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A peripheral head-mounted display (PHMD) is avisual display (monocular or binocular) mounted to the user's head that is in the peripheral of the user's field of view (FOV) / peripheral vision. Whereby the actual position of the mounting (as the display technology) is considered to be irrelevant as long as it does not cover the entire FOV. While a PHMD provide an additional, always-available visual output channel, it does not limit the user performing real world tasks.[1]
The term PHMD includes devices such as Google Glass, which are often misclassified as a Head-up display (HUD)[2] if following the original definition by NASA.[3] While NASA defined this term over centuries of space flight research,[3] it actually describes a display that addresses the eyes-free problem, by absolving the user from the need to angle down their head. Furthermore, it provides augmented information in the user's forward field of view (FOV), which is commonly projected on a windshield. In contrast, the Head-Down Display (HDD) is located at the instrument control panel.[3] Also, a HUD is mainly used to augment additional information into reality, which is technically not feasible yet for products such as Google Glass (lens focus on the display causes a blurred environment – see figure below).
This taxonomy for head-mounted displays is based on the property of its functionality and the ability of the human eye to perceive peripheral information, instead of being technology-dependent. In this article Human Factors for visual perception are being summarized, which are important to be taken into consideration when designing visual interfaces for PHMDs.