As a filmmaker drawn to the most visceral forms of cinema, it was probably inevitable that Kathryn Bigelow's high-adrenaline curiosities would lead her to virtual reality. On Friday at the Tribeca Film Festival the Oscar Winner director premiered her first VR experience, "The Protectors: Walk in the Rangers' Shoes," an eight-minute, 360-degree plunge into the lives of the Garamba National Park rangers in the Democratic Republic of the Congo. Bigelow directed it with Imraan Ismail, a virtual-reality veteran, and the two used the nascent, immersive medium to give a full sense of the dangers the 200 ragtag rangers face daily in guarding the Delaware-sized park.