«Comparative Content Analysis of Virtual Environments Using Perceptual Opportunities CLIVE FENCOTT Virtual Reality Applications Research Centre, ...»
• Mystery objects - partially obscured/revealed objects, strange or unknown objects, both closed and open doors and doorways.
• Active objects - movement, flashing lights, sounds changing pitch or volume
• Objects of desire - objects that have some benign significance to the visitor and more particularly to the task at hand
• Objects of fear - objects that have some malign significance to the visitor and to the task at hand
• Alien objects - objects that belong to another world, VE, or context altogether, 2D maps, strange symbols to indicate the end of levels
• Sensational objects - objects which attract attention through non-visual senses, spatialised sounds, vibrations, smells etc.
• Awesome objects - large, famous, expansive, etc.
• Dynamically configured objects - objects that are relocated in space/time In addition an attractor may exhibit a combination of characteristics. For instance a flashing light may be partially or wholly obscured behind an archway or other object and yet its effects may still be perceived. A sensational object such as a localised sound or a seabird above a beach may be also dynamically configured in that it 'reappears' in different places to indicate an affordance, help or information, for example.
2.2.2. CONNECTORS Connectors are configurations of POs that help visitors achieve goals by supporting strategic thinking, making plans, semantic matching, and exploration (Smith et al,1999). Connectors are thus the means by which visitors make connections, both mental and 'physical', between attractors which stimulate goal formation and retainers which allow visitors to achieve their goals and deliver objectives specific to the purpose of the VE. The actual objective of a retainer might well be hidden or not clear from the point of view of its attractor(s) but lower level goal formation should lead visitors into situations where objectives can be realised. Connectors are the means by which visitors are coaxed into following a particular course, choosing between possible courses, or changing course perhaps because they are approaching the limits of
the VE. There are three types of connectors:
• Choice Points
• Deflectors There are various techniques that can be used including direction signs; new routes appearing, degraded reality and so on. They can be closely allied to guide and limit sureties that seek to achieve similar objectives through unconscious perception. Thus an axis might lead a visitor into a position where an attractor becomes perceivable and follow this to a previously undiscovered retainer. Choice points are noted by Murray to be of great dramatic potential in interactive media (Murray,1997). However, Bleszinski cautions that the consequences of making choices should be at least hinted at so that a perceptive visitor will be able deduce the consequences of their choices or at least understand them after the fact (Bleszinski,1999). Deflectors are unconscious counterpoints of choice points which offer a choice between high levels and low levels of detail to lead the visitor into a loaded choice. As the culture and cultural acceptance of VEs grows it may well be the case that all deflectors will be perceived as unconscious guide and limit sureties.
2.2.3. RETAINERS Retainers are major patterns of interaction that seek to deliver specific objectives of the VE and collectively therefore its purpose. Retainers should be designed to deliver the memorable experiences of the VE as well as ensuring that visitors linger appropriately from time to time as they move around the world. In virtual tourism for instance the longer visitors linger overall the more likely they are to find the virtual experience memorable and perhaps retain the desire to actually visit the place the VE is modelling.
Retainers come in two forms, local and peripatetic. They seek to keep visitors in a particular place in the VE, in the case of the local form, or provide visitors with interactions that they can access from wherever they are in the VE, as is the case with the peripatetic form. The local form may be dynamically configurable as in such games as Driver, a game by Reflections, where retainers in the form of getting out of collisions can occur anywhere in the game space.
2.3. SHOCKS Shocks are not perceptual opportunities normally built into VEs but arise as by-products of the design and construction process. They give rise to perceptions that jar, that aren't received as expected in the established context of the VE. They draw attention to the mediated nature of the environment and thus undermine presence. Shocks are thus perceptual bugs that need to be actively sought out and eliminated.
• end of the world shock - in earlier versions of the cliff lift there were a variety of shocks such as the sea not being big enough so that visitors could see where it ended
• film set shock - buildings etc. only complete from certain angles, called Breaking the Metaphor in Snow Crash (Stephenson,1993).
• polygon leaks - seeing through cracks between solid objects to something/nothing beyond.
• latency and motion sickness
• and so on
3. PERCEPTUAL MAPS Surprises should work together in patterns to form possible temporal orders on retainers and thus the coherent set of purposive experiences that are intended to deliver the purpose of the world. Perceptual maps, as these patterns are called, are thus an abstract characterisation of the comprehensible labyrinth (Murray,1997;Arseth,1997). Attractors should draw attention to sites of retainers and, if properly designed, lead visitors around the world in a meaningful way using connectors. Attractors may also themselves be retainers. Seen from a distance an animated object may act as an attractor but when experienced close up the object may be some sort of vehicle to ride in and control thus becoming a retainer. Patterns of attractors, connectors and retainers may be quite localised and in effect work as games. The oystercatcher avoiding visitors in the cliff lift works in this fashion (Fencott,1999b).
A perceptual map consists of the specification of the set of intended perceptual opportunities and their intended configurations. This will mean that when implemented in a VE they will allow a visitor to accumulate, over time, a set of experiences that maintain a sense of purposive presence. A perceptual map should therefore contain specifications of the range of sureties and surprises together with the perceptual interrelationships. We have already stated that sureties are the mundane details that seek to establish the believability of the world.
Since surprises are of three forms namely attractors, retainers and deflectors they will require
different kinds of information to specify them. However, some general rules apply:
• visitors should be rewarded if they follow attractors
• retainers don't have to have attractors
• retainers can be their own attractors
• retainers can have multiple attractors
• connectors should lead to an attractor or directly to a surprise
• thus connectors, like attractors, should be rewarded if followed
• limit sureties can back up limit deflectors as the last line of defence to prevent end of the world shocks.
• And so on
3.1. PERCEPTUAL MAPS AS A TABLE OF SURPRISESThe simplest way of documenting an intended perceptual map is by way of a table with three columns which relate attractor/connector/retainer triples. Rows indicated the suggested relationships left to
right and cells give brief descriptions. Their generic form is thus:
Attractor Connector Retainer Details of attractor, the goal Resources available to affect Activity or other reward identifiable it should generate is the planning the achievement of the goal as a major part of achieving purpose retainer identified as a result of the attractor left Perceptual maps have much in common with the way painters arrange the composition of a work so as to catch the viewers attention and lead it around the canvas in a particular way. Although it is not possible to tell a story in a VE as in a film or TV program, there is never the less an important narrative potential in VEs which needs to be designed for. This refers to the purposive accumulation of experience.
This is more obvious in 3D games or Virtual Training Environments (VTEs) such as the classic Hubble Space Telescope VTE used for training the flight team (Loftin et al,1994). Because of resource limitations, objects should only be placed in a VE if they provide a clearly identified perceptual opportunity integrated into the VE's perceptual map. They will then support the purpose of the world if they are conducive of the aesthetic pleasures of agency, narrative potential, presence and transformation.
3.2. SURTIES AND SURPRISES WORKING TOGETHER
Sureties and surprises in VEs work together much in the way jokes do:
• My dog has no nose!
• How does he smell?
The first two lines are unremarkable and mundane, sureties. The third line comes as a surprise but is plausible from the logic of the first two statements. Jokes seem to be all much like this - you set up an imagined and consistent, however fantastical, world and then give it a bizarre, implausible twist, which must somehow be derivable from the former. Sureties and surprises in VEs work together, supporting each other and thus the virtuality they inhabit by seeking to catch and retain the attention of the visitor and thus maintain presence and belief. If a perceptual map constitutes the labyrinth then sureties are the means by which it is grounded, virtually, in a believable world.
4. CONTENT ANALYSIS USING POsIn this section of the paper we will apply POs to the analysis of a range of VEs from both the traditional VR community and the games industry. The documentation of these analyses can be quite lengthy and for this reason only summaries are presented.
4.1. HUBBLE SPACE TELESCOPE VTE The Hubble Space Telescope VTE is a classic high-end VE that was used to train the ground based flight team for NASA's Extra Vehicular Activities (EVAs) to repair the Hubble space telescope (Loftin et al,1994). The system utilised a Head Mounted Display (HMD), data glove to point and select objects, joystick controls for movement, sophisticated sound to deliver intelligent help system. It was thus highly immersive in the technological sense of the embodying interface as all movement is also mediated.
Evaluative questionnaires and qualitative feedback to evaluate its effectiveness accompanied the VTE.
Experimental results showed the VTE to have been highly effective in familiarising the ground-based staff with the intended activities of the astronauts. The latter incidentally did not experience the VTE but made use of a water based simulation system instead.
4.1.1 SURETIES FOR PRESENCE
• Vection - space shuttle cargo bay interior and telescope itself,
• Depth Sureties - no long range depth sureties, the known dimensions of the cargo bay and telescope itself,
• Perceptual Noise – the basic details of the Hubble including that not used on the particular EVA,
• Degraded Reality – space itself is its own degraded reality,
• Limit Sureties – see above
• Self Image - space suit glove that responds to user hand movement in the data glove
• Past - stages in the repair mission already accomplished.
• Physics - weightless in space, etc.
4.1.2. SURETIES FOR CO-PRESENCE There is no co-presence as such except the on-line intelligent help system, which uses audio as if from the mission control team.
4.1.3. SURPRISES Attractors
• Objects of desire - known components for next task of repair mission, Hubble itself is an object of desire when world first entered
• Alien attractors - green dot over next component of mission if unsure what to do next, red pointer on finger of glove for accurate interaction, opening mechanisms for compartments etc.
• Axes - no physical axes such as corridors, and so on, but cargo bay provides sight lines, and hubble, virtual axis formed by sight line to next part of Hubble to interact with. Being weightless is space means the axis of sight can be the axis of movement.
• Choice Points - components to choose, open, select, insert, remove etc.
• Deflectors – interesting components not part of the EVA, the abyss of space itself.
NB. Additional external resources are provided in the form of on-line audio help, and green dots to indicate the location of the next part of the mission.
• Undertaking the specific details of the pre-planned stages of the EVA 4.1.4. A PERCEPTUAL MAP FOR THE HUBBLE VTE The Hubble VTE consists of a set of separate repair missions which correspond very closely to the separate levels of single player games such as shoot-em-ups, 3rd person stealth games and so on. Each level is tightly constrained in that the repair is broken down into an ordered set of tasks and each task is itself broken into a sequence of specific interactions which includes precise navigation instructions as well as repair activities. Thus we have a highly specified set of attractor, connector, retainer groupings supported by real-time help where necessary. The perceptual map can thus be seen as a recipe rather than an offering of a table of surprises.
4.1.5. OBSERVATIONS Hubble is a VR classic partly because its rigorous evaluation demonstrated the appropriateness of VR in stimulating the required learning experiences. But also because of its pragmatic use of the aesthetics of the medium through alien attractors: the red pointer, green dots, etc. which if used subtly to help the user are not seen as shocks detracting from presence. In Hubble retainers take precedence. Successfully undertaking predetermined tasks, perceivable consequence is one of its primary pleasures because all the high level goals and objectives are set for the user. Transformation is also a major pleasure of Hubble because the ground based flight team could temporarily become astronauts.