[Eeglablist] Your Brain Scan Looks Different on Mac and PC

[Arnaud Delorme]

Dear all,

some of you might have heard this distressing news: FreeSurfer, the well known fMRI brain imaging software, gives different results depending on the operating system.

http://www.ncbi.nlm.nih.gov/pubmed/22675527

Is it the same for Matlab? We have performed basic tests and Matlab numerical computation seems to be relatively OS. We have tested 

A - Matlab 7.8.0.347 (R2009a) on Windows XP
B - Matlab 7.11.0.584 (R2010b) on Mac OS X (Lion)
C - Matlab 7.14.0.739 (R2012a) on Fedora core 3.3.6-3.fc16.x86_64

We have tested the ERSP time-frequency decomposition function newtimef.m on the EEGLAB epoched tutorial dataset ('eeglab_data_epochs_ica.set'). We have kept all default values. 

A and B were strictly identical. It might be important to note that Windows XP was running on top of Mac OSX in a WMWARE virtual machine so the same Intel processor was being used in both cases. The difference between A/B and C was 4e-11% on average. Still it was not strictly equivalent. This type of difference might become more important for algorithms such as ICA which are iterative. We had noticed for example that ICA should not be run in simple precision or the ICA components would be qualitatively much poorer (EEGLAB forces double precision on the data before running ICA). Any comments or further tests welcomed.
Thanks,

Arno