Hi Luiz,

The 'a:b' syntax is just a different way to specify stimulus patterns, and you can use either an 'a:b' format or an input file of the irregular timing, or both of them combined for the '-tstim' option.

I might be wrong, but this is my wild guess for '-tstim': no matter which stimulus mode you feed into waver, the program assigns 1 for those time points in some fixed precision specified in the program (0.1 seconds?) around those irregular time points (in the case of an input file) or during a time strech of duration (in the case of 'a:b'), and 0 for the rest. Then the sequence of 1's and 0's is convolved with the ideal impulse response function or basis function you selected in waver to generate a hemodynamic response function.

The final output would be sampled from the modeled response function at each TR. In this sense the precision/duration of stumulis would be the precision specified in the program in stead of TR.

Hope I guessed it correctly.

Gang