[Eeglablist] time dilation on Tucker-Davis-via-neuroscan CNT import

[Hamish Innes-Brown]

More info:  when you export a CNT file as ASCI and look in the header, the
sample rate does indeed come up with all decimal points intact, so there
must be a place in the CNT file header which contains the full precision of
the sampling rate, mustn't there?...


for example:

[Subject],
[Date],
[Time],
[Channels], 64
[Rate], 488.281250
[Type], Continuous
[Rows], Points
[Electrode Labels]
[      O1], [      O2],  etc



Maybe the easiest solution is to resample the CNT file to a more normal
sampling rate before importing to EEGlab



On Feb 17, 2008 11:54 PM, Ross Fulham <Ross.Fulham at newcastle.edu.au> wrote:

> Hamish,
>
> Neuroscan CNT files store sampling rates as a 16 bit integer quantity (in
> Hz). So the problem with sampling rates being rounded down is occurring when
> you convert the data to Neuroscan, not when you import the neuroscan file
> into EEGLAB.
>
> Ross
>
>
>
>
> ------------------------------------------------------------
> Dr Ross Fulham
> Research Officer
> Room 1025, Ph: 492 46636, Fax: 492 46608
> Centre For Mental Health Studies
> James Fletcher Hospital
> Newcastle, NSW. Australia.
>
> Functional Neuroimaging Laboratory,
> Discipline of Psychology
> School of Behavioural Sciences,
> The University of Newcastle.
>
> e-mail Ross.Fulham at newcastle.edu.au
> ------------------------------------------------------------
> >>> Hamish Innes-Brown <hinnesbrown at gmail.com> 02/15/08 4:37 PM >>>
>  Hi all, I am having a strange problem on importing continuous EEG where
> the
> time of events (and the whole EEG) is stretched a little bit on importing
> the data.
>
> It's a bit of a convoluted process getting the data from a TDT system into
> EEGlab, what we do is this:
>
> 1) Export the channel data from the TDT tanks (to CSV files)
> 2) Read the CSV data into Neuroscan and add the events from the TDT event
> log
> 3) Load the CNT file in to EEGlab using pop_loadcnt
>
> The weird thing is that the data is all slightly "slowed down" when read
> into EEGlab - events and EEG features are delayed in time.  I think this
> might be a problem with how a sampling rate that's not a multiple of one
> is
> read from the CNT file.  The TDT sampling rate is 488.28125, and once read
> into EEGlab, the EEG.srate value has dropped all the decimals and become
> "488".
>
> Has anyone else had problems importing data with such strange sampling
> rates?
>
> I'm aware there is a direct TDT import plugin but so far I haven't been
> able
> to get that to work (I think our TDT installation is missing some vital
> parts), and we also use the Neuroscan CNT files for another parallel
> analysis...
>
> Thanks.
>
>
> -hamish-
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20080218/6999004f/attachment.html>