Ziaad,
thanks for the note. Yes, what you say is correct. Calculate gradients of eccentricity and polar angle along the surface, calculate fields sign at each node and detect field sign flips. At least, this is one way. There are many applications of this. One may want to know whether some effects include V1 or not, for instance. Or one may want some relative measures of the aera of V1 vs V2 vs V3 in each subject. I'll look into what is already available within AFNI/SUMA, as you suggested, and get back to you with some ideas (or some more questions :). Ziad S. Saad wrote:

> Hello Gorgio,
>
> Some of the tools required for retinotopy analysis may already
> exist in AFNI and SUMA. The missing components would be the
> calculation of activation delay gradients along the surface
> which are used to create field sign maps and the detection of
> field sign reversals.
> I was tempted to implement these methods at various points in
> my adult life but have lacked in time, motivation (few need it)
> and data. If you have a pretty good idea of what you need to do
> and what additions to AFNI/SUMA would streamline the process, I
> would be willing to implement them.
>
> cheers,
> -ziad