单字法定向遗忘中情绪指示符对记忆编码过程的影响

Effects of Emotional Picture Cues on Directed Forgetting Using the Item Method: An ERPs Study at Encoding

本实验使用ERPs技术,操纵情绪图片作为指示符,探讨在情绪指示下对中性名词的定向遗忘效应;根据提取阶段对项目再认的正确与否结合编码阶段的指示,将编码阶段指示符呈现时的ERPs叠加平均为4类：指示记住/记住（RR）,指示记住/忘记（RF）,指示忘记/记住（FR）,指示忘记/忘记（FF）,来考察指示上的情绪效应以及两种情绪下的记住、忘记意向。结果发现：行为结果上,两种情绪指示下均存在定向遗忘效应。350~600 ms时段,在额区和中央区位置指示记住条件（指示记住/记住和指示记住/忘记）下,正性情绪的波形比负性情绪显著更正,这一结果反映了效价评估过程,体现了对正性刺激的偏好;左侧顶区位置的指示忘记/忘记条件下,负性情绪的波形比正性情绪的波形更正,说明负性情绪指示忘记时对项目较弱的抑制作用;而指示忘记/记住条件下并不存在情绪效应。此外,正性情绪作指示时,在记住意向（指示记住/记住和指示忘记/记住）和忘记意向（指示记住/忘记和指示忘记/忘记）上都存在差异;负性情绪作指示时并不存在记忆意向上的差异。由此可见,正性情绪作指示时的加工更加灵活,且在指示忘记上更有效。

The ability to intentionally forget emotional irrelevant or unwanted materials is vital for memory function. The item method, which is the one of two main variants of directed forgetting paradigm, is the typical approach to exploring the mechanisms of intentional forgetting in the laboratory. When the item method was used, the predominant explanation of directed forgetting effects emphasizes selective encoding, while evidence supporting inhibition control during encoding and retrieval is also observed. ERPs studies on directed forgetting during encoding attempt to seek inhibition evidence and separate encoding effort from encoding success. Many studies have found that the to-be-forgotten cues elicited early enhanced positive waves in frontal and prefrontal areas, indicating strong activation of inhibitory processes. Meanwhile, intentional forgetting involves different brain areas compared with unintentional forgetting and intentional remember. ＇researches-on-directed-forgetting-of e-m-ot-io-nai-materials showed that emotional stimuli are exempt from forgetting or have a diminished directed forgetting effect when compared with neutral stimuli. Unlike previous studies on directed forgetting of emotional events with neutral symbols as cues （eg, ＂RRRR＂ as the to-be-remembered cue and ＂FFFF＂ as the to-be-forgotten cue）, the current study used emotional pictures as cues to create two experiment manipulations. The first manipulation used positive pictures as the to-be-remembered cues and negative pictures as the to-be-forgotten cues; the second used negative pictures as the to-be-remembered cues and positive pictures as the to-be-forgotten cues. The purpose of the two manipulations is to examine the electrophysiological correlates of the intentional forgetting of neutral nouns using the item-method directed forgetting paradigm. Twenty female undergraduate students participated in the experiment. During study phase, participants were instructed to remember half of a series of presented words （TBR） and to forget the other half （TBF） according the emotional picture cues. During test phase, they pressed one of the mouse buttons to indicate whether the word was presented at study phase or not. We used the behavioral recognition data to sort ERPs time-locked to the picture-cues into 4 conditions based on the combination of memory instruction and behavioral outcome： RR （TBR hit）, RF （TBR_miss）, FR （TBF_hit） and FF （TBF miss）, to investigate the emotional effects on the 4 experimental conditions and the processes underlying successful implementations of intentions to forget （i.e., RF vs. FF ） and intentions to remember （i.e., RR vs. FR）. Directed forgetting, that is reduced recognition of to-be-forgotten words, occurred for both positive picture as cues and negative conditions. At 350-600ms, it was found that positive picture as to-be-remembered cues elicited a more positive wave than negative ones （under the ＇RR＇ and the ＇RF＇ condition） in the middle frontal and central areas which are involved in the evaluation of the emotional valence of stimuli, and this result could reflect a preference toward pleasant pictures. But ERP amplitudes were larger for negative pictures compared to positive ones under the ＇FF＇ condition in the left parietal region, which suggests weaker inhibition for the item under the condition of negative pictures as ＇FF＇ cues. There were no significant differences between the positive and negative pictures under the ＇FR＇ condition. Moreover, when the positive pictures are as cues, there were significant differences between the intentional and unintentional remember conditions （＇RR＇ vs. ＇FR＇） and between the intentional and unintentional forget conditions （＇RF＇ vs. ＇FF）, whereas when the negative pictures are as cues, no such comparisons were observed to be significant. Our results show that flexible control of memory may be effective even in conditions in which negative pictures were used as cues, although it requires more effort than that in conditions using positive pictures as cues. Moreover, positive emotion is more effective as to-be-forgotten cues.