The Annals of Applied Statistics

The shuffle estimator for explainable variance in fMRI experiments

Yuval Benjamini and Bin Yu

Full-text: Open access

Abstract

In computational neuroscience, it is important to estimate well the proportion of signal variance in the total variance of neural activity measurements. This explainable variance measure helps neuroscientists assess the adequacy of predictive models that describe how images are encoded in the brain. Complicating the estimation problem are strong noise correlations, which may confound the neural responses corresponding to the stimuli. If not properly taken into account, the correlations could inflate the explainable variance estimates and suggest false possible prediction accuracies.

We propose a novel method to estimate the explainable variance in functional MRI (fMRI) brain activity measurements when there are strong correlations in the noise. Our shuffle estimator is nonparametric, unbiased, and built upon the random effect model reflecting the randomization in the fMRI data collection process. Leveraging symmetries in the measurements, our estimator is obtained by appropriately permuting the measurement vector in such a way that the noise covariance structure is intact but the explainable variance is changed after the permutation. This difference is then used to estimate the explainable variance. We validate the properties of the proposed method in simulation experiments. For the image-fMRI data, we show that the shuffle estimates can explain the variation in prediction accuracy for voxels within the primary visual cortex (V1) better than alternative parametric methods.

Article information

Source
Ann. Appl. Stat., Volume 7, Number 4 (2013), 2007-2033.

Dates
First available in Project Euclid: 23 December 2013

Permanent link to this document
https://projecteuclid.org/euclid.aoas/1387823308

Digital Object Identifier
doi:10.1214/13-AOAS681

Mathematical Reviews number (MathSciNet)
MR3161711

Zentralblatt MATH identifier
1283.62216

Keywords
Analysis-of-variance encoding models explainable variance fMRI permutations prediction random-effects shuffle estimator vision

Citation

Benjamini, Yuval; Yu, Bin. The shuffle estimator for explainable variance in fMRI experiments. Ann. Appl. Stat. 7 (2013), no. 4, 2007--2033. doi:10.1214/13-AOAS681. https://projecteuclid.org/euclid.aoas/1387823308


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Supplemental materials

  • Supplementary material: Supplementary material. We provide proofs for Lemmas 1 and 2 in the supplementary, as well as describe and prove conditions for consistency of the shuffle estimator.