对刺激朝向改变的自动加工:事件相关电位的证据

利用事件相关电位（ＥＲＰ）技术，探讨非注意状态的刺激朝向改变是否引起自动加工。刺激为具有一定朝向（垂直和水平各５０％）和一定空间频率（低频９０％，高频１０％）的光栅。要求被试忽略光栅朝向，对高频光栅作反应。刺激呈现时间为５０ｍｓ，刺激间隔在２５０至４５０ｍｓ之间随机变化。低频光栅刺激被分为两类，“匹配”（与前一刺激朝向相同）和“失匹配”（与前一刺激朝向不同）。结果发现，失匹配刺激比匹配刺激诱发出更大的枕区Ｐ１、更大的前额－中央区Ｎ１以及更大的前部与顶区Ｐ２，但前部与顶区的Ｎ２却更小。这些ＥＲＰｓ变化提示，视觉对非注意的刺激朝向变化进行了一定程度的自动加工；视觉通道可能存在类似听觉失匹配负波（ＭＭＮ）的、然而机制不同的自动加工成分

AUTOMATIC PROCESSING TO STIMULUS ORIENTATION CHANGE:EVIDENCE FROM EVENT-RELATED POTENTIALS

Whether there is automatic processing to unattended orientation change was investigated in the present study, by recording event-related potentials(ERPs). Gratings with certain orientation(horizontal and vertical gratings occured in equal probability) and spatial frequency(high-and low-spatial-frequency gratings occured 10% and 90%, respectively) were used as stimuli. The subjects' task was only to respond to the high-spatial-frequency gratings, irrespective of their orientation. The stimulus duration was 50ms, and the inter-stimulus interval (ISI) was randomly ranged from 250 to 450ms. According to the relationship of orientations between the two successive gratings, a present grating was categorized as "match" (orientation of a present grating is the same as the previous one) and "mismatch" (orientation of a present grating is different from the previous one). Results show that, mismatched stimuli elicited larger occipital P1,larger anterior N1,and larger anterior and parietal P2,as compared with matched stimuli, whereas the amplitudes of anterior and parietal N2 were smaller in response to the mismatched stimuli. The results suggest that, automatic processing to unattended orientation change was performed to some extent by our visual system. Moreover, it suggested that, there might be ERPs counterparts of auditory mismatch negativity (MMN) in visual modality, but there might also be different neural mechanism for the counterparts.