[FieldTrip] fieldtrip Digest, Vol 16, Issue 25

[Stephen Politzer-Ahles]

Hi Giulia,

The data certainly do look a bit weird to me, and as Enzo suggests
specifying 32 or 16 bits may help. Also, have you tried reading the data
using ft_preprocessing()<http://fieldtrip.fcdonders.nl/reference/ft_preprocessing>rather
than ft_read_data()? In my experience the high-level function
(ft_preprocessing) is easier to work with and handles a lot of the
complicated stuff for you, so unless you have a special reason to need to
read your data with the low-level functions then you might have more luck
just using ft_preprocessing.

Best,
Steve Politzer-Ahles

Message: 5
> Date: Mon, 19 Mar 2012 13:32:34 -0400
> From: Enzo Brunetti <enzo.brunetti at gmail.com>
> To: Giulia Rizza <giulia.rizza at tiscali.it>,     Email discussion list for
>        the FieldTrip project <fieldtrip at donders.ru.nl>
> Subject: Re: [FieldTrip] Neuroscan .cnt files
> Message-ID: <2CD6708A-A08A-4AF0-92BB-B78029DF2B76 at gmail.com>
> Content-Type: text/plain; charset="us-ascii"
>
> Dear Giulia,
> I could not see your dropbox link showing the plot, but a known reported
> problem with importing .cnt neuroscan files is that the file header does
> not specify the actual precision of your data (typically 32 bits with new
> neuroscan systems, 16 bits previously). If you are importing 32 bits data
> without explicitly defining it previously, you can obtain the type of
> signals you are talking about (the default importing option is '16bits').
> If this is the case, you must to specify this in the cfg input structure of
> the reader function, as:
>
> cfg.headerformat         =  'ns_cnt32';
> cfg.dataformat              =  'ns_cnt32';
> cfg.eventformat            =  'ns_cnt32';
>
> in addition to the other specific fields of the structure.
>
> Also, you can visit this link:
> http://fieldtrip.fcdonders.nl/faq/i_have_problems_reading_in_neuroscan_.cnt_files._how_can_i_fix_thisfor more information.
>
> I hope this could help you.
> Best
>
> Dr. Enzo Brunetti F.
> ---------------------------
> Institute of Biomedical Sciences
> Faculty of Medicine
> University of Chile
>
>
> On Mar 19, 2012, at 11:25 AM, Giulia Rizza wrote:
>
> > Dear Fieldtrippers,
> > hi to everyone and thanks in advance for your time.
> > I'm not
> > an expert and I'd like to share with you a problem I found in reading
> cnt files
> > acquired with Neuroscan.
> >
> > I read the data with ft_read_data function and I find
> > the attached link Plot1, for instance the first channel. It seems that
> the
> > signal is forced to pass per zero every two samples, so I tried to read
> them
> > excluding the even samples and I find the result in Plot2, while
> excluding the
> > odd values I find the result in Plot3.
> >
> > http://dl.dropbox.com/u/28258961/Plot01.
> > rar
> >
> > Unfortunately there are still some problems since the maximum value that
> > can be represented (about 900) is smaller than some values in the data
> and the
> > result is that I find a sharp change of sign. How can I fix it?
> >
> > Thanks to
> > anyone who can help me
> >
> > Giulia
> >
> >
> > E' nata indoona: chiama, videochiama e messaggia Gratis. Scarica indoona
> per iPhone, Android e PC: http://www.indoona.com/
> > _______________________________________________
> > fieldtrip mailing list
> > fieldtrip at donders.ru.nl
> > http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
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