[Eeglablist] How to choose proper High-pass (low-cutoff) filter?

[Steve Luck]

In addition to the excellent suggestions provided by others, you may want to read chapter 5 in my book (An Introduction to the Event-Related Potential Technique, 2005, MIT Press).  It provides a description of how filters work in the time domain, which makes it clearer how filters may distort your data.

In general, it is worth keeping in mind that, for transient ERP responses, filters will always distort your data to some extent.  The amount of distortion is sometimes extremely small, and the benefits of filtering may greatly outweigh these small distortions.  However, the amount of distortion can be very large, leading you to wildly incorrect conclusions.  To avoid this, you need to either (a) use very mild filters (wide passband and shallow slopes, or (b) really understand how filters work.  If in doubt, take an artificial waveform that is similar to your data and run it through the filter.  This will allow you to see how the filter is distorting the data.

Steve Luck

> On 11/18/12 9:41 AM, 诸梦妍 wrote:
>> Dear eeglablist,
>> 
>> I would like to know whether there are any limitation or rules in filtering EEG data, or if there are someone who could recommend some papers about how high-pass filter change the data. 
>> 
>> I have read some basic principles about how filter works, but still don't know how to choose a proper High-pass parameter to remove artifacts without distorting the data. I knew some researchers use 0.01Hz, some would recommend  0.1, 0.5 or 1Hz and some recommend not using High-pass filter at all. 
>> 
>> The thing is, I found some participants' EEG waves in my experiments had large amount of slow drift, which could be removed by a 0.3Hz filter. However, I don't know whether that would distort the data greatly. What I want to observe are P300, N400 and P600 components as well as some sustained late negativity in ERP and also 3-70Hz in Time-Frequency domain. 
>> 
>> Thanks for any information you may supply me with.
>> 
>> Zhu Mengyan
>> -- 
>> Mengyan Zhu
>> Psychology department, Peking University
>> Dormitory 2061, Building 48,No.5 Yiheyuan Road, Haidian District, Beijing 100871, China 
>>  E-mail: bj12116 at gmail.com
>> 






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