Fiore L, Corsini G, Geppetti L
Dipartimento di Scienze del Comportamento animale e dell'Uomo, University of Pisa, Italy.
J Neurosci Methods. 1996 Dec 28;70(2):177-84. doi: 10.1016/s0165-0270(96)00116-1.
Two non-linear, high-pass filters based on the median filter are proposed and tested as substitutes for linear filtering in applications involving multiunit neural recordings. The first, the median-based high-pass (MH) filter, operates by subtracting the output from the input of the median filter; it is aimed at preserving the shape of the impulses. The second, the negative median-based high-pass (NMH) filter, sets at zero the positive values in the output of the MH filter; it is aimed at transforming the impulses into monophasic waves placed on a flat baseline. When applied to experimental recordings and to a template action potential, the two median-based filters clearly outperformed two corresponding procedures based on a linear filter (moving-average filter). They did not produce appreciable distortions of the impulses, whereas their two counterparts induced or enlarged lateral lobes, as is the rule for linear high-pass filters. The recording display was much improved and impulse identification was made easier. When the two filters were applied to simulated recordings and the mean output was estimated by averaging and cross-correlation, a certain degree of performance deterioration was assessed in conditions of sustained activity and/or noise, with a resulting growing similarity to the mean output of the two corresponding, moving-average-based filters.
本文提出了两种基于中值滤波器的非线性高通滤波器，并将其作为线性滤波的替代方法，用于多单元神经记录相关的应用中进行测试。第一种是基于中值的高通（MH）滤波器，它通过从输入中减去中值滤波器的输出来运行；旨在保留脉冲的形状。第二种是基于负中值的高通（NMH）滤波器，它将MH滤波器输出中的正值设置为零；旨在将脉冲转换为置于平坦基线的单相波。当应用于实验记录和模板动作电位时，这两种基于中值的滤波器明显优于基于线性滤波器（移动平均滤波器）的两种相应方法。它们不会产生明显的脉冲失真，而它们的对应方法则会像线性高通滤波器那样诱导或放大旁瓣。记录显示得到了很大改善，脉冲识别也变得更容易。当将这两种滤波器应用于模拟记录，并通过平均和互相关来估计平均输出时，在持续活动和/或噪声条件下评估了一定程度的性能下降，结果与基于移动平均的两种对应滤波器的平均输出越来越相似。
