Time Course of Age related Emotional Preference--论文代写范文精选

在年轻人的阶段,大脑活动没有情感差异的区别,然而,对于老年人，悲伤比快乐的刺激并没有引起更大的影响。和与年龄相关的积极效应,表现为消极的偏好在年轻和老年人没有偏好。这篇论文代写范文进行叙述。

Abstract 
Studies of the age-related positivity effect have demonstrated that older adults have a generalized preference to positive stimuli or avoidance to negative stimuli compared with younger adults. However, it remains unclear when and how this positive effect occurs in task-irrelevant affective processing in the aging brain. The present study investigated age-related emotional preference in one task-irrelevant affective stimuli processing by event-related brain potentials (ERPs) measurement with a specific focus on the time course of older adults' emotional processing and regulation. Younger and older adults completed a modified oddball task in which the deviant stimuli were affective faces. 

In the relatively early time window, the brain activities were not modulated by emotional valence in younger adults, yet the sad stimuli elicited a larger P3a than the happy and neutral ones in older adults. In the late time window, the sad stimuli elicited a larger positive slow wave than the happy stimuli in younger adults. Contrarily, at the later processing stage older adults' valence differences were eliminated. In general, we found time course differences in how older adults processed task-irrelevant affective stimuli compared with the young, and an age-related positivity effect occurred in the late time window, manifested as a negativity preference in younger and no preferences in older adults. 

These results provided evidence for supporting socioemotional selectivity theory from an ERP approach. Key words emotional positivity effect, aging, event-related brain potentials, oddball, time course It has been claimed that, although aging is commonly associated with a decline of cognitive function, emotional regulation remains stable or even enhanced across the adult lifespan[1] . This aging effect has been characterized as either a preference for positive stimuli or a preference to avoid negative stimuli for older adults, and this age-related positivity effect has been reported in various domains including memory, attention, decision making, etc.[2-6] .

According to socioemotional selectivity theory[7] , there is a shift from knowledge-pursuit goals toward emotional-regulation goals as people age. Older adults perceive time as limited and prioritize emotionallymeaningful goals, thus the positive effect emerges as positively valenced stimuli are considered more emotionally meaningful. With regard to this emotional goal, Mather and colleagues[8-9] have further asserted that cognitive control plays a key role in this age-related positivity effect such that only older adults with sufficient cognitive control are able to display age-related positivity effects. Otherwise, as in divided-attention experimental conditions, older adults no longer show a positivity effect in memory[8] , or the reversal of typical positivity effect may occur[9]; that is, their preferences resemble those of younger adults with general human negativity dominance from evolutionary perspective [10] . 

Accordingly, the implementation of age-specific emotional preference in older adults is temporally-delayed, as the processes need time to fully access cognitive resources. Contrary to socioemotional selectivity theory, which emphasizes the selective processes between knowledge and emotional goals, dynamic integration theory [11-12] identifies a dynamic balance between emotional optimization and differentiation, and worsened cognitive function associated with age complicates attempts to maintain both. Therefore, older adults compensate by favoring the optimization of positivity and avoiding emotional differentiation complexity. From this perspective, the difficulty associated with integrating and accepting negative feelings with age should be time course invariant and emerge immediately upon stimulus onset, as positivity is a generic response and is not superimposed on existing negative responses[5] . 

On account of this temporal element, the time course of emotional stimuli processing should be carefully considered so that the effect of differentially-accessed cognitive resources on any age-related positivity effects may be measured. The former theory suggests that whether the general human automatic negative preference or the age-related positivity bias is observed changes as a function of the time course due to differences in cognitive resources accessed over time, but the latter theory predicts constant positivity effects over time. 

To date, only one study has directly investigated the time course of agerelated preferences by eye-tracking measurement [5] . They asked participants to observe face pairs and recorded their gaze patterns. Age-related preferences toward happy faces only occurred 500 ms or later after stimulus onset and increased linearly, suggestive of socioemotional selectivity theory. However, older adults' slower eye movement could have delayed the appearance of positivity preferences, which may have contributed to the failure to observe differences between age groups in the early time course. Other than eye-tracking measurement, eventrelated brain potentials (ERPs) could be another powerful tool for addressing the time course issue of age-related preferences toward emotional stimuli. 

The modified oddball paradigm with classic ERP components uses a sequence of standard and target stimuli interrupted by infrequent deviant emotional stimuli, and it has been used to investigate emotional processing theories in several previous studies. The deviant stimuli elicit P3a, a subcomponent of the P300 reflecting an involuntary switch of attention from the primary task to distracters modulated by different emotional valences; the infrequently-presented target stimuli elicit P3b, reflecting the subsequent memory processes engaged in stimulus information storing [13] . This modified oddball paradigm with clear ERP index is an effective means of investigating the time course of age-related emotional preferences. (论文代写)

The goal of the present study was to use timesensitive ERP measures associated with emotional stimuli to examine the age differences of brain activities modulated by valence, with a specific focus on the time course of older adults' emotional processing and regulation. Participants completed a modified oddball task in which their primary task was to detect bigger geometric figures (target stimuli) out of normal ones (standard stimuli), and the deviant stimuli were emotional faces that did not require explicit response. In task-irrelevant emotional processing, we predicted that at the early stage when emotional stimuli were involuntarily processed, the sad faces would attract more attention and elicit a larger P3a compared with happy and neutral ones in both younger and older adults as negative information is generally more salient for humans. In contrast, at the later stage when the emotional-regulation goal has been activated in older adults, the general human negative preferences could be suppressed resulting in no valence differences in brain potentials of older adults.(论文代写)

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