Gabor filter bank for gist features
Here is my understanding of these points. I apologize if my answer comes too late. I post it anyway in the hope it helps someone.


The 4 parameters in the param vector respectively controls the radial width, radial location, angular width, and angular location of the filter in the Fourier domain. In other words, the filter's response is a (separable) Gaussian function of the frequency modulus and orientation (that is, the polar coordinates). The parameters #2 and #4 gives the location of this Gaussian while parameters #1 and #3 gives its scale. However, I have no explanation regarding the "magic" values (maybe they were simply obtained by trial &amp; error).
These filters are not Gabor filters since their Fourier transforms are not Gaussian functions of the 2D frequencies. On the figure you showed, Gabor filters would result in ellipsoid curves instead of these drop-shaped curves. I guess the authors made this choice to have a better coverage of the spectral plane.