Goals and means in action observation : a computational approach

Many of our daily activities are supported by behavioural goals that guide the selection of actions, which allow us to reach these goals effectively. Goals are considered to be important for action observation since they allow the observer to copy the goal of the action without the need to use the exact same means. The importance of being able to use different action means becomes evident when the observer and observed actor have different bodies (robots and humans) or bodily measurements (parents and children), or when the environments of actor and observer differ substantially (when an obstacle is present or absent in either environment). A selective focus on the action goals instead of the action means furthermore circumvents the need to consider the vantage point of the actor, which is consistent with recent findings that people prefer to represent the actions of others from their own individual perspective. In this paper, we use a computational approach to investigate how knowledge about action goals and means are used in action observation. We hypothesise that in action observation human agents are primarily interested in identifying the goals of the observed actor’s behaviour. Behavioural cues (e.g. the way an object is grasped) may help to disambiguate the goal of the actor (e.g. whether a cup is grasped for drinking or handing it over). Recent advances in cognitive neuroscience are cited in support of the model’s architecture

Cognitive neuroscience on the move

Contains fulltext : 72816.pdf (publisher's version ) (Open Access)inaugural address RU, 17 april 200818 p

Integration of structure-from-motion and symmetry during surface perception

Contains fulltext : 90338.pdf (publisher's version ) (Open Access)Sinusoidal motion of elements in a random-dot pattern can elicit a striking percept of a rotating volume, a phenomenon known as structure-from-motion (SFM). We demonstrate that if the dots defining the volume are 2D mirror-symmetric, novel 3D interpretations arise. In addition to the classical rotating cylinder, one can perceive mirror-symmetric, flexible surfaces bending along the path of movement. In three experiments, we measured the perceptual durations of the different interpretations in a voluntary control task. The results suggest that motion signals and symmetry signals are integrated during surface interpolation. Furthermore, the competition between the rotating cylinder percept and the symmetric surfaces percept is resolved at the level of surface perception rather than at the level of individual stimulus elements. Concluding, structure-from-motion is an interactive process that incorporates not only motion cues but also form cues. The neurofunctional implication of this is that surface interpolation is not fully completed in its designated neural “engine,” MT/V5, but rather in a higher tier area such as LOC, which receives input from MT/V5 and which is also involved in symmetry detection.17 p

Joint-action coordination of redundant force contributions in a virtual lifting task

Contains fulltext : 56291.pdf (publisher's version ) (Open Access)In this study we investigated redundancy control in joint action. Ten subject-pairs (dyads) performed a virtual lifting task in which isometric forces needed to be generated with two or four hands. The participants were not allowed to communicate but received continuous visual feedback of their performance. When the task had to be performed with four hands, participants were confronted with a redundant situation and between-hand force synergies could, in principle, be formed. Performance timing, success rates, cross-correlations and relative-phase analyses of the force-time functions were scrutinized to analyze such task-dependent synergies. The results show that even though the dyads performed the task slower and less synchronized in the joint than in the solo conditions, the success rates in these conditions were identical. Moreover, correlation and relative-phase analyses demonstrated that, as expected, the dyads formed between-subject synergies that were indicative of force-sharing in redundant task conditions.25 p

Object manipulation from a perception-action perspective,Object-manipulatie vanuit een perceptie-actie perspectief

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Computational handwriting models: Issues and trends

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A study of handwriting production: educational and developmental aspects

Contains fulltext : mmubn000001_078175259.pdf (publisher's version ) (Open Access)Promotor : A. Thomassen181 p

Non-Linear aspects of joint coordination in blackboard writing

The present study focuses on the inter-joint coordination of the shoulder, elbow and wrist joints in circular hand displacements that were performed in the sagittal and fronto-parallel plane. In the latter plane, the experimental task was comparable to blackboard writing. Twelve right-handed participants drew in each plane clockwise and counter-clockwise circles at nine positions. The task, audibly paced at 1, 1.5 and 2 Hz, was performed without visual control. The displacements of seven IREDs that were fixated on the relevant joints were sampled at a rate of 100 Hz by means of a 3D-motion tracking system (Optotrak 3020). Shoulder, elbow and wrist angular excursions were derived as well as three coordination measures, viz. correlations between joint velocities and means and standard deviations of the relative phase between neighbouring joints. The results confirm the expectation that in sagittal-plane movements the shoulder and elbow are more strongly coupled than the elbow and wrist. However, effects due to typical characteristics of joint architecture, like built-in mechanical "joint-play" and closed packed positions, also proved to differentially affect the stability of the joint coordination. These factors induced a plane and position-dependent proximal-to-distal shift of joint coupling. It is concluded that besides polyarticular muscles and inertial coupling, functional properties of joint surfaces form an important determinant of joint coordination which fact, to date, has been neglecte