任务定势对自动语义激活过程调节作用的ERP研究

摘要：本研究致力于探讨自上而下的因素对自动加工的影响。选取的自上而下因素为任务定势，自动加工过程为自动语义激活过程。研究采用ERPs技术，中文词汇为刺激，利用掩蔽启动范式，采用反应时和N400为指标。实验任务有三个：对问号后出现的词进行生物/非生物的词汇分类判断；对圆圈后出现的词进行是否含上下结构的字的词汇结构判断；对带“*”的词进行真词/假词判断。研究发现先前完成的任务形成的任务定势会对随后的自动语义激活过程产生调节作用：在词汇分类判断任务后，掩蔽启动刺激对靶刺激产生启动效应。在词汇结构判断任务后，掩蔽启动刺激对靶刺激没产生显著的启动效应。

An ERP Study of the Task-set Effect on Automatic Semantic Activation

The study manily concerned the top-down modulation on automatic processing, which could modify the classical automatic processing theory and give suggestions for implicit study methods. Top-down modulation is the function of the brain to modulate and select task-related information and allocate attention to it so that we can accelerate information processing. Automatic processing is defined as a process that needs little attention and cognitive resources compared with controlled processing. Recent findings questioned the classical automatic processing theory by stating that automatic processing may also be modulated by top-down factors including intention, task-set, temporal attention, spatial attention, expectation, etc. We improved the previous studies by modifying the paradigm and using Chinese stimuli. The study used a masked priming paradigm to investigate if the top-down task-set factor could modulate automatic semantic processing by ERPs. The subjects were asked to perform categorization tasks or structure decision tasks of the former stimuli (primes) and lexical decision tasks of the latter ones (targets). So, there were two kinds of task-sets: semantic and perceptual . The stimuli were Chinese two-character words and pseudo-words cited from other articles. And the masks were a series of "#". 14 undergraduate students were chosen as subjects (6 males, 8 females). The mean age (±SD) was 21.9±(1.6) . The mean amplitude and peak latency of N400 which epoched between 300~450ms at F3,FZ,F4,C3,CZ,C4,CP3,CPZ,CP4,P3,PZ,P4,PO3,POZ,PO4 electrodes and the RT (response time) were used as indexes. The behavioral data and the electrophysiological data were acquired simultaneously by the software Stim 2 and Scan 4.2. We used Repeated-ANOVA. The experimental design was 2 (task factor: semantic task & perceptual task) × 2 (priming conditions: prime-target semantic related & unrelated). And the electrode factor was introduced as statistical analysis proceeded. The main behavioral result was that the main effect of task factor was significant, F(1,13)=7.703, p< .05, and the reciprocal effect between task factors and priming conditions was significant, F(1,13)=6.354, p< .05. Under the condition of semantic task-set, the RT of prime-target semantic related (838±130 ms) vs. unrelated(814±126 ms)was significantly different, F(1,13)=8.631, p< .05. The main result of electrophysiological data was that the reciprocal effect between task factor and priming conditions was significant, F(1,13)=4.819,p< .05. By further analysis, we found that under the condition of semantic task-set, the amplitude under the prime-target semantic related vs. unrelated conditions were significantly different, F(1,13)=7.167, p< .05, Mrelated=4.230μv, SD= .855μv, Munrelated=3.054μv, SD= .817μv. The conclusion is that automatic semantic activation can be modulated by the top-down task-set factor.