[FieldTrip] [Fieldtrip] frequency issue in beamfomer

[X Chen]

Dear Fieldtrip developers and users,

 

Since  a while I am
struggling with a question regarding the frequency range used in beamfomer,

 

The length of each data epoch is
1 second, resulting in ±1Hz
frequency smoothing while performing ‘mtmfft’ method together with a hanning
taper.    Nevertheless, when the frequency band of interest is
4~7Hz at sensor-level,

how to make the frequency range
as the frequency of interest in source analysis? At sensor level, the
permutation test offer a configuration setting for frequency average which
resolves the issue.

 

One possible solution, which I
have tried consisting of using ‘dpss’ taper instead of ‘hanning’ taper, setting
the frequency of interest to 5.5Hz, padding the epoch to 2s and setting the
tapsmofrq = 1.5. The resulting 5.5 ±1.5Hz
is just the range needed. Is it a feasible way? If it is, will the setting of
padding influence the source analysis result to some degree?

 

The other possible solution I
have considered, is to average the output of frequency analysis, including
‘powspctrm’ and ‘crsspctrm’ across the selected range manually. Then the
average result from the frequency range will output to source analysis? Is this
correct?

 

Thanks
for your help,

 

Chen

 		 	   		  
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