[FieldTrip] Grand mean

Schoffelen, J.M. (Jan Mathijs) jan.schoffelen at donders.ru.nl
Wed May 13 14:53:01 CEST 2020

Dear Sarah,

It is not clear what error message you get, nor why you think you should ft_timelockanalysis/ft_timelockgrandaverage/ft_topoplotER.

Some pointers:
-For a mathematical operation to be applied to numeric data that resides within a fieldtrip-style data structure you’d use ft_math.
-What you want to do (i.e. adding or subtracting estimates of frequency specific power estimated for different frequency bins) probably requires some manual intervention with the data, because FT will likely prevent you to do so, since it checks whether the frequency bins for the to-be-combined data structures match. I could type some recipe now, but since you are not too clear on the details so I’d rather not spend time on that now. Also, I’d like to give other people the opportunity to chime in here :).

Best wishes,

On 11 May 2020, at 16:43, sarah.kirchler at gmail.com<mailto:sarah.kirchler at gmail.com> wrote:

Dear Fieldtrip Users,

thank you for all the help you’ve given me already.
Now I am trying to make the sum and the difference of the Grand mean from/between two frequencies I measured with an EEG.
I read that it is possible to make a datastructure using {} within ft_timelockbaseline and then use the option cfg.operation(x1-x2 and so on) as a operation of function ft_topoplotER to make this sum/these differences.
Now my Problem is that I don’t need to make the baselinecorrection via ft_timelockbaseline because I don’t have the baseline in the datasegment I’m interested in. So I tried to build the datastructure for cfg.operation within ft_timelockanalysis but Fieldtrip doesn’t allow this and I get an error message.

My questions are now:
1. Can I make the difference also within the ft_timelockgrandavverage function or do I have to make the difference lawer in ft_topoplotER?
2. If so, how can I or form a datastructure I can use in cfg.operation or make the difference differently with some other function?

I hope you understand me,
to all you extraordinary brains: thank you in advance,


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