[Eeglablist] Single-precision data vs. double-precision data in Matlab

[Philip Michael Zeman]

Hello all,

Two questions:

Is the current best practice to use single precision representation of the 
raw EEG data?

I've just upgraded from EEGLab 4.515 to 6.x  and I've noticed that the data 
are not stored in the EEG.data structure as single precision numbers.  In my 
experimentation, I found that runica in some cases does yield different 
results for double vs. single precision data.

Is there a quick and easy way to change the representation of the data in 
EEGLab 6.x back to double precision representation?




Regards,

Phil Zeman




----- Original Message ----- 
From: "Julie Onton" <julie at sccn.ucsd.edu>
To: <sklein at berkeley.edu>
Cc: <eeglablist at sccn.ucsd.edu>
Sent: Monday, April 14, 2008 4:16 PM
Subject: Re: [Eeglablist] Time-frequency analysis (subtraction first or 
analysis first)


>I agree that the time/frequency analysis should be performed first, and 
>THEN subtraction.
> Subtraction of the EEG time courses (ie, in the time domain) will give a 
> very different result
> compared to the (frequency domain) ERSP subtraction. EEGLAB's newtimef() 
> called from the
> commandline performs this very operation on two datasets corresponding to 
> two different
> conditions.
>
> Best, Julie
>
> -- 
> Julie Onton, PhD
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation
> University of California, San Diego
> (858) 458-1927 ext 17
> http://sccn.ucsd.edu/~julie
>
>> Dear Arnaud,
>> Are you sure about your recommendation of the first statement being 
>> correct?
>> Suppose the two conditions happen to be quite similar in producing alpha 
>> or
>> gamma oscillations. Since the two conditions are the same, one would like
>> the desired outcome to be a *cancellation *of the two power plots. 
>> However,
>> since the occurrence of the oscillations likely happen at different time
>> points (and with different phases) early subtraction would still leave 
>> the
>> oscillations and the outcome would be equal or even stronger power rather
>> than cancellation. Or am I thinking about it improperly?
>> Stan
>>
>> On Sun, Apr 13, 2008 at 10:53 AM, Arnaud Delorme <arno at cerco.ups-tlse.fr>
>> wrote:
>>
>>> Dear Hsu,
>>>
>>> only your first statement is correct. The second one could be correct if
>>> you could pair the trials, but it would be very rare that you would want
>>> to do this (since trials are recorded at different times and are usually
>>> not paired between conditions). Look up the help of the newtimef
>>> function which allows computing differences between power between
>>> different conditions and newcrossf which allows computing difference
>>> between phase coherence images.
>>>
>>> Best,
>>>
>>> Arno
>>>
>>> Hsu, Shen-Mou wrote:
>>> > Dear list-memebers,
>>> >
>>> > Suppose that I am interested in comparing two conditions A and B in
>>> terms of their power and phase coherence. I was wondering which one of 
>>> the
>>> following steps is more theoretically correct. 1. After segmentation,
>>> calculate the EEG differences between the condition A and B and then 
>>> perform
>>> time-frequency analysis on the differences. 2. After segmentation, 
>>> perform
>>> time-frequency analysis on the EEG data of the condition A and B
>>> respectively and then compute the power or phase coherence differences
>>> between two conditions. Any comments would be much appreciated.
>>> >
>>> > Many thanks,
>>> >
>>> > Shen-Mou Hsu
>>> >
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