Shuji Zhao
email: zhao@ensea.fr

Frédéric Precioso
email: precioso@ensea.fr

Matthieu Cord
email: matthieu.cord@lip6.fr

SPATIO-TEMPORAL TUBE KERNEL FOR ACTOR RETRIEVAL *

Keywords: Face recognition, Video object, Actor retrieval, Kernel on bags, Spatio-Temporal Tube Kernel

This paper presents an actor video retrieval system based on face video-tubes extraction and representation with sets of temporally coherent features. Visual features, SIFT points, are tracked along a video shot, resulting in sets of feature point chains (spatio-temporal tubes). These tubes are then classified and retrieved using a kernel-based SVM learning framework for actor retrieval in a movie. In this paper, we present optimized feature tubes, we extend our feature representation with spatial location of SIFT points and we describe the new Spatio-Temporal Tube Kernel (STTK) of our contentbased retrieval system. Our approach has been tested on a real movie and proved to be faster and more robust for actor retrieval task.

INTRODUCTION

Content-Based Image Retrieval (CBIR) has attracted a lot of research interest in recent years. Significant progress has been achieved in the performance of object categorization and retrieval systems in the domain of multimedia retrieval. In this paper we focus on video and retrieval of actors in movies.

Recent actor retrieval systems are following quite similar processing chain:

• Face detection: this step is based on Viola & Jones detector [START_REF] Viola | Rapid object detection using a boosted cascade of simple features[END_REF], or derived versions, in most works. • Feature extraction: face segmentation resulting in a face video tube then local visual feature extraction from this video tube. • Feature representation: one feature vector, a set of vectors or more complex spatial structures to represent video tubes. • Classification: methods based on projections onto a visual dictionary or based on machine learning techniques.

Fig. 1 shows our actor retrieval framework. Instead of considering precise facial features (eye, mouth, etc.) as in related works [START_REF] Sivic | Person spotting: video shot retrieval for face sets[END_REF][3], we want to avoid introducing prior knowledge and thus focus on more generic feature which make our system adaptable to other semantic video objects, eg. cars. Furthermore, kernel-based methods allow us to exploit recent machine learning techniques as active learning.

In [START_REF] Zhao | Actor retrieval system based on kernels on bags of bags[END_REF] a video object is represented by a set of temporally consistent chains of local descriptors SIFT (a bag of bags of features) without considering the position of each chain. Integration of spatial information became recently more important in CBIR research works as illustrated by Fergus et al. [START_REF] Fergus | A sparse object category model for efficient learning and exhaustive recognition[END_REF] constellation model, Felzenszwalb et al. [START_REF] Felzenszwalb | A discriminatively trained, multiscale, deformable part model[END_REF] pictorial model or Heisele et al. [START_REF] Heisele | Categorization by learning and combining object parts[END_REF] object parts. In kernel-based framework also propositions have been made with Pyramid kernel [START_REF] Lazebnik | Beyond bags of features: Spatial pyramid matching for recognizing natural scene categories[END_REF] or kernel on pairs of regions [START_REF] Gosselin | Kernel on bags for multi-object database retrieval[END_REF]. In this paper, we design a new kernel in order to integrate spatial information in our spatiotemporal tubes and provide optimizations to tube extraction.

TUBE EXTRACTION OPTIMIZATION

In [START_REF] Zhao | Actor retrieval system based on kernels on bags of bags[END_REF] the faces of actors are detected by Viola & Jones detector [START_REF] Viola | Rapid object detection using a boosted cascade of simple features[END_REF] and segmented by ellipses which approximate face contours. A video object is then defined by a video tube made of face regions in the successive frames of a shot. From a face video tube, we extract a set of temporally consistent chains of local descriptors SIFT, that we call a spatio-temporal (feature) tube.

One of the main issues with considering such feature tube representation lies in the size of data to process. In this paper, we propose three improvements to enrich while reducing our representation of the visual features: (a) parameter optimization of descriptor SIFT to make it adaptive to the data; (b) intra-tube chains tracking to obtain more consistent and more compact chains for each video tube and thus reduce computational complexity; (c) tubes with Spatial Position.

Adaptive parameter of SIFT descriptor

For the extraction of descriptor SIFT, we found out that the number of SIFT points extracted is quite sensitive to the scale of the "first octave" (see [START_REF] Lowe | Distinctive image features from scale-invariant keypoints[END_REF]). We optimize the scale of the first octave by multiplying the scale of face image by a coefficient λ = 2 n (n = . . . -2, -1, 0, 1, 2 . . .). n is selected to set the scale of the first octave in a certain interval (50 to 100 pixels in width), hence we can extract SIFT points even if the image is small and reduce the number of irrelevant points extracted in big images.

Intra-Tube Chain Tracking

In order to improve the consistency of chains and reducing the numbers of chains in a tube, we propose to link together several short chains into one long chain (Fig. 2). The intra-Fig. 2. Intra-tube chain tracking (solid lines: consistent chains, dash lines: noise, green lines: link of two short chains) tube tracking is achieved by matching two short chains if their average SIFT vectors are similar enough (L 2 distance below 200 in our case) and average normalized positions of the two chains close enough (below 0.2 in our work). See Fig. 4 for the definition of normalized positions. Thus, the chains of descriptors SIFT become more consistent and the number of chains per tube is highly reduced. See Fig. 3 (a)(b) for two examples of intra-tube tracking. To evaluate the consistency of the SIFT descriptor along a chain, we show temporal stability of some long chains of SIFT with the images of Fig. 3 (c)(d)(e). One line in any of these images represent a 128dimensional SIFT vector while in column you can see the variation of one of these 128 values along its tracked chain.

Tubes with Spatial Position

We introduce the position of each SIFT chain in the representation of the tube, so that we strengthen the comparison between same parts of face. The position of a chain is defined by the mean normalized position of SIFT points (x, y) in the chain, see Fig. 4.

SPATIO-TEMPORAL TUBE KERNEL (STTK)

Kernel on Tubes (Without Position)

Let us denote T i a tube, C ri a chain and SIF T mri a SIFT vectors. Using set formulation: T i = {C 1i , . . . , C ki } and C ri = {SIF T 1ri , . . . , SIF T pri }, we have designed our major kernel on tubes in [START_REF] Zhao | Actor retrieval system based on kernels on bags of bags[END_REF] by weighted "power-kernel" [START_REF] Gosselin | Kernel on bags for multi-object database retrieval[END_REF]:

K pow (T i , T j ) = r s |C ri | |T i | |C sj | |T j | k(C ri , C sj ) q 1 q
(1) where |C ri | represents the size (number of frames) of the chain C ri ; |T i | represents the size of the tube T i ; k(C ri , C sj ) is the minor kernel on chains, a Gaussian χ 2 kernel:

k(C ri , C sj ) = exp - 1 2σ 2 1 C ri -C sj 2 C ri + C sj (2)

Spatio-Temporal Tube Kernel (STTK)

The kernel of Eq.( 1) defines a similarity function considering exhaustively all the chains of tube T i with all the chains of tube T j , wherever are their positions on the face. That is to say, we compare not only the left eye chain of tube T i and left eye chain of tube T j , but also left eye chain of tube T i and mouth chain of tube T j . In this paper, we redefine the minor kernel on chains by adding a term taking into account the relative positions of two chains:

(C ri , sj ) = ri , C sj )e - (x ri -x sj ) 2 +(y ri -y sj ) 2 2σ 2 (3)
where ri C sj ) is minor in Eq.( 1); (x ri , y ri ) is the mean position of SIFT points in chain C ri of tube T i . Furthermore, we propose to improve the of lengthy chains, as well as lengthy tubes, by modifying the weights on chains:

|C ri |/|T i | into |C ri |/ |T i |.
Hence, the major kernel on tubes becomes:

K pow (T i , T j ) = r s |C ri | |T i | |C sj | |T j | k (C ri , C sj ) q 1 q
(4) With this new kernel on tubes, we improve the importance of the comparison between two chains approximately at the same position, eg. left eye chain of tube T i and left eye chain of tube T j . For the comparison between two chains at much different positions, eg. left eye chain of tube T i and mouth chain of tube T j , the weight is reduced. Thus, the importance of this matching in the evaluation of the similarity is also lowered.

EXPERIMENTS

We have tested our actor retrieval framework on the same database of [START_REF] Zhao | Actor retrieval system based on kernels on bags of bags[END_REF], 200 faces tubes of 11 actors from the movie "L'esquive". The mean number of faces in a tube is 54. These 200 tubes have been used as input to the interactive machine learning system of RETIN [START_REF] Gosselin | Active learning methods for interactive image retrieval[END_REF], with SVM core using our weighted kernel on tubes. The interactive retrieval process with RETIN is presented in Fig. 6. We have evaluated the retrieval precision for 3 actors from the database and proved the efficiency both in reducing the calculate time and in improvement of precision comparing with the work of [START_REF] Zhao | Actor retrieval system based on kernels on bags of bags[END_REF].

Optimized Feature Extraction

From each of the 200 tubes, we have extracted the visual features step by step: (a) Extraction of descriptors SIFT for each image. We have optimized the parameters of SIFT to reduce the number of chains for each tube. The mean number of SIFT chains in a tube is reduced from an average of 169 (result of [START_REF] Zhao | Actor retrieval system based on kernels on bags of bags[END_REF]) to an average of 64; (b) Intra-tube chain tracking. This enable us to get more consistent and more compact chains of descriptors SIFT. The average number of SIFT chains in a tube is then reduced again from 64 to 49.

For comparing a tube of n chains with another tube of m chains, the number of comparisons in our kernel is n × m (see Eq.4). Thus, with (a) and (b), the new system is about 169 49 2 ≈ 12 times faster than our previous system. We have evaluated the impact of these modification on visual feature extraction. The results are, if not identical as previous ones, even a little better thanks to the reduction of noise by removing small chains, see Fig. 5 for the comparison of MAP(Mean Average Precision) for one actor.

Spatio-Temporal Tube Kernel (STTK) Evaluation

We have extracted not only tubes of SIFT vectors, but also the position of each SIFT location in face image. We then input these spatio-temporal tubes of SIFT vectors integrating spatial position, into the interactive kernel-based retrieval system RETIN [START_REF] Gosselin | Active learning methods for interactive image retrieval[END_REF], with our STTK kernel function (Eq.4). We have also tried to compare the distance between the positions of two chains before computing the kernel. We compare only pairs of chains which are not too far (d 2 < 0.2 in our experiments). We thus reduce again the of our algorithm.

We focus on results for a small training set (less than 10 examples). The MAP curves of retrieval of one actor (Lydia), see Fig. 7(a), and the MAP curves of retrieval averaged over three actors (Lydia, Crimon and Hanane), see Fig. 7(b), show that our STTK method is more efficient than a kernel on spatio-temporal tubes without integrating spatial information.

CONCLUSIONS

In this paper, we have presented a efficient actor retrieval system, which considered a face video tube as a video object. From a video tube we extracted a "tubes" of visual features as well as spatial location of features. The design of a new kernel embedding this spatial constraint has been proved to be more powerful for actor retrieval in a real movie. Next step will be to devise kernel functions, like Fischer kernels, from generative models as constellation model or pictorial model mentioned in the introduction.

Fig. 1 .

 1 Fig. 1. STTK-based actor retrieval system.

Fig. 4 .

 4 Fig. 4. Normalized position of SIFT point. Scale and orientation of the ellipse represent scale and orientation of the SIFT point.

Fig. 3 .

 3 Fig. 3. Intra-tube chains tracking. (a)(b) Example of two tubes, SIFT points along the same chain are in same color (the scale and orientation of ellipses represent the scale and orientation of SIFT). (c)(d)(e) Consistency of three SIFT chains of tube T1.

Fig. 6 .

 6 Fig.6. Results of our interactive actor retrieval system based on RETIN system, for the film "L'esquive", one image represents one tube: (a) Query initialization with one request; (b) First results: tubes ranked regarding the tubes similarities; (c) Second iteration with one more positive example(green squares) and two negative examples (red squares); (d) Results after 2 iterations.

Fig. 5 .

 5 Fig. 5. MAP(%) of kernel on tubes Kpow for short / long chains, q = 2, σ1 = 1.

Fig. 7 .

 7 Fig. 7. MAP(%) of kernel on tubes Kpow (without position) and K pow (with position), q = 2, σ1 = 1, σ2 = √ 0.05. (a) result for one actor (b) result averaged on 3 different actors


Jean-Jacques Girardot

Territorial Intelligence and Innovation for the Socio-Ecological Transition

Objective

This paper presents the main innovative aspects of the Catalyse method and of the concept of territorial intelligence, which are mobilized for the project new-Life "Cooperate and observe to achieve the socioecological transition in Europe".

European Network of TerritoriaI Intelligence

ENTI gathers research teams and territorial actors at designing, arguing, managing and assessing actions of sustainable development which improve the welfare of citizens and of territorial communities.

Catalyse, cooperative observation method

ENTI was initiated from 1990 through the dissemination of territorial observatories "Catalyse" in Europe in multi-sector partnerships cooperating at the inclusion of social declassed groups and at the sustainable development of vulnerable territories.

Territorial Intelligence concept

Territorial intelligence formalized the use of information technology and communication to catalyze the co-construction of multidisciplinary knowledge and knowledge across sectors and strengthen the effectiveness of concerted action for sustainable development.

Mobilize the individual projects

Develop collectives services, based on the needs of people -rather than overall skills of the actorsexpressed during the development of an individual project as part of an individualized monitoring.

Use information and communication technologies

Catalyse introduce the use of information and communication technology to share information and knowledge, analyze and act together, inform and mobilize the territorial community.

Multicriteria methods and spatial tools

Catalyse promoted of spatial and multi-criteria fundamental methods and spatial analysis tools to differentiate the needs of social groups and territorial responses

Territorial observation

The territorial observation is the toolto share information in a multidisciplinary, multisector and multiscalar. It should provide stakeholders and citizens with an equal and transparent access to information and knowledge, with monitoring tools to develop, manage and evaluate sustainable development actions.

Territorial intelligence innovations

Multidisciplinary knowledge

Territorial intelligence was suggested in order to advance the multidisciplinary knowledge that "enables to improve the understanding of the links between the socio-ecological transition and growth as well as the role of innovation.

Dynamic vision of territories

Territorial intelligence suggested dynamic vision of the territory, combining the potential of a geographic space and the capabilities of a community.

Involve communities and practitioners

As collective vision of the dynamics of the territories, territorial intelligence involved communities, stakeholders, and practitioners in the research, with a view to enhancing innovative development projects and better instruments for coordinated governance to allow territorial actors to elaborate, manage and evaluate projects of sustainable development.

Share, co-construct, cooperate

Sharing information between scientific disciplines, sectors and territorial scales is provided to co-construct knowledge and collaborative projects combining economic, social, environmental and cultural objectives of sustainable development.

Participatory territorial governance

Participatory governance allowing citizens and stakeholders to participate in decision making is also a requirement to draw up and implement together actions appropriate to local capacity and constraints, and to improve the welfare of all by reducing social, environmental and cultural local costs globalization.

Culture and education

The evolution of culture and education is still a favorable condition for accession and cooperation of citizens and territories in the socio-ecological transition

new-LiFE research project

The project "Cooperate and observe for a successful socio-ecological transition in Europe" suggested by ENTI, the European Network of territorial Intelligence, meets about topic "Europe moving towards a new path of economic growth and social development" of the 7 th

New-LiFE Hypothesis

research programme of the European Union.

new LiFE hypothesizes that a new development model based, not on a financial criterion and selfish behaviour, but on improving the welfare of each while ensuring a minimum of well being for all, is able to ensure the successful transition socio-ecological in Europe and worldwide , if it is based on cooperation and the territorial observation, if this model is driven by a plural design of innovation, if it is based on co-constructed knowledge across the territories and if it is animated by a truly participatory territorial governance.

Innovative research dimensions

• Well-being

• Socio-ecological transition • Combination of development objectives

Well-being

The policies of the European Union, which are oriented from a decade "into a sustainable knowledgebased economy" … "need to be reassessed and adapted to the new requirements of a transition to a socioecological model of development. The new "Europe 2020" agenda made to foster these new development and social well-being trajectories needs an accompanying research agenda."

Socio-ecological transition

"In order to succeed the socio-ecological transition" in a context of crisis characterized by many global challenges, the EU must adapt its policy framework and common rules "to strive for accelerated transformation of the financial, economic and environmental structures and policies as well as modernisation of social welfare and development of high quality standards of the environment."

Combining development objectives

new-LiFE also refer to activity "paths towards sustainable development", characterized at "combining economic, social and environmental objectives" and cultural ones, in Europe and worldwide.

  caENTI caENTI integrated a network of research teams and local players to harmonize at the European level the territorial intelligence tools, to study the basic methods and tools for generic analysis of the territories and analyze the principles of participatory governance of action research. Coordination action FP6 caENTI ENTI ENTI offers an ambition of international scientific exchanges and practices on local action for sustainable development, territorial observation and local governance for the combination of economic, social, environmental and cultural information on innovative local initiatives. Réseau européen d'Intelligence territoriale Catalyse innovations • Mobilize the individual projects to build concerted actions • Use information and communication technologies • Application of multicriteria methods and spatial tools • Territorial observation


Aliyah Morgenstern

The Self as Other: Selfwords and pronominal reversals in language acquisition

Introduction

Very early on, children can assimilate representations of themselves that adults verbally propose to them and eventually take them up in their own discourse. It is therefore particularly interesting to study self-reference as a "window to the child's emerging selfconcept " (Bates 1990, 165) constructed in and thanks to social interaction. In this paper, I focus on subject self-words and pronouns with their shifting reference (Jespersen 1922[START_REF] Jakobson | Essais de linguistique générale[END_REF][START_REF] Benveniste | La nature des pronoms[END_REF]). When we use the term 'subject', we can refer to four distinctive notions: 1) the grammatical subject, 2) the semantic subject, (the agent for example), 3) the topic, 4) the speaker. Referring to the self in the first person seems to be very complex at the theoretical level. The idea has founded an entire linguistic tradition after Emile Benveniste's famous writings about the ego (1966). We can therefore wonder how young children are able to join those four levels in a unique marker, in French 'je' ('I'). However, this acquisition process is not salient, or catastrophic in Thom's sense (1977). Parents do not remember the first day their child used 'I', whereas they will remember the first use of 'mummy', 'daddy', or striking linguistic phenomena. However, as we were doing research focused on French children's self-words, we noticed the use of 'tu' (you) and of 'il' (he) instead of 'je' (I) by some children for a short period [START_REF] Morgenstern | L'altérité dans l'identité: quand l'enfant parle de lui à la deuxième personne. "Identité(s)[END_REF]. This phenomenon is referred to in the literature as pronominal reversal. Despite the fact that it is a minor phenomenon, and quite rare, it does seem to play a significant role in the mastery of the pronominal system. It can help us understand how children deal with shifting reference and shed some light on the problems they encounter when they try to use formal, linguistic marks to convey the distinction between the self and the non-self. Moreover, pronominal reversal is frequently observed in language disorders, especially in autism [START_REF] Bettelheim | The empty fortress[END_REF]. The study of reversals as a normal development, even if infrequent, may therefore also contribute to the understanding of pathological language development.

Previous hypotheses on children's use of self-words will be discussed followed by theories about pronominal reversals. I will then present analyses of the data of two French little boys: Léonard who occasionally uses the third person instead of the first person for a short period, and Guillaume who, around the same age, sometimes uses the second person instead of the first person.

I. Children's selfwords

Between the ages of 18 and 30 months, various markers are used by French-and Englishspeaking children to refer to themselves [START_REF] Brigaudiot | Me found it, I find it. A la recherche de 'je' entre deux et trois ans. Faits de langues -la personne[END_REF][START_REF] Budwig | A developmental-functionalist approach to child language[END_REF][START_REF] Morgenstern | L'enfant apprenti-énonciateur. (L'auto-désignation chez l'enfant en français[END_REF][START_REF] Morgenstern | Un JE en construction. Ontogenèse de l'auto-désignation chez l'enfant[END_REF]:

-Ø form (null form), or absence of form. Speaking of oneself is implicit. The speaker relies on shared situation and background with the interlocutor. In that context, it would also be interesting to study Sign Languages because there is no need to mark the grammatical subject when it is the speaker and when there is no contrastive agency. The signer's body is the grammatical subject, thus when the signer and the grammatical subject coincide, there is no need for a grammatical marker.

-The use of the child's name, which is not correct in adult language and has been described as referring to the "social self" [START_REF] Bain | The self and other words of a child[END_REF][START_REF] Cooley | A study of the early use of self-words by a child[END_REF]).

-Another case, accusative in French ('moi'), but also the genitive in English ('my') [START_REF] Budwig | A developmental-functionalist approach to child language[END_REF], Morgenstern, 2003a).

-Another person, second or third person (Morgenstern 2003b).

Between two and a half and three, the use of je / I gets stabilized and the other markers tend to disappear in the subject function. At the same time, children stop having a strictly deictic use of language and manipulate different tenses, aspects, modalities [START_REF] Nelson | Monologue as the linguistic construction of self in time[END_REF]).

The following questions could therefore be raised:

-How could we account for the simultaneity of these forms for a determined period of time (in our data from 2;3 to 2;8)? -Are these forms used at random or do they have different values according to the context they are used in?

In previous work [START_REF] Morgenstern | L'enfant apprenti-énonciateur. (L'auto-désignation chez l'enfant en français[END_REF][START_REF] Morgenstern | Un JE en construction. Ontogenèse de l'auto-désignation chez l'enfant[END_REF], I assigned two main values to self-words produced in discourse by children between 18 months and 3 years old:

1) The referential value: it focuses on who does the action (there is a contrastive agency). For example the child says: "moi fait la photo"/ I'm the one who films (takes the picture), as he is trying to take the camera from my hands. The self-word is used in context with a contrastive value and is very marked with name and moi (similar to Budwig's "high transitivity" value 1989).

2) The modal/expressive value: the child under analysis expressed his desires, will, projects, points of view as in "veux zouer à la pâte à modeler" (I want to play with the clay). At first, the child used the null form, preverbal vowels and little by little, [Ø] became [y] then

[z] and finally, around three, je. These self-words can be seen as subjectivity indicators: the child considers the situation he is in, does not find it satisfactory and uses language to express what he would like to substitute for the reality he has before him [START_REF] Danon-Boileau | Getting Vygotskian about theory of mind: Mediation, dialogue, and the development of social understanding[END_REF]. He therefore produces utterances such as: "j'entends pas maman, tu peux mettre plus fort" (I can't hear Mum, could you make it louder?). But he will also give his opinion "je trouve qu'elle est jolie cette musique" (I like this music).

I also found a difference between the use of self-words in discourse and in narratives.

Léonard used the third person 'i/il' for a short period to refer to himself in narratives. In order to tell narratives, children must word internal representations consisting in images, words and a theatrical development. They mentally view the scenes in which they have been a major participant and therefore see themselves as a character among others. That might be a reason for their use of the third person just before two and a half years old.

The language addressed to the two children in our study is particularly relevant since Léonard's mother uses the third person in contexts in which she creates stories about him (she happens to be a writer). Guillaume's mother never uses the third person when she speaks to him. Léonard, makes fairly frequent use of third person pronouns for a few months to refer to himself, while Guillaume uses the second person quite frequently in this function. We will examine in which contexts the two children use these forms, which at first seem quite deviant.

We will try to show how by resorting to alterity (second or third person instead of first person), the child represents himself differently and asserts his own identity through other standpoints, other perspectives, other "voices" [START_REF] Bakhtin | Speech genres and other late essays[END_REF] in dialogic contexts.

II Pronominal reversal

Pronominal reversal is rare in children whose linguistic behaviour is typical, but is quite frequently mentioned in the literature. Studying those errors children make in the output may be a way to raise "specific questions whose answers may shed light on the mechanism of pronoun acquisition" (Chiat 1989: 383). Besides, pronoun reversals are frequently observed in language disorders, especially in autism since it is part of Kanner's original description as well as Asperger's. Kanner wrote: "Personal pronouns are repeated just as heard, with no change to suit the altered situation (…). Not only the words but also the intonation is retained" (1943: 244).

The initial attempt to explain the phenomenon was made in terms of echolalia and of autistic children's difficulties in recognizing people as centres of subjectivity and as the occupants of reciprocal roles in discourse since, of course, the use of personal reference terms varies depending on the speech role one occupies in the conversation. The study of reversals as a normal development (even if infrequent) might therefore contribute to the understanding of pathological language development.

Many hypotheses have been made to explain reversals. These include: a) the name hypothesis: the idea that pronouns used as names [START_REF] Clark | From gesture to word. On the natural history of Deixis in language acquisition[END_REF]. b) the person hypothesis [START_REF] Charney | Speech roles and the development of personal pronouns[END_REF]; a given pronoun is taken to refer to a constant person or set of persons, leading to pronoun reversals.

c) The risk taking hypothesis: precocious children take the risk of using pronouns and fail to perform a deictic shift [START_REF] Dale | Pronoun reversals: who, when, and why?[END_REF].

The above hypotheses involve various factors which can explain reversals -Lack of semantic knowledge: not knowing which words are pronouns [START_REF] Bellugi | From gesture to sign: Deixis in a visual-gestural language[END_REF].

-Simple imitation of the speech heard: "I'll help you" uttered by a child may contain two pronominal reversals and the child may be asking for help which would be a consequence of reliance on imitative, holistic strategies of language learning.

-Not understanding perspective shifting [START_REF] Loveland | Learning about points of view: spatial perspective and the acquisition of I/you[END_REF] -The nature of the input. It could be impoverished (Oshima-Takane 1992) and the child needs to observe speech directed to others containing personal pronouns.

All those interpretations pertain to the fact that children do not use pronouns like adults as corresponding to speech roles. In our data pronominal reversal is not consistent and always occurs along with adequate usage. So we were highly interested in the "perspectiveshifting hypothesis" proposed by [START_REF] Chiat | Context-specificity and generalization in the acquisition of pronominal distinctions[END_REF], according to which those "errors" would be a deliberate use of reversals to shift mental perspective. In her study of Matthew's reversals, Chiat argues that this perspective-shifting hypothesis cannot be confused with the mere imitation interpretation since reversals occur in novel constructions. She shows that "many of the reversals in both directions occur in contexts where the addressee's point of view is being expressed (…) reversed you and your occur in references to himself that Matthew would hear from other people: in utterances of threat, warning, accusation, prediction, or permission" (Clark 1974: 377). This hypothesis is in contradiction with authors saying that children cannot take the other's perspective and therefore do not comprehend the reversible nature of pronouns. According to Pettito (1987), up to a certain age, children can only refer to themselves since their language is egocentric. But Piaget (1962) did answer Vygotsky's criticism (1934) of the notion of egocentric language and proposed the word 'centrism', meaning that the child cannot differentiate his perspective and the perspective of others.

Oshima-Takane (1992) explains that children understand the relation between pronouns and speech roles when they see two speakers talking to each other and become aware that the second person pronoun refers to the addressee. She therefore emphasizes the importance of vision (also see [START_REF] Oshima-Takane Yuriko | Pronominal semantic confusion in a hearing impaired child[END_REF]. A few studies on the acquisition of pronouns by blind children conclude that there is some delay in the use of the first person pronoun and a lot of reversals [START_REF] Selma | Self-representation in language and play: observations of blind children[END_REF], Sampaio 1991[START_REF] Danon-Boileau | Getting Vygotskian about theory of mind: Mediation, dialogue, and the development of social understanding[END_REF]. Loveland

(1984) also insists on the spatial aspects of pronoun acquisition and the importance of seeing different speakers in the activity of dialogue in order to understand perspective shifting.

However Perez-Pereira's thorough study does not support the claim that blind children in general use personal reference terms late and with a great deal of reversal errors. Pérez-Péreira does agree with Oshima-Takane on the implication of the "failure to observe pronouns in speech addressed to another person" and also mentions the impact of the "large proportion of directives and requests used by mothers" (1999: 677), which may prevent some blind children from using the correct pronouns. We can conclude from those controversial studies that blind children are probably able to compensate their lack of vision by the fact that they can hear and listen to speech, which is not addressed to them. They must develop the quality of internally locating speech partners in space from what they hear. But that capacity depends on the children's environment and development, therefore some blind children are hindered in their pronoun acquisition and some are not. [START_REF] Chiat | If I were you and you were me: the analysis of pronouns in a pronoun-reversing child[END_REF] considers pronouns as being plurifunctional, which has to do with the possibility of adopting another's point of view as adults occasionally do explicitly by saying ("I wouldn't do that if I were you"). She illustrates her perspective-shifting hypothesis with examples such as: C -When you're (speaker) a big boy you (speaker) can go to play tennis. Not only is the child using 'you' to refer to himself, expressing the addressee's point of view and shifting perspectives, but he is speaking for the adult. The child might be uttering this mixture of prediction and permission" with an evaluation of his future capacities just because that is the kind of utterance he usually hears in the same type of situation. The child says what he expects to hear or what should be said in the present situation. If this is the case, we might not consider the use of the pronoun 'you' as a reversal and as being the incorrect form, but think of the whole sentence as being uttered by the wrong speaker. In fact the utterance could be what the child expects, or would like, to hear in the present situation.

A longitudinal study of Léonard and Guillaume's use of the second and third person pronouns for self-reference, will help to analyze this possibility.

III The third person

The data I used for this study consists in the video recordings and lined transcriptions of Léonard, age 20 months to 39 months which are part of the Paris Corpus on the CHILDES database (Mac Whinney 2000, the data was analyzed in [START_REF] Morgenstern | Un JE en construction. Ontogenèse de l'auto-désignation chez l'enfant[END_REF].

Each self-word used in subject position by Léonard during this period of time was counted and analyzed. Three periods could be distinguished in the data: I non adult uses 1;7 to 2;2; II All self-words 2;3 to 2;7; III Adult uses mainly 2;8 to 3;3.

Table 2: Percentage of Léonard's self-words

During the second period, Léonard uses all the forms and in particular 'il'. He talks about himself in the third person, marking the discourse object without identifying it to the speaker. That represents over 20% of his self-words during this period, so it is quite an important phenomenon. But only a detailed analysis of the data can allow us to understand whether it is used at random or if it has a specific function.

The analysis of an extract of the data will help us understand Léonard's use of selfwords and in particular his use of the third person in autobiographical narratives.

Léonard's father asks him a question about what he did in nursery school. This question shows the child that his parents need information only he knows, they did not witnesses the events that took place at school. The child is therefore led into the narrative mode.

(1) P: Qu'est-ce que t'as fait à la crèche aujourd'hui? What did you do in nursery school today? L: atata lakeʃlafelafe / lapatamodle (axx la crèche, l'a fait, l'a fait, la pâte à modeler) In nursery school I did, I did modelling clay Fifteen minutes later, as he is getting ready for his bath, Léonard is naked in his mother's arms and is a little aggressive with her: she kisses his arms and he erases the kisses with his hand and says "no kiss on my arms".

( This distance between the child who is about to take a bath at home and the child in kindergarten is marked by the use of the third person. Besides, since the little boy was filmed, we were able to see that when he produces his utterance, he does not look at his interlocutor.

His gaze is vague as if he were concentrating on the scene he is visualizing in his mind. That reminds us of Cuxac's analysis of narrative in French Sign Language [START_REF] Cuxac | La langue des signes française, les voies de l'iconicité[END_REF]: when the signer is engaged in a narrative, he does not look at the interlocutor, he is not embodying his own self, but a character in a story, as opposed to discourse.

Then there is a clarification of the identity of the two protagonists thanks to the mother's question: "David de la crèche?" (David from kindergarten). Léonard does not answer directly but localizes another actor and uses a name, his own name.

L.: leonaila/leonaadipaadadib. (Léonard, (he) said pan to David Léonard uses his name to talk about the agent once he needs to mark the various places and roles of the characters in the scene. As a narrator, he shares his parents' point of view and relates the scene as if he were a mere observer; he names himself with his name as if someone else were narrating the scene. This identity splitting enables him to distinguish between the world of kindergarten and the world of home. As he narrates, he also mimes the scene, which creates a link between Léonard as speaker and Léonard as actor. The body of Léonard the speaker (including his arm hitting in the air) enables him to show his mother the character Léonard in his narrative. This is similar to what happens in narratives in Sign language; the signer's body becomes the character of the story, which is called personal transfer.

I systematically studied all Léonard's uses of the third person to refer to himself and I observed that he only uses 'il' when he is making some kind of narrative which implies the wording of a cinematographic projection of the events which unwind in his head. The images he sees arouse the same feeling of otherness as the image of oneself in a photo or in a mirror.

And we know that during that same period, children do not refer to themselves by saying je or moi when they talk about their image but by their name or the third person [START_REF] Zazzo | Reflets de miroir et autres doubles[END_REF].

During this period, Léonard uses the third person instead of the first person to construct a character, an Other, who is elsewhere and who is naughty since he says pan to David, rips the book apart, eats up all the cakes… Guillaume, the second little boy presented in this study, happened to use the second person for a few months to refer to himself. The following part focuses on his productions of pronominal reversals.

IV The second person

Guillaume was recorded every two weeks from his birth to the age of six. The transcription was made by his mother, immediately after each recording so as to have as much information as possible, and was checked by a second researcher. His mother also kept a diary (Brigaudiot & Nicolas, 1990).

For this study we selected only part of the data from 1;71 to 2;10, from the time both the forms elided t' and tu appear in formulaic expressions, as in "t'entends" (you hear ?) or "tu vois" (you see) to the stabilization of the use of tu to refer to the addressee.

We counted and analyzed each self-word used in subject position by Guillaume during this period of time.

We also distinguished three periods in the data: I non adult uses 1;7 to 2;2; II All selfwords 2;3 to 2;7; III Adult uses mainly 2;8 to 2;10.

Table 3: Percentages of Guillaume's self-words

The second period is the one we are interested in for that is when the child uses tu (you). It represents 12% of the uses of self-words in the data during that period. Example 3 is an extract in which various subject self-words are used in the same sequence.

(3)

Guillaume 1 : Ze vais tourner la farine. Ça y est, mis partout. T'as tourné ! T'as tourné l'oeuf !! I'm gonna mix the flour. Done, put everywhere. You mixed, you mixed the flour ! Mother 1 : Bien ! Good ! Guillaume 2 :Ah ça colle. Ze veux encore tourner un oeuf. Encore un. Oh it's sticky. I wanna mix some more egg. Another one. Mother 2 : Tourne amour, tourne.

Mix honey, mix. G. looks at his mother. Guillaume 3 : Ai tourné.

've turned. Mother 3 : Maintenant il faut encore un oeuf.

Now we need another egg.

His mother is about to break the egg. Guillaume holds out his hand. Guillaume 4 : Guillaume i fait casser un oeuf !!! Guillaume he does it / breaks an egg G. is making the inventory of all the shoes in the house. He tries on his father's shoes, takes a few steps and says: "bravo tu marches", (congratulations you're walking!) Once he has started to accomplish this, we find tu as the marked form. Does this tu mean I ? Is the child really the one who is supposed to congratulate himself? Is he the right speaker for that utterance? Shouldn't his mother be saying it? We can consider the situation as being an accomplishment (from the child's perspective at least). This utterance is very similar to previous utterances that have been addressed to him in comparable situations. The child could be expressing his own pride by using an utterance usually produced by his mother in similar situations, showing he has internalized previous dialogic situations and adopting a form of discourse in which he expresses another's perspective on himself (Fernyhough, 2008). That enables him to speak about himself as if another person were addressing the utterance to him.

We can therefore consider this tu as a device to mark both identity and otherness. It is very interesting to notice that the mother continues the dialogue without asking any questions on the reference of this tu. She understands this tu as referring to the child.

(5) Guillaume (2;05) has eaten a peanut. G: t'as avalé encore ! / You swallowed again! M: non, une seule cacahuète, pas tout. / No, only one peanut, not all of them.

Here the child is misbehaving, and it could even be considered dangerous. It is the same tu the child uses when he runs on the sidewalk and stops just before crossing the road, and says "tu traverses pas" (don't cross). It can also remind us of when the little child says 'no' or shakes his head as he is about to touch a dangerous object. We can see that the child is producing an utterance out of a fixed scenario. He uses his auditory memory with a situation associated to a sort of quotation. He therefore applies the formula 'tu + predicate' to a situation. It is as if he were snatching the mother's utterance out of her mouth, as if he were borrowing her role, her place in the dialogue, as if the most important was not who says it but that the utterance should be spoken. The script exists; he does not create an utterance, but uses it because it applies to the present situation.

Here again, his mother has continued the dialogue without asking who this 'tu' was.

But there comes a day when the clarification of the reference becomes an issue. And this moment coincides with metalinguistic play.

(6) Guillaume 2;7 (last 'tu for je' in the data) G et M talk about absent toys. M: y'en a beaucoup ! i sont de quelle couleur ?/ There are many of them! What color are they? G: bleu / blue M: oh c'est pas vrai / ah that's not true G rit: t'es menteur ! / you're a liar! M: t'es un menteur, ah ah ah, t'es un menteur ! i sont pas bleus i sont rouges !/ you're a liar, ah ah ah, you're a liar! They're not blue, they're red! G: i sont rouges, menteur ! / they are red, liar ! M: petit menteur, tu joues hein ma puce. / little liar, you're playing, aren't you darling. G: t'es un petit menteur. / you're a little liar. M: t'es un petit menteur. / you're a little liar. G: maman t'es un menteur. / Mummy you're a liar M: ah moi j'suis pas menteuse non. (…)/ Oh, I'm not a liar, I'm not. G: non, papa i dit p'tit menteur papa, après idit p'tit con. / No, Daddy says little liar and after he says little asshole.

The quotation "t'es un petit menteur" (you're a little liar) is playful. The mother has just told the child he is not telling the truth. The expression "t'es un petit menteur" is teasingly manipulated as the mother points out "tu joues" (you're playing). The child even compares the mother`s and the father's speech. He now has enough distance with reported speech to play with roles and perspectives.

Our analyses point to two levels of pronominal reversal in Guillaume's data: a) During the first period, this special tu is used in an utterance that is a sort of echo of speech previously addressed to him. The situation the child is in reminds him of a previous experience (or of several previous experiences) during which a similar utterance was produced. Therefore, he makes a comment using the second person pronoun and expressing his own pride or shame as if he were his mother congratulating or scolding him. We can call this an assimilation process; the echo is applied to the current event with no distance at first. But that process is fundamental in the construction of a theory of mind, it is a first step. It reminds us of what autistic children do when they reverse pronouns. b) There is a second level in which the echo is transformed into metalinguistic play. It becomes similar to reported speech. The mother plays this metalinguistic game with him because she intuitively knows he has a theory of mind. There is the necessary distance. We see Guillaume use a kind of false speech; he is joking, he is playing with his mother and deliberately manipulating an utterance she must have addressed to him.

After that stage, all uses of tu for I in older children and adults will be metalinguistic and deliberate in one way or another. It may be the case that autistic and psychotic children do not reach that second level, and stay at the level of assimilation in which their speech sounds like an echo of speech addressed to them, in a seemingly similar situation, without their having fully appropriated the content of what they say about themselves. But even if they do not assert themselves as authors of the content, their use of the other's perspective is a first step towards internalization of another's speech.

After that period of pronominal reversal, Guillaume will always use je to refer to himself in dialogue in subject position.

Conclusion

Léonard and Guillaume use the second and the third person instead of the first person when they need to separate the agent and the speaker. They give the impression that another person is speaking and it enables them to present themselves with another voice at certain moments, extraordinary moments, when they have been either villains or heroes and to unveil other facets of their selves. This could be glossed by saying: "I'm talking about myself as if it weren't me talking". The self as other, seen through the eyes of another. This all happens at a non-conscious level and it is all solidly anchored in reality since the child is talking about feats or naughty behaviour he has actually carried out. This hypothesis emphasizes the role of addressed speech (Perez-Pereira 1999) and of the care-giver as "self regulating other" [START_REF] Stern | The interpersonal world of the infant, Basic books[END_REF] throughout language acquisition. But there is a sequel to this splitting up of their self. A few months later, the children in this study invented an alter ego to which they gave another name in order to be able to speak about another self. Around the age of 2;05, Léonard abandons the third person to refer to himself but he makes up the character of Jean-Patou and makes him the author of all his misbehaviour: Jean-Patou broke the little bed for example because he jumped on it so much, he tore up the book because he didn't like the story. Guillaume invents the character Rouda who is his hero and does all the great things he would like to do. So the children talk about another individual who is their other self, the good or the bad self. They create a fictional character, an alter ego who can be either naughty or extraordinary. This phenomenon has already been mentioned in the literature and is often reported by parents [START_REF] Astington | The child's discovery of the mind[END_REF].

The two children kept their imaginary friend for a few months (Léonard), and over a year (Guillaume), and then gave them up.

At a certain time in the genesis of the pronominal system, pronominal reversals vanish from the data of typically developing children. These children merge their role as speaker and as agent, topic, grammatical subject, into one form. They conceive of themselves with a certain permanency, linked to Piaget's object permanency and can keep their integrity, their identity in time. As Ricoeur writes in Soi-même comme un autre: "Il ne s'agit pas de s'assurer qu'on parle de la même chose, mais qu'on peut l'identifier comme étant la même chose dans la multiplicité de ses occurrences.

Or cela ne se fait que par repérage spacio-temporel : la chose reste la même en des lieux et des temps différents " (1990: p?).

(The issue is not to make sure you talk about the same thing, but that you can identify it as being the same thing in the multiplicity of its occurrences. That can only be done in the spatio-temporal frame: the thing stays the same in various places and times).

At the end of the acquisition process, at around 3 years old, children join the grammatical subject, the semantic subject, the subject of conversation in a single form, and the first person pronoun, but they have gone through a transition period during which they could separate these various levels and produce various markers, breaking away from regular adult forms.

The child then understands that these various facets of her/his self marked in the different forms he used (null form, filler syllables, name, third person, accusative form, genitive form) do not alter the unity of his identity. At the end of the process, the child has become a speaker, or in enunciative theories, an enunciator. S/he can speak of her/himself and judge her/his own self through what s/he has been and has done in the past, what s/he is and does in the present, what s/he will do and be in the future or would like to be and do. S/he therefore succeeds in breaking apart from the other, from the other's speech and has built her/his own place in dialogue, on the intersubjective scene.

filler, name, moi, il, moi il, je, moi je

	Period 1	Period 2	Period 3
	1;7 to 2;3	2;2 to 2;7	2;7 to 3;3
	No adult form Ø, filler, name,	All forms Ø, Over 80% adult forms je, moi je
	moi, il

Table 1 : Léonard's self-words

 1 The percentage of the forms used in the three periods are shown in table 2.

	AGE	Ø	filler	moi	il	name	name+	je	moi je
							il
	Period 1	32	46	10	5,2	3,6	2	1,2	0
	1;8-2;2
	Period II	26,75	29,25	5,5	21,5	0	0	11,75	5,25
	2;3-2;7
	Period III	11,25	2,75	4,5	2	0	0	59,5	18,5
	2;7-3;3

  The child is going to combine the narrative mode and his aggressive mood by reinitiating his entry into the narrative from a visual and gestural association. He gives the impression he is re-living the scene and punctuates his speech with violent gestures. He tells the story by embodying the scene and helping his parents actually visualize what went on.

	2)	L: ladipã adavib (l'a dit pan à David)/ he said pan to David
		M: T'as dit pan à ... / you said pan to…
		L: ladip ladipã adavib (l'a dit p… l'a di pan à David) / he said pan to David
		P enters the bathroom.
		P: T'as dit pan à David? / you said pan to David?
		L: wi / yes
		M: David de la crèche? David from nursery school
		L: leonaila / leonaadip ladipã adadib (Léonard il a, Léonard a dit p… l'a dit pan
		a David) / Leonard, Leonard said pan to David
		M: Pourquoi? / why?
		L: wi / yes

M: Pourquoi t'as dit pan à David? David il t'avait dit pan aussi? / Why did you say pan to David? Did he say pan to you too? L: pabodadibpaboadadib (pas beau David, pas beau à David) / not nice David, not nice.

Table 3

 3 presents the percentages of self-words according to the period.

		Ø	vowel	name	moi	il	tu	je	Moi je	C'est moi
										qui
	Period I	57	21,5	9	6,5	6
	1;7 to
	2;2
	Period 2	52,5	10	6,4	5,7	2,1	12	11,3
	2;3 to
	2;7
	Period III	35,5	1,8					43,6	16,4	2,7
	2;8 to
	2;10

The notation for ages is number of years;number of months. Example: 1;7 = 1 year and 7 months.

All occurrences of tu (you) in the data were coded and analyzed whomever they referred to. As shown in graph 1 there are two peaks, one at 2;4 and then after a decline, the use of tu rises again and becomes more or less stable.

Insert Graph 1: Percentage of tu (over number of utterances) in Guillaume's data

We categorized those occurrences according to whether they were adult uses (tu meaning the addressee) versus non adult uses (tu meaning the child) as shown in graph 2.

Insert Graph 2: Guillaume's uses of tu

We can make two important remarks: 1) Reversals only occur once the second person form is already part of the child's productions and used adequately but in formulaic expressions.

2) Reversals might be a necessary stage for that particular child before the use of adult like tu (referring to the second person) in non-formulaic utterances.

We will examine a few extracts in detail.

(4) Guillaume 2;3 G. is making the inventory of all the shoes in the house and he makes comments. G: C'est à papa / It's Daddy's. M: C'est les souliers de papa / It's Daddy's shoes. G: Peux, veux à mettre, veux. / Can, want put, want. M: Tu veux les mettre ? / You want to put them on? G: Oui he puts on his father's shoes comme ça marche. / Yes. Like that walk. M: Hein ? / What? G: he stands up with the shoes on Marcher comme ça. / Walk like this. M: Tu veux marcher comme ça ? / You want to walk like this? G: Ouais he takes a few steps bravo tu marches ! ! / Yea. Congratulations! You're walking.