Marie-Thérèse Nicolas
email: mnicolas@univ-montp2.fr

Caussidier Claude
email: claude.caussidier@umontpellier.fr

Learning how to make links: The relevance of studying the concepts of Tibetan medicine and its teaching

Keywords: Tibetan Medicine, education, complexity, transmission, conceptual maps

Nowadays, in Western countries a major problem in science education is to teach the students how to organize and make links between different fields or different concepts. This problem does not appear to be an issue for Tibetan medicine teaching. Therefore, we studied the conditions of transmission and appropriation of knowledge of Tibetan medicine.

We show that Tibetan medicine keeps clear of both the positivism reductionism and of the "experimental method" which are still very much in use in Western medical studies. The concepts of the Tibetan medicine system illustrate Edgar Morin's paradigm of complexity and systemic conceptions of nature, of the human beings and of their relations with the environment.

In addition, the Tibetan way of learning allows the conservation and the anchoring of complexity in the mind of the students. This is the consequence, not only of the construction of the training academic course, but also of the knowledge management through what one can consider the equivalent of "conceptual maps" in the form of trees of medicine. These trees, by allowing the visualization of complexity, help the students to progress with the knowledge, and, by preserving an approach at the same time total and rational, foster the emergence of a direction to diagnose, to advise and to treat a health imbalance.

Introduction

In Western countries, a general problem in education comes from the fact that the knowledge is presented in fragments. The students have great difficulties to establish links, for example in biological sciences [START_REF] Hage | Le morcellement des connaissances en physiologie : du constat à la remédiation[END_REF]. Consequently, it is interesting and possibly helpful to study other systems of transmission and training in different contexts that those of the Western world. This motivated our interest in the Tibetan medicine training field.

For the last part of 20 th century, researchers and teachers from the West have alerted on this problem of fragmentation of knowledge. Thus, Morin (1999a) wrote: "The separation of the knowledge in different disciplines makes unable to seize what is woven together". [START_REF] Panikkar | Médecine et religion[END_REF] observes that "modern science is one brilliant system of "catalogation" (=classification system)... but reality cannot be cut out in pieces ". It is a problem which is also found in medicine training particularly nowadays with the development of the paradigm of "the Evidence Based Medicine" which characterizes a person only by statistical and iconographic data. Then the question arises: how to acquire knowledge and to preserve a medical approach which does not split up, which does not divide the mind and the body (this body which becomes more and more virtual, [START_REF] Sicard | La médecine sans le corps[END_REF], and which is able to consider at the same time the person and the world? With this problem in mind we analyzed the teaching of Tibetan medicine based on the question: how do the Tibetan doctors favor the construction of conceptions of health which do not isolate the part from the whole?

Western bio-medical approach

Indeed, in Western countries, since Auguste Comte (19 th century) and the positivist method, there is a division of the sciences based on a hierarchy of the disciplines. Furthermore, the inheritance of the paradigm of Descartes (17 th century) leads to a mechanical conception of man governed by the law of reason. Nature is reduced to an observable and handling material and, in consequence, there is separation, exclusion and dissociation between man and the natural universe. The power of the experimental method used in the West has then a major drawback which is the unavoidable simplification of the studied object. For example, the study of the whole body becomes reduced to that of an organ, or of a cellular category, or even, of a type of membrane receptor.

In medicine and obviously in its training prevails a vision of an abstracted individual which is serialized and only put in figures and statistics. [START_REF] Bertola | Ethique et éducation[END_REF] and [START_REF] Sicard | Réflexions sur le progrès en médecine[END_REF] analyzed well this approach in which the patient is often reduced to his disease or to his biological parameters provided by quantified statistical data and images. Thus, it remains only the facts and a body-object, object of diagnosis, object of therapies. The rule is the standard and not the person. However, nowadays, two opposite positions arise. First, there is an awareness of this simplifying situation which led to the proposition of a new paradigm: the paradigm of complexity, which has been defined by the French sociologist and philosopher Edgar Morin. He wrote, in "Les sept savoirs nécessaires pour l'éducation du futur" (1999a) the following report: "La parcellisation et la compartimentalisation des savoirs rendent incapable de saisir ce qui est tissé ensemble" 1 . In the domain of life sciences and education, Trocme-Fabre (2006) emphasized the fact that: "L'acte de relier est le fondement même du vivant" "Savoir apprendre, c'est savoir se relier" 2 . Finally, in the medical field, [START_REF] Sicard | Réintroduire l'éthique au fondement même de l'acte médical[END_REF] observed that "Nous sommes arrivés à un degré de parcellisation de l'être humain qui me semble extrême dans le sens où, par exemple, un cardiologue refusera d'entendre parler de neurologie et réciproquement" 3 . The second position, in medical sciences, is the focus on a deeper extent of the dissociation of man and its mechanical conception. It is illustrated by the EBM (Evidence Based Medicine). EBM presents a vision of the individual only characterized by his medical parameters [START_REF] Sicard | Réflexions sur le progrès en médecine[END_REF]). In the end, there is a reduction of the patient to his disease [START_REF] Khzami | L'impact de l'enseignement de la biologie sur la construction de la distinction entre le normal et le pathologique chez les élèves du secondaire marocain[END_REF].

Tibetan medicine and complex thought

The paradigm of complexity of [START_REF] Morin | Introduction à la pensée complexe[END_REF] is based on three principles (see below). Our analysis of the concepts of Tibetan medicine, led us to think that they are in accordance with the paradigm of complex thought [START_REF] Nicolas | Enseigner la médecine: comment apprendre à faire des liens?[END_REF].

The three principles of Morin's paradigm of complexity are named: the dialogic principle, the recursive principle and the hologrammatic principle (1990):

-The dialogic principle « allows to maintain duality in the unity » by associating two opposite terms which are complementary, and the subject and the object cannot be separated. Tibetan medicine considers that there are two states in every natural element, according to logic: if there is a poison, there must be a cure.

1 The Seven Complex lessons in education for the future: "The fragmentation and the compartimentalization of knowledge make it impossible to seize what is weaved together." 2 "To connect is the foundation of life". " To know how to learn, it is to know how to make connections". 3 "We have reached a degree of fragmentation of the human being which seems to me extreme in the sense that, for example, a cardiologist will refuse to hear about neurology and conversely" ( -The second principle is the recursive principle. According to Morin, a recursive process is « a process in which the products and the effects are at the same time the causes and the production of what produce them ». This principle breaks off the linear thought. In Tibetan medicine, we can recognize this principle in the way of how is considered the triggering and the treatment of a sickness in relation with the three humors. If a sick patient accepts to treat its unbalance by changing his diet or his behavior, there will be a recursive (feedback) loop, not only affecting the unbalanced humor, but also the two other ones which then will be back to work in balance.

-The third principle or hologrammatic principle considers that "The part is inside the whole and the whole is in the part". This can be illustrated by the Tibetan practice of taking the pulse since the pulse reflects directly the state of the organ. If there is a problem at the level of an organ, the pulse changes and the doctor will diagnose it.

The Tibetan medicine concepts illustrate the paradigm of the complex thought in its design of the person within her/his environment as well as in the approach of its various components, each one functioning in a dynamic balance and in an interdependent way.

The paradigms of Western and Tibetan medicines can be schematically summarized in the table below:

Question

Western medicine (bio-medicine)

Tibetan medicine (Sowa Rigpa)

What is medicine? -the standardized, statistical standard, coded, full of imagery, objective, measurable, -the prevention, the normalized, standardized risk, -not concerned (or rarely) with the psychological aspects of the health, -situation of activism: propose heavy treatments etc.... performance and efficiency: it is necessary to act.

-global approach of the individual and the individual in his environment, -Tibetan medicine is individual, every individual is unique, -takes charge of psychological aspects of the health, -importance of listening to the patient.

How is the body considered?

-a mechanics, -coded data.

-a dynamic and changeable stream every minute, always in relation, -humors and elements * in balance: healthy body, * in imbalance: sick body. Note: the same concepts are present in Hippocratic medicine.

What is the conception of man? -I.... the other …. separated, -I....nature and environment …separated, -a set of needs.

-individual singular in his history and at the same time global, and a psychological and social individual.

What are the invariants?

-bodyspirit physical and material structures (organs, functions).

-5 elements -3 nyepas: not outside elements of the patient but qualities recognizable in the natural environment where human beings live, -their relations.

How is the sickness considered?

-a biological problem, -something foreign, abnormal, coming generally from outside.

-a disorder, an internal imbalance which affects the whole person. Note: same concepts as in Hippocratic medicine.

Question

Western medicine (bio-medicine)

Tibetan medicine (Sowa Rigpa)

What are the causes of the physical disorders?

-physiological causes, often unique, -foreign agents, -often a single external agent, -linear causality.

-multiple causes: plural and varied causes resulting from a context and a set of circumstances (immediate causes, distant causes, internal causes, behavior, character, environmental causes, karma), -NEVER an external causeoriginally, the causes are in the mind, -recursive causality, complexity.

How is the treatment elaborated? -organic care (medicines, surgery) -eliminate the symptoms -advice on life style, -advice on behavior, -then treatment by medicine, -making the patient aware of his responsibility.

In addition, one of the characteristics of Tibetan medicine concepts is that nothing, whether in the components or in the concepts is permanent. [START_REF] Morin | Introduction à la pensée complexe[END_REF] notices also this impermanence when he writes "Living beings only seem to form solid and stable bodies". Another characteristics as Dr. Donden (2001) points out is that, in Buddhist philosophy, "all the things exist in interdependence, and nothing is endowed of an independent nature". Each individual is at the same time singular in his history and is connected to the others and his particular environment because, as [START_REF] Bitbol | De l'intérieur du monde, pour une philosophie et une science des relations[END_REF] underlines "we cannot be extracted from the world…. and of the relations which we maintain with the world". The patient is seen like a whole in relation to the others, to the environment, to the various components of himself and of his history. There is distinction but not duality or exclusion between the body and the mind: the subject is a living being, a physical support which hosts a mental continuum. It is also "a receptacle for the transformation, not only of food during digestion, but also of our experiments of the ordinary life and our emotional answers" [START_REF] Dorjee | Heal your spirit, heal yourself[END_REF]. This is in opposition to our Western way of thinking since our perceptions conceive and perceive the things in an opposite way.

Let us look more closely at the concept of health: in Tibetan medicine it is far distant from the Western one where the criterion of health is the capacity to work. Panikkar notes that, in traditional medicines, the health is not "a perfectly regulated machine which is operational but that an healthy organism expresses harmony within himself and with the universe and this allows him to taste the "beatitudo" which is the characteristic of the man" [START_REF] Panikkar | Médecine et religion[END_REF]. And about this health/happiness or Sukkha, Matthieu Ricard (2005) specifies: "Sukkha, it is a way to be, a healthy state of mind which impregnates all the emotional states and remains solid and stable through the ups and downs that everyone can have to face during his life". For the practitioners of Tibetan medicine, the best advice than one can give to somebody to be in good health can be summarized as follows [START_REF] Dorjee | Heal your spirit, heal yourself[END_REF]: "Think before speaking, think before eating, think before deciding, think before acting" to which Dr. P. Dorjee adds: "smile at least three times a day".

In bio-medicine, bodies and phenomena are identical from a patient to another [START_REF] Sournia | Héraclite ou l'intuition de la science[END_REF], whereas for Tibetan medicine, each patient is a unique case. Western medicine protects, fights against the attacks (virus or bacteria for example) coming from outside; it "manages", it acts from outside to eliminate the symptoms and this appeared extremely powerful in many fields.

Then arises a question: how is taught this complexity in order to promote and to maintain a construction of the designs of health and the environment which does not isolate the part from the whole? We saw that the concepts of Tibetan medicine fit with the complex thought, and we will show now that the way of learning allows the conservation and the anchoring of the notion of complexity in the mind of the student.

Teaching and learning Tibetan medicine: educational practices. How is complexity integrated by the student?

In Tibetan medicine teaching itself there are different points we would like to underline: -there is initially an oral transmission by the reading of the text, then transmission of the direction with the explanations. The emphasis is placed on listening and the attention.

-there are always several presentations of the text: initially in a condensed way (framework), then in a more detailed way (explanations), then come the instructions and, lastly, the synthesis to support the assimilation and to get an overall vision.

For the teachers, transmission of medicine should guide the student in order to enable him to experiment the medical knowledge. But, there is also a knowledge which is not communicable by words and which is acquired only by experience. It is what [START_REF] Morin | Complexité restreinte, complexité générale[END_REF] calls "to understand as a human" or "to understand as a subject" or to understand in the first person. Thus the master, the professor, is not only centered on the contents of the knowledge to teach, but on the learning and its relation with the contents. He transmits also values which the student needs in his practice of care.

The table below summarizes the main characteristics of the teaching in the Western and Tibetan medicines.

Question

Western medicine (bio-medicine)

Tibetan Medicine (Sowa Rigpa)

What is teaching? -informative enrichment (simplifying thought), -juxtaposition of disciplines.

-changes of conceptions (complex thought), -creation of links.

What is taught?

-disciplines, -

-what connects.

How?

from the beginning, learning by disciplines, by large fields (anatomy, functions ...)

1 st year students see everything, 2 nd year, they see everything, 3 rd year, they begin to go into details and they separate.

How is scientific knowledge elaborated?

-based on the exclusion: the subject on one side, the object of knowledge on the other one: dualistic approach of the world, -the object to be known is outside the subject, -focused almost exclusively on the physiological processes of the physical body (reductionism).

-no exclusion, intervention of the subjectivity, -the object to be known is the subject, -the knowledge is suited to a context.

What are the teaching methods?

-formal education, frontal type, -written notes, -case studies.

-formal education, frontal type, -reading the text = oral transmission, -then explanation = transmission of the meaning, -stress put on the attention and on the listening.

What has sense?

-the biological markers, outside references, -notion of cause is more and more replaced by the notion of risk.

-the person is never mixed up with her/his disease.

What are the ethics of medicine teaching?

-not explicit.

-way of listening to the teaching, -way of giving the teaching.

How are repetition and memory considered?

-accumulation of knowledge usually in a linear way.

-the non-forgetting of the known object and protection from the distraction (clarity and concentration), -considered as source of renewal and deepening, -deeper and deeper integration of the knowledge in each student's life (interiority).

In Tibetan medicine training, it is necessary to establish the link between the knowledge obtained by the study (= intellectual understanding) and the links with the own experience of the student (= inward understanding, i.e. first person understanding). The most outstanding features of the educational practices are the importance of the transmission lineage and the emphasis placed on memorizing. In the first chapter of Basic Tantra of Gyud Zhi, there is an expression which comes repeatedly. It is an imperative injunction to the student: "LEARN and UNDERSTAND".

What is understanding?

It has the meaning of the Latin « comprehendere »: to take together, to take with oneself, that is: -listening to the teaching (notice that in Tibetan language, the verb to listen means also to remember), -memorizing in order to meditate upon it, i.e. to become accustomed to it, -understanding it as an instruction, in other words to integrate it completely, -putting it into practice. In other words, to understand has the meaning of "realization" i.e. result of the three main trainings: Study -Reflection -Meditation which, if they are correctly accomplished, led to the control of the mind.

What is learning?

To learn is not to accumulate knowledge. But in the same way that when a child learns how to read, he must pass by the stage of training on the alphabet, the Tibetan medical student has to pass the stage of training the Gyud Zhi by rote learning. Then, studying it and its strong bases will able him to practice his medical art. Because as [START_REF] Krishnamurti | Réponses sur l'éducation[END_REF] writes "To learn must never be an additive process. To really learn is an active process. … There is an enormous difference between learning and acquiring knowledge. Throughout the world, education consists simply of this acquisition of the knowledge, and thus, the spirit blunts, it ceases learning. It is satisfied to acquire. This aiming of acquisition directs all our lifestyle and, consequently, imposes limits on the experiment. Whereas the fact of learning is unbounded".

For [START_REF] Giordan | Apprendre![END_REF] to learn "is to organize a system of conceptions", but also [START_REF] Giordan | Apprendre[END_REF] to learn "is not only to transmit or receive, it is also to transform the ideas, ways of reasoning". The emphasis placed on memorizing points out the art of the memory such as it has been developed in Occident in the antiquity and the Middle Ages (Yates, 1966;[START_REF] Carruthers | Machina memorialis[END_REF]. In the Western countries, one considers in general that the repetition and the memory are used for the accumulation of knowledge, and this in a linear way, whereas Tibetan medicine teaching considers an organization of the knowledge with its origin, its history and its lineages. This allows to present and integrate the history of this medicine and the way in which the knowledge have been established and transmitted. This aspect stressing the connections with history is closed to what Morin (1999b) underlines: "the history should play a key function… while making it possible to the student to incorporate the history of its nation." Repetition and perseverance are characteristics of the methodology of training, associated with the attention and the concentration.

Role of memory and meditation in the process of training

Let us point out that for [START_REF] Carruthers | Machina memorialis[END_REF], memory has two distinct aspects during the Middle Ages, among the Greeks (Aristotle) or among the Latin (Cicerone): first the recording, the entry of information, mnesis in Greek or memoria in Latin and second, the recollection, the exit, anamesis or reminiscientia.

In Buddhist philosophy, there are two meanings for memory. One is to remember, i.e. to make emerging in the mind a concept, a fact which was not present before; the other, is to avoid forgetting. This supposes that the object, the concept, is present in the mind and that one avoids forgetting it. It is what is active during meditation. The text is not considered as something that one should have on the shelf of his library (or nowadays in her/his computer) in order to be consulted, it must be totally integrated. In the Western world, memorization is not well considered because it is thought to only reproduce in a passive way a previous experience. But recent research starts to stress the importance of the memory and meditation in the training (Bjork, 2014). Recently in the West, meditation, in the form of mindfulness, has been advocated as a useful tool both for medical practice and for the training of medical undergraduates [START_REF] Epstein | Mindful practice in action (1): technical competence, evidence-based medicine, and relationship-centered care[END_REF]. Indeed, it has been observed that medical doctors are uncomfortable when facing unfamiliar situations can lack empathy, and that undergraduates are experiencing anxiety resulting in reduced performances. Consequently, it is recommended that mindfulness would be used as a pragmatic tool to promote awareness, reflection and humility (for review, Lowell, 2012).

The lineage of transmission

With memorizing, another aspect to be underlined is the importance of the oral transmission of Tibetan medicine and thus of the transmission lineage [START_REF] Meyer | Gso-ba Rig-pa[END_REF][START_REF] Nicolas | Enseignement de la médecine et pensée complexe[END_REF]. In the West, the development of the "big science" led to an anonymous knowledge (Morin, 1990b) whereas this is not the case in Tibetan medicine. And this could be related to the construction of the Tibetan language itself which underlines this aspect. Indeed, it is the origin of the information which is important, and it is the verb ("being" which has the two forms in Tibetan) which gives the source of information. And thus, the first form of the verb "to be" is employed when personal information is expressed, and the second form when it is factual information [START_REF] Tournadre | Manuel de Tibétain standard, langue et civilisation[END_REF]. The transmission lineage thus passes personal information, directly from master to disciple since the origins of Gyud Zhi. The medical knowledge is thus anchored in an history and has solid roots. And it is through the transmission lineage that the medical art history is preserved and transmitted.

The importance of ethic

Another striking aspect of the Tibetan medicine teaching compared to the bio-medicine one is the importance put on ethic, i.e. the manner of leading one's life. A medical doctor must have at least six fundamental qualities: analytical mind, expression of compassion and a good heart, ethic, patience, effort and concentration, wisdom. These characteristics are not only due to his commitment to take care for the body and the mind, but also to his motivation and his final goal: the liberation of cyclic existences [START_REF] Drungtso | Basic concepts of Tibetan medicine[END_REF]. According to Dr. Choedrak (1996) a doctor must develop the following qualities: he must be able to look after all the disorders, never be discouraged by the encountered difficulties. He must have a very strict discipline and look at his patient as he would his own parents. He must be creative and enthusiast, and to have a steadfast courage.

There is also in the education of the Tibetan doctor a dimension which is essential: it is what we can call the interiority. It is neither measurable, nor quantifiable. It is nevertheless the base of all educational action. As noted by [START_REF] Filliot | L'éducation spirituelle ou l'autre de la pédagogie[END_REF] "Oublier cette dimension essentielle, c'est réduire l'apprentissage à une mécanique sans signification humaine au profit du culte de la performance" 3 . The teacher passes on values, in particular the rules of ethics and behavior, to the future doctors, values which they will express themselves in their relations with their patients.

In the West, ethics is often reduced to an ethic of normality with imposed standards from the outside or lies on "ethical dilemmas", not directly related to a conduct of life [START_REF] Bertola | Ethique et éducation[END_REF]. On the contrary, Tibetan medical practitioners put at the center of their concern the subject who is unique. They develop an ethic which "approaches more the wisdom than the reason. It is a question of understanding what is to be good rather than to have a correct judgement. A wise (or virtuous) person is the one who knows what is the good and who does it spontaneously" [START_REF] Varela | Quel savoir pour l'éthique[END_REF]. It is what the medical student (amchi student) must develop. In France, according to [START_REF] Sicard | Réintroduire l'éthique au fondement même de l'acte médical[END_REF], the re-introduction of ethics in medical studies is "a necessity" and, recently, in a few medical schools, courses on ethics are now proposed to the medical students [START_REF] Khan | L'enseignement et la recherche en éthique à Paris-Descartes[END_REF].

Management and communication of knowledge with a complex approach: modernity of Tibetan medicine trees: trees of knowledges or conceptual maps

The management of the knowledge is one of the most acute questions at the university education level, i.e.: how to master the information, the knowledge of medicine, its concepts, in order to have at once a global and precise organized vision of it?

In other words: how to make links? One of the main answers is mapping.

In Western medicine, there has been recent creation and development of a whole family of tools to organize the spatial representations of concepts, because (according to [START_REF] Tricot | Cartographie sémantique[END_REF]) "the problem is not any more the indexation of the information, but that of a global apprehension of the knowledge". It is what is called mind mapping, knowledge mapping, abstract map or concept map. The concept maps [START_REF] Novak | Learning how to learn[END_REF] are maps of organization of ideas or concepts and they are not a linear representation of the information. They visually express the concept of interrelation, an essential concept in any learning, and they allow to show and to visualize the links.

In Tibetan medicine there is a specific example of a concept map: the trees of medicine. These are innovations of the methods of teaching since they are supposed to have been used as soon as the Gyud-Zhi has been written. Drawn and formalized with colors as they are in the thanka by Sangye Gyatso, in the 17 th century.

The tree is an ideal metaphor allowing to showing, at a first glance, a set of items which are interrelated. In the West, the idea of the tree has also been developed around the 13 th century, but their conception is different than that of the Tibetan medicine ones. They often show a complete symmetry. In the Tibetan trees of medicine, this symmetry does not exist. In these didactic constructions, there is exposure of the knowledge in such a way as to see, immediately the numerous factors taking place and associated to (for example) maintain balance or produce imbalance. The structure of the tree establishes a model which allows to showing the complexity, illustrating that everything exists only in connection and relation with other phenomena. These trees are spectacular illustrations of a non-simplifying teaching which develops the complex thought by allowing the contextualization of knowledge [START_REF] Nicolas | Enseignement de la médecine et pensée complexe[END_REF]. Moreover, they are associated with an oral transmission which teaches awareness and contextualization of one's knowledge. This illustrates the path to pertinent knowledge, proposed by Morin (1999a) in the « Seven Complex Lessons in Education for the Future ».

Conclusion

In summary, we observed that the concepts of Tibetan medicine are in accordance with the contemporary paradigm of the complex thought that Morin supports and promotes. Moreover, the way and the methods of learning allow the preservation and the anchoring of the complexity in the mind of the student. This procedure is substantiated with a pedagogic tool "the trees of medicine", which can be compared to the contemporary mind mapping or concept mind. Finally, the way of teaching Tibetan medicine, follows the requirements defined by the UNESCO [START_REF] Delors | The four pillars of Education[END_REF] in the four pillars of education which are: learning to know, learning to do, learning to be, learning to live together.

If Western medicine, due to its too numerous separated disciplines, has difficulties to take into account all the aspects needed for its comprehension, the Tibetan doctor knows to preserve and to have from the beginning of his studies an integrated vision and a systemic approach of the person in her/his environment. Tibetan medicine and its teaching offer us an example of thinking. It appears to us as an illustration of a lively complexity, taught and always operational and operative in Himalayan context. We think that the West, in its own context, could find profit in considering and taking into account this approach.

« To forget this essential dimension, it is to reduce the training to a mechanic without human significance with the profit of the worship of the performance" (personal traduction)


Alexis Paljic
email: alexis.paljic@inria.fr

Jean-Marie Burkhardt
email: jean-marie.burkhardt@inria.fr

Sabine Coquillart
email: sabine.coquillart@inria.fr

Evaluation of pseudo-haptic feedback for simulating torque: a comparison between isometric and elastic input devices

In this work, we investigate whether pseudo-haptic feedback is suitable for simulating torque feedback. Pseudohaptic feedback is based on the coupling of visual feedback and the internal resistance of an input device which passively reacts to the user's applied force. An experiment was conducted to evaluate this feedback and compare isometric and elastic input devices. It involved compliance discrimination between real torsion springs and pseudo-haptic simulated torsion springs. Results show that torque haptic feedback was successfully simulated, with a difference in performance between device types. The elastic device yielded better resolution but higher subjective distortion of perception compared to the isometric device. Results are discussed on the basis of user answers, answer time, and applied torque.

Introduction

Torque gives important information in everyday manipulations, such as opening bottles or turning a key. Mounting parts of a mechanism, or peg-in-a-hole tasks, often involve torque constraints on the object being manipulated. This is inherent to the complex nature of human movements which are a combination of translations and rotations, thus, force reaction of mechanically constrained objects is very likely to contain a torque component. Torque information can be computed in virtual environments to provide the user with force feedback. Studies show that force feedback can be a valuable technique in domains like medical simulation [START_REF] Basdogan | Virtual environments in medical training: Graphical and haptic simulation of laparoscopic common bile duct exploration[END_REF] or collaborative environments [START_REF] Basdogan | An experimental study on the role of touch in shared virtual environments[END_REF] [START_REF] Sallnäs | Supporting presence in collaborative environments by haptic force feedback[END_REF]. Torque feedback may be simulated with active devices. The 6dof Phantom [START_REF] Massie | The phantom haptic interface: A device for probing virtual objects[END_REF] [START_REF]Sensable technologies[END_REF], the delta haptic device [START_REF] Grange | Overview of the delta haptic device[END_REF], the Virtuose 6D [START_REF] Haption | [END_REF] or the Freedom6s [START_REF]Mpb technologies[END_REF] can provide the user with torque feedback in addition to translational force feedback. A magnetic levitation haptic interface [START_REF] Berkelman | Interacting with virtual environments using a magnetic levitation haptic interface[END_REF] offers six degrees of freedom force feedback. Some systems are dedicated to torque feedback, such as the Gyro Moment Haptic Interface [START_REF]Gyro moment haptic interface[END_REF] or a Hand-Held Torque Feedback Device by Fukui et al. [START_REF] Fukui | Handheld torque feedback device[END_REF]. Ho et al. proposed a ray-based haptic rendering [START_REF] Ho | Ray-based haptic rendering: force and torque interactions between a line probe and 3d objects in virtual environments[END_REF] for force and torque feedback. Using a line probe and two Phantom devices, users were able to touch and feel virtual objects with a line segment model of the probe and perceive torque information, which is not possible with single point interaction.

Another way to provide haptic feedback is through the use of cross-modal interactions. Biocca et al. [START_REF] Biocca | Visual touch in virtual environments: An exploratory study of presence, multimodal interfaces and cross-modal sensory illusions[END_REF] defined these as "perceptual illusions in which users use sensory cues in one modality to fill in the missing components of perceptual experience." and studied how such techniques can improve a user's sense of presence. In their study, Biocca et al. list different cross-modal sensory interactions. Among them are cross modal transfer (or synesthesia) and cross-modal enhancement or modification. Synesthesia is an extreme case of cross modal interaction "in which sensory information of one sensory channel produces experiences in another unstimulated sensory channel that receives no apparent stimulation from the virtual environment". They report results from an experiment that supports the existence of visual/haptic synesthesia, which enhances the user's sense of presence. Pseudo haptic feedback, proposed by Lecuyer et al. [START_REF] Lecuyer | Pseudo-haptic feedback: Can isometric input devices simulate force feedback[END_REF] is a form of synesthesia. The authors defined pseudo-haptic systems as "systems providing haptic information generated, augmented or modified, by the influence of another sensory modality [START_REF] Lecuyer | Boundary of illusion : an experiment of sensory integration with a pseudo-haptic system[END_REF]. They reported a study showing its ability to feed back force cues.

The background of this work is to extend the use of pseudo-haptic feedback to torque feedback and to investigate which of isometric or elastic input is the most suitable for this purpose. Our objective is to use torque pseudo-haptic feedback in an immersive virtual environment. To do so, there is a need to provide both theoreticallygrounded and empirically-validated rationales for the design of 3D interfaces. We mean to develop our knowledge of user-interface principles with which to develop a low cost pseudo-haptic device for use in an immersive environment.

The concept of pseudo haptic feedback requires that the passive device resist user-applied forces, thus it must have mechanical properties that allow this behavior. This can be implemented either by using an isometric device (with infinite stiffness and no displacement) or by using an elastic device (with a finite internal stiffness and displacement during manipulation).

The purpose of the user study presented in this paper is to evaluate the suitability of pseudo-haptic feedback for torque feedback and compare two passive isometric and elastic devices.

The paper begins with an overview of previous work in the field of pseudo-haptic feedback and torque and stiffness discrimination studies. It is followed by a description of the method, setup, and results of the experiment in Section 3. Results, based on psychophysical methods, are discussed in Section 4.

Previous Work

Lecuyer et al. conducted an experiment to measure the possibility of providing the user with haptic information by means of a passive input device combined with visual feedback. The device used was the Spaceball, which was considered as isometric in [START_REF] Lecuyer | Pseudo-haptic feedback: Can isometric input devices simulate force feedback[END_REF] because of its small displacement, but in this paper we will consider it as elastic, according to the definition that we proposed in the Introduction. A task of stiffness discrimination between real and virtual springs was used in the study. Results showed that subjects were able to discriminate successfully between a virtual spring and a real one. Two parameters were computed to characterize the subjects' performance when using the device, based on the psychophysics tradition. The first of these is the Just Noticeable Difference (JND) which is the just detectable variation of intensity of a specific stimulus. It corresponds to the value of the stimulus (here, the pseudohaptic spring) for which 75% of users perceive a difference in relation to the reference spring. The second is the Point of Subjective Equality (PSE), the value of the virtual spring stiffness that is perceived as equal to the real spring stiffness. The authors found an average JND of 13.4%. An illusion phenomenon was observed since the proprioceptive sense of the subjects was blurred by visual feedback.

To our knowledge, few studies on torque discrimination have been done. Jandura et al. [START_REF] Jandura | Experiments on human performance in torque discrimination and control[END_REF] conducted experiments to characterize human performance in sensing and controlling torque. They found a JND of 12.7% when the reference torque was 60mN•m. Our interest in the role of the type of input device (isometric or elastic) in pseudo-haptic simulation was raised by different studies. A study by Zhai [START_REF] Zhai | Investigation of feel for 6DOF inputs: Isometric and elastic rate control for manipulation in 3D environments[END_REF] evaluated elastic versus isometric rate control devices (in opposition to position control devices) in a 3D object positioning task. He found that the richer proprioceptive feedback afforded by an elastic controller is necessary for achieving superior performance in the early stages of learning. Subjects performed equally well with the isometric controller in later learning stages. In another work, Tan et al. [START_REF] Tan | Manual resolution of compliance when work and force cues are minimized[END_REF] conducted experiments on compliance (inverse of stiffness) discrimination in which work cues were eliminated and force cues minimized. The average JND for compliance ranged from 15% to 99% and was much larger than the average JND obtained from previous compliance discrimination experiments in which both work and terminal force cues were available to the subject. They concluded that manual resolution of compliance deteriorates when force and/or work cues are reduced or eliminated. These studies may support the hypothesis that pseudo-haptic feedback for torsion simulation could be better simulated with an elastic input device that would allow the user to have more proprioceptive information, as well as work and force cues, to help his perception. The next section presents the experiment which studies this hypothesis.

Method

To evaluate the proposed torque feedback and compare between isometric and elastic input, we chose a three-factor between subjects, repeated-measures design. Two groups of subjects went through a stiffness discrimination task between real torsion springs and virtual torsion springs that are pseudo-haptically simulated. For the first group the input device was isometric, and for the second group elastic. The independent factors were: 1) Type of device (isometric or elastic), 2) Real spring stiffness (two different real torsion springs were used), and 3) Virtual spring stiffness.

Setup

We built a prototype system that enables users to manually compare real torsion springs and pseudohaptic torsion springs (see Figure 1). The users were able to operate the system by manually turning plastic caps. Two caps are dedicated to real torsion spring manipulation and one is used to simulate a pseudo haptic torsion spring. The prototype presented in Figure 1 has one more cap, corresponding to a third real spring that was not used in the experiment.

Real Torsion springs

Two real torsion springs were used in the experiment, known to the user as the "real springs". Users estimated the compliance of the real torsion springs by manually turning the plastic caps which offered resistance to rotation. This was done by embedding axles into the structure. On each axle, we fixed a plastic cap that the subjects could grip and turn. The rotational movement of each cap was constrained by springs fixed to the axle as shown in Figure 2. The cap has grooves on its edges to let the user grip it easily. Friction effects were minimized by applying a lubricant to the contact points between the axle and the structure. The torsion constant of each torsion spring was empirically derived: we measured the weight needed to rotate the cap through a given angle, given the cap diameter (3.1cm). Values of the two torsion spring constants were

C1 = 2.0510 -2 N •m•rad -1 and C2 = 3.210 -2 N •m•rad -1 .
In the following, we will use the term "stiffness" to refer to "torsion constant". These two real springs were chosen to have stiffnesses that are representative of two common real-world situations: a weakly stiff spring (spring 1), and a medium stiff spring (spring 2). During preliminary experiments, we also chose the stiffness of spring 2 to avoid user fatigue (we limited maximum torque).

Pseudo-haptic simulated torsion spring

The pseudo haptic simulation consists of two elements: the passive input device and the visual simulation. The visual simulation represents a cap of the same size and aspect as the real ones (see Figure 3).

Figure 2. Real torsion spring assembly

Its rotational behavior is computed from the simulated virtual stiffness C v . C v is simulated using Hooke's law [START_REF]Gyro moment haptic interface[END_REF]. Given the torque applied by the user Γ u on the input device and the simulated C v , the simulation sets the angular position of the virtual cap at θ v .

Γ u = C v • θ v (1)
The visual simulation runs on a Pentium III 800MHz PC, with a 21" CRT monitor monoscopic display, at a 50Hz frame rate. The passive input device uses one of the caps, coupled to a FlexiForce force sensitive resistor (FlexiForce TM ELF TM system, Sensor B101-M). The FlexiForce sensor is connected to a PC workstation running the visual simulation. The isometric or elastic nature of this input device is a key issue of this work.

Isometric input device:

The isometric input device is realized with a static cap so its real stiffness is infinite. The cap is connected to the FlexiForce sensor as shown in Figure 4. By isometric we mean that the device itself is not moving, however the user's fingers can be deformed during manipulation. The device was calibrated with a maximum 7% error. The group that did the experiment with the isometric device was made up of 17 people without known visual and haptic impairments. 5 had corrected vision. There were 3 women and 14 men, aged from 26 to 53. 2 were left-handed and 15 were right-handed.

Elastic input device:

The elastic input device was realized using a real spring and by embedding the force sensor as shown in Figure 5. It had a finite internal stiffness and allowed rotation of the cap during displacement. The derived torsion constant of the device was C = 9.96 • 10 -2 N •m•rad -1 . The device was calibrated with a maximum 6% error. The group that did the experiment with the elastic device was made up of 2 women and 15 men. All of them were right handed, they were aged from 25 to 33, and all had normal or corrected vision.

Procedure

The method used was a constant stimuli method with a two-alternative forced choice. We carried out the experiment with more subjects (17 subjects in each group) than in the usual psychophysics studies (3 or 4 subjects), in order to evaluate the ability of this setup to give torque feedback to a wider variety of users. However, to reduce user fatigue, we used a smaller number of trials. Subjects were presented with a set of 32 experimental comparison trials. Two real springs were used (numbered 1 and 2 on the setup). The presented virtual spring had a virtual stiffness that was chosen from among 8 values of -40%, -30%, -20%, -10%, 10%, 20%, 30%, and 40% of the presented real spring stiffness. Each case was presented twice, yielding 32 comparisons (2 repetitions × 2 real springs × 8 virtual springs), whose order of appearance was randomly shuffled. The users sat in front of the computer screen, with the experimental system within the reach of their dominant hand. Much attention was paid to ensure that each torsion spring, real or virtual, was held with the same finger, arm and body configuration throughout the test. Subjects placed their forearms on a pile of paper that raised the hand to the height of the caps. For each test the person had to decide "which of the real or virtual springs is the stiffer?" and typed the answer on the keyboard. Subjects were asked to look at the real spring when manipulating it, and to look at the visual feedback when testing the virtual spring. A maximum turning limit was indicated on both real and virtual springs at 90 • . A cardboard cover was placed over the input device (virtual spring) so the subjects could not see the cap while turning it. Subjects were asked to start each test by real spring manipulation. They could switch between real and virtual springs without restriction. No information about the exactness of the answers was given during the tests. In order to familiarize the subjects with the task, each subject had ten trial tests before the beginning of the experiment.

Gathered data

• Answer. The answer for each real/virtual spring comparison was recorded.

• Applied Torque. The value of the torque applied on the device during the tests was stored for each user.

• Answer time. Time elapsed between the presentation of the comparison spring and the answer.

• Type of strategy. The subjects were also asked to describe their strategy for discrimination, if any.

• Perceived displacement of the device. At the end of the tests the subjects were asked to draw the estimated angle of rotation of the plastic cap used on the input device. We insisted that this be the physical rotation and not the visual feedback.

Results

Just Noticeable Difference, Point of Subjective Equality.

The analysis of answers follows the usual method described in [START_REF] Gescheider | Psychophysics Method, Theory, and Application[END_REF] to compute the JND and PSE 1 . All subjects' answers were added together and used to trace psychometric functions for each real torsion spring. The psychometric function represents the proportion of "virtual spring is stiffer" answers, as a function of the comparison (virtual) stiffness. We assumed that this function corresponds to a normal distribution of 0 average and a standard deviation equal to 1. Under this assumption, Z-score transformation of the proportion of "virtual spring is stiffer" answers yields a linear function (see Figure 8). Usual parameters (JND, PSE) are calculated using a linear regression of the Z-score. The Weber fraction is the JND divided by the stimulus intensity (real spring stiffness). The literature sometimes assimilates the Weber fraction to JND, as we will in this paper. It will be given as a percentage of the reference torsion spring stiffness. The PSE is calculated for a proportion of 50% of "virtual spring is stiffer" answers, which is interpreted as random answers (0.5 probability for either answer). In this paper we will consider the PSE as a subjective distortion (or error) of perception, but this doesn't mean that we assume a one-to-one correspondence in the relation between perceived and actual stiffnesses. Some subjects always answered that the virtual spring is stiffer; we will refer to these subjects as "purely haptic". The ratio of purely haptic subjects was 2/17 for the isometric device, and 6/17 for the elastic device. We chose not to consider these subjects in JND and PSE analysis.

Z-score transformation of the psychometric function, on which the calculation of JND and PSE is based, is shown 1 See definition of JND and PSE in Section 2 in Figure 8. Figure 9 shows the JND and the PSE for both experiments. For the isometric device, values of JND were: 28.2% for spring 1 and 14.2% for spring 2. The PSE value for which the virtual spring is perceived as equal to the real spring is P SE 1 = 2.11•10 -2 N •m•rad -1 for spring 1 and P SE 2 = 2.75•10 -2 N •m•rad -1 for spring 2. This corresponds to subjective distortion of perceptions of +2.8% and -14% of the real spring values as shown in Figure 9. For the elastic device, values of JND were respectively 9.1% and 4.4% for springs 1 and 2. PSE values were P SE 1 = 1.59•10 -2 N •m•rad -1 for the spring 1 simulation and P SE 2 = 2.70•10 -2 N •m•rad -1 for spring 2. These values correspond to a subjective distortion of perception of -22.5% and -15.36% relative to the real spring stiffness (Figure 9).

Applied Torque. The obtained torque vs. time curve is a succession of peaks (local maximum values of torque).

The number of peaks for each comparison was calculated. Average number of peaks is 4.78 (σ=0.83) for the isometric device and 4.84 (σ=1.41) for the elastic device. This value seems not different between type of device, nor between comparison spring values. Peak values shows important difference between isometric and elastic devices. Figure 6 shows average peak values and standard deviation of peak values within each comparison, for each device type.

Figure 6. Average of torque peaks for each comparison between the two real springs (C1 and C2 stiffnesses) and the presented virtual springs, with standard deviation bars.

Answer time.

Figure 7 shows answer times for both isometric and elastic modes.

Perceived displacement of the device. In the isometric device group, 13 persons were subject to a displacement illusion, since they reported a displacement of the static cap. We emphasize here that the subjects could not see the plastic cap, as it was intentionally hidden by a cardboard cover. The average perceived rotation of the device was 27.2 • (σ=25.6 • ) 2 for all the subjects. For the elastic device group, the perceived rotation of the input device was 59.3 • (σ=17.7 • ). This also corresponds to a displacement illusion, since the maximum elastic device rotation was 22 • , which corresponds to the maximum 90 • allowed rotation of the virtual cap.

User strategy. Subjects reported having three strategies: A "static" strategy, in which they compared stiffnesses by estimating the torque for a fixed angle, a "dynamic" strategy, involving several back-and-forth movements without paying much attention to the terminal displacement, and finally some users reported using a combination of these strategies. Table 1 reports the results for user strategy. 2 Standard deviation

Discussion

Results show that subjects were able to compare real and simulated torque forces with both devices. Performance varies depending on input device type: subjects discriminated the real and virtual springs with a better resolution when using an elastic device than with the isometric device, on the basis of JND results. Since these are stiffness JNDs, we cannot compare them to the torque JND (12,7%) found in [START_REF] Jandura | Experiments on human performance in torque discrimination and control[END_REF]. The movements of the fingers and hands are more important with the elastic device, this can give the user a better proprioceptive sense. Internal stiffness of the elastic device and rotation can give the user information relative to his mechanical work. These two types of information can explain a better performance with the elastic device. Tan et al. [START_REF] Tan | Manual resolution of compliance when work and force cues are minimized[END_REF] found that the existence of mechanical work information increases the user resolution in stiffness discrimination tasks, and that proprioception is likely to provide such information. On the basis of PSE values shown in Figure 9, we can observe that there is an overestimation of the virtual springs for the elastic device. This phenomenon appears with the isometric device too, but only for the stiffer spring comparisons. This could be explained by the measured average torque (peak values) applied on the device, which is systematically higher with the elastic device.

The maximum applied torque seems not to depend on the simulated stiffness; moreover, it seems almost constant over the different simulated springs. This result shows that the successful discrimination between real and pseudo-haptic simulated springs does not directly rely on actual forces, nor on actual mechanical work, but relies more on a haptic illusion. This haptic illusion could occur with respect to perceived terminal force or perceived mechanical work. As a hypothesis, we propose that the subjects may use a "perceived mechanical work" which combines perceived displacement of the device and applied torque. Further work is needed to address this hypothesis: it would be interesting to study the perceived displacement of the device as a function of simulated stiffness.

We carried out an ANOVA on answer time with repeated measures. Analysis is done with two within-subjects factors: 1) Presented virtual stiffness, as a percentage of reference stiffness and 2) reference stiffness, and one betweensubjects factor: device type, isometric or elastic. Results show a non-significant effect of device type on answer time (F(1,24)=3.889, p=0.06), with a tendency of longer answer times with the elastic device (average 24.04s, and 19.21s for isometric). There is no significant influence of reference stiffness nor presented virtual stiffness. There is a significant two-way interaction between device type and presented virtual stiffness (F(7,168)=2,88 (p<0.007)). Answer time seems not to be affected by variations of virtual stiffness with the isometric device, but it is affected with the elastic device: the smaller the difference between real and virtual springs, the longer the answer time. It seems that the difficulty of the discrimination increases when the difference between the real and the virtual springs decreases for the elastic device. This phenomenon resembles the real situation, whereas difficulty seems constant over the comparisons for the isometric device. This could characteristic of a more realistic feedback for the elastic device.

In both experiments, subjects experienced an illusion phenomenon. It is difficult to quantitatively compare the magnitudes of these two illusions since their nature is different: for the isometric device there is an illusion of displacement while there is no actual displacement of the device, whereas for the elastic device the illusion leads to an overestimation of the actual displacement. Qualitatively, we can consider that perceiving a displacement where there is none is a greater illusion. This can be interpreted as a com- pensation for the lack of actual proprioceptive feedback. The strategy reported by the users is not significantly different between the two devices. Conversely, on the basis of torque recordings, the actual behavior of users seems to be a more "dynamic" strategy: there are about 5 peaks of applied torque for all comparisons, and an average peak duration (including increase and decrease time) of 0.35s (σ=0.075) for the isometric and 0.81s (σ=0.17) for the elastic device. This reinforces the hypothesis that a mechanical work cue is used, based on a series of turns on the device. There were two haptic-oriented subjects (whose answers are always "the virtual spring is stiffer") for the isometric device, and six for the elastic device. It isn't possible to conclude that this difference is significant on the basis of our current data (χ 2 = 2.615, n.s). If confirmed, such a tendency could be due to the more realistic haptic behavior of the virtual spring with the elastic device, leading to a higher proportion of "physically correct" answers that the virtual spring is always stiffer.

Conclusion

In this work, we investigated whether pseudo-haptic feedback is suitable for simulating torque. Experimental results show that users were able to discriminate pseudohaptic simulated torsion springs and real springs. Results for perception resolution (JND) showed better performance when using an elastic input device compared to an isometric one. The elastic device yields a better resolution but a higher subjective distortion of perception compared to the isometric device. On the basis of applied torque measurements, we proposed the hypothesis that a cue called "perceived mechanical work" is used during the discrimination.

Applications such as surgical training for flexible endoscopy could gain from pseudo-haptic torque feedback, as the user could perceive forces from a virtual endoscope tip through navigation wheels used to control the endoscope. Another possible application would be training on a virtual lathe, where the user controls the cutting of a piece of wood with control wheels (as in the real situation). Pseudo-haptic torque feedback through control wheels would give him information about the forces applied on the piece of wood, and train him to avoid its breaking.

Future work will deal with integrating torque pseudohaptic feedback in an immersive virtual environment such as a responsive workbench. Haptic feedback could be performed with a tracked hand-held or wearable system, enabling the user to test mechanical properties of objects in the environment.

Figure 1 .

 1 Figure 1. Front view of the experimental setup.

Figure 3 .Figure 4 .

 34 Figure 3. Visual feedback of the virtual torsion spring

Figure 5 .

 5 Figure 5. Elastic input device assembly. The device's cap rotation is elastic thanks to a real spring and the force sensor is placed so a metallic plate presses on it when torque is applied to the device.

Figure 7 .

 7 Figure 7. Answer time for isometric and elastic mode (with standard deviation bars).

Figure 8 .

 8 Figure 8. Z-transformation of psychometric function for isometric and elastic devices.

Figure 9 .

 9 Figure 9. Just Noticeable Differences and Point of Subjective Equality, on virtual springs, for each real -reference-spring stiffness C1 and C2.

Table 1 . Subject's strategy: Ratio of answers for each device type (17 subjects per device)

 1

		Static strat-	Dynamic	Combination
		egy	strategy	of strategies
	Isometric 11/17	4/17	2/17
		(64, 7%)	(23, 5%)	(11, 8%)
	Elastic	12/17	3/17	2/17
		(70, 6%)	(17, 6%)	(11, 8%)

Acknowledgements

This research was funded by the Regional Council of Ilede-France and the French Ministry of Research within the RNTL Perf-RV project.