Mahdi Khelfaoui

Yves Gingras

Maël Lemoine

Thomas Pradeu

The visibility of philosophy of science in the sciences, 1980-2018

Keywords: philosophy of science, visibility, sciences, bibliometrics, citation analysis

In this paper, we provide a macro level analysis of the visibility of philosophy of science in the sciences over the last four decades. Our quantitative analysis of publications and citations of philosophy of science papers, published in 17 main journals representing the discipline, contributes to the longstanding debate on the influence of philosophy of science on the sciences. It reveals the global structure of relationships that philosophy of science maintains with science, technology, engineering and mathematics (STEM) and social sciences and humanities (SSH) fields. Explored at the level of disciplines, journals and authors, this analysis of the relations between philosophy of science and a large and diversified array of disciplines allows us to answer several questions: what is the degree of openness of various disciplines to the specialized knowledge produced in philosophy of science? Which STEM and SSH fields and journals have privileged ties with philosophy of science? What are the characteristics, in terms of citation and publication patterns, of authors who get their philosophy of science papers cited outside their field? Complementing existing qualitative inquiries on the influence of specific authors, concepts or topics of philosophy of science, the bibliometric approach proposed in this paper offers a comprehensive portrait of the multiple relationships that links philosophy of science to the sciences.

Introduction

Philosophers, and other scholars of the social sciences and humanities, have only recently started to use quantitative methods to analyze the structure of the field of philosophy and its different subfields. For instance, using bibliographic coupling, [START_REF] Noichl | Modeling the structure of recent philosophy[END_REF] found that the disciplinary structure of philosophy was quite cohesive, and that the 2 usual division between analytic and continental philosophy was in fact overstated. Some authors have applied text mining and computational topic-modeling algorithms to identify the historical evolution of key research topics in major philosophy of science journals [START_REF] Malaterre | What Is this thing called Philosophy of Science? A computational topic-modeling perspective 1934-2015[END_REF][START_REF] Malaterre | Revisiting three decades of Biology and Philosophy: A computational topic-modeling perspective[END_REF]. Others have used co-citation analysis to identify the set of central journals defining the field of philosophy of science [START_REF] Wray | Philosophy of science: What are the key journals in the field?[END_REF], the publications and authors that have had the most influence in the fields of philosophy of science [START_REF] Wray | Philosophy of science viewed through the lens of "Referenced Publication Years Spectroscopy[END_REF] and analytical philosophy (Petrovich and Buonomo 2018), as well as the representative topics of the discipline of philosophy [START_REF] Healy | A co-citation network for philosophy[END_REF].

Finally, other authors have applied bibliometric methods to study the relationship between philosophy of science and other fields or disciplines. Weingart (2014) used co-citation networks and bibliographic coupling to analyze the relationship between philosophy of science and history of science. Kreutzman (2001) used author co-citation analysis to study the relationship between philosophy of science and epistomology, while [START_REF] Mclevey | Interdisciplinarity and insularity in the diffusion of knowledge: An analysis of disciplinary boundaries between philosophy of science and the sciences[END_REF] developed exponential random graph models to assess the effect that publishing in science journals has on the accumulation of symbolic capital inside the field of philosophy of science. Building on these studies, our paper aims, using citation analysis and citation networks, at assessing the changing visibility of philosophy of science in other fields of the natural sciences, engineering and mathematics (STEM) and the social sciences and humanities (SSH) over the last four decades.

Whether philosophy of science is, should be, or could be, useful to science and/or influences, should influence, or could influence science is a longstanding debate that has been recently reignited by philosophers of science as well as scientists (e.g. [START_REF] Pernu | Philosophy and the front line of science[END_REF][START_REF] Pigliucci | The borderlands between science and philosophy: an introduction[END_REF][START_REF] Rovelli | Physics needs philosophy. Philosophy needs physics[END_REF][START_REF] Laplane | Why science needs philosophy[END_REF][START_REF] De Haro | Science and philosophy: A love-hate relationship[END_REF][START_REF] Boniolo | Life sciences for philosophers and philosophy for life scientists: What should we teach?[END_REF]. Advocates of a wider diffusion of ideas and tools developped in philosophy of science, and of a tighter relationship between philosophy of science and the sciences, have mainly relied on individual examples of philosophers of science who have made significant philosophical contributions to understanding and resolving scientific problems, clarifying scientific concepts or critiquing scientific assumptions [START_REF] Laplane | Why science needs philosophy[END_REF]. However, up to now, there are few empirical analyses that have assessed, on a larger scale, the extent to which the knowledge produced inside the field of philosophy of science has been actually used, or at least referred to, in science (Pradeu et al., submitted). This paper sheds light on this issue from a broader and more quantitative perspective, by measuring the visibility of philosophy of science papers in the sciences, through citations made to philosophy of science journals by STEM as well SSH disciplines. Explored at the three levels of disciplines, journals and authors, this quantitative analysis allows us to unveil several features of the relationship and interface between philosophy of science and a large and diversified array of disciplines.

In this paper, visibility is defined through the citations that the field of philosophy of science, its journals and its authors, has received from other sciences over the last four decades. We use the term "visibility" of philosophy of science in the sciences, rather than "influence" or "impact", because "visibility" describes in a more neutral and accurate way the very fact of being cited. Indeed, a philosopher doesn't need to be formally cited by authors from other sciences to influence them. For instance, although Einstein acknowledged the influence that David Hume and Ernst Mach's philosophy had on his theory of special relativity [START_REF] Norton | How Hume and Mach helped Einstein find special relativity[END_REF], this influence did not translate into formal citations from his physics papers to Hume's and Mach's philosophical works. Another form of implicit scientific acknowledgement was underscored by sociologist Robert K.

Merton, who identified the phenomenon of "obliteration by incorporation", according to which classic sources, although considered foundational, stop being cited (e.g., Galileo, Newton, Einstein) as they become taken for granted in a given scientific field [START_REF] Merton | The Matthew effect in science II: Cumulative advantage and the symbolism of intellectual property[END_REF].

While influence doesn't necessarily translate into visibility, on the opposite, visibility does not necessarily mean influence. Indeed, as noted by MacRoberts and MacRoberts (1986, p. 167), "the mere presence of a reference is not a marker of influence, nor is the absence of a reference evidence that it is uninfluential". In that respect, [START_REF] Moravscik | Some results on the function and quality of citations[END_REF] opposed "organic" and "perfunctory" citations, to establish the difference between citations that are "truly needed for the understanding of the referring paper" and express a genuine influence, and citations that are "mainly an acknowledgment that some other work in the same general area has been performed" (Moravscik and Murugesan 1975, p. 8). Since it is not the purpose of this paper to qualitatively evaluate the nature of citations made to philosophy of science by other disciplines, we refer to citations made to philosophy of science articles, journals and authors outside the field of philosophy of science as the visibility of philosophy of science in other sciences. We are here interested in the visibility of philosophy of science works in science at a global level, and propose a macroscopic analysis of the links between the discipline of philosophy of science and other scientific disciplines like biology, physics, mathematics, etc. Despite the existence of perfunctory citations, it remains that the act of citing a paper provides a reliable proxy for evaluating the degree of symbolic recognition that disciplines, journals and authors receive in the reward system of science [START_REF] Merton | The sociology of science. Theoretical and empirical investigations[END_REF], as has been already documented in many sociology of science and bibliometric studies [START_REF] Cole | Scientific output and recognition: A study in the operation of the reward system in science[END_REF][START_REF] Garfield | Citation analysis as a tool in journal evaluation -journals can be ranked by frequency and impact of citations for science policy studies[END_REF][START_REF] Price | A general theory of bibliometric and other cumulative advantage processes[END_REF][START_REF] Merton | The Matthew effect in science II: Cumulative advantage and the symbolism of intellectual property[END_REF][START_REF] Gingras | Bibliometrics and Researh Evaluation. Uses and Abuses[END_REF].

Analyzing citation flows between disciplines and citation networks contribute to our understanding of the structure of relationships, at a macro level, that philosophy of science maintains with other disciplines. Using quantitative bibliometric methods helps answer questions such as: what is the degree of openness of various disciplines to the specialized knowledge produced in philosophy of science? Which STEM and SSH fields and journals have privileged ties with philosophy of science? What are the characteristics, in terms of citation and publication patterns, of philosophy of science authors who get their philosophy of science papers cited outside their field? All these questions could, of course, be explored through qualitative inquiries and interviews on the influence of specific authors, topics or subfields of philosophy of science on other disciplines, but these inquiries could only offer a very limited portrait of the global structure of the multiple relationships that links philosophy of science to STEM and SSH disciplines. The global structure of those links can only be made visible by using tools developed in bibliometrics over the last forty years [START_REF] Price | Little Science, Big Science[END_REF]. In this paper, we have deliberately stuck to a descriptive stance, as our aim is first to replace hypothetical or fantasized views -that either exaggerate or downplay the visibility of philosophy of science in the sciences -with empirically validated data of the kind of relations they really entertain. In a complementary paper (Pradeu et al. submitted), we will try to characterize the precise philosophical content of the papers that happen to be much cited by scientists.

Bibliometric definition of the field of "philosophy of science"

In order to obtain a representative landscape of the field of philosophy of science, we have selected 17 major philosophy of science journals included in the Clarivate Analytics Web of Science (WoS) database, one of the most commonly used in bibliometric studies, which also contains data on thousands of journals in all STEM and SSH disciplines. That same database also gives us all the citations to the papers published in the selected philosophy of science journals coming from journals in the STEM and SSH disciplines between 1980 and 2018. The WoS includes the Science Citations Index Expanded, the Social Sciences Citation Index, and the Arts and Humanities Citation Index.

The disciplinary classification of journals used in this paper is that of the U.S. National Science Foundation5 . This classification has the advantage of categorizing each journal into one single discipline, which avoids double counting and attributing citations made by a given journal to several disciplines. While philosophy of science is not formally defined in this classification as a single field or specialty of philosophy, we consider our list of 17 major philosophy of science journals as representative of the field, because they obviously include all the journals that most philosophers of science recognize as central in that Of course, philosophy of science articles are sometimes also published in more generalist philosophy journals, such as The Journal of Philosophy or Nous, and most importantly in philosophy of science books and edited volumes. In this study, citations made to philosophy of science books and book chapters are not included in our sampling, since this would have required to identify beforehand and manually all philosophy of science books that have been published in the last several decades -an obviously impossible task. However, given that our aim is not to construct a list of "most cited" people but to analyze the global links between disciplines, our selected list of 17 central philosophy of science journals allows us to define a representative community of authors in that field. Although citations made to philosophy of science books and book chapters are not counted, the several thousand articles contained in our list of 17 central philosophy of science journals, which are cited over a period of 40 years, provide us with a very strong statistical sample to determine the general structure of citation flows from STEM and SSH disciplines to philosophy of science as a discipline. Given that books are still important in philosophy, one could also argue that we should take into account citations coming from books and not only from journal articles. However, we have shown elsewhere that such an inquiry does not change substantially the general pattern observed through the lens of academic journals [START_REF] Gingras | Do we need a book citation index for research evaluation[END_REF]. The basic reason is that it would be very unlikely that a prominent or visible philosopher of science who would be cited for influential monographs or for papers he or she has published in general philosophy journals would not also have published papers in philosophy of science journals, and thus be cited for these papers. For all these reasons, we are confident that our list of 17 major philosophy of science journals provides a very representative, though not exhaustive, sample of the academic production in that field.

We assess the visibility of philosophy of science, that is of all authors who did publish in the selected journals regardless of their backgrounds and affiliations, in the other scientific fields at three levels: disciplines, journals and authors. At the discipline level, we analyze citation flows from STEM and SSH disciplines to the field of philosophy of science, as defined by our list of 17 journals. More precisely, we count the references made, between 1980 and 2018, by all disciplines to each of the 17 philosophy of science journals.

The results obtained in this part of the paper allow us to determine which STEM and SSH disciplines are the most likely to cite philosophy of science, since we don't expect the external visibility of philosophy of science to be evenly distributed amongst all disciplines.

In addition to establishing the degree of openess of STEM and SSH disciplines to philosophy of science, the results also allow us to define its level of insularity, that is, the degree to which a field is self-referencing. Total citations to philosophy of science from other disciplines are then calculated for each decade of the 1980-2018 period, in order to observe possible variations over time. Finally, in order to establish if the levels of insularity and visibility observed for philosophy of science are low, normal or high, we compare the results with those obtained for the the remaining field of general philosophy, as well as those obtained for the field of science studies, which shares a similar interest in science as philosophy of science, but from sociological and historical perspectives.

From the discipline macro level, we move a step further to analyze the visibility of philosophy of science in other sciences at the journal level. We do this by ranking the top-10 journals of each the STEM and SSH disciplines that cite the most philosophy of science journals and the top-5 philosophy of science journals cited by these disciplines. We thus focus on the journals that cite philosophy of science the most, though these journals are not necessairly the ones that are themselves the most cited in their own scientific discipline (as a way of illustration, in biology, these ten journals are, in the recent period: Acta Biotheoretica, Journal of Theoretical Biology, Evolutionary Biology, Theory in Biosciences, Cladistics, Evolution, Biosystems, Journal of Experimental Zoology Part B, Biology Direct, and the Journal of Evolutionary Biology). While citation flows at the discipline level help us identify the STEM and SSH disciplines that cite the most philosophy of science, citation analysis at the journal level provides us with a more precise idea of the subfields of these discipline that have a particular affinity with philosophy of science. For instance, in biology, we expect, for obvious reasons, that journals in the subfield of evolutionary biology are more likely to cite philosophy of biology articles than journals in the subfield of biochemistry or oceanography. Similarly, in physics, we expect theoretical physics journals to be more likely to cite philosophy of modern physics articles than applied physics or optics journals. The list of top-10 citing and top-5 cited journals is also established for each decade of the 1980-2018 period, in order to observe possible variations over time. Similarly, a time analysis of the top-5 cited philosophy of science journals in each citing discipline makes it possible to observe variations over time in the philosophy of science journals that are of interest to other disciplines. For instance, if biology consistently cites philosophy of science journals, we expect that Biology & Philosophy, as well as Studies in History and Philosophy of Biological and Biomedical Sciences will appear amongst the most visible philosophy of science journals in these disciplines. We also expect that, with the rise of ethical issues in the contemporary practice of medicine and biology, medicine and biomedical sciences will show over time a more pronounced interest for medical ethics and bioethics journals, such as Theoretical Medicine and Bioethics.

Journal rankings only provide a limited description of citation flows from STEM and SSH journals to philosophy of science journals, since they only give, for each citing discipline, information on the top-10 citing and top-5 cited journals. In complement to these rankings, we generated citation networks, using the open-source visualization software Gephi [START_REF] Cherven | Network graph analysis and visualization with Gephi[END_REF], to provide a more comprehensive picture of the citation relationship between philosophy of science journals and all other STEM and SSH journals. Citation networks are represented by nodes connected by edges. Each node represents either a citing journal or a philosophy of science cited journal. Nodes representing philosophy of science journals are colored in red, in order to distinguish them from other citing journals. Edges represent citations from STEM or SSH journals to philosophy of science journals. The more a STEM or SSH journal cites a given philosophy of science journal, the thicker will be the edge that connects them. The more a philosophy of science journal receives citations from different STEM or SSH journals, the more central its position will be in the network, and the larger the size of its node will be. We show three different networks that represent citation flows from STEM journals, social science journals, and humanities journals to our 17 philosophy of science journals. In order to facilitate the visibility of the main nodes of the network, we only show links between journals with at least 15 citations between 1980 and 2018. One of the main features of the Gephi software is its use of the Louvain community detection algorithm to identify coherent clusters (identified by nodes of the same color) within a larger network [START_REF] Blondel | Fast unfolding of communities in large networks[END_REF]). In our case, these clusters represent different communities of journals that share the particularity of citing the same philosophy of science journals. In this regard, citation networks do not only provide a more comprehensive picture of the journals who cite philosophy of science, but also allow to define sub-communities of citing journals, which might be composed of different STEM, social science or humanities disciplines.

From the journal level, we then move to the author level. We define a list of authors who have contributed as first authors at least one article in one of the 17 philosophy of science journals and have received for their articles at least 20 citations from STEM journals or 20 citations from philosophy of science journals, between 1980 and 2018 (we apply the 20 citations threshold over the period to keep the number of authors in the network manageable). While the choice of counting citations to first co-authors is dictated by technical constraints, it remains that 86% of the articles published in our sample of 17 philosophy of science journals are single authored. Moreover, it is very unlikely that any important philosophy of science author would be cited solely for articles where he or she appears as second or third co-author. Thus, we are confident that by counting citations only to first co-authors, and by using a low citation threshold of 20 citations over a 30 years period, we adequatley capture the global visibility of philosophers of science. Through this method, we can define three different communities of authors: 1) authors of philosophy of science articles who remain mostly cited, and therefore visible, in the field of philosophy of science; 2) authors who get cited in both philosophy of science and STEM disciplines; and 3) authors who get mostly cited, and are thus mainly visible, in STEM disciplines. We then use the citation and publication patterns of these authors to identify the characteristics that seem to allow their philosophy of science articles to transcend the boundaries of their field and gain visibility in science disciplines.

Which scientific disciplines cite philosophy of science journals?

We start by assessing the visibility of philosophy of science in other sciences at the discipline level. In Figure 1, an alluvial chart provides the distribution of citations from different STEM and SSH disciplines to philosophy of science, between 1980 and 2018. It shows that 30.2% of all citations to philosophy of science come from that field, and that 19.7% come from the rest of philosophy. Overall, 49.9% of the citations made to philosophy of science journals come from philosophy, broadly defined (i.e., including philosophy of science). Our results confirm McLevey's et. al. finding that "roughly half of the citations to articles in (philosophy of science) journals come from journals in different disciplines" [START_REF] Mclevey | Interdisciplinarity and insularity in the diffusion of knowledge: An analysis of disciplinary boundaries between philosophy of science and the sciences[END_REF]. With 28.8% of citations, SSH is the second grand disciplinary field citing philosophy of science. Psychology, health and science studies are the three SSH discplines that cite the most philosophy of science journals. With 21.3% of citations, STEM is the third grand disciplinary field citing philosophy of science.

As in SSH disciplines, citations to philosophy of science are not evenly distributed among STEM disciplines. Indeed, clinical medicine, biology and physics are the three disciplines where philosophy of science is the most visible, while it is almost invisible in a field such as chemistry, or earth and atmospheric sciences. These differences might be explained by the fact that those disciplines tend to be more applied and less fundamental. The fact that some sub-specialties of philosophy of science, like philosophy of chemistry or enginering, developed only recently may also contribute to explain that low level of visibility.

Another part of the explanation for the tendency of some scientists to cite philosophy of science could come from some recent evolutions in the field of philosophy of science. These evolutions might include: i) an increasing focus on philosophy of special sciences (philosophy of biology, physics, and so on) rather than general philosophy of science [START_REF] Mizrahi | The case study method in philosophy of science: An Empirical Study[END_REF]; ii) the emergence of "philosophy of science in practice", an approach "dedicated to fostering the pursuit of a philosophy of science that considers theory, practice and the world simultaneously, and never in isolation from each other" [START_REF] Ankeny | Introduction: philosophy of science in practice[END_REF];

iii) an emphasis, by an increasing number of philosophers of science, on advancing science rather than simply discussing science. We have proposed an in-depth analysis of this latest aspect in another paper (Pradeu et al. submitted). We called it "philosophy in science", and defined it by the use of philosophy as a toolbox to help solve scientific problems. "Philosophy in science" is particularly prone to have a higher visibility in science, because it tends to raise the exact same questions that scientists themselves are trying to solve in their daily practice.

Figure 1 -Distribution of citations to philosophy of science journals coming from other disciplines between 1980 and 2018 (%)

As shown in Table 1, when compared to philosophy of science, the rest of the field of philosophy is significantly more self-referencing, since 57.1% of citations to philosophy are internal to this field (excluding philosophy of science), while 9.4% of citations to philosophy are from philosophy of science journals. This difference between philosophy and philosophy of science is mainly attributable to an effect of field size. Indeed, since the field of philosophy includes significantly more journals and researchers than the subfield of philosophy of science, it is not surprising that many more citations are generated within the field of philosophy, since the potential number of citing items is larger. While its share of citations from SSH disciplines is equivalent to that of philosophy of science (27.5%), the rest of the field of philosophy receives, as could be expected, much less citations from STEM disciplines, with only 5.9%, comparatively to 21.3% for philosophy of science.

When compared to the field of science studies, which also has an interest in science but from a more sociological and historical perspective, philosophy of science has a similar visibility in STEM disciplines (21.3% for philosophy of science vs 18.5% for science studies). Both fields also have a similar level of insularity or percentage of self references (30.2% philosophy of science vs 29.2% for science studies). received from philosophy has decreased from 25.9 to 19.9% during the same period. This result suggests that the specialty of philosophy of science has grown in size, including more journals and more researchers, and become more autonomous from the rest of philosophy.

The disciplines of health and clinical medicine are those where philosophy of science has increased its visibility the most as compared to other STEM and SSH fields (from 1.7 to 6.1% in health, and from 2.8 to 5.2% in medicine). This can be explained by the rise of ethics-related issues in these two fields, reflections that generate more citations to publications on medical ethics in the field of philosophy of science. Other disciplines where the visibility of philosophy of science has not changed significantly over time are biology, physics, mathematics, engineering, professional fields and science studies. It is also interesting to observe that the visibility of philosophy of science has experienced an important decline in psychology (from 8.1 to 4.8%), economics (from 2.8 to 1.2%), and language and linguistics (from 2.5 to 1.1%). However, this decline might only be apparent and biased by the fact that three interdisciplinary journals with a huge philosophical focus, Philosophy and Psychology, Economics and Philosophy, Linguistics and Philosophy are classified in the WoS database as being part of these three disciplines and not as philosophy journals. When citations to these three journals are considered as citations to philosophy of science journals, the visibility of philosophy of science in psychology declines from 8.1 to 5.7%, in economics from 2.9% to 1.7%, and in language and linguistics from 5.0% to 4.6%.

Thus, while the decline of the philosophy of science in psychology and economic is confirmed, the inclusion of Linguistics and Philosophy in the list of philosophy of science journals shows that the visibility of philosophy of science has remained stable over time in the discipline of language of linguistics. It is well known that the distribution of citations within a set of journals is not homogeneous and rather follows in general a power law such that a minority of journals account for the large majority of the citations received. It is thus useful to observe the level of concentration of citations among the top-ten citing journals for each citing discipline.

This measure gives an indication of the degree of dispersion of citations made to philosophy of science among the many journals of each citing discipline. The more citations are concentrated in the top-10 citing journals, the more the interest of that discipline in philosophy of science is restricted to a limited number of journals, which may indicate that there exists a sub-community of that discipline with a special interest for those philosophical questions about their science. As shown in In Appendix A, the visibility of philosophy of science is further analyzed by looking, for each discipline and decade, at the top-10 journals citing philosophy of science, as well as the top-5 cited philosophy of science journals. In some STEM disciplines, the top-10 journals citing philosophy of science share the particularity of focusing on the theoretical foundations and principles of their discipline and of hosting scientific papers of a conceptual and philosophical nature. This is, for instance, the case of biology which counts amongst its top-10 citing journals Acta Biotheoretica, the Journal of Theoretical Intelligence, Minds and Machines, Kybernetes). Synthese, followed by Philosophy of Science, is the most cited philosophy of science journals by both disciplines of mathematics and engineering and technology. This is not surprising since some subfields of these two disciplines share a similar interest in philosophy of science.

Medicine and health share a common interest in ethical and bioethical issues raised by philosophy of science. The top-10 medicine journals citing philosophy of science journals cover a wide spectrum of medical specialties, ranging from biomedicine, internal medicine, epidemiology, pediatrics, geriatrics, critical care, psychiatry, to brain research.

This disciplinary diversity confirms a result obtained in Table 3 that

Network of relations between journals

The relationship between citing STEM and SSH journals and cited philosophy of science journals can be further explored through journal citation networks presented in figures 2, 3, and 4. disciplines, but focusing on bioscience and medicine [START_REF] Milojevic | Nature, Science, and PNAS: disciplinary profiles and impact[END_REF], cite philosophy of science journals with a particular inclination for philosophy of biology and philosophy of medicine.

Figure 3 shows the network of citation between social science journals citing philosophy of science journals. The network is structured by three communities in blue,

The visibility of philosophers of science in other sciences

Though disciplines have particular structural characteristics, they are of course composed of researchers with their own social characteristics and intellectual contributions to the field. We will now look at the last level of analysis, that of authors of the articles published in the 17 journals that for us are representative of the field of philosophy of science. Being interested in the links of that discipline to other scientific disciplines, and not in the internal dynamic of philosophy of science itself, we limit our focus on citations coming from STEM fields to authors who published in our set of philosophy of science journals. For this purpose, we construct a network that connects scientific disciplines to philosophers of science. -48 philosophers of science (30.1%) have published at least 5 peer-reviewed articles in STEM journals.

-14 philosophers of science (8.8%) belong to both previous categories (they are amongst the top-100 cited philosophers of science and have also published more than 5 STEM peer-reviewed articles).

-27 philosophers of science (13.5%) belong to none of these categories.

-15 philosophers of science (7.5%) are active in the subfield of bioethics, especially medical ethics.

Overall, 79% of philosophers of science who get cited in both fields of philosophy of science and STEM are either highly cited authors in the field of philosophy of science or intervene frequently in science, through the frequent publication of peer-reviewed articles in journals of STEM disciplines. In other words, two main categories of philosophers of science are more likely to be cited by both scientists and philosophers of science: those who achieve high visibility in their own field (philosophy of science) may be able to extend this visibility to STEM fields, while those who publish frequently in STEM disciplines may also get their philosophy of science articles visible in STEM. The remaining of the central community is composed of philosophers and scientists: 10 philosophers who specialize in subfields other than philosophy of science compose 5% of the community, and 30 scientists, half of them biologists, compose 15% of the community. Finally, only one social scientist, Herbert A. Simon, is present in this community. The overarching message that comes out of our detailed analysis of the growing visibility of philosophy of science in other scientific fields is that, contrary to what many may think, philosophy of science as a specialized field is far from autarchic and closed on itself. On the contrary, its work is in fact quite visible in many other scientific disciplines.

Our results also suggest that abstract and general discussions on the usefulness or not of philosophical reflections for the work of practicing scientists should take these empirical results into account in future discussion.

This raises an important practical question: if one is convinced that philosophy of science can have a fruitful dialogue with the sciences, how may this dialogue be facilitated in practice? Part of the solution will certainly come from scientists themselves: by inviting philosophers of science to co-author papers, participate in scientific meetings, and so on.

Needless to say, any influential scientist saying that philosophy of science has impacted their scientific research will be much more convincing to the scientific community than philosophers of science claiming that they have had such an impact. Another manner to increase our links with the sciences is the development of interdisciplinary curricula.

Philosophers of science, especially the younger ones, already have, in most cases, a strong background in science. Yet this could be strengthened, and it could also be more valued in

  domain. These journals are: Philosophy of Science, The British Journal for the Philosophy of Science, Synthese, Studies in History and Philosophy of Science (and its offsprings Part A, B, and C from 1998 onward), Erkenntnis, European Journal for the Philosophy of Science, International Studies in the Philosophy of Science, Journal for General Philosophy of Science, Foundations of Science, Hyle, History and Philosophy of the Life Sciences, Biology & Philosophy, Theoretical Medicine and Bioethics, Journal of Medicine and Philosophy, Medicine Health Care and Philosophy. In addition to including the most central journals in philosophy of science (Wray 2010), this list of 17 journals covers large areas of philosophy of science, where researchers are the more active, such as philosophy of biology, philosophy of physics, and philosophy of medicine which is well represented with three journals. 6

Biology, and

 and Theory in Biosciences. Journals focusing on the topics of evolution (Evolution, Evolutionary Biology), biological systematics (Systematics Biology, Systematics Zoology, Systematics Botany), and cladistics (Cladistics) are also amongst the top biology journals citing consistently philosophy of science across the whole studied period. Unsurprisingly, the most popular philosophy of science journal cited by the discipline of biology is Biology & Philosophy; it is followed by Philosophy of Science, The British Journal for the Philosophy of Science, Studies in History and Philosophy of Science (before 2000), and Studies in History and Philosophy of Science -Part C (which has an obvious focus on biology), also remain consistently in the top-5 cited philosophy of science journals over the whole analyzed period.In the case of physics, the top-10 journals citing philosophy of science are also interested in the theoretical and conceptual foundations of the discipline. Over the four decades, Foundations of Physics remains the top journal citing philosophy of science, followed by International Journal of Theoretical Physics. American Journal of Physics also consistently cites philosophy of science, which is not surprising, since this journal has a strong focus on methods and pedagogical issues in the teaching of physics, which can benefit from philosophical insights for the transmission of knowledge in this discipline. Some specialties of physics seem also more likely to cite philosophy of science journals than others. It is the case of particle physics, atomic and molecular physics (Physical Review D, Physical Review A), which might cite philosophy of quantum physics articles, gravitation (Classical and Quantum Gravity), and mathematical physics (Philosophical Transactions of the Royal Society -Part A, Journal of Mathematical Physics, Physics Journal A). Between 1980 and 1999, Philosophy of Science is the most cited philosophy of science journal by physics journals, but it is replaced in the 2000-2018 period by Studies in History and Philosophy of Science -Part B, which has an exclusive focus on the history and philosophy of modern physics. Citations to philosophy of science journals from the discipline of mathematics come from three main specialties: probability and statistics, logics, and applied mathematics. Between 1980 and 1999, mathematics journals citing philosophy of science are mainly focused on issues of statistical inference and probabilistic causality on the one hand (Annals of Statistics, American Journal of Statistical Inference), and logic on the other hand (Journal of Symbolic Logic, Annals of Pure and Applied Logic). While philosophy of science articles remain visible in logic journals between 2000 and 2018, mathematics applied to computer science and artificial intelligence (Fundamenta Informaticae, Annals of Mathematica and Artificial Intelligence) become much more open to philosophy of science during the same period. By contrast, between 2000 and 2018, statistics journals almost disappeared from the top-10 mathematics journals citing philosophy of science. In engineering and technology journals, citations to philosophy of science journals are mainly concentrated in the subfield of computer science, more particularly around the topics of fuzzy sets, artificial intelligence and cybernetics (Fuzzy Sets and Systems, Artificial

  showed that, over the four analyzed decades, medicine has the lowest concentration of philosophy of science citations in its top-10 citing journals. In other words, as compared to other STEM and SSH disciplines, interest for philosophy of science in medicine is more widely spread across its different specialties. In the social sciences of health, citations to philosophy of science journals come mainly from medical ethics and nursing ethics journals (Medical Ethics, Bioethics, Nursing Ethics). The journal Social Science & Medicine also cites highly philosophy of science journals, mainly for articles related to medical and social ethics. Unsurprisingly, three philosophy of science journals, with a large focus on ethics and bioethics, are the most cited by both medicine and health disciplines: Journal of Medicine and Philosophy, Medicine, Heath Care and Philosophy, and Theoretical Medicine and Bioethics. In the field of psychology, the top-10 journals citing philosophy of science are mainly concentrated in the two subfields of behavioral science (Behavioral and Brain Sciences, Journal of Brain Behavior) and cognitive science (Cognition, Cognitive Science). Theoretical psychology journals, such as Theory in Psychology and New Ideas in Psychology, as well as interdisciplinary journals such as Frontiers in Psychology and Psychology and Philosophy (which is devoted to studying the links between psychology and philosophy) are also amongst these top-10 citing journals over the four decades analyzed here. The most cited philosophy of science journals in psychology are also the most central in the field of philosophy of science (Wray 2010): Philosophy of Science, The British Journal for the Philosophy of Science, and Synthese. Finally, in the field of science studies, philosophy of science articles are mainly cited by sociology of science and technology journals (Social Studies of Science, Science, Technology and Human Values), history of science (Isis, History of Science), and history of biology journals (Journal of the History of Biology, British Journal for the History of Science). The most cited philosophy of science journals in science studies is Studies in History and Philosophy of Science -Part A, which is not surprising since philosophy of science is closely linked with the field of science studies (including history of science), through the intermediate field of history and philosophy of science (HPS) (see Figure 1 in Weingart 2015, p. 208).

Figure 2

 2 figures 2, 3, and 4. Figure2shows the network of STEM citing journals and philosophy of science cited journals. The network displays four distinct citing communities which are colored in blue, green, red and purple. At the right of the network, the blue community represents STEM journals that cite philosophy of medicine journals, with Journal of Medicine and Philosophy being, by far, the most cited in this community. Unsurprisingly, STEM journals in the blue community belong exclusively to the discipline of medicine.The green community at the center of the network is mostly composed of biology journals (with a few other biomedical science journals) citing Biology & Philosophy, then, to a lesser extent, Studies in History and Philosophy of Biological and Biomedical Sciences, and, marginally, History and Philosophy of the Life Sciences. The orange community at the left of the network is composed of physics journals that cite mainly Studies in History and Philosophy of Modern Physics, and to a lesser extent Studies in History and Philosophy of Science -Part A. The purple community at the top of the network is composed of mathematics and computer science journals first citing Synthese, and then Erkenntnis. Two philosophy of science journals stand at intermediate positions between different communities. The main one, Philosophy of Science, is cited by journals from the four communities and stands at the heart of the network, which reflects the variety of topics tackled by its articles and the centrality of this journal, not only in the field of philosophy of science, but also as seen from STEM journals citing philosophy of science. Slightly offcentered at the right of the network, The British Journal for the Philosophy of Science is cited by all communities except medicine. Finally, it is interesting to notice the intermediate position of two science journals in the network, PLoS One and Science. Their particular position reflects the fact that these journals, known for covering all scientific

  green and orange. The blue community at the right of the network is composed of social sciences of health journals citing philosophy of medicine journals. The green community, at the bottom left of the network, is composed of science studies journals. The top part of this community is structured around sociology and history of science journals mainly citing Studies in History and Philosophy of Science -Part A, while the bottom part, where history of medicine journals are more present, is structured around Studies in History and Philosophy of Biological and Biomedical Sciences, as well as History and Philosophy of the Life Sciences. It is interesting to notice the intermediate position held by Social History of Medicine, which cites both philosophy of life science journals (in the green community) and philosophy of medicine journals (in the blue community). Biology & Philosophy and British Journal for Philosophy of Science are situated at the border of the science studies journals community, and the community in orange. The latter is populated by journals from various disciplines (economics, professional fields, sociology), but largely dominated by psychology journals, especially those specialized in behavior and cognition. This orange community is divided in two sub-communities, one structured around Synthese and the other around Philosophy of Science. As was the case in the previous network of STEM journals citing philosophy of science journals, Philosophy of Science also occupies a central position in the whole network of social sciences journals, being cited by journals from the three communities.

Figure 4

 4 Figure4shows the network of relationships between humanities journals, featuring disciplines such as philosophy, history, and language and linguistics, citing philosophy of science journals. Four communities, in blue, green, orange and purple are visible. The most important community, in purple at the top left of the network, includes a majority of philosophy journals and is centered around Synthese, which is also the most cited journal in the whole network. Philosophy journals in the purple community also tend to cite British Journal for Philosophy of Science, Philosophy of Science and Erkenntnis. Another smaller community, in orange at the bottom left, is also composed of philosophy journals but is

Figure 4 -

 4 Figure 4 -Network of Humanities journals citing philosophy of science journals (1980-2018)

Figure 5

 5 shows citations from STEM and philosophy of science fields (each represented by a single node) to authors who have published at least one paper as a first author in one of the 17 philosophy of science journals before 2018. To make the network legible, we show only links for authors having at least 20 citations from the STEM field or from philosophy of science in the 1980-2018 period. The more citations an author receives from the fields of STEM or philosophy of science, the thicker is the edge that connects that author's node to the discipline citing him or her. As shown in Figure5, the network is strikingly structured by three distinct communities of authors. The community at the right of the network is composed of 297 authors who are mostly cited by philosophy of science journals, meaning that their articles do not transcend the boundary of their field. Authors featured in this community are in large majority philosophers of science, or philosophers who publish at least part of their works in philosophy of science journals. The two other communities are the most interesting to analyze, since they are composed of authors who get some of their philosophy of science articles cited not only in philosophy of science but also in STEM disciplines. Their work thus appears more visible to scientists than those of the first group.The community at the left of the network represents authors of philosophy of science articles who are mainly cited by journals of STEM disciplines. A detailed analysis of the 169 author names composing this community shows that it mainly includes scientists who have published one or several articles in philosophy of science journals. These articles have mainly attracted the attention of other scientists, since they are largely cited by STEM

Figure 5 -

 5 Figure 5 -Network of authors of philosophy of science articles cited at least 20 times in STEM or philosophy of science, 1980-2018

  philosophy departments. In parallel, scientists should receive training in history and philosophy of science, not aiming to transform them or to challenge their practice, but rather to help them better understand how to use philosophers' unique competences to improve their scientific practice.More work is now needed on the converse question: what is the place of the various sciences in philosophy of science? While the influence of individual scientists and scientific theories on the development of philosophy and philosophy of science has often been documented (e.g.[START_REF] Dewey | The influence of Darwin on philosophy and other essays in contemporary thought[END_REF][START_REF] Sanchez-Gonzalez | Medicine in John Locke's philosophy[END_REF][START_REF] Bitbol | Schrödinger's philosophy of quantum mechanics[END_REF][START_REF] Stjernfelt | Simple animals and complex biology: Von Uexkull's two-fold influence on Cassirer's philosophy[END_REF][START_REF] Howard | Einstein and the development of twentieth-century philosophy of science[END_REF], a macro-level analysis of the visibility of the sciences in contemporary philosophy of science, based on citation flows and networks, though probably more difficult to implement, could reveal specific properties of the field of philosophy of science that have not been made visible in our study or have also been ignored by qualitative studies.

Table 1 -Distribution of citations made to philosophy, philosophy of science and science studies journals from other disciplines Research fields Philosophy of science Philosophy Other Social sciences and humanities Natural Sciences and Engineering Philosophy of science

 1 Table2provides the distribution of citations to philosophy of science made by other disciplines, for each decade of the 1980-2018 period. The breakdown by decade makes visible the variations through time in the share of citations made by each major

		30.2	19.7	28.8	21.3
	Philosophy	9.4	57.1	27.5	5.9
	Science	2.7	1.4	77.4	18.5
	studies			(29.2 in science
				studies)

discipline to philosophy of science. The level of self-referencing of philosophy of science has increased from 26.9% to 31.8% between 1980 and 2018, while the share of citations

Table 2 -Distribution of citations to philosophy of science journals made by STEM and SSH disciplines, percentage by decade

 2

	Discipline	1980-1989	1990-1999	2000-2009	2010-2018
	Philosophy of Science	26.9	27.9	29.2	31.8
	Philosophy	25.9	19.7	17.2	19.9
	Biology	4.2	4.6	5.5	3.4
	Physics	2.3	2.9	3.4	3.3
	Engineering & Technology	2.0	4.1	3.7	2.8
	Mathematics	1.5	1.2	1.5	2.0
	Biomedical Research	1.2	1.7	2.6	3.3

Table 3 ,

 3 a first general observation is that, between 1980 and 2018, the concentration of citations to philosophy of science has declined in all other disciplines' top-10 citing journals, except for mathematics which, after a significant decline in concentration (from 68.2 to 50.5% between 1980 and 2009), has increased to its initial level, due to an important surge in citations to philosophy of science journals in the Review of Symbolic Logic. Overall, philosophy of science has

	enjoyed a larger spread and visibility among science journals of disciplines other than
	mathematics over the last four decades. Disciplines where citations to philosophy of
	science journals have dispersed in a larger number of journals are science studies, physics,
	engineering and technology, health, medicine, and economics. Disciplines where

concentration of citations has not changed substantially are psychology, language and linguistics, and biology.

Table 3 -Proportion of citations to philosophy of science coming from top-10 citing

 3

		journals, by discipline
	Discipline	1980-1989	1990-1999	2000-2009	2010-2018
	Philosophy	43.1	46.8	40.8	31.3
	Biology	40.3	35.9	39.9	30.6
	Physics	79.4	77.6	55.0	56.6
	Engineering & Technology	64.7	57.9	59.5	47.0
	Mathematics	68.2	54.5	50.5	69.3
	Clinical Medicine	38.4	20.6	14.9	20.6
	Health	63.3	55.8	52.6	44.1
	Psychology	52.5	47.4	48.5	48.6
	Science Studies	88.2	85.2	70.9	60.5
	Economics	71.7	61.7	62.0	53.7
	Language & Linguistics	73.1	81.1	80.1	68.6

Table 4 -Distribution, by discipline, of authors whose philosophy of science articles are mostly cited in STEM fields

 4

	Discipline	Number of authors	% of authors
	Biology	42	24.7
	Medicine	25	14.7
	Physics	18	10.6
	Mathematics	13	7.6
	Engineering	9	5.3
	Other STEM disciplines	3	1.8
	Bioethics	22	12.9
	Philosophy of science	12	7.1
	Philosophy	16	9.4
	Social sciences	10	5.7
	The community at the center of the network is composed of 200 authors whose
	philosophy of science articles receive citations from both philosophy of science and STEM
	fields. Of these 200 authors, 79.5% are philosophers of science, 5% are philosophers
	mainly active in subfields other than philosophy of science, 15% are scientists, and 0.5%
	are social scientists. We categorized authors as philosophers of science, philosophers
	mainly active in subfields other than philosophy of science, or scientists based on the
	subfields and journals where they published the most frequently, the disciplines in which
	they received their PhD, and their departmental affiliations. What make philosophers of
	science of this central community visible in both philosophy of science and STEM
	disciplines? An analysis of the publication and citation patterns of this limited group of 159
	authors provides some answers, as shown in Table 5:
	-55 out of 159 philosophers of science from this community (34.6%) also figure
	amongst the top-100 most cited authors in philosophy of science journals between 1980
	and 2018.

Table 5 -Distribution of philosophy of science authors who are cited by both philosophy of science and STEM disciplines Author category Number of authors % of authors

 5

	Top-100 cited philosophers of science	55	27.5
	Philosophers of science with at least 5	48	24.0
	papers in STEM
	Philosopher of science belonging to both	14	7.0
	above categories
	Other philosophers of science	27	13.5
	Philosophers (other than philosophers of	10	5.0
	science)
	Bioethicists	15	7.5
	Scientists	30	15.0
	Social scientists	1	0.5
	Total	200	100.0

https://www.nsf.gov/statistics/nsf13327/pdf/tabb1.pdf

journals. This is for example the case of computer scientists Joseph Goguen and Lotfi Zadeh, who have been abundantly cited by mathematicians and engineers for two paper on fuzzy logic they published in Synthese [START_REF] Goguen | The logic of inexact concepts[END_REF][START_REF] Zadeh | Fuzzy logic and approximate reasoning[END_REF]. These citations to Zadeh and Goguen partly explain why Synthese is the most cited philosophy of science journal in the disciplines of mathematics and engineering and technology. Famous physicists Albert Einstein, Niels Bohr and Edwin Schrödinger, whose philosophy of science papers have been published in the 1930s and 1950s are still cited nowadays by physics journals. But most physicists that are cited in STEM journals for articles they published in philosophy of science journals are still active, including Mario Castagnino,

Stephen Adler, Charles H. Bennett, Michele Campisi, and Diederick Aerts. Some prominent biologists have also published philosophy of science papers that are highly cited in STEM journals, such as Theodosius Dobzhansky, John Maynard Smith, Daniel Simberloff, Brian K. Hall, Richard Michod, and others. Scientists from different STEM disciplines are also present in this community, which is actually mainly populated by scientists, not professional philosophers of science. As shown in Table 4, 24.7% of these authors are mainly active in the field of biology, followed by medicine, physics, mathematics and engineering. This result suggests that scientists from these STEM disciplines might also be the most likely to publish articles in philosophy of science journals. Bioethicists, mostly in medical ethics, form 12.9% of the community, while social scientists, mostly from the fields of psychology and science studies, only form 5.7% of the community. Interestingly, the community also includes 9.4% of philosophers mainly active in subfields of philosophy other than philosophy of science, and 7.1% of philosophers of science whose papers are mainly cited in STEM fields.

Appendix A -Top-10 journals citing philosophy of science and top-5 cited philosophy of science journals (by discipline)


Nathanael Jarrasse
email: jarrasse@isir.upmc.fr

Markus Kuhne

Nick Roach
email: n.roach@imperial.ac.uk

Asif Hussain
email: asif.hussain09@imperial.ac.uk

Sivakumar Balasubramanian

Etienne Burdet
email: e.burdet@imperial.ac.uk

Agnès Roby-Brami
email: roby-brami@isir.upmc.fr

Nathanaël Jarrassé

Markus Kühne

Analysis of grasping strategies and function in hemiparetic patients using an instrumented object

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

I. INTRODUCTION

The impairment of grasping ability is very frequent in stroke survivors: more than half of them remain with an impairment of the upper extremity largely contributing to the disability in the daily life function [START_REF] Jorgensen | Outcome and time course of recovery in stroke. part i: Outcome. the copenhagen stroke study[END_REF] and to the limitation of social participation. However, despite the importance of this question and the large number of rehabilitation techniques recently proposed for the rehabilitation of reaching to grasp and grasping [START_REF] Krakauer | Motor learning: its relevance to stroke recovery and neurorehabilitation[END_REF], there still lacks comprehensive studies on grasping function and manipulation after stroke. In addition, there is also a lack of pertinent methods for the assesment of grasping function in hemiparetic patients. Most of the existing methods are either based on the measure of elementary impairments (e.g. pinch force measured by a dynamometer) or on functional tests quantified by rough scores summarizing the success/failure of the attempts to grasp a battery of objects [START_REF] Wolf | Assessing motor function test as outcome measure for research in patients after stroke[END_REF]. The existing methods do not allow analyzing precisely neither the determinants of complex impairments induced by stroke nor the mechanisms of their consequences on function. In particular, they miss the ability of the patients to develop alternative grasping strategies if the precision grip is impaired [START_REF] Bensmail | Botulinum toxin to treat upper-limb spasticity in hemiparetic patients: grasp strategies and kinematics of reach-to-grasp movements[END_REF].

We have developed an instrumented object in order to bridge the gap between elementary measures and functional scores for a better therapy and follow-up of stroke patients. The first practical aim was to afford quantitative measures able to be applied to a large range of upper-extremity function, i.e. from the detection of slight impairments to the evaluation of gross grasping disability. The second aim was that the method should be usable in clinics, and thus easy to use, robust and low-cost. In addition, our aim was to provide a generic tool to analyze hand function in healthy subjects. This article first describes the technical solution used for the mechanical design and instrumentation of this device. Then, preliminary results obtained during experiments with healthy subjects and brain-injured patients are presented in order to put forward some pertinent variables that could be used for fundamental investigation about grasping and, looking further ahead, for clinical assessment.

II. STATE OF THE ART FOR THE QUANTITATIVE ANALYSIS OF PREHENSION

A. Precision grip

In healthy subjects, many existing studies are devoted to precision grip. The precision grip as defined by Napier in his pioneering study [START_REF] Napier | The prehensile movements of the human hand. The Journal of bone and joint surgery[END_REF] is a multipulpar opposition between fingers and thumb for precision tasks. However experimental studies were most often focused on the precision grip between the thumb and index, analysed thanks to an instrumented object measuring load force and grip force coordination during a lifting task. Extensive studies have largely demonstrated that grip force was tightly coupled to load force and that both grip and load force rates were both modulated in an anticipatory way as a function of object properties (size, shape, contact surface) [START_REF] Johansson | Coordinated isometric muscle commands adequately and erroneously programmed for the weight during lifting task with precision grip[END_REF], [START_REF] Flanagan | predictive mechanisms and object representations used in object manipulation[END_REF]. The maximum grip force is produced in an anticipatory way in order to remain slightly above the margin of security to avoid object slip. In addition, the regulation of grip force during the holding of the object is strongly dependant of tactile afferents from the skin of the finger pulp [START_REF] Johansson | Sensory-motor coordination during grasping and manipulative actions[END_REF]. Some studies [START_REF] Flanagan | Modulation of grip force with load force during point-to-point arm movements[END_REF], [START_REF] Hermsdorfer | Deficits of anticipatory grip force control after damage to peripheral and central sensorimotor systems[END_REF] showed that the dynamics of object displacement could also be anticipated as observed on the evolution of the grip force signal.

B. Complex hand-object interactions

More complex hand-object interactions have been studied with specific research-oriented instrumentation. The extensive studies of tri-digit [START_REF] Winges | Multidigit control of contact forces during rotation of a hand-held object[END_REF] or multifinger [START_REF] Zatsiorsky | Multifinger prehension: an overview[END_REF] dynamic coordination use specific instrumented objects that needed placing precisely each finger on a force sensor. These studies demonstrated a sharing pattern of forces between fingers, based on anatomical constraints, and finely regulated synergies in order to generate forces and moments on the object as a function of task instruction. However, these methods are not usable in patients who cannot precisely position the tip of their fingers on sensors. Other studies on the coordination of hand and fingers for grasping an object recorded the multiple joint rotations during reaching and grasping thanks to an instrumented glove or to optic methods [START_REF] Santello | Postural hand synergies for tool use[END_REF]. These analyses showed that the complex kinematic of hand and fingers could be explained by additive synergies combined as a function of the object shape and anticipated during the reaching phase. These complex methods are not used in clinical practise.

C. Hemiparetic patients

There are several but relatively few analysis of grasping function in hemiparetic patients in grasping [START_REF] Lindberg | Affected and unaffected quantitative aspects of grip force control in hemiparetic patients after stroke[END_REF] or a grip to lift task [START_REF] Nowak | Deficits of predictive grip force control during object manipulation in acute stroke[END_REF]. They show a longer time before lift-off, impairments of grip-lift coordination with excessive grasping forces. The analysis of power grasp is generally limited to the measure of force with a Jamar Dynamometer. Nowak and Hermsdorfer [START_REF] Nowak | Objective evaluation of manual performance deficits in neurological movement disorders[END_REF] developed an autonomous instrumented object which has been use to document grasping in several pathological conditions. However this instrumented object was limited to 2 forces measurement: the grip force and the vertical load force. Presently, there is no device that can be used in clinics to detect more complex manipulation difficulties, nor methods that can be used for the discrimination and analysis of alternative strategies using the whole hand for grasping.

III. METHODS

A. Instrumented object

The apparatus used in this study is an addition to the existing set of instrumented objects for rehabilitation and assessments presented previously in [START_REF] Hussain | A modular sensor-based system for the rehabilitation and assessment of manipulation[END_REF]. It has been developed by the Human Robotics Group of Imperial College London. It comes in the form of a parallelepiped (see Fig. 1) whose dimensions are 108 mm length, 70 mm width and 40 mm depth and whose weight is 340 grams.

The object uses an embedded electronic board MIMATE (Multimodal Interactive Motor Assessment and Training Environment, see [START_REF] Roach | Learning to design rehabilitation devices through the h-card course: Project-based learning of rehabilitation technology design[END_REF] for more informations). This object measures its accelerations, rotational velocities and orientations (thanks to an IMU) along with the value of distinct forces applied normally to its six surfaces (up to 20 N). It then transmits these values wirelessly through bluetooth to a distant computer, at a 100Hz frequency approximatively.

B. Subjects

Five healthy subjects (22-28 years old, 2 women) volunteered to participate to this preliminary study, as well as six hemiparetic patients (34-62 years old, 4 women) from the department of Physical Medicine and rehabilitation of the Raymond Poincaré Hospital in Garches, France. The patient's clinical and functional data are summarised in Table I. Functional activity of patients was evaluated by the Frenchay Arm Test (FAT) [START_REF] Wade | Measurement in neurological rehabilitation[END_REF]. This tests gives results from 0 to 5 since it scores five prototypal gestures as possible [START_REF] Jorgensen | Outcome and time course of recovery in stroke. part i: Outcome. the copenhagen stroke study[END_REF] or not (0). All subjects were naive to the system and experiments.

C. Installation and tasks

The participants seated in front of a table on which the object was put in front of his/her midline. Seven tasks were studied (see Fig. 1), with three repetitions per task. The first five tasks were grip-lift tasks: the instruction was to lift the object a few centimeters above the table to hold it a few second and to put it back on the table in the following conditions. • Task 1, Precision grip: along the lateral sides of the object (arrows on figure).

• Task 2, Slippery precision grip: same as previous, but with a cotton glove.

• Task 3, Whole hand grasping without thumb: between the palm and the four fingers around the object.

• Task 4, Whole hand grasping with thumb: same as previous, but with the thumb on the top side.

• Task 5, Global grasping from the top of the object.

The two last tasks were more complex manipulation tasks.

• Manipulation 1, Tilting: the instruction was to lift the object and to put it back on the table its top below (rotation around an horizontal axis). The instruction did not precise if the object could slide between the fingers.

• Manipulation 2, Handling : the instruction was to lift the object and to rotate it around its main axis with the fingers.

D. Analysis of the results

The present analysis is limited to the force measured by the load-cells and kinematics and dynamics data computed thanks to the embedded IMU. These data were interpolated according to the time stamp to obtain vectors with 0.001s time samples (100Hz). The first step was to detect the times of interest by an automatic analysis visually checked (Fig. 2). The onset (t r ) and end (t f ) of grasping were determined with a threshold of 0.2 N for the sum of the 6 forces. The force sensor of the bottom indicates the loading/unloading of the object on the table. The object is lift-off when the value is -3.4 N (offset weight of the object). The timing was measured as the time when the bottom force reached (lifting t l ) or quitted (deposit t d ) the plateau, with a threshold of 0.1 N. The time of the peak force (t p ) was measured between t l and the plateau and the values of force data at this time noted. Positive force peaks measured by the bottom sensor were also detected and evaluated. The means of the three repetitions were computed, as well as the means over the different subjects of the experiment.

IV. ANALYSIS OF GRASPING COORDINATION IN HEALTHY SUBJECTS

A. Grip-lift tasks 1) Precision grip: Figure 2 shows typical example of lift with a precision grip. During precision grip, the force increased Fig. 2. Example force data during precision grip (task 1). Time scale 10 ms. Times: onset of movement t r , lifting (t l ), peak force (t p ) deposit (t d ) and end of movement (t f ). Each trace is one trial. The force sensors are indicated in legend.

regularly on both lateral sensors until lift at t l (492 ± 48 ms after t r ). The mean lateral forces were respectively 7.9 ± 0.9 and 7.2 ± 0.9 at t l and continued to increase to reach 8 ± 0.96 and 7.8 ± 0.9 at t p (637 ± 63 ms after t r ). In parallel the force on the bottom sensor decreased. After lift-off the force on the lateral sensors decreased to reach a plateau, (sometimes followed by a later and smaller peak) until the time of deposit t d , when they were 6.5 ± 1 and 6.14 ± 0.9. Then, the force of the lateral sensor decreased and that of the bottom sensor increased during 442 ± 57 ms until t f . The precision grip task with a glove gave a similar picture with much higher levels of force (reached 15.10 ± 1.06 and 14.86 ± 1.05) that remained high during the whole lift-off period. The timing of lifting was slower (t l was attained 652 ± 98 ms and t p 866 ± 127 ms after t r , i.e. around 200 ms more than without glove) but the deposit was performed faster (in 280 ± 47 ms).

2) Whole hand grasping: During the task with whole hand grasping, the evolution followed a similar picture, except that the force increased also in a greater number of sensors and reached a greater level. Figure 3 shows typical example of lift with a power grasp. The timing of lifting with the whole hand (task 3) was similar to that of precision grip (t l was attained 407 ± 54 ms and t p 647 ± 149 ms after t r ). In contrast, the timing for the tasks 4 and 5 was markedly slower (t l was attainted in respectively 872 ± 87 ms and 802 ± 108 ms and t p in respectively 1118 ± 154 ms and 930 ± 115 ms). The whole hand grasping tasks were also characterized by a positive peak on the bottom sensor that we called 'bump' indicating that the participant pressed downward on the object. For task 3, this bump was short (120 ± 28 ms) small (0.7 ± 0.1) and inconstant. In contrast, it was greater and longer for tasks 4 and 5 (respectively 2.6 ± 0.2 and 2.2 ± 0.3 attained at 325 ± 45 ms and 287.3 ± 51 ms after t r ).

3) Grasp-lift coordination:

The co-variation between the bottom force signal indicating the loading/unloading of the Fig. 4. Examples of three strategies for the tilting task in healthy subjects: Fig. 4.A shows tilting by hand rotation with constant grasping force, Fig. 4.B rotation through pushing on the rear face and relaxation of grasping force, and finally Fig. 4.C shows tilting started before lifting strategy. Same legend as Figure 2.

object on the table and the grasping forces was studied during lift-off (between t r and t l ) and deposit (between t d and t f ).

Figure 5 shows the results in a representative subject. The diagrams shows that, during precision grip, the grasping force for lifting (left) is tightly related to the loading of the object (negative values on the force bottom sensor). This is also observed for the deposit period (right). Precision grip performed with the glove gave similar results with higher levels of force. In contrast, grasping with the whole hand was more irregular: the grasping force increase while the object is pushed on the table before lifting (indicated by positive values on the force bottom sensor).

B. Manipulation tasks

1) Tilting: During the tilting task, several strategies were observed. In some cases, the participant tilted the object by rotating the hand, without relaxing his grasping strength (Fig. 4A). In contrast, the tilt was obtained by pushing on the rear face, inducing a brisk rotation while relaxing the grasping strength (e.g. in Fig. 4C where the tilt begins even before lifting). In other intermediate cases (Fig. 4B), the object was tilted in several steps each accompanied by a decrease of the grasping strength.

2) Handling: The task to turn the object around its main axis imposes complex sequential movement of the fingers. According to the constraint of this task, all the subjects made the rotation in several steps. Figure 6 shows a representative example, each rotation step illustrated by a grey zone.

After lifting the object, the first rotation step (A) was obtained by passing the grasping strength from the lateral to the front sensors. The second step (B) was made without change of the main contact face of the box. The main rotation occurred in (C) with rapid alternation of force contact on the lateral and front-rear faces. After the last rotation, the object is returned to its original orientation and grasping pattern then released on the table. Note that during all transitions, the object is maintained by the bottom face (the offset value of the sensor is reduced). A similar picture was obtained in most of the trials.

V. DIVERSITY OF GRASPING IMPAIRMENT AND STRATEGIES OBSERVED IN HEMIPARETIC PATIENTS.

We present here some preliminary and simple analysis of data gathered with 4 brain-injured hemiparetic patients from 35 to 62 years old (excluding subject 4 who had also hand orthopedic problems, and subject 2 who was only able to complete task 1 and 2 because of some technical problems). Our goal here is to define a certain number of indexes or dependant variables that could qualify patient recovery state and assesses his/her performances.

A. Grasping forces analysis

Figure 7 shows that the sequence of events for precision grip (task 1) in a patient with a moderate disorder is similar to that observed in healthy subjects. However, there are several important differences: the onset of lifting is slow and irregular with a "bump" on the object characterized by an increase of the force signal on the bottom sensor. The force signal from the lateral grasped sides increase irregularly before attaining the peak force, then do not exhibit a regular plateau as in healthy subjects but rather a sharp and irregular decrease with oscillations. The deposit is irregular with a vibration.

1) Grasping force levels and variations:

We first quantified the amount of grasping force required to lift the object. We considered the data from Tasks 1 and 2 (precision grip with and without a glove) and 3 (power grasping without the use of the thumb) and made some comparison between results obtained with the population of healthy subjects and 4 poststroke hemiparetic chronic patients.

For this purpose we therefore only considered forces applied on the the functional faces of the object during lift-off. Mean force levels and standard deviations are shown in the Figure 8. We observe that the average grasping force level is higher with patients than with healthy subjects, with an average increase of 47.18% for tasks 1 and 3. Results from task 2 (with the glove) have to be considered carefully because of the load-cell saturation that occurred around 17 N : one can imagine that similar value of force increase would have been observed if the range of the load-cells was larger, instead of the presently measured 9.6% of increase. The force STD values that are increasing by 177%, 49.5% and 36% in tasks 1, 2 and 3 respectively may illustrate the large variations of the level of grasping force applied by patients (important decrease) during lift-off. Fig. 8. Grasping force level (and standard deviation) on functional surfaces during tasks 1, 2 (precision grip with and without glove) and 3 (power grip without thumb) calculated for when the object is lifted up and averaged over 5 healthy subjects and 4 patients, and the 3 trials.

2) Grasping force repartition: In order to study the alteration of the grasping strategies of hemiparetic patients, rather than problems of local force generation or control, we used a "radar' representation of the means of force applied on each of the six surfaces of the iBox during lift-off. Grasping strategy can indeed be seen as the repartition of forces among the different surfaces of the object, i.e. the shape of the hexagon on a radar plot, whereas the scaling of this hexagon would give informations on force level variations. As an example, Figure 9 shows the force repartition for task 5 (grasping from above) for healthy and patients. Fig. 9. Mean force repartition (averaged during the time when the object is lifted) for task 5 (grasping from above) for each subject and patient (averaged over the 3 trials).

Apart subject 2, healthy subjects seem to use similar grasping strategies with some scaling variations (force level variations). In comparison, patients appear to use very different force repartition to complete the task. This is particularly easy to spot with task 5 (grasping from above) that could be performed with different force repartitions, contrary to other experiments (like precision grip or power grasp) in which strategy variability is more constrained by the task instructions.

B. Grasping dynamics

1) Grasping force oscillations: An interesting characteristic of patient sensorimotor pathology can also be extracted from the grasping force profile: oscillations be observed in the force application that seems to be correlated with some position oscillations of the grasped and held object (measured through the vertical accelerations of the object). A typical example (patient 6 performing task 1, precision grip) can be seen in Figure 10, in which one 2Hz oscillation frequency can be identified on the amplitude spectrum of the acceleration obtained with a simple Fast Fourier Transform (FFT). 2) Smoothness of the movement: The Spectral Arc Length (SAL) smoothness metric developed in [START_REF] Balasubramanian | A robust and sensitive metric for quantifying movement smoothness[END_REF] was applied to angular velocity of the subtasks in each trial. SAL is a robust, dimensionless measure of the length, and thus the complexity, of a frequency spectrum curve over the bandwidth of interest. For this study, the upper frequency bound was set to 20 Hz as this is typically sufficient to capture normal and abnormal human motions [START_REF] Balasubramanian | A robust and sensitive metric for quantifying movement smoothness[END_REF]. Fig. 11 presents the smoothness value of Fig. 11. Measure of smoothness (spectral arc length) averaged over subjects (4 patients and 5 healthy subjects) and trials (3) for the grasping and lifting tasks (task 1-5) the vertical velocities during tasks 1 to 5. Angular velocities were calculated by numerical differentiation on the vertical acceleration, to which was subtracted the gravity acceleration, thanks to the reconstruction of the object posture made from the information from the 9 DoF IMU.

A clear decrease of the smoothness can be observed with patients, ranging from 9% (task 5) up to 65% (task 2).

C. Manipulation tasks 1) Tilting task: Four patients succeeded in performing the tilting task (manipulation 1).

Figure 12 illustrates two examples. In Fig. 12.A, after an initial the patient turns the object with several partial releases of the grasping strength, exhibiting a strategy similar to that of healthy subject illustrated Fig. 4.B. The patient illustrated in Fig. 12.B is more irregular. Tilting is performed after a first phase of tilting in the opposite direction and the repartition of force exceeds the two lateral sensors. Fig. 12. Two examples of three strategies for the tilting task in healthy subjects: Fig. 12.A shows a strategy with several partial releases whereas Fig. 12.B is similar to healthy subject strategy. Same legend as Figure 2.

2) Handling task: Despite repeated attempts, most of the patients did not succeed in the handling task (manipulation 2). This shows that they were not able to make the individuated finger movements needed to turn the object within the hand. Only one patient succeeded (patient 6), but she did not use the 5th finger to support the weight of the object in a vertical position. Rather, she held the object more horizontally in such a way that its weight was mostly supported by the palm.

VI. DISCUSSION

The preliminary results obtained with the iBox open several tracks for further research. Even if it does not provide the positioning and the kinematics of each finger over the surfaces, it gives access to reliable force, kinematics and dynamics variables and can enable experimenters to finely characterise grasping strategies in healthy subjects and in physically or neurologically affected individuals.

The grasp-lift coordination of precision grip which has been largely studied previously is important since it highlights the anticipatory control of grip force as a function of object properties before lifting. We show here that the data from the iBox can be used to further study this anticipatory control. Moreover, the iBox gives access to additional quantitative (force and motion) data during more complex hand-object interaction such as grasping with or without the thumb and other manipulation tasks. Unimanual manipulation of an object is a particularly complex and difficult task since the coordinated fingers must simultaneously move the object and ensure its equilibrium. Although these tasks typically demonstrate human dexterity and are the topic of many recent studies in humanoid and anthropomorphic robotics (see e.g. [START_REF] Bicchi | Hands for dexterous manipulation and robust grasping: A difficult road toward simplicity[END_REF]), they have paradoxically been little studied quantitatively in humans [START_REF] Zatsiorsky | Multifinger prehension: an overview[END_REF].

In this paper we examined two different manipulation tasks. We observed that for tilting task the healthy subjects chose three different strategies, probably differing according to usual motor habits, avoiding or not uncomfortable hand postures [START_REF] Rosenbaum | Cognition, action, and object manipulation[END_REF] at the risk of object slipping, or to different understandings of the task. This illustrates the great variability of human strategies during object/tool manipulation. The handling task was still more demanding but all the healthy subjects succeeded. The force data highlighted interesting phases of force production on different sides of the object alternating with the holding of the object by the bottom face, presumably thanks to the fifth finger. These strategies obviously need further studies to be characterised and studied in various sensorimotor or environmental contexts.

We also demonstrated in this paper that the Box device can be used for the physiopathological analysis of motor performance in patients suffering from sensorimotor disorders. All the patients succeeded in the grip to lift tasks, even the most impaired with associated orthopaedic problems. The presented data show that the patients trying to make precision grips exhibit several atypical features relative to healthy subjects: they apply excessive grasping force, push downward before grasping, the grasp to lift phase is longer and more irregular with eventually some slips, the distribution of force is spread over more than two opposite sides, the time evolution of the force signal is irregular with sharp decrease or irregularities and oscillations, and motion smoothness is altered.

The results of patients trying to grasp with precision grip are roughly similar to the whole-hand grasping performed by healthy subjects (tasks 3-5). Further studies are needed with quantitative comparison in order to precise whether grasping in hemiparetic patients can be explained by impairments of precision grip, replaced by whole hand grasping, or if both precision grip and whole hand grasping are really impaired. The application of excessive forces (more than is required to complete the lifting tasks) may correspond to two different problems: a motor control problem with which the patient is not able to finely tune his force production; and a sensory problem, with which he/she is not able to perceive the amount of force applied, and regulate it thanks to a feedback loop. Observed sharp decrease of force after the first peak is con-sistent with a loss of perception that could bring patients to apply more force than is required and then, thanks to visual feedback (object is not slipping), to minimise the grasping force. According to these preliminary results we also recently updated the design of the iBox, in order to measure grasping forces up to 20 N.

The periodic irregularities during the holding of the object may have several physiopathological causes such as tremor and spasticity, which can be inferred from a frequency analysis [START_REF] Machowska-Majchrzak | Analysis of selected parameters of tremor recorded by a biaxial accelerometer in patients with parkinsonian tremor, essential tremor and cerebellar tremor[END_REF]. In the patient with mid-brain stroke whose data are shown in Fig. 10, the 2Hz frequency suggests a cerebellar tremor rather than spasticity as initially suspected (clonus has a higher frequency around 7 Hz). Furthermore, numerous information can be extracted from the repartition of the force on the sensors embedded in the Box object. The grasping strategies can be be characterised through the analysis of the force repartition among the object faces beyond a generic analysis of the force levels measured by load cells. Accordingly, future experiments may let the patient grasp the object as they spontaneously prefer. Presumably, this would lead to a variety of hand-object force repartition that could be categorised by an automated pattern analysis. This kind of analysis could be also used to quantify the transitions between complex object manipulation phases in healthy and impaired subjects.

Finally, the iBox seems to be suitable for the clinical assessment of grasping, and the various tasks proposed with the iBox may encompass a variety of functional levels. Patients with a severe motor impairment can take the object with gross whole hand grasping while patients with a mild disorder may exhibit specific impairments when performing complex manipulation tasks. The case studies of a few subjects presented in this paper illustrated the capabilities of iBox to characterise sensorimotor impairments and enabled us to develop suitable metrics, which may complement assessment using standard clinical scales. Nevertheless, some more rigorous experimental campaigns with larger populations of patients and subjects (also with similar age range) along with statistical analysis will now be conducted in order to establish proper comparisons between sensorimotor strategies.

Fig. 1 .

 1 Fig. 1. Illustrations of the 5 grasping tasks and the 2 manipulation tasks.

Fig. 3 .

 3 Fig. 3. Example of force data during power grasp with thumb (task 5) in a representative healthy subject. The force sensors are indicated in legend.

Fig. 5 .

 5 Fig.5. Coordination of grasping and bottom forces during lifting between t r and t l (left) and deposit between t d and t f (right) (see Fig.2for time events placement). The diagram shows the value of the left sensor for precision grip and of the front sensor for whole hand grasping as a function of the value of the bottom sensor. Each line represents one repetition in one representative subject (3).

Fig. 6 .

 6 Fig. 6. Example of handling task in healthy subjects. Same legend as Figure 2.

Fig. 7 .

 7 Fig. 7. Example of force data during precision grip performed by an hemiparetic patient.

Fig. 10 .

 10 Fig. 10. Task 1 (precision grip) performed by a patient: A. Grasping forces and norm of the acceleration of the object. B. Amplitude spectrum of the acceleration during the task.

TABLE I .

 I

			CLINICAL CHARACTERISTICS OF PATIENTS
	ID	Cause	Pathology	FAT	Exp. performed	Remarks
	1	Stroke	Mild left hemiparesis	3	Task 1-7, Manip. 1-2	Manip.2 unsuccessful
	2	Stroke	Moderate right hemiparesis, aphasia	4	Task 1-2	Technical problem
	3	Stroke	Mild right hemiparesis	4	Task 1-5, Manip. 1-2	Thumb use for task 3. Manip.2 unsuccessful
	4	Traumatic brain injury	Severe paresis, hand orthopedic condition	0	Task 1-3	Grasp between thumb and forearm
	5	Stroke	Mild right hemiparesis, spasticity, hypoesthesia	3	Task 1,3-5, Manip. 1-2	Manip 2 unsuccessful
	6	Angiome at age 7, Mid brain Stroke	Spasticity, syncinesia, cerebellar syndrom	5	Task 1-5, Manip. 1-2	-

June 24-26, 2013 Seattle, Washington USA

ACKNOWLEDGMENT We acknowledge Pr. Bussel and the team of occupational therapists from the department of neurological rehabilitation, Hôpital Raymond Poincaré, for their constructive suggestions and assistance for the experiments with the patients. This work has been partly supported by UK-UKIERI IND/CONT/E/1172/182, the FP7-PEOPLE-2012-ITN project No 317488: CONTEST and by a Short Term Scientific Mission funding from the COST Action TD1006 European Network on Robotics for NeuroRehabilitation.