Believability and enactive interfaces Elena Pasquinelli Institut Jean Nicod

Characterization of believability: 1.Anti-realism hypothesis 2.Appropriate action hypothesis 3.Fulfillment of expectations hypothesis

1. The anti-realism hypothesis Believability does not depend on stimulus realism –The extension objection. The achievement of realism as simulation cannot be always taken as a goal when believability is an objective too: case of the representation of entities and objects that do not exist in the real world –The dynamic character of perception objection. The completeness of the stimulus condition is neither necessary nor sufficient in order to produce believability and confer objectivity (O’Regan & Noe, 2001; Casati & Pasquinelli, 2003) –The Uncanny Valley objection. anectodic evidence of negative reactions triggered by realism in the reproduction of the physical aspect of robots and fictional entities (Mori, 1970; Pasquinelli, 2006)

1. The anti-realism hypothesis Believability does not depend on realism as illusion of reality –Type of response objection. Spectators and users do not take the fictional content for real: responses are not exactly the same ones that spectators and users would express in presence of real events with the same content Perceptual awareness. Spectators are able to differentiate depictions from reality because the ambient array is specified in a different way by parcels of the real world and by depictions (Stoffregen, 1997) Cognitive awareness. Awareness is not only perceptual but also cognitive, as shown by the example of theater –Fulfillment of expectations objection. Evidence in cognitive sciences and VR studies testifies the role of expectations in believability (Geers, 2002; Garau, 2003; Castelfranchi, 2003). The fact of taking the experience with the fictional or virtual world as real might be counterproductive because it activates “expensive” expectations that cannot be fulfilled

2. The appropriate action hypothesis Believable items will elicit significantly different types of actions than non believable ones (quantity and quality of action) –Paradox of fiction (Radford, 1975) Appropriateness to the contents of the experience: –Notion of affordance (Gibson, 1969) –Experimental studies on exploratory procedures in haptic touch (Lederman & klatsky, 1987) Appropriateness to the context of the experience: –In respect to the context, appropriate actions fully exploit the possibilities that the device offers to the user; non-appropriate actions exploit only part of the possibilities of the device or are not permitted by the device –Explains the difference between the reactions deployed in the course of experiences with the real world and in the course of corresponding experiences (experiences with the same content) with fictional or virtual worlds

Appropriate actions and the evaluation of enactive interfaces What is the specificity of enactive interfaces in respect to the appropriate action hypothesis? 1.the context (interface) makes it possible to interact through action  Appropriate behaviors in enactive interfaces include appropriate motor behaviors 2.the perceptual content is actively modified by the motor actions of the user and the user perceives the results of his motor actions  rich, informative, complex perceptual outcomes for believable experiences 3.new action-perception couplings can be proposed (sensory substitution)  new patterns of believability in respect to the experience with the real world

3. The fulfillment of expectations hypothesis The appropriateness of the behaviours is strongly related to the coherence of the experienced situation –Adaptive level: Violations of coherence have a negative effect upon adaptive behaviours (Castelfranchi, 2003; Stein & Meredity, 1993, Festinger, 1957). The perceptual system actively works to maintain coherence (Bruner & Postman, 1949; Geers, 2002; Garau, 2003) –Epistemic level: Violations of coherence alert to the presence of some error: when coherence is violated (through the violation of expectations at different levels) the subject gains a special insight in his cognitive functioning (since he is alerted to the possibility that his experience might be false (Castelfranchi, 2003; Lorini, 2005; Davidson, 1984; Dennett, 1991). This judgment is equivalent to a judgment of non-believability

Relevant expectations for believability Beliefs that belong to symbolic forms of knowledge Expectations that are related to some form of mastery and apprenticeship of motor actions and relative perceptual consequences or to connections between perceptual systems : –illusions, perceptual performances and surprise (Bruner, 1966; Merleau- Ponty, 1946; Berthoz, 2001; 0’Regan & Noe, 2001). –tendency of projecting implicit knowledge about biological motion in the observation (and kinesthetic perception) of dynamic events (Viviani, 1990; Viviani & Stucchi, 1989; Viviani, Baud-Bovy & Redolfi, 1997) In any case, active expectations: –expectations activated by the contents of the experience –expectations activated by the context of the experience –expectations de-activated by the context of the experience

Expectations and enactive interfaces What is the specificity of enactive interfaces in respect to the fulfillment of expectations hypothesis? –Prominent role of non-symbolic expectations –Prominent role of coherence between expectations raised by perception and possibilities of action –Possibility of modifying action-perception couplings (experience, training)

Characterization of believability –Minimalistic characterization of believability: no reference to resemblance to stimulus, no reference to deception of non- mediation –Operational characterization of believability: believability is what can be objectively measured in terms of quantity and quality of action (appropriateness to contents and context) and subjectively measured in terms of the fulfilment of expectations and of surprise –General and contextualized characterization of believability: believability in general depends on the preservation of coherence and the fulfillment of expectations; only expectations that are activated by the contents and the context of the experience count for believability; other expectations are de-activated