimuli remains generally uncontrolled in the aging positivity-effect literature.
The relative distinctiveness of emotional stimuli might also contribute to EEM. Emotional stimuli are inherently more salient than neutral stimuli, in the sense that they have a greater “absolute” significance because of their unique attributes stored in long-term memory (e.g., compare a facial expression of pain to a neutral expression; Schmidt, 1991). But emotional stimuli are also distinct in a “relative” sense, because they are often more salient than other, neutral stimuli presented close in time. Relative distinctiveness might influence memory to a greater extent than absolute distinctiveness (Schmidt, 1991, 2002). The EEM effect is commonly explained by the properties inherent to emotional stimuli (e.g., their high arousal; McGaugh, 2004), but it may also be due in part to the use of study designs that increase the relative distinctiveness of emotional items. Indeed, young adults’ EEM seems greater when emotional and neutral items are studied/tested together in mixed (i.e., emotion-heterogeneous) lists than when each emotion category is studied/tested separately in unmixed (i.e., emotion-homogeneous) lists (Dewhurst & Parry, 2000; Hadley & MacKay, 2006; McDaniel et al., 2005; Schmidt & Saari, 2007; Talmi, Luk, et al., 2007; Talmi & McGarry, 2012). The unmixed study lists reduce the relative distinctiveness of the emotional stimuli, by presenting emotional and neutral items in isolation from one another, which subsequently reduces EEM.
Few aging studies have used unmixed designs (e.g., Emery & Hess, 2011) or have directly contrasted unmixed and mixed sets of stimuli (e.g., Grühn, Scheibe, & Baltes, 2007; Grühn, Smith, & Baltes, 2005). Interestingly, none of the authors just listed reported a positivity bias in older adults. In fact, one of these studies (Grühn et al., 2005) showed that increasing relative distinctiveness improved older adults’ memory for negative words. To our knowledge, currently no study has considered both item interrelatedness and distinctiveness when examining older adults’ positivity bias. The effects of relative distinctiveness on semantically matched negative, positive, and neutral pictures remain unclear. Although several behavioral (Isaacowitz, Allard, et al., 2009; Isaacowitz et al., 2006b) and neural (Cacioppo et al., 2011; Dolcos et al., 2002; Mather et al., 2004; St. Jacques et al., 2009) studies have suggested that older adults prioritize positive stimuli, it is possible that these differences are only present when the positive stimuli are relatively distinct as compared to the other stimuli. If distinctive processing underlies the positivity effect in older adults, then positive stimuli should receive particularly high processing priority when test items are presented together in mixed sets. In contrast, all emotional and neutral stimuli should be processed equally well when they are presented in separate unmixed sets, thus attenuating or even abolishing older adults’ positive memory bias. In other words, the positivity bias in older adults might result from a temporary, contextual advantage given to positive information when it is processed in relation to other information, rather than from a permanent and absolute memory decrease for negative information.
The aim of this study was to examine whether semantic relatedness and relative distinctiveness can explain emotion-enhanced memory in young adults, and more specifically, the positivity bias in older adults. In Experiment 1, we performed a conceptual replication of Talmi, Luk, et al. (2007), who found that both semantic relatedness and relative distinctiveness influenced young adults’ memory for negative and neutral pictures. To build on their work, we also tested memory for positive pictures (which were absent from their original study) in a sample of young adults in Canada. In Experiment 2, we used the same experimental design with young and older adults in France.
To examine item interrelatedness, neutral pictures were either low (unrelated neutral) or high (related neutral) in semantic relatedness−that is, interrelated to an extent similar to that in emotional pictures. In addition, participants processed the emotional pictures in either a distinctive manner (mixed condition), with all items studied together, or a nondistinctive manner (unmixed condition), in which each picture category was studied and recalled separately (similar to Talmi, Luk, et al., 2007). We expected participants to recall more emotional pictures when these were more highly interrelated or more relatively distinct than the neutral pictures (Talmi, 2013; Talmi & McGarry, 2012). Furthermore, we predicted that relative distinctiveness would influence the presence of young adults’ EEM and older adults’ positivity bias. More specifically, we expected that young adults (Experiments 1 and 2) would recall more emotional pictures than related-neutral pictures in the mixed condition, but not in the unmixed condition, when distinctiveness was controlled. We also expected young adults to remember more negative than positive pictures in the mixed condition only. In contrast, we expected older adults (Experiment 2) to show a positive memory bias in the mixed condition, which would disappear or become weaker in the unmixed condition. Both age groups were always expected to remember more emotional pictures than unrelated-neutral pictures (i.e., the classic EEM pattern), regardless of distinctive processing.
A final consideration was the influence of recall delay, which occurred 1 min and 45 min after picture presentation. The 1-min delay (replicating Talmi, Luk, et al., 2007) was long enough to test for early EEM (Talmi, Grady, Goshen-Gottstein, & Moscovitch, 2005) and all of our research hypotheses, while ensuring high recall rates in the older adults. The 45-min delay was more exploratory. Some research has suggested that EEM is stronger when it is tested over a delay (Yonelinas & Ritchey, 2015) and that older adults’ positivity bias could be strengthened by repeated testing (Mather & Knight, 2005). We included two relatively brief intervals in order to examine these effects on early EEM in young and older adults.
In Experiment 1 we examined whether Canadian university students’ early EEM could be accounted for by semantic relatedness and distinctive processing. The experimental conditions and procedures were similar to those used in Talmi, Luk, et al. (2007, Exp. 1), with the addition of a positive picture category. We expected students to remember more emotional than neutral pictures, but only when the emotional pictures were more interrelated and/or were relatively distinct. Furthermore, we expected students to remember more negative than positive pictures when the items were processed in mixed sets.
Forty-seven young adults (under 35 years old) were randomly assigned to either the mixed (n = 24; 20 women, four men; mean age = 19.67 years) or unmixed (n = 23; 20 women, three men; mean age = 19.57 years) condition. The participants were University of Ottawa students who received course credit for participating. All provided written informed consent and completed the tasks in their choice of English or French. Data from an additional four participants were excluded because of a visual memory impairment, current drug abuse, incomplete study session, and incomplete data due to microphone error. Participants were further screened for high levels of depressive symptomatology based on the z-score distribution of the Centre for Epidemiologic Studies Depression scale (Radloff, 1977), which resulted in no additional exclusions. This study was approved by the University of Ottawa Research Ethics Board (#H12-14-14).
The target images consisted of 16 positive, 16 negative, 16 related-neutral and 16 unrelated-neutral pictures. The related-neutral pictures depicted domestic scenes of people, objects, or scenes around the house (e.g., man painting a room, ironing board, or backyard), whereas the unrelated-neutral pictures had no obvious thematic link (e.g., blue mug, buffalo, or outdoor staircase). Approximately one-third of the pictures in each category portrayed people, and the remaining pictures illustrated objects, animals, or outdoor landscapes. An additional 16 pictures (four per category) were chosen as buffer images. Some of the negative, related-neutral, and unrelated-neutral pictures were drawn from Talmi and McGarry’s (2012) collection, but others, in addition to the positive pictures, were selected from the International Affective Picture System (P. J. Lang, Bradley, & Cuthbert, 2008), the Geneva Affective Picture Database (Dan-Glauser & Scherer, 2011), and the internet.
Table of contents :
CHAPTER 1. INTRODUCTION AND LITERATURE REVIEW
Positivity Effect in Aging
Limitations in the Literature
Emotion-Enhanced Memory (Extrinsic Factors)
Cognitive Factors Influencing Encoding and Retrieval
Mood-Congruent Memory (Intrinsic Factor)
Conditions for Mood Congruence
How Could Mood Congruence Explain the Positivity Effect?
Studying Mood in the Laboratory
CHAPTER 2. RESEARCH ARTICLES
Study 1. Semantic Relatedness and Distinctive Processing May Inflate Older Adults’ Positive Memory Bias
Study 2A. Mood Induction Using Online Videos
Study 2B. Effects of Mood Manipulation on Emotional Memory Biases in Young and Older Adults
Study 3. Do Mood and Time Perspective Predict Emotional Memory Bias? A Test of Mood Congruence and Socioemotional Selectivity Theory in Young Adults
Study 4. Recruitment Matters: How Young Adult Sampling Might Affect Emotion-Enhanced Memory
CHAPTER 3. DISCUSSION AND CONCLUSION
Summary of Findings
Inconsistency in Emotional Memory Bias
Experimental Manipulations Affected Older Adults but not Young Adults
A Positivity Bias or a Positivity Effect?
The How and Why of the Positivity Bias in Aging
Cognitive Mechanisms Behind the Positivity Effect
Mood Influences on Positive Memory
Relevance of Appraisal Theory of Emotion
Implications for the Field
Socioemotional Selectivity Theory