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Hi Gaël, This is independent of the dimensionality reduction - under the model the group has a single associated time course which is estimated via the rank-1 approximation. There are further implications wrt dimensionality reduction, but the main point is independent thereof. best Christian On 22 Jul 2009, at 08:32, Gael Varoquaux wrote: > Hi Christian, > > Thank you for the answer. I had read the article wrong, and thought > that > tensor-ICA was applied to individual principle components, and not the > raw data. After reexamination of the article it is clear to me that > the > dimension reduction is applied on all subjects enforcing identical > time > loading vectors. > > Thank you, > > Ga�l > > On Sun, Jul 12, 2009 at 07:53:34AM +0100, Christian F. Beckmann wrote: >> Hi >> Tensor-ICA assumes consistent response in time by virtue of >> calculating >> the rank-1 approximation between the temporal response profiles >> of the >> different subjects/sessions. For resting FMRI data we recommend the >> concat-ICA approach (choose 'Multi-session temporal >> concatenation' in the >> GUI) The Tensor-ICA algorithm (incl the rank-1 approximation) is >> outlined >> in >> Beckmann and Smith. Tensorial extensions of independent component >> analysis >> for multisubject FMRI analysis. Neuroimage (2005) vol. 25 (1) pp. >> 294-311 >> [1]http://dx.doi.org/10.1016/j.neuroimage.2004.10.043 >> hth >> Christian >> On 12 Jul 2009, at 03:46, Gael Varoquaux wrote: > >> Hi, > >> I have been told that Tensor-ICA was not suited for paradigm- >> free group >> analysis, such as resting-state acquisitions. I was unable to >> understand >> the justification behind this. The claim was that for data >> acquired >> without paradigm on different subjects, the time series would be >> different, and thus the tensor model would not apply well. >> However, this >> puzzles me, as ICA is performed on principle components, and >> not raw >> time-series. > >> Did I miss-understand the underlying reasons for avoiding >> Tensor-ICA on >> paradigm-less data? Is there a paper that would enlighten me? > >> Cheers, > >> Ga�l _______________________________________________ Christian F. Beckmann, DPhil Senior Lecturer, Clinical Neuroscience Department Division of Neuroscience and Mental Health Imperial College London, Hammersmith Campus Rm 419, Burlington Danes Bldg, Du Cane Road, London W12 0NN, UK Tel.: +44 (0)20 7594 6685 --- Fax: +44 (0)20 7594 6548 Email: [log in to unmask] http://www.imperial.ac.uk/medicine/people/c.beckmann/ Senior Research Fellow, FMRIB Centre University of Oxford JR Hospital - Oxford OX3 9DU Tel.: +44 (0)1865 222551 --- Fax: +44 (0)1865 222717 Email: [log in to unmask] http://www.fmrib.ox.ac.uk/~beckmann