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Dear FieldTrip community,<br>
<br>
Up until now, many users and functions relied on a predefined way to
define proximal or neighbouring sensor, namely using a distance
measurement. We changed the functionality of ft_neighbourselection
and related functions, which will be explained in the following.<br>
<br>
<b>1 - The user is obliged to define and verify channel neighbours</b><br>
Driven by some thoughts and current discussion going on in the
FieldTrip mailinglist, we decided to change neighbourselection.
Within the next days, all functions which require information about
proximal or neighbouring sensors will be required to have a
cfg.neighbour field that you as the user have to specify explicitly.
This may be obvious for some functions, such as cluster statistics
on channel level, but not so much for other functions such as planar
gradient computation or channelrepair. <br>
<br>
In order to ease the way of getting into the whole
neighbourselection issue, we wrote 3 FAQs:<br>
<a class="moz-txt-link-freetext"
href="http://fieldtrip.fcdonders.nl/faq/how_can_i_define_neighbouring_sensors">http://fieldtrip.fcdonders.nl/faq/how_can_i_define_neighbouring_sensors</a><br>
<a class="moz-txt-link-freetext"
href="http://fieldtrip.fcdonders.nl/faq/how_does_ft_neighbourselection_work">http://fieldtrip.fcdonders.nl/faq/how_does_ft_neighbourselection_work</a><br>
<a class="moz-txt-link-freetext"
href="http://fieldtrip.fcdonders.nl/faq/how_can_i_define_my_own_neighbourhood_template">http://fieldtrip.fcdonders.nl/faq/how_can_i_define_my_own_neighbourhood_template</a><br>
<br>
Please note that you can use ft_neighbourplot to see the current
neighbourselection and verify whether this seems like a good choice.
Although we try to come up with extremely smart ways to compute
neighbours of your data, selection of neighbours can still be highly
subjective. Therefore, we also decided to do the following:<br>
<br>
<b>2 - Neighbours can be defined using different methods</b><br>
<br>
Since the near beginning of FieldTrip, neighbours were selected
based on a 'distance' approach, meaning that nearby sensors were
defined as neighbours. This has shown to be valid for some systems
given a predefined distance (neighbdist) of 4cm, whereas other
systems needed a different neighbdist. <br>
In order to reduce subjectivity and arbitrariness of the maximal
distance of a sensor to be called 'neighbour', we implemented a
'triangulation' approach. For more information, see the
corresponding FAQ above. <br>
However, since systems around the world should be similar in terms
of sensor position, we decided to implement a 'template'-based
approach, which loads a predefined neighbour-template from file. It
is up to you to decide what approach you are most comfortable with.
The standard behaviour of ft_neighbourselection still is the old
'distance' approach.<br>
<br>
<b>3 - Call for neighbour templates<br>
</b><br>
Now, dear community, you may become active and share your
neighbour-templates. Here at the Donders, we are primarily working
with the CTF275 system and have thus quite some expertise and
experience. For this system, you can already find a template in the
newer FieldTrip versions. We will continue improving the
neighbourdefinition of this template and try to be as objective as
possible. Furthermore, we will start creating templates for other
systems as well and try to optimize these. However, when it comes to
other systems, also including EEG systems, you might be more
experienced. Therefore, we would like to ask whether you want to
share your expertise and send the neighbourstructure that you are
using on your system to us (== me). I will then try to incorporate
your subjective selection with ours, probably after some discussion.
If you are willing to support us in that respect, please do <b>not</b>
send a mail to the mailing-list but to my personal mail address, as
I will be organizing the templates: <a
class="moz-txt-link-abbreviated"
href="mailto:jm.horschig@donders.ru.nl">jm.horschig@donders.ru.nl</a>
Thanks in advance for your cooperation.<br>
<br>
Best regards on behalf of the developer team,<br>
Jörn<br>
<pre class="moz-signature" cols="72">--
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands
Contact:
E-Mail: <a class="moz-txt-link-abbreviated" href="mailto:jm.horschig@donders.ru.nl">jm.horschig@donders.ru.nl</a>
Tel: +31-(0)24-36-68493
Web: <a class="moz-txt-link-freetext" href="http://www.ru.nl/donders">http://www.ru.nl/donders</a>
Visiting address:
Trigon, room 2.30
Kapittelweg 29
NL-6525 EN Nijmegen
The Netherlands</pre>
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