[FieldTrip] Invisible data after ft_resampledata

[Emilie Caspar]

Dear Fieldtrippers, 

Just a follow-up email to know if someone already got this problem of « Invisible trials » after downsampling and has an idea about how to solve the problem.

Kind regards, 

Emilie


---------------------------------------------
Emilie CASPAR

Associate Professor 

Department of Experimental Psychology, Ghent University
office: Henri Dunantlaan, 2 - Floor 2, Room 94

lab’s website: https://moralsocialbrain.com/ <https://moralsocialbrain.com/> 
personal website: https://emiliecaspar.home.blog/ <https://emiliecaspar.home.blog/>
Université libre de Bruxelles (office & contact): DB10.138 / +32 2 650 32 95


> Le 21 oct. 2021 à 14:40, Emilie Caspar via fieldtrip <fieldtrip at science.ru.nl> a écrit :
> 
> Dear fieldtrippers, 
> 
> I am trying to downsample my EEG data, originally recorded at 2048 Hz.
> 
> I run the following code:
> 
>     cfg = [];
>     %cfg.channel = {'A1', 'B2', 'A5', 'B5', 'B6', 'B8', 'A15', 'B20', 'B15', 'B16', 'A13', 'B18', 'A27', 'A28', 'A31', 'A29', 'A30', 'A32', 'B32', 'A21', 'A31', 'B26', 'EXG1', 'EXG2', 'EXG3', 'EXG4'}%'B15';
>     cfg.dataset    = [ file.name];
>     cfg.bpfilter    = 'yes';
>     cfg.bpfreq      = bpfilterRange;
>     cfg.bpfiltord   = bpfilterOrder;
>     cfg.reref       = 'yes';
>     cfg.refchannel  = chansRef;
>     allData_preprosses = ft_preprocessing(cfg);
>     
>     cfg = [];
>     cfg.resamplefs = 512;
>     data_DS = ft_resampledata(cfg, allData_preprosses);
>     
>     
> When I look at individual trials for artefact rejection, something very weird happens. Basically some trials become ‘invisible’ (sorry, I don’t find any other way to describe it), see figure attached. It seems that the data do exit though because when I average my visible trials to the invisible ones, it results in an invisible ERPs graph. But when I remove the trials containing the invisible data, an ERP graph does appear (please don’t pay attention to the quality of the data, this is just an example without any cleaning).
> 
> It seems there is a logic to the phenomenon, because if I downsample to 1024Hz (so half of my initial 2048 Hz), only half of my data becomes invisible and if I downsample to 512Hz, a 3/4 of the data becomes invisible.
> 
> I have tried the same with a different coding, with this time downsampling before filtering as follows, but the output is exactly the same.
> 
> display('downsample each channel')
>          cfgp         = [];
>                 cfgp.dataset = [file.name];
>                 cfgr            = [];
>                 cfgr.resamplefs = 512;
>                 display('Resampling')
>                 for i= chansAll
>                     cfgp.channel = i;
>                     datp         = ft_preprocessing(cfgp);
>                     datr{i}      = ft_resampledata(cfgr, datp);
>                     clear datp
>                 end
>                 cfg = [];
>                 datall = ft_appenddata(cfg, datr{:});
>         
>     display('Filters')
>     
>     cfg = [];
>     cfg.dataset    = [ file.name];
>     cfg.bpfilter    = 'yes';
>     cfg.bpfreq      = bpfilterRange;
>     cfg.bpfiltord   = bpfilterOrder;
>     cfg.reref       = 'yes';
>     cfg.refchannel  = chansRef;
>     data_DS = ft_preprocessing(cfg, datall);
> 
> 
> Does anyone have any idea regarding this phenomenon?
> 
> Thank you in advance!
> 
> Best regards, 
> 
> Emilie
> 
> <Downsampling.001.jpeg>
> ---------------------------------------------
> Emilie CASPAR
> 
> Associate Professor 
> 
> Department of Experimental Psychology, Ghent University
> office: Henri Dunantlaan, 2 - Floor 2, Room 94
> 
> lab’s website: https://moralsocialbrain.com/ <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmoralsocialbrain.com%2F&data=04%7C01%7Cemilie.caspar%40ulb.be%7C9eaa583fc9f2496f3d9708d99494a638%7C30a5145e75bd4212bb028ff9c0ea4ae9%7C0%7C0%7C637704188432821811%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=X9emmQ51jam6Zr%2FzU1ntTu4F%2FAWsPVUwbwMPtsxLOhw%3D&reserved=0> 
> personal website: https://emiliecaspar.home.blog/ <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Femiliecaspar.home.blog%2F&data=04%7C01%7Cemilie.caspar%40ulb.be%7C9eaa583fc9f2496f3d9708d99494a638%7C30a5145e75bd4212bb028ff9c0ea4ae9%7C0%7C0%7C637704188432831766%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=RSBTcOxejkzdWKA9QOyJZKXBD%2F5bGyFC12%2FKCpKl8GY%3D&reserved=0>
> 
> Université libre de Bruxelles (office & contact): DB10.138 / +32 2 650 32 95
> 
> 
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> https://doi.org/10.1371/journal.pcbi.1002202

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