[Eeglablist] Re-Referencing Question

[Joseph Dien]

You can get a sense of the extent to which linking the ears is going to  
distort things for a given dataset by looking at the difference between  
the two waveforms when recorded separately.

Cheers!

Joe

On Wednesday, June 11, 2003, at 03:59 PM, Robert Lawson wrote:

> Earlier in the thread, someone mentioned the problems with ear  
> reference. I have read some theoretical papers claiming that linking  
> the ears leads to a shunt and thence to inaccurate data. However, all  
> the empirical studies I have seen found no difference between  
> mathematically and physically linked ears. Does anyone know of any  
> empirical data that shows physically linked ears are at all different  
> from mathematically linked ears?
>
> Robert Lawson
>
> Joseph Dien wrote:
>
>> The only way to get an estimate of the left ear reference site  
>> activity is to compute an average reference but since, as you say,  
>> there are not enough channels, you would end up improperly imputing  
>> common activity at the recording sites to the reference site as well.  
>> If you want to rereference to a mean ear reference, you add the left  
>> ear channel to the data array (the left ear referenced to itself is a  
>> flat line of zeros) and then subtract the mean of the left and right  
>> ear channels from the entire array. You should be able to do this  
>> manually in Matlab if eeglab isn't set up to do this yet. You might  
>> want to read my paper on referencing for more info:
>>
>> Dien, J. (1998). Issues in the application of the average reference:  
>> Review, critiques, and recommendations. Behavioral Research Methods,  
>> Instruments, and Computers, 30(1), 34-43.
>>
>> Cheers!
>>
>> Joe
>>
>>     Our specific eeglab question relates to how (or maybe if), using
>>     eeglab's re-referencing pop-up window, both the above recording
>>     options
>>     could be correctly rereferenced to mathematically linked ears  
>> while
>>     obtaining/maintaining a recorded signal for all six locations Cz,  
>> C3,
>>     C4, Fz, F3, F4. The re-referencing window allows one to enter one  
>> or
>>     more (at least it appears that more than one can be used) channel
>>     number(s) for the new reference but in the above scenario (a) the
>>     left
>>     and right ears are not both available as channel numbers (for  
>> obvious
>>     reasons because Le ear was the reference).
>>
>>
>>
>> ---------------------------------------------------------------------- 
>> ----------
>>
>> Joseph Dien
>> Assistant Professor of Psychology
>> Department of Psychology
>> 2007 Percival Stern Hall
>> Tulane University
>> New Orleans, LA 70118-5698
>>
>> Office: Room 3061
>> Phone: (504) 862-3300
>> Fax: (504) 862-8744
>> E-mail:jdien at tulane.edu
>> www: http://www.tulane.edu/~jdien/Dien.html
>>
>> Starting Fall 2003:
>> Department of Psychology
>> 426 Fraser Hall
>> 1415 Jayhawk Blvd
>> University of Kansas
>> Lawrence, KS 66045-7556
>>
>
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------------------------------------------------------------------------ 
--------

Joseph Dien
Assistant Professor of Psychology
Department of Psychology
2007 Percival Stern Hall
Tulane University
New Orleans, LA 70118-5698

Office: Room 3061
Phone: (504) 862-3300
Fax:   (504) 862-8744
E-mail:jdien at tulane.edu
www: http://www.tulane.edu/~jdien/Dien.html

Starting Fall 2003:
Department of Psychology
426 Fraser Hall
1415 Jayhawk Blvd
University of Kansas
Lawrence, KS 66045-7556