Douglas Mental Health University Institute, Montréal, Québec, Canada.
Clin Neurophysiol. 2012 Apr;123(4):741-54. doi: 10.1016/j.clinph.2011.08.025. Epub 2011 Sep 29.
The purpose of the present study was to clarify in which experimental conditions the semantic processing of repeated words is preserved.
We contrasted a short (250 ms) and a long (1000 ms) stimulus onset asynchrony (SOA) in two different experiments, using a relatively low proportion of related words (30%). One group of participants performed a lexical decision task (LDT) and a second group performed an explicit semantic matching task with the same words (except for pseudowords) and the same task parameters. In both tasks, word stimuli consisted solely of two prime and two target words repeated throughout the experiment.
The effects of semantic priming on reaction time (RT) and the amplitude of the N400 ERP were absent for both the short and the long SOA in the LDT. In contrast, in the explicit semantic task, these effects were significant. In this task, the activity of N400 generators in the left superior temporal gyrus and the inferior parietal cortex significantly differentiated primed and unprimed trials but this effect did not interact with SOA.
Our results indicate that task instruction is critical to preserve semantic processing with repeated presentations.
Using explicit semantic designs, it may be possible to study associative or categorical relations between individual concepts.
本研究旨在阐明在何种实验条件下重复词的语义处理得以保留。
我们在两个不同的实验中对比了短（250 毫秒）和长（1000 毫秒）刺激起始时距（SOA），使用了相对较低的相关词比例（30%）。一组参与者进行词汇判断任务（LDT），另一组则使用相同的词（除了伪词）和相同的任务参数进行显式语义匹配任务。在这两个任务中，词刺激仅由两个前导词和两个目标词组成，在整个实验中重复出现。
在 LDT 中，无论是短 SOA 还是长 SOA，语义启动对反应时间（RT）和 N400 ERP 振幅的影响都不存在。相比之下，在显式语义任务中，这些影响是显著的。在这个任务中，左颞上回和下顶叶皮层的 N400 发生器的活动显著地区分了启动和未启动的试验，但这种效应与 SOA 没有交互作用。
我们的结果表明，任务指令对于重复呈现时保留语义处理至关重要。
使用显式语义设计，可能有可能研究单个概念之间的联想或类别关系。
