Were the visual and odor aspects hidden from the participants? If you put some monkeys in a blank white room to do some tasks and some others in a room with visible Flora and the smell of Earth and plants, I suspect the lattre group would perfo better even with O2 an CO2 levels constant.

Sorry.. I meant do expirements measuring cognitive performance relative to co2, find an optimal level, and if so is that level what you'd typically get outdoors?

I didn't mean "why don't you just open a window."