Campbell & Robson (1968) published a swept-frequency, swept-contrast grating. The stripes are visible (above threshold) at the bottom and invisible at the top. If we were equally sensitive to all spatial frequencies then the line dividing the visible from the invisible region woud be horizontal. In fact, however, it bows upwards (maximum sensitivity) at a spatial frequency of about 5 cyles per degree (cpd). A high quality version of Campbell & Robsons grating can be downloaded from Izumi Ohzahwas web page.
Here is a similar grating which varies not in luminance but in texture.