1. A system for controlling display of an image in response to muscle exertion by a user having a vertebral column, a left limb, a right limb, and viewpoint orienting muscles, said system comprising: a non-head-mounted yoking means including a left member shaped and positioned for being gripped by the left limb during viewpoint orienting exertion of the viewpoint orienting muscles, and a right member shaped and positioned for being gripped by the right limb during viewpoint orienting exertion of the viewpoint orienting muscle, where the yoking means rotates about the vertebral column in response to said viewpoint orienting exertion of the viewpoint orienting muscles when the user's left limb grips the left member and the user's right limb grips the right member; a sensing means, operably associated with the yoking means, for sensing at least one of a force and a displacement in response to rotational movement of the yoking means about the vertebral column in response to said viewpoint orienting exertion of the viewpoint orienting muscles with the left limb gripping the left member and the right limb gripping the right member, and for generating at least one sensor output signal indicating of each said force and each said displacement; and a control means, operably associated with the sensing means, for receiving each said sensor output signal and generating image control commands in response thereto, wherein the image control commands correspond to at least one of said force and said displacement and provide a nonlinear mapping of the rotational movement of the yoking means to change of the image, wherein said change of the image represents viewpoint rotation.