When compared with younger adults, older adults tend to favour emotionally positive material over emotionally negative material, a phenomenon that has been termed the ageing positivity effect (Carstensen & Mikels, 2005). The positivity effect has been demonstrated across a number of measures, including attention, recall, and recognition memory. For example, older but not younger adults recall and recognize more positive than negative images (Charles, Mather, & Carstensen, 2003), show attentional preferences towards positive faces and away from angry faces (Isaacowitz, Wadlinger, Goren, & Wilson, 2006b), and show greater amygdala activation in response to positive than negative images (Mather et al., 2004). Given the potentially harmful consequences of avoiding negative information, I propose that the ageing positivity effect may provide benefits that offset its costs. Because positive affect is known to be associated with better immune functioning, I suggest that the positivity effect is maintained in older adults in part as a health protective strategy, and thus a greater focus on positive information should be associated with indicators of better immune functioning. In this thesis, I test this hypothesis.
Chapter 1 provides a review of research investigating the ageing positivity effect, examines literature investigating the links between positivity, immune functioning, and ageing, and provides a cost-benefit analysis of the positivity effect. Chapter 2 includes the method and results of a longitudinal study investigating the links between the ageing positivity effect and immune function. In this study, I assessed positivity in recall and blood indicators of immune function (Epstein-Barr virus antibodies, CD4+ and CD8+ t-cell counts, and CD4 percent activation at HLA-DR) among older adults across a three year period. I found that for older adults, greater positivity in recall predicted significantly higher CD4 counts and lowered CD4 activation two and three years later. The effect of positive recall on CD4 counts and activation three years later was mediated through CD4 counts and activation two years later. I also found that the magnitude of the positivity effect in recall at initial measurement predicted the magnitude of the positivity effect in recall and recognition memory one year later, suggesting that there is stability in positivity across time. Chapter 3 provides a discussion of the study results and implications. I conclude that these data suggest that older adults may show a positivity effect in part to combat immunosenescence and increasing health challenges.