xcnt - EEG/MEG Raw Data Viewer
Contents
-----------------------------------------------------------------------------
EEP 3.1 Max-Planck-Institute of Cognitive Neuroscience 1996-99
xcnt 3.21 (OSF1 V4.0 alpha) Wed Sep 15 13:30:15 1999
-----------------------------------------------------------------------------
xcnt <cnt> [<trg in>] [<rej in>] [<cfg>] [options]
options:
-r <reref cfg> enable rereferencing
-f <fir> enable FIR filtering
-G <changrp> load this channel group file
-p <cmd pipe> create a remote control pipe
xcnt is a X/Motif based cnt file viewer. It allows EEG/MEG raw data
inspection and interactive manipulation of trigger and rejection marks.
Overview
The effective initial xcnt setup results from this
configuration lookup/load sequence:
- Default display-related settings are loaded from the resource
database using the standard mechanism for X/Xt programs.
- User specific display-related settings are loaded from your personal
xcnt resource file (Options - Save Options), if any.
- Project/file specific settings are read from the configuration files,
which are passed as command line arguments or found automatically.
Configuration File
The xcnt-configuration file (default name "xcnt.cfg") is meant to store
project-specific settings as channel scalings, the initial set of channels
in the display etc. This configuration file is
optional. You can create one via File - Save Configuration As... and
adapt it to match your needs.
Resources
app-defaults/Xcnt
Some more permanent display options
can be saved from within xcnt (Options - Save Options). They are stored
as standard X resource lines in ~/.eep/xcnt.resources.
For xrdb gurus: these resources are written with full qualifiers and read after
all other resources with lowest priority.
You can load data only via command line arguments. You must supply at least a cnt
file. The other stuff is optional but recommended to load. There is no load
functionality in the xcnt menus.
You can locate a specific time in your record with the horizontal scrollbar,
with scrolling keys, by entering a start time or with a
lookup function. In detail:
- Scrollbar page increment/decrement, Cursor Down/Up, Page Down/Up:
- +/- 90% of the displayed window
- Scrollbar increment/decrement, Cursor Right/Left:
- +/- 40% of the displayed window
- Home/End:
- record start/stop
- Trigger Right/Left arrow button or key "t"/"T":
- locate next/previous trigger
(comma-separated lists of max. 32 triggers are allowed
in the trigger fields)
- Rejection Right/Left arrow button:
- set cursor #1 to the start of next/previous rejected epoch,
cursor #2 to it's end
You can set/clear trigger points and rejection epochs with the corresponing
buttons in the control area (rejections with the "r" and "c" keys too). Triggers
are deleted only if the correct code is entered in the textfield and if cursor #1
is at the correct sample position.
xcnt displays a warning if you try to leave it with unsaved changes.
The Options menu offers, among others, these display control facilities:
- Signal preprocessing and rendering:
- Reference...
To select/calculate a reference signal which is
substracted from other selected signals. The syntax
for the dialog fields is analogous to
the corresponding cntreref configuration file entries.
- FIR Filter...
To select a FIR filter coefficients file
which is applied to the input signals. Note that this kind of
filtering has not the same sophisticated discontinuity handling as
the cntfilter program.
- DC offset compensation
If enabled, substract the mean of each displayed signal epoch before
drawing (avoids drifts out of screen).
- Draw Min/Max Bars
If the time axis is scaled to display long epochs, each pixel of
screen would display many sample points of the signal.
To reduce time/memory consumption, xcnt
defaults to draw maximal two sample points in each screen pixel
and ignores intermediate points completely.
With this option enabled, all sample points are read/processed, and
an additional vertical line is drawed to indicate the range between
the minimum and the maximum value of all sample points which would fall
into this screen pixel.
- User interface details:
- Cursors
Select between different cursor types.
- Show Signal Values
Display values of one selected channel at the cursor positions
in the bottom control/status area. The channel is selected by
entering its label in the "Channel" field or by pressing
Ctrl+Button1 at the desired signal graph.
- Drag Signal
The displayed signal is moved together with the scrollbar
slider. Useful only if you have not too many channels and a
hellish fast computer...
- Save Options
Saves the toggle states in this menu and the size and position of
the main window and the channel legend. The settings saved this way
are restored the next time you start xcnt, provided you do not
override them in a configuration file.
The Channels menu offers the selection of Channel Groups as described below:
- Select...
To select a subset of the available channels. The entry dialog excepts regular expressions, or a comma-separated list of channel labels.
Often it is not very useful to display all channels of a EEG/MEG record
simultaneously. Channel groups allow the compilation of smaller
channel subsets.
Channel groups are defined in a text file
"channels.cfg". At startup, xcnt either loads the
file passed via the -G argument or tries to find this file as
(in this order):
./channels.cfg
./cfg/channels.cfg
../cfg/channels.cfg
../../cfg/channels.cfg
Two groups are created by xcnt itself:
- Native - all channels in the cnt file in their original order
- Startup - the channel selection from the configuration file(if any)
For each loaded channel group you will get a button in the
Channels menu.