Definition of believability.

A proposalBelievability is an objective for VR systems

Some objectives for VR Systems

Presence Immersion Realism User’s efficiency (enhancement of) (Action fidelity) (Being with)

Believability

PresenceDefinitions: 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

ImmersionDefinition: 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

RealismDefinition 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

User’s efficiency

Definition: Tantamount to successfully supported action in the environment

(Zahoric & Jenison, 1998)

Applications: Training Teleoperation

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)

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)

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

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

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

Enactive interfaces and believability

The concept of believability might be extended to the interaction mediated by enactive interfaces

BelievabilityProposal 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

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

Construction of Believable entities mediated by enactive interfaces

Respect the conditions that are responsible for the constitution of objective unitary, coherent objectsin the interaction with entitites of the real

world

Objectsin 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)

Objectivityin 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

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)

Bibliographic references

Held, R. M., & Durlach, N. I. (1992). Telepresence. Presence: Teleoperators and Virtual Environments, 1, 109-112.

Lombard, M., Ditton, T. (1997). At the hearth of it all : the concept of Presence. Journal of computer-mediated communication.

Riva, G., Davide, F., & Ijsselsteijn, W. A. (2003). Being There. Concepts, effects and measurements of user presence in synthetic environments. Amsterdam: IOS Press.

Sheridan, T. B. (1992). Musings on Telepresence and Virtual Presence. Telepresence, Presence:Teleoperators and Virtual Environments, 1, 120-126.

Slater, M., Steed, A. (2000). A virtual presence counter. Presence: Teleoperators and Virtual Environments, 9, 413-434.

Witmer, B. G., Singer, M. J. (1998). Measuring Presence in Virtual Environments: a Presence Questionnaire. Presence, 7(3), 225-240.

Zahoric, P., Jenison, R. L. (1998). Presence as being-in-the-world. Presence: Teleoperators, and Virtual Environments, 7, 78-89.

Bach-y-Rita, P. (1982). Sensory substitution in rehabilitation. In M. S. L. Illis, & H. Granville (Ed.), Rehabilitation of the Neurological Patient (pp. 361-383). Oxford, UK: Blackwell Scientific.

Davidson, D. (1982). Rational animals. Dialectica, 36, 318-327. Proust, J. (1997). Comment l'esprit vient aux bêtes, Essai sur la

représentation. Paris: Gallimard. Strawson, P. F. (1959). Individuals, An Essay in Descriptive Metaphysics.

London: Methuen.

Bruner, J., Postman, L. (1949). On the perception of incongruity: A paradigm. Journal of Personality, 18, 206-223.

O'Regan, K., Noe, A. (2001). A sensorimotor account of vision and visual consciousness. Behavioural and brain sciences, 24(5).

Pylyshyn, Z. W. (2001). Visual indexes, preconceptual objects, and situated vision. Cognition, 80, 1-46.

Rock, I., Victor, J. (1964). Vision and touch; an experimentally created conflict between the senses. Science, 143, 594-596.

Spelke, E. S. (1990). Principles of Object perception. Cognitive science, 14, 29-56.

Stoffregen, T. A., Bardy, B. G. (2001). On specification and the senses. Behavioural and brain sciences, 24, 195-261.

Treisman, A. (1996). The binding problem. Current opinion in neurobiology, 6, 171-178.

Welch, R. B., Warren, D. H. (1981). Immediate perceptual response to intersensory discordance. Psychological bulletin, 88, 638-667.