One of the assumptions of the paired t test is that the underlying data is normally distributed. I've read either the paired differences should be normally distributed, or, that the residuals should be normally distributed (which I thought was the case for ANOVAs / regressions).
I've also read that the residuals in this case ARE the paired differences (link), or that the residuals for a paired t test are the paired differences for each pair minus the mean difference overall (link).
So, is there one simple answer to my question: when checking the assumption of normally distributed data for a paired t test, should you be checking the paired differences, or residuals?