Abstract:

Age-related positivity effects refer to the phenomenon that older adults display a preference for positive rather than negative information in cognitive processing. Previous studies using neutral materials have found that WM performance declines with aging. In recent years, empirical and theoretical research have begun to explore the effect of emotional valence on WM performance in the elderly and have revealed an interaction between emotional valance and task-relevance on positivity effects. Positivity effects has been observed in WM studies with emotional valence acting as a kind of task-relevant information. For instance, older people have enhanced performance in WM tasks with positive emotional stimuli, and decreased performance on negative emotional stimuli. In contrast, less attention has focused on the area of emotional valence as task-irrelevant information in WM and conflicting findings also have been reported. Some studies have found that the presence of negative irrelevant emotional stimuli reduces WM performance of older adults, while other studies have found that positive distractors have greater interference on WM of older adults. These remind that both emotional valence and task relevance are critical components in the processing of positivity effects in WM. Preliminary neuroimaging studies have revealed age-related functional changes in the dorsal executive system (including the middle frontal gyrus and the parietal cortex) and ventral affective system (including the left inferior frontal cortex and the amygdala). The middle frontal gyrus and the inferior frontal gyrus are both involved in inhibiting task-irrelevant emotional stimuli in WM and are less activated in older adults than in young adults. More specifically, the middle frontal gyrus is involved in the selection of task-relevant information, while the inferior frontal gyrus plays an important role in resolving interference from emotional distractors within WM. The amygdala, which is deactivated among older adults, is activated in young adults during the processing of negative stimuli. The socioemotional selectivity theory and the dual-competition model have been found to mainly account for age-related positivity effects in WM. The socioemotional selectivity theory, a theory of emotional-motivational life-span development, explains positivity effects from future time perspective, the review of WM studies on age difference with emotional valence as task-relevant information provides empirical support for the socioemotional selectivity theory. The dual competition model emphasizes the influence of task-relevance of emotional materials on WM processing and holds that the difference on cognitive resources required by emotional information as task-relevant stimuli or task-irrelevant stimuli is the key factor that affects WM performance. It has been found that task-relevant emotional materials promote WM performance in older adults, and task-irrelevant emotional contents impair their WM performance, thus the current review of task relevance on WM performance in older adults is consistent with hypothesis of the dual competition model. The dynamic integration theory explains positivity effects from the perspective of cognitive decline. From this perspective greater differences would be observed between young adults and older adults with cognitive impairments, such as Alzheimer's disease patients, but there is a lack of empirical evidence to support the dynamic integration theory. Overall, future studies are warranted to explore the characteristics of emotional processing in different stages of WM in older adults. The event-related potential technique, which has been used to provide time-sensitive assessment of positivity effects in attention, holds great potentials in the study of time course of positivity effects in WM. The potential influences of internal encoding processes of emotional materials (affective words, emotional face, and emotional pictorial materials) on the mechanism of positivity effects in WM should be clarified in future studies. More psychophysiological and neuroimaging studies are needed to uncover the important neural circuits related to the impact of task-relevance of emotion on positivity effects. Finally, the underlying mechanisms and potential benefits of emotional WM training on the improvement of cognitive functions and emotional experience in the elderly should be investigated.

Key words: working memory, positivity effect, task-relevant, task-irrelevant, emotional valence