I'm not sure whether you mean to plot input (stimulus) or output (response). However, there is no direct way within AFNI to plot a time series such as you describe in a graph viewer.

What can be graphed is a time series file with a constant TR - the same as the dataset being graphed. This graph would appear above the central sub-graph from the dataset. This is the so-called "*.1D" input format, described in the AFNI manual somewhere. If you didn't care about the intensity part of the input, you might be able to convert the text file you are talking about to a *.1D format using the AFNI waver program. That would depend on the details.

It is also possible to display the graphs from one (or more) other dataset(s) on top of the graphs from the anatomical underlay dataset. In this case, the overlay graph depends on the voxel, whereas in the *.1D case, the overlay graph is the same for all voxels.

bob cox