this is the N64 bio sensor. you plug the cart into your controller, and clip the other end onto your ear. this tracks your heartrate and sends the information to whatever game you're playing with it
whatever game you're playing with it, by the way, is a fully-english japanese exclusive called Tetris 64. there isn't another game the nintendo 64 bio sensor works with. it was designed for, and packaged with, Tetris 64
again, no other game uses this! this heartrate sensor created for the nintendo 64 controller was only ever used for a mostly standard tetris game!
the bio sensor only exists to enable a single mode of play: Bio Tetris
bio tetris can be played as A, B, or C type like any other tetris mode. in this mode, the game tracks your heartrate and adjusts the pieces it generates for you to add tension or reward calm play. it does this by mixing in pieces from these two groups, based on whether your heartrate is high or low:
the pieces in group A are mixed in if your heartrate is low, and pieces from group B are mixed in when your heartrate is high. it's a really goofy idea, and i adore the ambition
supposedly (source: one youtube video) the heartrate tracking is pretty accurate compared to modern tracking devices, but the effects it actually seems to have on the game seem a bit random from the gameplay videos i've seen. you'll often get a group A piece immediately followed by a B piece. really makes me wonder how it all works!
gaming is all about collecting stranger and stranger shapes of plastic and it's time the game industry moved back towards that vision
