The effect of stationary, random phase discontinuities, on spatial frequency discrimination

We measured spatial frequency discrimination for sine wave gratings that had stationary, periodic, random phase shifts. Testing was conducted at 2.5, 5.0 and 10.0 c/deg. The effects of introducing phase shifts that occurred after a phase continuity in the range 1-8 cycles of the parent sine wave were examined in different experiments. We found that the Weber fraction for spatial frequency was an inverse linear function of the logarithm of the number of cycles of the sine wave in continuous phase. Discrimination performance improved as the number of cycles before the phase shift was increased. The results are compatible with models of spatial frequency discrimination that are based on the averaging of estimates of the spatial intervals between characteristic luminance features (Heeley, 1987a, b), and show also that performance on this task is related to the amount of information available in the retinal image.