Is there any precedent for smoothing more than once? I have fMRI data acquired with 2mm isotropic voxels. Prior to the individual subjects’ GLMs, I smoothed with a modest 3mm Gaussian kernel to preserve spatial resolution. The results of the individual subject analyses and the group level t-tests looked to be a reasonable smoothness.

But results of beta series connectivity analyses look pixelated, as if the data hadn’t been smoothed at all. The two attached images depict group-level t-test results. glm.PNG shows 3dttest++ results with betas generated by 3dDeconvolve as the dependent variable. beta_series.PNG shows 3dttest++ results with Fisher z transformed correlation coefficients as the dependent variable. I can’t think of a good reason for the beta series analysis data being less smooth than the conventional GLM data. Would it make sense to smooth the beta series data prior to computing the correlations even though the data that generated the beta series had already been smoothed?