vlt.neuro.vision.oridir.index.fit2fitdidiffsum

  FIT2FITDIDIFFSUM - direction selectivity index (DSI) from double gaussian fit of direction tuning curve

   DIIND = vlt.neuro.vision.oridir.index.fit2fitdidiffsum(R)

     Calculates the direction selectivity index (DSI) from a double gaussian fit
     of a direction tuning curve.
     The DSI is defined as DSI = (Rpref - Rnull) / (Rpref + Rnull)
     where Rpref is the response to the preferred direction and Rnull is the response
     to the direction opposite to the preferred direction (that is, the null direction).

     R is a 2-row vector. The first row is the directions that were evaluated by the
     fit (e.g., [0:359] is the most common for 1 degree steps between 0 and 359), and
     the second row is the response of the fit for each angle.

     See also: vlt.fit.otfit_carandini, vlt.neuro.vision.oridir.index.fit2fitoi, vlt.neuro.vision.oridir.index.fit2fitdibr, vlt.neuro.vision.oridir.index.fit2fitdi