Peripheral Head-Mounted Display (PHMD)

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A Glass prototype seen at Google I/O in June 2012 Google Glass detail.jpg
A Glass prototype seen at Google I/O in June 2012
Do-It-Yourself Peripheral Head-Mounted Display: Besides the Optical Display this prototype also incorporates a Camera, Capacitive Touch Sensitive Field, Microcontroller. DIY PHMD.jpg
Do-It-Yourself Peripheral Head-Mounted Display: Besides the Optical Display this prototype also incorporates a Camera, Capacitive Touch Sensitive Field, Microcontroller.

A Peripheral Head-Mounted Display (PHMD) describes a visual 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]

Contents

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.

Characteristics

The two pictures illustrate the difference between detailed and peripheral information. Detailed and peripheral information.png
The two pictures illustrate the difference between detailed and peripheral information.

The most important uniqueness is that the user's FOV is not being fully covered, allowing the user to perform real world tasks without limitations, while not having the pretension to raise or create immersion, such as HMDs often aim for. For current display technologies, while projecting image onto the eye, the screen needs to be focused by the pupil to enable a clear reading of the screen, thus the environment becomes blurred and out-of-focus. So a PHMD such as Google Glass is capable of displaying detailed information, when the pupil is focusing the display itself, as it also allows for peripheral information when the eye focuses on the real world. Still, simple information such as notifications are perceivable when focusing on the real world instead of the display.

Physiological Factors: Visual Perception

Research shows that designing an optimal visual output for Head-Mounted Displays is a complex issue, since there are several physiological factors that significantly impact users’ perception. [4] The following effects are known in research:

Depth of Focus / Field

Switches permanently by refocusing on objects, which is different in distances to the user. A display mounted somehow to user's eye has fixed focal distance. Focusing information such as presented on a screen leads to a change in the depth of focus. This causes blurring of information presented at other layers, which especially degrades the perception of high spatial frequency information such as text.

Eye-Movements

Are actually done at a specific angle of 10°. To focus an object out of this angle, head movements are used automatically for support. However, when wearing an HMD with eye-movements that exceed this angle, since head movements do not have any effect on the interface, a drop in comfort might occur due to tired eye muscle.

Field-Of-View

Describes the FOV. The User's eye has a viewing angle of 94° from the center and 62° on the nose side. [5] The vertical angle is about 60° upwards and 75° downwards. HMDs often do not cover the whole FOV, which is also a reason for increased cybersickness.

Binocular Rivalry

Describes the phenomenon, which occurs when dissimilar images are presented to the human eye. [6] [7] As the two images captured by each eye is incompatible for stereo processing, they fight for visual dominance over the other eye's side view, resulting in alternating views from the two eyes, where the non-dominant view is almost unseen. This effect often occurs when wearing a monocular HMD. In this setup, researchers [8] also observed objects that completely vanish for several seconds from user's attention.

Visual Interference

Describes the phenomenon when both eyes perceive different images that are overlapping, but the brain is not able to distinguish between those. This phenomenon is also known as the inability for visual separation.

Phoria

Describes a muscle state of the eye, when the eyes are not focusing on a specific point. There are three different states, which can be distinguished: Esophoria, Exophoria, Orthophoria. While one eye is closed or being obstructed by a display, phoria can occur, which has the potential to cause Vertigo and Nausea as well. [9]

Eye-Dominance

Although the user has two eyes, one eye is predominantly used. The other eye is used to make corrections and provide additional spatial information. It is recommended to wear a monocular HMD over the dominant eye. [4]

Peripheral Perception

The picture is describing the visual perception in the human's field of view. It shows the differentiable Areas and Angels for Perception of Motion, Color, Shape & Text. Visual Perception Human FOV.png
The picture is describing the visual perception in the human's field of view. It shows the differentiable Areas and Angels for Perception of Motion, Color, Shape & Text.

While most of these factors mentioned above become problematic when both eyes are covered with displays, a single display resting in the peripheral vision can be considered to be unproblematic, since it does not permanently influence the perceived picture of the real world.

As mentioned earlier, there are two types of information being perceivable with a peripheral head mounted display: (1) detailed information: when consciously focusing on the display and (2) peripheral information: through the human's visual perception, when focusing at the 'real world'. (see also picture above)

Most obvious changes are “motion”, which can be perceived over the whole spectrum of the FOV. In a smaller angle, change in color is also quite well perceivable (see figure). In contrast, perceiving shapes and reading text requires very dedicated attention of the pupil. However, when being very focused on a dedicated task, rough changes in shapes are still perceivable in a peripheral way. [10] Even in the field of Human-Computer Interaction, there have been investigations on this visual “peripheral channel”, such as peripheral color perception with eyeglasses. [11] Furthermore, researchers proposed to additionally utilize an eye tracker for a peripheral head-mounted display, in order to improve user experience. [5] There has also been investigations on which display positions are most suitable. [8] It has been found out that notifications presented at the middle and bottom areas of our human vision is more noticeable. However, top and middle positions are less distracting and more comfortable and preferred by the users. Among all the positions, the middle right position was found to strike the best balance between noticeability, comfort, and distraction.

While most HMDs suffer badly of the effects of binocular rivalry, Depth of Field and Phoria it is different for the PHMD. Since the PHMD is not totally covering the FOV and also not augmenting information on real objects, it is not affected by known problems monocular HMDs usually suffer from, such as the effect of attention switching between reality and projection. Such problems have been figured out over centuries of airspace research and usually occur when trying to augment reality. [12] These potential dangers, when operating in critical situations, such as taking part in traffic, are less pronounced for PHMDs.

Peripheral Interaction

Since the PHMD is resting in the peripheral of the user's FOV, it has a high availability and can be quickly demanded by focusing it. Furthermore, significant changes - depending on the stimuli - of the screen content is still perceivable without focusing the display. [11] This effect can be used to design peripheral information (e.g. such as visual notifications for incoming emails, approaching appointments, warnings). An efficient response to such perceived information could be accomplished in quick peripheral input, such as a quick hand movement. This way, the user is not being greatly interrupted while completing real world tasks. In Human-Computer Interaction research this is also denoted as Peripheral Interaction [13]

Notwithstanding, suitable input modalities for PHMDs that are not socially awkward remain to be discovered. Negative or positive social effects by wearing a PHMD and devoting attention on the screen while taking part in a conversation might be present, but are not proven yet. In addition, taking part in traffic while focusing on a visual input modality can lead to a considerable decrease of attention to the road (see also Semantic memory & Multimodal Interaction). However, compared to smartphone interaction, a quick switch to real world tasks is attainable, because there is no need for getting the device out of a pocket or bag. Furthermore, a PHMD does not need to be held by the user's hands, which offers a fully hands-free interaction. Since it is always available, it can provide peripheral visual information at any time, whereas peripheral information on smartphone in a pocket is not at all or barely perceivable (e.g. in a club/discothèque, while walking).

Related Research Articles

Binocular vision Ability to perceive a single three-dimensional image of surroundings with two eyes

In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Neurological researcher Manfred Fahle has stated six specific advantages of having two eyes rather than just one:

  1. It gives a creature a "spare eye" in case one is damaged.
  2. It gives a wider field of view. For example, humans have a maximum horizontal field of view of approximately 190 degrees with two eyes, approximately 120 degrees of which makes up the binocular field of view flanked by two uniocular fields of approximately 40 degrees.
  3. It can give stereopsis in which binocular disparity provided by the two eyes' different positions on the head gives precise depth perception. This also allows a creature to break the camouflage of another creature.
  4. It allows the angles of the eyes' lines of sight, relative to each other (vergence), and those lines relative to a particular object to be determined from the images in the two eyes. These properties are necessary for the third advantage.
  5. It allows a creature to see more of, or all of, an object behind an obstacle. This advantage was pointed out by Leonardo da Vinci, who noted that a vertical column closer to the eyes than an object at which a creature is looking might block some of the object from the left eye but that part of the object might be visible to the right eye.
  6. It gives binocular summation in which the ability to detect faint objects is enhanced.
Stereoscopy Technique for creating or enhancing the illusion of depth in an image

Stereoscopy is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from Greek στερεός (stereos) 'firm, solid', and σκοπέω (skopeō) 'to look, to see'. Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope.

Monocular

A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and usually also prisms. Most modern monoculars use prisms instead of relay lenses to ensure an erect image, resulting in a lightweight, compact telescope. The typical volume and weight of a monocular are less than half of a pair of binoculars having similar optical properties, making a monocular easier to carry and also proportionally less expensive. This is due to the fact that binoculars are essentially two sets of monoculars packed together — one for each eye. Monoculars only produce one 2-dimensional image, while binoculars produce two parallaxed images to allow stereopsis and depth perception.

Depth perception Visual ability to perceive the world in 3D

Depth perception is the visual ability to perceive the world in three dimensions (3D) and the distance of an object. Depth sensation is the corresponding term for animals, since although it is known that animals can sense the distance of an object, it is not known whether they perceive it in the same subjective way that humans do.

Field of view Extent of the observable world seen at any given moment

The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.

Head-up display Transparent display presenting data within normal sight lines of the user

A head-up display, also known as a HUD, is any transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of the name stems from a pilot being able to view information with the head positioned "up" and looking forward, instead of angled down looking at lower instruments. A HUD also has the advantage that the pilot's eyes do not need to refocus to view the outside after looking at the optically nearer instruments.

A stereo display is a display device capable of conveying depth perception to the viewer by means of stereopsis for binocular vision.

Diplopia Double vision

Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results in impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

Head-mounted display Type of display device

A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet, that has a small display optic in front of one or each eye. An HMD has many uses including gaming, aviation, engineering, and medicine. Virtual reality headsets are HMDs combined with IMUs. There is also an optical head-mounted display (OHMD), which is a wearable display that can reflect projected images and allows a user to see through it.

Monocular rivalry

Monocular rivalry is a phenomenon of human visual perception that occurs when two different images are optically superimposed. During prolonged viewing, one image becomes clearer than the other for a few moments, then the other image becomes clearer than the first for a few moments. These alternations in clarity continue at random for as long as one looks. Occasionally one image will become exclusively visible and the other image invisible.

Eye tracking Measuring the point of gaze or motion of an eye relative to the head

Eye tracking is the process of measuring either the point of gaze or the motion of an eye relative to the head. An eye tracker is a device for measuring eye positions and eye movement. Eye trackers are used in research on the visual system, in psychology, in psycholinguistics, marketing, as an input device for human-computer interaction, and in product design. Eye trackers are also being increasingly used for rehabilitative and assistive applications . There are a number of methods for measuring eye movement. The most popular variant uses video images from which the eye position is extracted. Other methods use search coils or are based on the electrooculogram.

Stereopsis is a term that is most often used to refer to the perception of depth and 3-dimensional structure obtained on the basis of visual information deriving from two eyes by individuals with normally developed binocular vision. Because the eyes of humans, and many animals, are located at different lateral positions on the head, binocular vision results in two slightly different images projected to the retinas of the eyes. The differences are mainly in the relative horizontal position of objects in the two images. These positional differences are referred to as horizontal disparities or, more generally, binocular disparities. Disparities are processed in the visual cortex of the brain to yield depth perception. While binocular disparities are naturally present when viewing a real 3-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth".

Pupillary distance

Pupillary distance (PD) or interpupillary distance (IPD) is the distance measured in millimeters between the centers of the pupils of the eyes. This measurement is different from person to person and also depends on whether they are looking at near objects or far away. Monocular PD refers to the distance between each eye and the bridge of the nose which may be slightly different for each eye due to anatomical variations. For people who need to wear prescription glasses consideration of monocular PD measurement by an optician helps to ensure that the lenses will be located in the optimum position.

Monocular vision is vision in which both eyes are used separately in animals and monocular vision in human species is vision when only one eye is used. By using the eyes in this way the field of view is increased, while depth perception is limited. The eyes of an animal with monocular vision are positioned on opposite sides of the animal's head, giving it the ability to see two objects at once. This is usually most commonly seen with prey animals, as the reason why their eyes are placed on either side of their head is to make it easier for them to look out for predators, which usually have forward-facing eyes to make it easier to find prey. However, there are some exceptions to this rule, usually if the predator is an animal that is often preyed upon by a greater predator or sport an anatomy that makes it very difficult for it to see straight, such as a short, stiff neck that would limit its head movement, and therefore would require its eyes to be on either side. Bimonocular vision also named two-eyed monocular vision or seeing in a monocular way over the entire field of view without visual field loss and without fusion is vision in which both eyes are used separately in human species and was discovered in 2018 by John Post a Belgian inventor in optics. The word monocular comes from the Greek root, mono for single, and the Latin root, oculus for eye.

Helmet-mounted display

A helmet-mounted display (HMD) is a device used in aircraft to project information to the pilot's eyes. Its scope is similar to that of head-up displays (HUD) on an aircrew's visor or reticle. An HMD provides the pilot with situation awareness, an enhanced image of the scene, and in military applications cue weapons systems, to the direction their head is pointing. Applications which allow cuing of weapon systems are referred to as helmet-mounted sight and display (HMSD) or helmet-mounted sights (HMS).

Chromostereopsis Visual illusion whereby the impression of depth is conveyed in two-dimensional color images

Chromostereopsis is a visual illusion whereby the impression of depth is conveyed in two-dimensional color images, usually of red-blue or red-green colors, but can also be perceived with red-grey or blue-grey images. Such illusions have been reported for over a century and have generally been attributed to some form of chromatic aberration.

Binocular summation refers to the improved visual performance of binocular vision compared to that of monocular vision. The most vital benefit of binocular vision is stereopsis or depth perception, however binocular summation does afford some subtle advantages as well. By combining the information received in each eye, binocular summation can improve visual acuity, contrast sensitivity, flicker perception, and brightness perception. Though binocular summation generally enhances binocular vision, it can worsen binocular vision relative to monocular vision under certain conditions. Binocular summation decreases with age and when large interocular differences are present.

Chameleon vision visual sense in the family of reptiles

The chameleon is among the most highly visually-oriented lizards, using this sense in prey capture, mating behavior, and predator avoidance. Unique features of chameleon vision include a negative lens, a positive cornea, and monocular focusing. The development of the chameleon visual system could have evolved to aid in prey capture and/or in predator avoidance.

Stereoscopic motion, as introduced by Béla Julesz in his book Foundations of Cyclopean Perception of 1971, is a translational motion of figure boundaries defined by changes in binocular disparity over time in a real-life 3D scene, a 3D film or other stereoscopic scene. This translational motion gives rise to a mental representation of three dimensional motion created in the brain on the basis of the binocular motion stimuli. Whereas the motion stimuli as presented to the eyes have a different direction for each eye, the stereoscopic motion is perceived as yet another direction on the basis of the views of both eyes taken together. Stereoscopic motion, as it is perceived by the brain, is also referred to as cyclopean motion, and the processing of visual input that takes place in the visual system relating to stereoscopic motion is called stereoscopic motion processing.

The MotionParallax3D displays are a class of virtual reality devices that create the illusion of volumetric objects by displaying a projection of a virtual object generated to match the viewer's position relative to the screen.

References

  1. ↑ Matthies, D.J.C., Haescher, M., Alm, R., & Urban, B. (2015). Properties of a peripheral head-mounted display (phmd). In International Conference on Human-Computer Interaction (pp. 208-213). Springer.
  2. ↑ Starner, T. (2013). Project glass: An extension of the self. In Pervasive Computing, IEEE, 12(2), 14-16.
  3. 1 2 3 Prinzel, L., & Risser, M. Head-up displays and attention capture. In NASA TechnicalMemorandum, 213000. 2004.
  4. 1 2 Laramee, R. S., & Ware, C. (2002). Rivalry and interference with a head-mounted display. In ACM Transactions on Computer-Human Interaction, 9(3), 238-251
  5. 1 2 Ishiguro, Y., & Rekimoto, J. (2011). Peripheral vision annotation: noninterference information presentation method for mobile augmented reality. In Proceedings of the 2nd Augmented Human International Conference. ACM, 8-11.
  6. ↑ Alais, D., & Blake, R. (1999). Grouping visual features during binocular rivalry. In Vision research, 39(26), 4341-4353.
  7. ↑ Collins, J. F., & Blackwell, L. K. (1974). Effects of eye dominance and retinal distance on binocular rivalry. In Perceptual and Motor Skills, 39(2), 747-754.
  8. 1 2 Peli, E. (1999). Optometric and perceptual issues with head-mounted displays. In Visual instrumentation: Optical design and engineering principles, 205-276.
  9. ↑ Z-Health Performance Solutions (2011). http://www.zhealth.net/articles/the-eyes-have-it
  10. ↑ Hau Chua, S., Perrault, S., Matthies, D., Zhao, S. (2015). Positioning Glass: Investigating Display Positions of monocular Optical See-Through Head-Mounted Display.
  11. 1 2 Costanza, E., Inverso, S. A., Pavlov, E., Allen, R., & Maes, P. (2006). eye-q: Eyeglass peripheral display for subtle intimate notifications. In Proceedings of the 8th conference on Human-computer interaction with mobile devices and services. ACM, 211-218.
  12. ↑ Rash, C. E., Verona, R. W., & Crowley, J. S. (1990). Human factors and safety considerations of night-vision systems flight using thermal imaging systems. In International Society for Optics and Photonics, Orlando, 16-20, 142-164.
  13. ↑ Hausen, D. (2013). Peripheral Interaction - Exploring the Design Space, PhD Thesis, Faculty of Mathematics, Computer Science and Statistics, University of Munich.
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