Percevoir l'imperceptible par l'action : l'exemple du mouvement biologique Christel Ildéi-Bidet, Alan Chauvin & Yann Coello Université Charles De Gaulle, Lille Université Pierre Mendès France, Grenoble

Théorie - Visual perception of human movement is thought to involve interaction between sensory processing and motor representations (including the mirror neuron system). - Motor representation can be viewed as a component of a predictive system, which includes a neural process that simulates the dynamic behaviour of the body in relation to the environment enabling thus to anticipate sensory, postural and/or spatial consequences (ideomotor principle, James, 1890).

Conceptually, this approach refers to the control theory based on internal model. According to the model, independently of whether a motor action is performed or not, a visual stimulus can be mapped in motor terms (inverse model) and a predictive model associated with action planning can be used to simulate the expected dynamic behaviour of the body in relation to the environment (forward model). visual stimulus Action planning inverse model Action execution Prediction of forthcoming sensory inputs Forward model Effect on environment Control theory and prediction Proprioception Vision True state

visual stimulus Action planning inverse model Action execution Prediction of forthcoming sensory inputs Forward model Effect on environment The role of the predictive model is to optimise the control of motor activity and also to provide by anticipation information about the feasibility of potential motor actions. Proprioception Vision True state

visual stimulus Action planning inverse model Action execution Prediction of forthcoming sensory inputs Forward model Effect on environment Predicted final state Space perception Because it carries information about the predicted final state of anticipated action, the predictive model can be considered as being the support for spatial perception in relation to action (e.g. peripersonal space). Proprioception Vision True state

Because it carries information about the predicted ongoing state of the body, the predictive model can also be considered as contributing to the understanding of movements performed by others. visual stimulus Action planning inverse model Action execution Proprioception Vision Prediction of forthcoming sensory inputs Forward model Effect on environment Predicted final state X Space perception Predicted ongoing state Movement perception True state

Arguments in favour of a role of motor representation in the perception of human movement - Observed movements are easier to perceive when they belong to the observer repertoire. (Calvo-Merino et al. 2005, 2006; Casile & Giese, 2006; Cross et al. 2006) - It is easier to recognise oneself from visual display than persons with who we have shared time before. (Loula et al., 2005) - Preferred observed dynamical visual stimuli are those that are congruent with motor laws. (Bidet-Ildei et al. 2006; Meary et al. 2005). - Patients with motor deficit (dysgraphia) show deficit in movement perception (writing). (Chary et al. 2004) - Visual exposure to biological motion improves subsequent visual perception of human action. (Daems & Verfaillie 1999; Nilsson et al. 1992; Olofsson et al. 1997; Pavlova & Sokolov 2000; Verfaillie 2000). - fMRI studies have shown shared cortical networks in movement production and observation. (Decety et al. 1997; Hari et al. 1998; Nishitani & Hari 2000; Rizzolatti et al. 1996).

Issue: Visual exposure to biological motion improves subsequent visual perception of human action. Is this also true for daily observed actions ? Rational: Activating motor representation by performing or observing a real action just before perceiving a human movement should improve perceptual performances. Mean : Performing or observing a real motor action just before performing the perceptual discrimination of a point light display presenting a human action (priming effect) Task: Discriminating a biological motion in difficult perceptual condition (visual mask).

Stimuli

21 masks: 0 dot…220 dots Step: 11 dots 600 ms

110…220 dots Step: 11 dots Chance level

Selection of 11 masks: 110 dots… 220 dots Step: 11 dots 600 ms

Prior information Methods Two groups of 15 participants (Mean age = 24.8years, SD = 6.8years) Prior visual information (running-man, neutral stimuli) 132 trials (6 trials* 11 masks* 2 directions) Session duration: about 15 minutes Duration 30 secondes

Specific effect of the gender in the perception of biological movement ? (Cutting & Kozlowski, 1977)

47% Prior information Neutral: 5 Males 10 Females Running: 7 Males 8 Females 50% 56%48%

47% Prior information Neutral: 5 Males 10 Females Running: 7 Males 8 Females 50% 56%48% 7 Females, 8 Males (mean age= 30 years) Judging the probability that the point-light stimulus was either a man or a woman. 55 masking dots (84% of correct perception) 52% Male - 48% Female No gender effect

Prior information differenciating the gender Prior information Methods Three groups of 9 females and 9 males (Mean age = 20.7years, SD = 2.7years) Prior visual information (running-man, running-female, neutral stimuli) 132 trials (6 trials* 11 masks* 2 directions) Session duration: about 15 minutes Duration 30 secondes

Selection of 11 masks: 110 dots… 220 dots Step: 11 dots

Chance level 56%

Effect of prior actual activity ? Methods One group of 9 females and 9 males (Mean age = 22.7 years, SD = 2.7 years) Prior motor information (running in the corridor for 30 seconds) 132 trials (6 trials* 11 masks* 2 directions) Session duration: about 15 minutes Prior motor information

Chance level 56% 54%55%

Conclusion - Performing or observing a real human action for only 30 seconds is enough to improve later visual perception of biological motion in a difficult perceptual context. - This effect can obviously be explained by the contribution of motor representations in the visual processing of biological movement. - The gender effect indicates furthermore that interaction between motor and sensory information depends on the observer motor repertoire which seem different for males and females.