I made my son a black and white checkerboard on a piece of foam for visual stimulation a month or so ago (I call it his "brain board"

). I also see there are lots of B & W infant stimulation flashcards available for DL on this site.
At what age do babies typically stop benefiting as much from B & W stimulation? Is it once they've learned to "creep" as Doman calls the cross-pattern crawl on all fours? Right now my son rocks tremendously, scoots, and launches himself forward, but he hasn't yet mastered full on crawling yet. I know Doman mentioned a correlation between improved vision and learning to crawl, but right now my son will watch baby signing time from across the room, makes exceptional eye contact from far away, so I think his vision is great even though he is not fully on the move.
Does the B & W stimulation still serve a purpose after the vision is that developed?