Effective degrees of freedom and the RFT resel count

In one of neuroimaging's key papers, Worsley et al. (1992) introduced the concept of a resolution element (resel) as an intuitive parametrisation of the roughness-adjusted search volume underlying random field theory's expression for corrected p-values. In another key development, Worsley and Friston (1995) showed that temporal correlation in a linear model reduced the effective degrees of freedom (eDF). Here, we illustrate a surprising connection between these quantities, which may have application to multiple comparison correction on data with elaborate statistical dependence that can make RFT over-conservative.