To address the two limitations of Experiment 1 outlined above, we conducted a second experiment. Here, we included a control writing condition, in which participants were not oriented to think about time in a particular manner, but rather described activities that they had completed that day. This allowed us to determine whether participants in the limited time horizon condition show enhanced positivity in recall, whether participants in the expansive time horizon condition show reduced positivity in recall, or whether both effects occur simultaneously. We also included assessments of mood. This allowed us to determine whether reflecting on a limited future induces a negative mood state, and how this in turn affects the positivity of participants’ recall.
A total of 150 adults (46 women) were recruited via Amazon’s Mechanical Turk (mTurk), an online portal that connects people willing to do short web-based tasks with people who need those tasks completed. Data obtained from mTurk participants have high test-retest reliability (Buhrmester, Kwang, & Gosling, 2011) and do not significantly differ from data obtained from in-person laboratory study participants (Paolacci, Chandler, & Ipeirotis, 2010) Participants were compensated US$1 upon completion of the study.
Of the 150 participants, we excluded 13 who reported having participated in a prior mTurk experiment using the same emotional pictures and 24 who reported a computer error in which the file names of the emotional pictures appeared alongside the pictures.Footnote 4 We also excluded two participants who failed to recall any of the critical pictures. This left a final sample of 111 participants: 39 in the expansive time horizon condition, 33 in the limited time horizon condition, and 39 in the control condition. This sample was on average 31.88 years old (SD = 9.52). Although participants ranged in age from 20 to 71 years, we did not recruit participants based upon their age. Because of this, the distribution of age was not normally distributed: 47.7 % of participants were aged 20–29, 33.4 % were aged 30–39, 13.5 % were aged 40–49, 4.5 % were aged 50–59, and only 0.9 % were aged 60 years or older. Participant age did not differ between the three experimental conditions, F(1, 108) = 0.78, MSE = 91.48, p = .46, η
2 = .01.
By chance, the three experimental conditions marginally differed in the number of women assigned to them, F (2, 108) = 2.94, MSE = 0.24, p = .06, η
2 = .05. There was a numerically lower proportion of women in the limited time horizon condition (24.2 %) than in either the expansive time horizon (48.7 %) or control condition (48.7 %). However, Bonferonni-corrected post-hoc comparisons showed that these differences were not statistically significant. The reported patterns of results do not change when including gender as a covariate.
Participants had a broad range of educational backgrounds: 0.9 % had completed some high school, 11.7 % had a high school diploma, 32.4 % had “some college,” 17.1 % had a 2-year Associates level college degree, 33.3 % had a 4-year Bachelor’s level college degree, 3.6 % had a Master’s degree, and 0.9 % had a Ph.D., J.D., or M.D. degree. By chance, education significantly differed among the three experimental conditions, F(2, 108) = 4.06, MSE = 1.35, p = .02, η
2 = .07. Bonferroni-adjusted post-hoc analyses showed that this was because participants randomly assigned to the control condition had significantly higher levels of educational attainment than those assigned to the limited time horizon condition, p = .02. No other pairwise comparison was significant (all p’s > .29). The reported patterns of results do not change when including education as a covariate.
As a baseline measure of mood, participants first completed the Positive and Negative Affective Scale (PANAS; Watson, Clark, & Tellegen, 1988). This 20-item questionnaire lists ten positive and ten negative emotional adjectives and participants rate the extent to which they are currently feeling each adjective.
Participants were then randomly assigned to either the limited time horizon, expansive time horizon, or control condition. These conditions differed only in the writing activity that was next completed. The instructions for the writing activities used in the limited and expansive time horizon conditions were identical to those used in Experiment 1 with one exception – here, the sentences stating that participants should assume good health were printed in bold and underlined. As described in the Supplementary Material, in Experiment 1 participants in the expansive time horizon condition were more likely to write about their health despite the fact that instructions in both conditions stated that participants should assume good health. In Experiment 2, we examined whether this linguistic difference would remain when these statements were highlighted. See the Supplementary Materials for more details on these linguistic analyses.
In contrast to the other two conditions, the control condition’s writing activity did not include a preamble asking participants to think about time in a specific manner. Rather, these participants responded to four questions about their current daily activities (see Appendix 2), which were designed to be similar in topic to those answered in the limited and expansive time horizon conditions (see Appendix 1). For example, whereas participants in the limited and expansive time horizon conditions speculated on how their daily activities would be affected by changes in life expectancy, participants in the control condition listed the activities they had completed that day. For analyses of the linguistic content of participants’ writing activity responses, see the Supplementary Materials.
Immediately after the writing activity, participants in all three conditions indicated their mood using a sliding scale. Responses could range from 0 (very negative mood) to 100 (very positive mood).
Participants next completed an emotional picture memory task. The picture stimuli used in this task were seven positively-valenced and seven negatively-valenced pictures drawn from the IAPS (Lang et al., 1999).Footnote 5 They were all low in arousal, and arousal level did not differ between the positive and negative pictures. In contrast to Experiment 1, in Experiment 2 we used an incidental encoding task. This procedural change was made for two reasons. First, it ensured that participants did not make notes about the pictures for the upcoming memory test. Second, it was expected to increase the likelihood of observing a positivity effect; results of a recent meta-analysis suggest that the positivity effect is larger during incidental compared to intentional encoding (Reed, et al., 2014). During the incidental encoding task pictures were shown in a single random order. The picture slideshow progressed automatically, and participants could not go back and review pictures after they had disappeared. Each picture was shown with either a red or a yellow border, and participants were asked to indicate the border’s color. Since this was an online study, this ensured that participants attended to all of the pictures during the encoding period. Each picture was shown for 5 s. This was an increase in exposure time compared to Experiment 1 (in which each picture was shown for only 2 s). This procedural change ensured that participants had adequate time to both note the color of the border and also attend to the content of each picture. Across participants each picture appeared equally often with a red border as it did with a yellow border. To buffer against primacy and recency effects, we also included four non-critical neutral pictures, two of which appeared at the beginning of the slideshow and two at the end. Immediately after viewing the pictures, participants completed a surprise, self-paced, free recall test. Here, they typed short descriptions of as many of the pictures as they could recall.
Finally, at the end of the study participants provided demographics information and also indicated whether they had encountered any technical problems or had seen the emotional picture stimuli in a previous experiment.
A picture was scored as correctly recalled if the participant provided a description that matched the picture. Recalled pictures were classified by valence according to their IAPS ratings. Only 33 of the 690 responses could not be scored (4.8 %); a single-factor between-groups ANOVA on the number of non-scored responses provided by each participants showed no significant difference among the three conditions, F(1, 108) = 1.31, MSE = 0.37, p = .28, η
2 = .02. To ensure reliability of the ratings, a second rater independently coded for the presence of the 14 critical pictures in each of the recall protocols. As in Experiment 1, reliability with the primary rater was high, Cohen’s kappa = 0.93, p < .001. A single-factor between-groups ANOVA confirmed that there was no significant difference among the three conditions in the total number of pictures recalled, F (2, 108) = 0.45, MSE = 5.77, p = .64, η
2 = .008 (see Table 2).
We next turned to the first primary aim of Experiment 2: Did the positivity of recall differ between the three conditions? To answer this, we conducted a single-factor between-groups ANOVA on the relative positivity of participants’ recall. As in Experiment 1, we defined this as the number of items recalled that were positive minus the number that were negative divided by the total number of items recalled (for the number of items recalled as a function of valence and time horizon condition see Table 2). As shown in Fig. 2, the positivity of participants’ recall significantly differed among these three conditions, F(2, 108) = 3.17, MSE = .20, p = .046, η
2 = .06. In follow-up independent t-tests, participants’ recall in the limited time horizon condition was marginally more positive than that of participants in the expansive time horizon condition, t(70) = 1.93, p = .057, d = .46, and significantly more positive than that of participants in the control condition, t(70) = 2.50, p = .015, d = .60. In contrast, the positivity of recall did not differ between participants in the expansive time horizon and control conditions, t(76) = 0.48, p = .63, d = .11. Thus, whereas a focus on limited time horizons increased the positivity of recall, a focus on expansive time horizons did not decrease it.
As in Experiment 1, the magnitude of the positivity bias in the limited time horizon condition was negatively associated with the participants’ overall levels of recall (r = −0.69, p < .001), such that lower overall recall was related to a stronger positive bias. However, unlike in Experiment 1, there was no significant correlation between total recall levels and the magnitude of the positivity effect in the expansive future condition (r = −0.21, p = .20). There was also no relationship between these variables in the control conditions (r = 0.07, p = .65).
Mood and free recall
Our second aim was to test the role of mood in modulating our results. We hypothesized that reflecting on a limited future would induce a negative mood. However, it was unclear how this would in turn affect the positivity of recall. On the one hand, there could be a negative correlation between these factors; a reduced mood in the limited time horizon condition could lead to enhanced positivity if people selectively recall the positive pictures as a means of enhancing positive emotion. In other words, mood could serve as a mediating variable and explain why our time horizon manipulation affected the positivity of participants’ recall. On the other hand, there could be a positive correlation between these factors; a reduced mood could lead people to engage in mood-congruent processing and attenuate the positivity of their recall. In other words, a reduced mood in the limited time horizon condition could serve as a suppressor variable, reducing the predictive strength of our time horizon manipulation in accounting for the subsequent positivity of participants’ recall.
To address these questions, we first examined whether our time horizon manipulation affected mood. At the outset of the study, mood (as assessed via the PANAS) did not differ between the conditions; a single-factor between-group ANOVA revealed no significant differences in either positive or negative PANAS scores among the three conditions, F(1, 108) = 0.71, MSE = 74.35, p = .50, η
2 = .01 and F(1, 108) = 0.35, MSE = 16.45, p = .70, η
2 = .01, respectively. In contrast, after completing the writing activity, mood (as assessed via a sliding scale from 0 to 100) significantly differed among the conditions, F(2, 108) = 4.60, MSE = 501.17, p = .01, η
2 = .08.Footnote 6 Follow-up independent t-tests showed that after the writing activity, participants in the limited time horizon condition were in a significantly worse mood (M = 60.18) than participants in either the expansive time horizon (M = 72.41), t(70) = −2.08, p = .04, d = .50, or control condition (M = 75.56), t(70) = −3.28, p = .002, d = .79. Mood did not vary between participants in the expansive time horizon and control conditions, t(76) = −.63, p = .53, d = .14. Thus, whereas a focus on limited time horizons induced a negative mood, a focus on expansive time horizons did not significantly affect mood either positively or negatively.
How did mood affect the positivity of participants’ recall? Across the three conditions there was a positive correlation between these two variables; the higher the participants’ mood the greater their positivity of recall, r = .23, p = .015. Thus, collapsing across the three conditions, people engaged in mood-congruent processing and had a tendency to recall the positive pictures when in a positive mood.
In summary, the previous results have shown (a) that participants in the limited time horizon condition were in a worse mood, (b) that a lower mood was generally associated with lower positivity in recall, (c) that despite their lower mood (and thus their propensity to engage in mood-congruent processing and display a negativity bias), participants in the limited time horizon condition surprisingly had higher positivity in recall than participants in the other two conditions. Taken together, these results suggest that changes in mood do not mediate the relationship between our time horizon manipulation and the positivity of recall. Rather, reflecting on a limited future appears to enhance the positivity of recall (presumably because of reduced time horizons) but the strength of this relationship may be suppressed by the accompanying negative mood that is induced. To test this, we next used the logic of a mediation analysis to examine whether the strength of the direct path between our time horizon manipulation and the positivity of participants’ recall would change after accounting for mood (see Fig. 3). In a typical mediation analysis, the strength of the direct path is weakened after accounting for the intervening (mediating) variable. In contrast to this, we expected the strength of the direct path to be enhanced after accounting for the intervening (suppressive) variable.
As shown in Fig. 3, in separate regression analyses we found that time horizon condition (entered as 0 for either the expansive time horizon or control condition and as 1 for the limited time horizon condition) was significantly related to both mood and the positivity of recall. We then conducted another regression analysis where time horizon condition and mood were simultaneously entered as predictors of the positivity of recall. Here, both time horizon condition and mood predicted the positivity of recall. Furthermore, the relationship between time horizon condition and the positivity of recall was significantly strengthened after accounting for mood, Sobel test Z = −2.20, p = .028.
Replicating Experiment 1 results, participants in the limited time horizon condition displayed higher positivity than participants in the expansive time horizon condition. Novel to Experiment 2, we also included a control writing condition. Compared to this condition, we found that thinking about a limited future increased the positivity of recall. In contrast, a focus on expansive time horizons did not decrease it.
We also examined the role of mood in modulating the observed effects. We found that reflecting on a limited future lowered mood. However, this did not explain why participants in the limited time horizon condition had enhanced positivity in recall. Overall, our results showed that reflecting on a limited life expectancy enhanced the positivity of recall, likely by reducing time horizons and increasing participants’ motivation to optimize their emotional experience. However, this enhanced positivity was attenuated by the accompanying negative mood state that was induced by reflecting on having only 6 months left to live.