The human field of view is 120 degrees, so you can't see outside that area without turning your head.
この場合、次のような言い方ができますよ。
ーThe human field of view is 120 degrees, so you can't see outside that area without turning your head.
「人間の視野は120度なので、それより外の領域は首を回さないと見えない」
human field of view で「人間の視野」outside that area「それより外の領域」
to turn one's head「頭/首を回す」
ご参考まで!