A virtual object that represents a tangible object is displayed in a three-dimensional image. Responsive to a first input which may be movement of the tangible object, the virtual object moves within the three-dimensional image. Alteration of how the three-dimensional image is displayed occurs responsive to a second input. For example, virtual medical tools can be controlled by manipulating tangible tools to perform procedures and tasks virtually. Eye tracking can be used to generate variable angular resolution in the field of view in a head display unit with which the three-dimensional image is displayed. Digital objects may be used to cause the viewer's eyes move from feature to feature in a saccades fashion or a smooth tracking fashion.
