Abstract: The spatiotemporal analysis of brain activation during the execution of same-different judgments [including the different color stimulus pair (DC), the different shape stimulus pair (DS) and the same stimulus pair (Same)] was performed in 12 normal young adult subjects using high-density event-related brain potentials (ERPs). We want to reveal the neural basis of “same” and “different” judgments. We can judge which is correct between the dual-process model and single-process model that previous experiments want to prove with behavioral research. The behavioral data showed that the same-different judgments yielded a robust fast-same effect as indexed by longer RT for DC and DS than Same. Scalp ERP analysis revealed the neurophysiological substrate of the fast-same effect: a more negative N2 component in DC and DS as compared to Same was found between 280 and 320 ms post-stimulus over midline fronto-central scalp regions. Following that period, DC and DS elicited a more negative P3 component than Same did about 450 ms after onset of the stimuli which might reflect the comparison and recognition of the partial character of the stimulus (the slow processing machine), and the latency of P3 was much shorter for Same than for DC and DS which was consistent with the behavioral data. Dipole source analysis (BESA software) of the original waveforms of DC and DS indicated that a generator of N2 mainly localized in the superior/anterior frontal cortex contributed to this effect, possibly in relation to early monitoring mismatch stimulus pairs. However, activation of the precuneus possibly resulted in N2 effect under Same condition, which was relative to holistic comparison (identify reporter). The results indicated that there might be different neural basis of “same” and “different” judgments. Our data support the dual-process model, and we think that IR and the slow processing machine work in order.

Key words: same-different judgment, fast-same effect, event-related brain potentials (ERPs), dual-process modal, identify reporter

摘要： 采用高密度的事件相关电位（ERPs）技术，记录分析了大学生被试在执行异同判断任务[包括不同颜色刺激对（DC），不同形状刺激对（DS）和相同刺激对（Same）]时的脑内时程动态变化。行为结果表明，“同”反应的确显著快于“异”反应，表现出明显的快同效应。ERP结果显示：在280-320 ms内，DS和DC条件均比Same条件诱发一个更负的N2成分。偶极子溯源分析表明，DC和DS条件下，N2可能起源于大脑的前扣带皮层（ACC）,可能与“异”反应早期不一致信息（颜色或形状）的认知监控和调节有关；反之Same条件下，N2成分可能起源于楔前叶，主要反映了“同”反应早期知觉识别中整体特征比较加工的过程（同一性指示器）。另外，在450 ms左右， DC和DS比Same条件均诱发了一个更负的P3成分，可能反映了对刺激局部特征的比较和识别（慢速比较器），并与选择性注意和资源分配等高级认知活动有关；并且，Same条件下P3成分的潜伏期更短，与行为结果一致。以上研究结果表明，异同判断中“同”反应和“异”反应可能有着不同的比较通道和大脑机制，支持双过程模型理论；同时表明，慢速比较器和同一性指示器可能是序列加工的。

关键词: 异同判断, 快同效应, 事件相关电位（ERPs）, 双过程模型, 同一性指示器