Abstract: The effects of deviant visual and auditory stimuli on event-related potentials were investigated in an intermodal oddball task. Tones of different pitch were used as auditory stimuli (standard:1000Hz, 85%, deviant 800Hz. 15%) and various single Chinese words and simple geometric figures were used as visual stimuli. Auditory and visual stimuli were presented sequentially to subjects at randomized ISI of 700-1300ms. The subjects were instructed to attend visual channel and ignore the auditory in one block and to attend auditory and ignore visual in the other with key-responses to the current attended stimuli. Results showed the deviant auditory stimuli elicited similar mismatch negativity (MMN) in both attended and unattended conditions. MMN's independence of attention in auditory modality may reflect the automatic processing of auditory sensory inputs. In the visual modality, the deviant stimuli elicited no MMN or MMN-like component in both conditions because of the parallel processing system of visual modality and its difficulty of establishing the memory trace. The enhanced P300 elicited by the auditory and visual deviant stimuli in active condition may reflect the representation updating of work memory. The results were consistent with Naatanen's observation on MMN.

Key words: Oddball paradigm, ERPs, MMN, P300, N2, P200, N2b, P3a

摘要： 本实验采用了视听双通道伪同时呈现的oddball模式，以汉字和简单几何图形为视觉刺激，1000Hz和800Hz的纯音为听觉刺激，使用注意通道(注意和非注意条件)×刺激概率(偏差刺激概率均为15%，标准刺激的概率均为85%)的2×2因素设计，来研究视觉和听觉偏差刺激在注意和非注意条件下诱发的事件相关电位(ERPs)。实验中视觉和听觉刺激随机序列地呈现给被试(刺激间隔ISI为700～1300ms)，被试被要求注意某一通道如视觉通道，而相应地忽视另一通道即听觉通道，以左右手触键反应，如左手反应视觉偏差刺激，右手反应视觉标准刺激。结果表明，听觉偏差刺激在注意和非注意条件下均诱发了类似的不匹配负波(MMN)；而视觉偏差刺激在注意和非注意条件下没有诱发MMN或类似MMN的成分，这是因为视觉系统的平行加工特性和难以对视觉影像产生记忆痕迹。听觉偏差刺激在注意条件下重迭了N2b成分并跟随了P3a成分，这种重迭和跟随反映了选择注意中的定向反应。注意条件下听觉和视觉的偏差刺激诱发了较大波幅的P300成分，反映了工作记忆中的表象更新。本实验的结果支持Naatanen对MMN所做的观察，听觉偏差刺激所诱发的MMN与注意条件的无关性反映了听觉通道中感觉刺激特征的自动化加工。

关键词: Oddball模式, ERPs, MMN, P300, N2, P200, N2b, P3a