Demiralp T, Ademoglu A, Schürmann M, Başar-Eroglu C, Başar E
Electro-Neuro-Physiology Research and Application Center, University of Istanbul, Istanbul, Turkey.
Brain Lang. 1999 Jan;66(1):108-28. doi: 10.1006/brln.1998.2027.
The P300 response is conventionally obtained by averaging the responses to the task-relevant (target) stimuli of the oddball paradigm. However, it is well known that cognitive ERP components show a high variability due to changes of cognitive state during an experimental session. With simple tasks such changes may not be demonstrable by the conventional method of averaging the sweeps chosen according to task-relevance. Therefore, the present work employed a response-based classification procedure to choose the trials containing the P300 component from the whole set of sweeps of an auditory oddball paradigm. For this purpose, the most significant response property reflecting the P300 wave was identified by using the wavelet transform (WT). The application of a 5 octave quadratic B-spline-WT on single sweeps yielded discrete coefficients in each octave with an appropriate time resolution for each frequency range. The main feature indicating a P300 response was the positivity of the 4th delta (0.5-4 Hz) coefficient (310-430 ms) after stimulus onset. The average of selected single sweeps from the whole set of data according to this criterion yielded more enhanced P300 waves compared with the average of the target responses, and the average of the remaining sweeps showed a significantly smaller positivity in the P300 latency range compared with the average of the non-target responses. The combination of sweeps classified according to the task-based and response-based criteria differed significantly. This suggests an influence of changes in cognitive state on the presence of the P300 wave which cannot be assessed by task performance alone.
P300反应通常通过对oddball范式中与任务相关（目标）刺激的反应进行平均来获得。然而，众所周知，由于实验过程中认知状态的变化，认知ERP成分表现出高度的变异性。对于简单任务，这种变化可能无法通过根据任务相关性选择扫描的传统平均方法来证明。因此，本研究采用基于反应的分类程序，从听觉oddball范式的整个扫描集中选择包含P300成分的试验。为此，通过小波变换（WT）确定了反映P300波的最显著反应特性。在单个扫描上应用5倍频程二次B样条小波变换，在每个倍频程中产生离散系数，每个频率范围具有适当的时间分辨率。刺激开始后，第4个δ（0.5 - 4 Hz）系数（310 - 430 ms）的正值是表明P300反应的主要特征。根据该标准从整个数据集中选择的单个扫描的平均值与目标反应的平均值相比，产生了更强的P300波，并且其余扫描的平均值在P300潜伏期范围内与非目标反应的平均值相比，显示出明显更小的正值。根据基于任务和基于反应的标准分类的扫描组合有显著差异。这表明认知状态的变化对P300波的存在有影响，而仅通过任务表现无法评估这种影响。
