I have no idea about cognitive science in particular, but in math and physics there is not a single worthwhile contribution that was not done either by PhD holders or PhD students. Just not a thing that happens.
Edit for pedants: in the last 50 years at least.
Edit2: one possible exception is that anonymous 4chan poster: https://en.wikipedia.org/wiki/Superpermutation
I have no idea about cognitive science in particular, but in math and physics there is not a single worthwhile contribution that was not done either by PhD holders or PhD students. Just not a thing that happens.
Edit for pedants: in the last 50 years at least.
Edit2: one possible exception is that anonymous 4chan poster: https://en.wikipedia.org/wiki/Superpermutation