Immersion & Presence - Definitions (pg. 38)

Apparently extracted from another report by Mel Slater, but ended up referring to another paper: Physiological Measures of Presence in Stressful Virtual Environments

Immersion: “[The] objective level of sensory fidelity a VR system provides.” Can technically be measurable and is dependent on rendering software, display technology, etc.
Presence: “[A] user’s subjective psychological response to a VR system.” Contextual, subjective user response. Typically what we refer to as the feeling of “being there”. Users can experience different levels of presence in the same VR environment.

Qualities of Visual Immersion:

Field of View (FOV): the size of the visual field (in degrees of visual angle) that can be viewed instantaneously,
Field of Regard (FOR): the total size of the visual field (in degrees of visual angle) surrounding the user,
display size,
display resolution,
Stereoscopy: the display of different images to each eye to provide an additional depth cue,
Head-based Rendering: the display of images based on the physical position and orientation of the user’s head (produced by head tracking),
realism of lighting,
frame rate, and
refresh rate.

Spatial Understanding: “The human brain is highly optimized for reconstructing 3D scenes from these images by exploiting depth cues such as stereopsis, motion parallax, perspective, and occlusion.” VR immersion offers many affordances such as spatial cues, stereo imagery, and head-tracking that lets users use their natural ability to understand motion parallax.
Information Clutter: “increased FOV, FOR, and display resolution could have this effect” (i.e. the removal of clutter via virtual desktops, interfaces, etc.)
Peripheral Awareness
Increased useful information bandwidth

The last two, at the time of writing this paper, are admittedly not well-explored yet.