meg-pd function "rawdata"

[Masaki Maruyama]

Hello,

The Fieldtrip function "preprocessing" cannot exactly detect timings of trials 
from one of our MEG dataset recorded using Neuromag 306 ch MEG system. 
The trials often precede by 0.1 second and sometimes delay by 0.9 second 
with respect to the exact time. I looked into several programs and the output 
of meg-pd function "rawdata" seems to be unusual. It reads the data file one 
second by one second from the begining of data, and the rawdata('goto', T) 
outputs a start time of read epoch as

rawdata('goto', 100.0) = 100.0
rawdata('goto', 100.1) = 100.0
…
rawdata('goto', 100.9) = 100.0
rawdata('goto', 101.0) = 101.0

These outputs are fine. However, in later period its output becomes

rawdata('goto', 102.0) = 102.0
rawdata('goto', 102.1) = 102.1
rawdata('goto', 102.2) = 102.1
…
rawdata('goto', 102.9) = 102.1
rawdata('goto', 103.0) = 102.1
rawdata('goto', 103.1) = 103.1
…

After 102.1 second the output delays by 0.1 second, which seems to be a 
causal of the wrong time detection of trials. I cannot find out why it happened 
in the MEG recording, but I like to see averaged fields from the data. Could 
you please give me advices? 

Thank you in advance for your kind advices.

 
Sincerely yours,
Masaki Maruyama

Inserm U.562 - Neuroimagerie Cognitive 
CEA/SAC/DSV/I2BM/NeuroSpin
Bât 145, Point Courrier 156 
F-91191 GIF/YVETTE, FRANCE

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