Rated 4.5 of 5.
Level of importance:
Rated 5 of 5.
Level of validity:
Rated 4 of 5.
Level of completeness:
Rated 4 of 5.
Level of comprehensibility:
Rated 5 of 5.
|Keywords:||intersubject information mapping, canonical, complex natural stimuli, Intersubject correlation mapping|
As the paper states in its introduction, one important way towards imaging studies of the behavior of the brain under natural conditions is the use of time continuous natural stimuli such as videos. However, this poses a data-analysis challenge since fully modelling such multidimensional stimuli is impossible. Inter-subject correlation (ISC, or intersubject correlation mapping (ICM)) is an already established technique of analysis of naturalistic stimulus data in fMRI (Hasson 2004). In this technique, subject’s bold responses are used to model other subjects’ bold responses. This ISC/ICM technique despite of its apparent simplicity has been shown to be surprisingly sensitive of detecting activations also with standard block design stimuli albeit the technique does not utilize any model of the stimulus (Pajula 2012). However, as the paper under review states, ISC mapping requires spatial matching of the subjects in Talairach space and therefore differences in individual functional anatomy (and the limited registration accuracy) limit its sensitivity particularly when studying higher order brain functions. This sensitivity problem is serious, I argue that it is more serious than in the traditional GLM based fMRI analysis, and often addressed by (excessive) smoothing. The paper under review proposes a much more sophisticated approach to solve the problem. Namely, it proposes to compute the first canonical correlations within search-light regions around each voxel. To me, this appears as very interesting idea and first results using this approach look promising. I only have few remarks about the paper, answering to which could further improve this very interesting work.
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