Hi Giulia,<br><br>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 <a href="http://fieldtrip.fcdonders.nl/reference/ft_preprocessing">ft_preprocessing()</a> 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.<br>
<br>Best,<br>Steve Politzer-Ahles<br><br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Message: 5<br>
Date: Mon, 19 Mar 2012 13:32:34 -0400<br>
From: Enzo Brunetti <<a href="mailto:enzo.brunetti@gmail.com">enzo.brunetti@gmail.com</a>><br>
To: Giulia Rizza <<a href="mailto:giulia.rizza@tiscali.it">giulia.rizza@tiscali.it</a>>, Email discussion list for<br>
the FieldTrip project <<a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a>><br>
Subject: Re: [FieldTrip] Neuroscan .cnt files<br>
Message-ID: <<a href="mailto:2CD6708A-A08A-4AF0-92BB-B78029DF2B76@gmail.com">2CD6708A-A08A-4AF0-92BB-B78029DF2B76@gmail.com</a>><br>
Content-Type: text/plain; charset="us-ascii"<br>
<br>
Dear Giulia,<br>
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:<br>
<br>
cfg.headerformat = 'ns_cnt32';<br>
cfg.dataformat = 'ns_cnt32';<br>
cfg.eventformat = 'ns_cnt32';<br>
<br>
in addition to the other specific fields of the structure.<br>
<br>
Also, you can visit this link: <a href="http://fieldtrip.fcdonders.nl/faq/i_have_problems_reading_in_neuroscan_.cnt_files._how_can_i_fix_this" target="_blank">http://fieldtrip.fcdonders.nl/faq/i_have_problems_reading_in_neuroscan_.cnt_files._how_can_i_fix_this</a> for more information.<br>
<br>
I hope this could help you.<br>
Best<br>
<br>
Dr. Enzo Brunetti F.<br>
---------------------------<br>
Institute of Biomedical Sciences<br>
Faculty of Medicine<br>
University of Chile<br>
<br>
<br>
On Mar 19, 2012, at 11:25 AM, Giulia Rizza wrote:<br>
<br>
> Dear Fieldtrippers,<br>
> hi to everyone and thanks in advance for your time.<br>
> I'm not<br>
> an expert and I'd like to share with you a problem I found in reading cnt files<br>
> acquired with Neuroscan.<br>
><br>
> I read the data with ft_read_data function and I find<br>
> the attached link Plot1, for instance the first channel. It seems that the<br>
> signal is forced to pass per zero every two samples, so I tried to read them<br>
> excluding the even samples and I find the result in Plot2, while excluding the<br>
> odd values I find the result in Plot3.<br>
><br>
> <a href="http://dl.dropbox.com/u/28258961/Plot01" target="_blank">http://dl.dropbox.com/u/28258961/Plot01</a>.<br>
> rar<br>
><br>
> Unfortunately there are still some problems since the maximum value that<br>
> can be represented (about 900) is smaller than some values in the data and the<br>
> result is that I find a sharp change of sign. How can I fix it?<br>
><br>
> Thanks to<br>
> anyone who can help me<br>
><br>
> Giulia<br>
><br>
><br>
> E' nata indoona: chiama, videochiama e messaggia Gratis. Scarica indoona per iPhone, Android e PC: <a href="http://www.indoona.com/" target="_blank">http://www.indoona.com/</a><br>
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