Settings - Visual FX? anyone has descriptions of what is what?

(have tried to ask on PCars forum...without success)

i was just wondering, on PS4 in Visual FX (setting)
is there anywhere an explanation what the various ON & OFFS do? the various subtle, full and etc options do?
i have searched in the digital manual found nothing and also nothing in forums.
also when u change settings generally, is there a button or way to reset to default settings? (this would apply to menu options and menus in the game)

thanks all!