Complex sentence: A FISA investigation, later proved, that drivers'reactions were too slow to keep up with the speed of the Group B cars, and drivers' eyes could not adjust their focus between the fast corners, resulting in tunnel vision.
Split into simpler sentences: A FISA investigation, later proved, that drivers'reactions were indeed too slow to keep up with the speed of the Group B cars. Drivers' eyes could not adjust their focus between the fast corners, which resulted in tunnel vision.