Discriminability of suprathreshold compound spatial frequency gratings.

We have investigated the detectability of small contrast changes in compound suprathreshold gratings, containing two sinusoidal components. We examined the relationship between the detectability of changes in each of the components alone and the detectability of changes in the two components together. It was found that for the pairs of spatial frequencies 1 and 9 c/deg there is a square law summation, but for spatial frequency pairs omega and 3 omega there is a greater summation which depends on the relative phases of the gratings' components. The results indicate the existence of broadband phase selective spatial frequency channels, of 2 octaves bandwidth.