Searching through functional space reveals distributed visual, auditory, and semantic coding in the human brain
Fig 4
Simulation of distributed versus localized representations.
We simulated fMRI data with varying degrees of localized signal. Signal localization was varied by sampling locations of signal voxels from a Gaussian Random Field (GRF) and varying its FWHM (x-axis). In particular, a GRF is simulated on the brain and the location of the signal voxels is determined by the highest values of the GRF. A GRF with high FWHM is smoother, so large values will tend to be clustered together. Therefore, for a GRF with high FWHM, the n highest values will be localized together. These highest values get more distributed as the FWHM decreases. We ran our RSA analysis for the first fully connected layer of AlexNet (see Methods). The error bars show 95% bootstrapped CIs and the dots represent individual subject improvements. As the signal transitioned from localized to distributed, the relative gain in performance of the functional searchlight increased.