1. Definition of believability. A proposal Believability is an objective for VR systems

2. Some objectives for VR Systems Presence Immersion Realism User’s efficiency (enhancement of) (Action fidelity) (Being with) Believability

3. Presence Definitions: Feeling of being there in the VE  Psychological state or experience of self-location (Slater, 2000)  Attentional state (Witmer & Singer, 1988) Perceptual illusion of non mediation (Lombard & Ditton, 1997) Applications: experiences with the real world (Noe, 2003) experiences with narrative media experiences with perceptual media (television, radio, telephone) experiences with VR systems

4. Immersion Definition: Psychological experience of being included and interacting with an environment  Immersion + involvement  presence (Witmer & Singer, 1988) Involvement = psychological experience when focusing attention on a set of stimuli Characteristic of the technology employed to produce presence  Number of senses stimulated (Slater, 2000) Applications: perceptual representations symbolic or narrative representations Experiences with VR-systems

5. Realism Definition Quality certain representations have (physical, external representation, not a psychological condition of the user (not internal representations) or of a perceived object.  Accurate perception of resemblance between simulator and simulated (UPS-believability-EI Lexicon) how closely does this resemble the real situation Types of realism:  Perceptual realism (feeling to fly in a realistic sky)  Social realism (interacting in a SF environment) Applications: Models of real objects/events Images, icons Computer graphics VR-systems

6. User’s efficiency Definition: Tantamount to successfully supported action in the environment (Zahoric & Jenison, 1998) Applications: Training Teleoperation

7. Action fidelity Action fidelity is defined in terms of relations between performance in the simulator and performance in the simulated system. Action fidelity exists when performance in the simulator transfers to behavior in the simulated system. An appropriate measure of action fidelity is transfer of learning, or transfer of training. Action fidelity is measured in terms of task performance. (UPS – Believability – EI Lexicon)

8. Being with Thus we define the presence as the primary sense of “being with” and the evaluation of presence (more or less of presence) as the capability of the instrumental situation (i.e. of the instrumentally manipulated object to be present for the instrumentalist) to perform the instrumental task. We assume here that presence is a pragmatic feature. There is no need to discuss about neither reality nor illusion of the reality. The computerized object is apart of the real world. The instrumental interaction with computerized object (with computer simulacrum) is a real situation that necessary has to exhibit all the sensorial and handled properties needed for human instrumental exercise. (INPG – Presence – EI Lexicon)

10. Definition of enactive interfaces Enactive interfaces are characterized by self-generated multi-sensory information involved in guiding behaviors: Perception  Multisensory perception Action | Action-perception loop  Perceptual effects of action  Perceptually guided action

11. Specificity of enactive interfaces Enactive interfaces are different from other media  books, narrative media, … do not allow a perceptual experience  TV, telephone, cinema, … are perceptual media that do not allow action of the user Enactive interfaces allow a kind of interaction with virtual entities which is similar to the interaction we have with real entities  Based on the action-perception loop

12. Believable entities in the real world One of the characteristics of our interaction with real entities can be defined believability or credibility:  Entities of the real world are trivially credible: in normal conditions we do not ask ourselves if they are projections of our imagination or if it is realistic that they are as they are This characteristic is based on the fact that the beliefs we form towards entities of the real world are relative to these entities as objects and as objective entities  Object: the entity is perceived as an unified, coherent structure and not a simple cluster of features  Objectivity: the entity is perceived as an independent, intersubjective entity and not a projection of the subject The concept of believability is thus related to the concepts of object and objectivity

13. Enactive interfaces and believability The concept of believability might be extended to the interaction mediated by enactive interfaces

14. Believability Proposal of definition: Condition which is suitable for producing the following specific circumstance:  The user forms beliefs about the entities within the VE as of objective, credible objects Applications: The notion of believability aims at being specific for HCI mediated by enactive interfaces

15. Differential character of believability It is possible to feel as if being in another place or book, to shift one own’s attention, to forget the presence of the medium, to perceive a very realistic scene, to perform efficiently, without forming beliefs about the objectual and objective nature of the entities the user interacts with

16. Construction of Believable entities mediated by enactive interfaces Respect the conditions that are responsible for the constitution of  objective  unitary, coherent objects in the interaction with entitites of the real world

17. Objects in the real world conditions that allow the construction of unitary, coherent objects pre-objects  object files and object indexes (Pylyshyn, 2001; Treisman, 1996)  conjugation of separately perceived features (Spelke, 1990) binding mechanisms (different theories)  spatial attention  spatial and temporal coincidence  sensorimotor contingencies (O’Regan & Noe, 2001)  global array (Bardy & Stoffregen, 2001) aspect of the multisensory percept  sensory dominance (Rock & Victor, 1964)  modality appropriateness (Welch & Warren, 1981)  minimization of variance (Buelthoff)  expectancies – coherence with previous experiences (Bruner, 1949)

18. Objectivity in the real world Conditions that influence objectivity:  conditions that allow distality (Proust, 1997) action (Bach-y-Rita, 1982)  conditions that allow reidentification (Strawson, 1959) Space  Conditions that allow intesubjectivity (Davidson, 1982) triangulation

19. Evaluation of Believable entities mediated by enactive interfaced Individuate the typical responses to believable objects:  Cognitive responses  Emotional responses  Behavioral responses Different types of evaluation: Verbal expression Non-verbal expression  Reidentification test for objectivity as non-subjectivity (Strawson, 1959)  Error/surprise test for objectivity (Davidson, 1982)

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