[Eeglablist] how to select channels for back-projection of ERP

[Makoto Miyakoshi]

Dear Elizabeth,

> try_strings and catch_strings

You are reading the code. That's not how to use it. Use EEGLAB
plugin/extension manager. 'File' -> 'Manage EEGLAB extensions' -> and
choose the plugin.

Makoto

On Tue, Aug 4, 2015 at 2:44 AM, Elizabeth Milne <e.milne at sheffield.ac.uk>
wrote:

> Thanks Makoto, that is very helpful. However, I'm not sure which inputs
> are required.
> Can you clarify what I need to enter for fig, try_strings and
> catch_strings.
> Best wishes,
> Elizabeth
>
> On 3 August 2015 at 23:09, Makoto Miyakoshi <mmiyakoshi at ucsd.edu> wrote:
>
>> Dear Elizabeth,
>>
>> A projection from ICs to channels is a 'forward projection'. We've been
>> using the word 'backprojection' in the wrong way, so I corrected it (at
>> least in my functions).
>>
>> In ICA, the polarity of map and time-series signal can be flipped by
>> applying -1 to the both. This is a fundamental uncertainty.
>>
>> > If I want to use this, or any other, IC to measure the amplitude /
>> latency of particular ERP deflections it is necessary to know which is the
>> correct channel to choose for back-projection. However, I am unsure as to
>> how to make this decision objectively.
>>
>> I wrote pvaftopo() plugin for this purpose
>> http://sccn.ucsd.edu/wiki/Plugin_list_process
>> pvaf is a new concept Scott proposed nearly 20 years ago which is
>>
>> percent variance accounted for (pvaf) = 100-100*var(all_data -
>> selected_ICs)/var(all_data)
>>
>> We'll publish IEEE EMBC conference proceedings soon for this year about
>> the study-level envtopo and pvaf, so you may want to refer to the paper
>> once it's published (Lee et al., IEEE EMBC conf proc 2015)
>>
>> Pick up the channel that is closest to the peak in the scalp maps and you
>> can choose the 'most accounted' channel objectively.
>>
>> I'm happy that there is finally a user asking for this plugin!
>>
>> Makoto
>>
>> On Fri, Jul 31, 2015 at 2:13 PM, Elizabeth Milne <e.milne at sheffield.ac.uk
>> > wrote:
>>
>>> Dear EEGLAB team,
>>> I have a question about resolving the "true" polarity of IC ERPs by
>>> back-projecting to channel data. Using erpimage, I have obtained the ERP of
>>> an IC, but the polarity is different (orthogonal) when back-projecting to
>>> different channels. In another example from a different IC, the polarity of
>>> the ERP does not change, but the amplitude of the signal is different
>>> depending on which channel is selected for back-projection.
>>>
>>> If I want to use this, or any other, IC to measure the amplitude /
>>> latency of particular ERP deflections it is necessary to know which is the
>>> correct channel to choose for back-projection. However, I am unsure as to
>>> how to make this decision objectively. Are there particular features that I
>>> should look at to make this decision more systematic, i.e. dipole
>>> projection? % power accounted for?
>>>
>>> If anyone can offer advice, or point out errors in my understanding I'd
>>> be very grateful.
>>>
>>> Many thanks,
>>> Elizabeth
>>>
>>> --
>>> Elizabeth Milne
>>> Reader in Cognitive Neuroscience
>>> University of Sheffield
>>> Western Bank
>>> Sheffield
>>> S10 2TN
>>>
>>> +44 (0) 114 222 6558
>>>
>>> http://www.autismresearchlab.group.shef.ac.uk/
>>>
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>>
>>
>>
>> --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
>
>
>
> --
> Elizabeth Milne
> Reader in Cognitive Neuroscience
> University of Sheffield
> Western Bank
> Sheffield
> S10 2TN
>
> +44 (0) 114 222 6558
>
> http://www.autismresearchlab.group.shef.ac.uk/
>



-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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