Thanks for the kind words, Gothictech! Sorry for the late response, must have missed this message. I believe there are readily available PS1 shaders and effects online. They're a common trope in horror games - the aesthetic of paying homage to the PS1 era of gaming, and by extension, their homage to the horror films of the '70s and '80s.
I'm the music guy though, so I'm not sure what specifically was done for the art style. It's definitely PS1 / PS2 / N64 era based. Whereas my influence was almost entirely horror movies themselves, insofar as how I approached the soundtrack. Horror games in the early era of gaming had limitations, whereas now I can purchase software synths emulating and recreating the very synths used by John Carpenter, or Goblin, or Fabio Frizzi, and so on.