vlt.neuro.vision.contrast.indexes.c50interpolated

  C50INTERPOLATED - find the value of C50 through interpolation

  C50I = C50INTERPOLATED(CONTRAST, RESPONSES)

  Given RESPONSES (N-point vector) and the corresponding stimulus
  CONTRAST values (N-point vector), return the contrast that gives
  the half maximum value via linear interpolation.

  The units of CONTRAST should be between 0 and 1. If values larger than
  1 are given, then it is assumed that CONTRAST is being given in units of
  percent, and CONTRAST is divided by 100. C50I will then be returned in units
  of percent.

  Note that this interpolated C50 does not equal the C50 of a Naka-Rushton equation.

  Example:
     c = 0:0.01:1;
     c50 = 0.2;
     r = 10*vlt.fit.naka_rushton_func(c, c50);
     figure;
     plot(c,r,'-o');
     xlabel('Contrast'); ylabel('Response'); box off;
     c50i = vlt.neuro.vision.contrast.indexes.c50interpolated(c,r);
     hold on;
     A = axis;
     plot([c50i c50i],[A(3) A(4)],'k--');