Sussman Elyse, Winkler István, Kreuzer Judith, Saher Marieke, Näätänen Risto, Ritter Walter
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Clin Neurophysiol. 2002 Dec;113(12):1909-20. doi: 10.1016/s1388-2457(02)00300-0.
Our previous study showed that the auditory context could influence whether two successive acoustic changes occurring within the temporal integration window (approximately 200ms) were pre-attentively encoded as a single auditory event or as two discrete events (Cogn Brain Res 12 (2001) 431). The aim of the current study was to assess whether top-down processes could influence the stimulus-driven processes in determining what constitutes an auditory event.
Electroencepholagram (EEG) was recorded from 11 scalp electrodes to frequently occurring standard and infrequently occurring deviant sounds. Within the stimulus blocks, deviants either occurred only in pairs (successive feature changes) or both singly and in pairs. Event-related potential indices of change and target detection, the mismatch negativity (MMN) and the N2b component, respectively, were compared with the simultaneously measured performance in discriminating the deviants.
Even though subjects could voluntarily distinguish the two successive auditory feature changes from each other, which was also indicated by the elicitation of the N2b target-detection response, top-down processes did not modify the event organization reflected by the MMN response.
Top-down processes can extract elemental auditory information from a single integrated acoustic event, but the extraction occurs at a later processing stage than the one whose outcome is indexed by MMN.
Initial processes of auditory event-formation are fully governed by the context within which the sounds occur. Perception of the deviants as two separate sound events (the top-down effects) did not change the initial neural representation of the same deviants as one event (indexed by the MMN), without a corresponding change in the stimulus-driven sound organization.
我们之前的研究表明，听觉背景能够影响在时间整合窗口（约200毫秒）内发生的两个连续声学变化是被前注意编码为单个听觉事件还是两个离散事件（《认知脑研究》12（2001年）431）。本研究的目的是评估自上而下的加工过程在确定什么构成听觉事件时是否能够影响刺激驱动的加工过程。
从11个头皮电极记录脑电图（EEG），以记录频繁出现的标准声音和偶尔出现的偏差声音。在刺激块中，偏差声音要么仅成对出现（连续特征变化），要么单独出现和成对出现。分别将变化和目标检测的事件相关电位指标，即失配负波（MMN）和N2b成分，与同时测量的辨别偏差声音的表现进行比较。
尽管受试者能够自愿区分两个连续的听觉特征变化，这也通过N2b目标检测反应的诱发得到表明，但自上而下的加工过程并未改变MMN反应所反映的事件组织。
自上而下的加工过程能够从单个整合的声学事件中提取基本听觉信息，但提取发生在比MMN所索引结果更晚的加工阶段。
听觉事件形成的初始过程完全受声音出现的背景所支配。将偏差声音感知为两个单独的声音事件（自上而下的效应）并没有改变将相同偏差声音作为一个事件的初始神经表征（由MMN索引），而刺激驱动的声音组织没有相应变化。
