[FieldTrip] Problem with unwanted 'normalisation' of data using ft_realtime_signalviewer

["Jörn M. Horschig"]

Hi Christian,

I had a quick look at these function. I think these values are a result 
of the fact that
a) power corresponds to the squared magnitude of a signal
b) is line 157 of ft_realtime_powerestimate, the power is divided by the 
number of channels.

Maybe put a breakpoint somewhere around line 130 and check step by step 
what happens to your data? Note also that this is just an example 
function, so it might not be practical for real experiment.

Best,
Jörn

On 4/17/2014 11:35 AM, Christian Walsh wrote:
> Dear community,
>
> My name is Christian Walsh and I am doing a Neural Engineering MSc. in 
> TCD in Ireland. My thesis is on the effects of timed auditory 
> stimulation on sleep quality. A sort of dumbed down and scaled down 
> version of a recent enough study by Ngo et al. (2013) entitled: 
> Auditory Closed-Loop Stimulation of the Sleep Slow Oscillations 
> Enhances Memory.
>
> For this, I detect peaks and troughs in the ongoing EEG data in 
> realtime. On detecting a trough, a sound is played back after an 
> initial delay. This is done so that the sound playback coincides with 
> the peak of the ongoing EEG data. Before I can actually perform this 
> experiment I need to setup the apparatus.
>
> To do this I have simulated realtime streaming and analysis using the 
> ft_realtime_signalproxy function in one MATLAB session and an 
> edited_ft_realtime_powerestimate and psychtoolbox function in another 
> session. This is all working fine. The problem is that the data that 
> is streamed in is normalised, scaled or something. i.e. the y-values 
> of the streamed data should range from around -150 uV to 150uV but the 
> edited_ft_realtime_powerestimate function only displays y-values 
> between around -2 and 2???
>
> I'm new to programming so apologies if this is a stupid question. I 
> have looked into editing some of the ft_read_data and 
> ft_preproc_baselinecorrect functions but have not found a solution.
>
> Advice would be appreciated,
>
> Cheers,
>
> Christian
>
>
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-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

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