Defining interactions: a conceptual framework for understanding interactive behaviour in human and automated road traffic

Rapid advances in technology for highly automated vehicles (HAVs) have raised concerns about coexistence of HAVs and human road users. Although there is a long tradition of research into human road user interactions, there is a lack of shared models and terminology to support cross-disciplinary research and development towards safe and acceptable interaction-capable HAVs. Here, we review the main themes and findings in previous theoretical and empirical interaction research, and find large variability in perspectives and terminologies. We unify these perspectives in a structured, cross-theoretical conceptual framework, describing what road traffic interactions are, how they arise, and how they get resolved. Two key contributions are: (1) a stringent definition of “interaction”, as “a situation where the behaviour of at least two road users can be interpreted as being influenced by the possibility that they are both intending to occupy the same region of space at the same time in the near future”, and (2) a taxonomy of the types of behaviours that road users exhibit in interactions. We hope that this conceptual framework will be useful in the development of improved empirical methodology, theoretical models, and technical requirements on vehicle automation

Methodologies to Understand the Road User Needs When Interacting with Automated Vehicles

Interactions among road users play an important role for road safety and fluent traffic. In order to design appropriate interaction strategies for automated vehicles, observational studies were conducted in Athens (Greece), Munich (Germany), Leeds (UK) and in Rockville, MD (USA). Naturalistic behaviour was studied, as it may expose interesting scenarios not encountered in controlled conditions. Video and LiDAR recordings were used to extract kinematic information of all road users involved in an interaction and to develop appropriate kinematic models that can be used to predict others behaviour or plan the behaviour of an automated vehicle. Manual on-site observations of interactions provided additional behavioural information that may not have been visible via the overhead camera or LiDAR recordings. Verbal protocols were also applied to get a more direct recording of the human thought process. Real-time verbal reports deliver a richness of information that is inaccessible by purely quantitative data but they may pose excessive cognitive workload and remain incomplete. A retrospective commentary was applied in complex traffic environment, which however carries an increased risk of omission, rationalization and reconstruction. This is why it was applied while the participants were watching videos from their eye gaze recording. The commentaries revealed signals and cues used in interactions and in drivers decision-making, that cannot be captured by objective methods. Multiple methods need to be combined, objective and qualitative ones, depending on the specific objectives of each future study. Document type: Part of book or chapter of boo

Methodologies to Understand the Road User Needs When Interacting with Automated Vehicles

Interactions among road users play an important role for road safety and fluent traffic. In order to design appropriate interaction strategies for automated vehicles, observational studies were conducted in Athens (Greece), Munich (Germany), Leeds (UK) and in Rockville, MD (USA). Naturalistic behaviour was studied, as it may expose interesting scenarios not encountered in controlled conditions. Video and LiDAR recordings were used to extract kinematic information of all road users involved in an interaction and to develop appropriate kinematic models that can be used to predict other’s behaviour or plan the behaviour of an automated vehicle. Manual on-site observations of interactions provided additional behavioural information that may not have been visible via the overhead camera or LiDAR recordings. Verbal protocols were also applied to get a more direct recording of the human thought process. Real-time verbal reports deliver a richness of information that is inaccessible by purely quantitative data but they may pose excessive cognitive workload and remain incomplete. A retrospective commentary was applied in complex traffic environment, which however carries an increased risk of omission, rationalization and reconstruction. This is why it was applied while the participants were watching videos from their eye gaze recording. The commentaries revealed signals and cues used in interactions and in drivers’ decision-making, that cannot be captured by objective methods. Multiple methods need to be combined, objective and qualitative ones, depending on the specific objectives of each future study

Study and modelling of drivers’ interactions based on the speech act theory, towards enriching the driving automation systems

This thesis studied the drivers’ communicative interactions, which constitute a necessary component of the driving task. These interactions are based on successive elementary communicative acts. It is a common observation that when drivers predict that their vehicle may be found in the future in dangerous proximity to another vehicle, they tend to intentionally communicate in advance their motion intent to the other involved drivers, so that they may jointly plan and execute a safe future motion plan. At a theoretical level, the objective of this thesis was to study the interactive part of the driving task, shedding light on the phenomenon of communication of drivers’ intent and their agreement on a future common motion plan. At a practical level, the aim of the thesis was to develop a model of drivers’ communicative interactions, for integration, as a manoeuvring negotiations level, in Driving Support and Automation Systems (DSAS), so that their functionality is more in accordance to human expectations.Chapter 2 studies the importance of the studied phenomenon of communicative drivers’ interactions, and how such interactions can be decomposed into elementary phases in the form of a flowchart and described in the form of a discussion between the involved drivers. Video recordings of natural overtakings on a highway, with two directions without central barrier, were used for a first empirical confirmation of the frequency and significance of such interactions. The analysis of 82 overtakings showed that the intent to overtake could be anticipated before the start of the manoeuvre in 45,12% of cases, through formal and informal cues. In 6 of the 22 cases when the intent could be anticipated and there was an oncoming vehicle, its driver modified the trajectory of the vehicle so as to facilitate the overtaking.Chapter 3 includes a literature review of cognitive drive models, such as the hierarchical model of Michon, the model of Wilde, the COCOM model, the situation awareness levels of Endsley, the ECOM model and the Joint Action Control model. All but one of these models are personal models, that focus on a single driver, and analyse how he/she performs the various activities necessary for the driving task. There is no clear reference or modelling of deliberate drivers’ communicative interactions before a manoeuvre, which aim to ensure their common understanding for the safer and more convenient manoeuvre conduct.Chapter 4 presents the evolution of attempts to design and develop DSAS and systems to recognise driver’s intent. The initial design attempts were based on parameters such as time to collision with the involved vehicle. Still, experience showed that warnings by such DSAS were not in agreement with drivers’ expectations. Thus, the recent design guidelines by the National Highway Traffic Safety Administration suggest that the timing of the warnings by DSAS should be based on the expected driver’s response time and on the deceleration level selected by the driver. So, several DSAS estimate risk of collision based on the forecasted future vehicles trajectory according to motion models. But, the warning distances calculated by such DSAS are large and not consistent with the risk assessment by an average driver. Indeed, several studies report that the acceptance of warning systems by drivers is rather limited. One possible reason is that the warnings of DSAS are not consistent with the drivers’ estimations and expectations. In this thesis it is argued that this occurs because DSAS do not consider in their design the drivers’ communicative interactions.Chapter 5 attempts to clarify some terms used when describing the phenomenon. Coordination can be regarded as the orchestration of behaviours so as to achieve a common aim and is considered to occur at a pre-conscious level. Cooperation can be regarded as an observed social interaction with a positive outcome for each of the involved players. Social behaviour is the behaviour which is oriented towards other people and social interactions are the acts, actions or practices of two or more “selves”, each oriented towards one another, i.e. any behaviour which seeks to influence or take into account the subjective experiences or intent of another self. In this thesis it is argued that driving is often a social activity, that drivers consider other vehicles as social units, as "animate human-vehicles", and largely base their expectations for the evolution of the traffic scene by observing and interpreting the behaviour of these social units. Then, it is analysed how driving can be considered as a joint activity, based on a Basic Agreement, which for driving can be considered to be the safe and smooth traffic on the road network for all road users. A joint activity also requires the existence of Common Ground, which for driving is based on the explicit rules of the Traffic Law but also on commonly accepted conventions, as argued in this thesis. It is also supported that when there is a risk for a breakdown of the Common Ground, when drivers are uncertain about others’ intent, they consciously seek to update and repair their Common Ground, trying to interact with other drivers, so as to communicate their motion intent and to agree on a safe future motion plan.Chapter 6 analyses how a behaviour which the observer can describe in semantic terms can be considered as a linguistic behaviour. Then, the Speech Act Theory of Austin (1962) and the classification of illocutionary acts by Searle (1975) are presented, which can be used for modelling non-verbal communicative acts, such as those studied in this thesis. In this framework, drivers’ communicative interactions can be modelled using the locutionary / illocutionary / perlocutionary typology by Austin. It is argued in this thesis that any communicative act in such interactions includes three types of acts, a "locutionary", an illocutionary and a perlocutionary one. The "locutionary" act conveys the sense and reference according to Austin. Such acts may be the use of the horn, the flashing of headlights, the lateral displacement of the vehicle towards the central lane marking or the deliberate close following of the lead vehicle. The illocutionary act conveys a certain force, for example “request” to empty the lane or “frightening” the lead “human-vehicle” so as to persuade him/her to change lane. The perlocutionary act is the act done due to the communicative act, for example the lead “human-vehicle” facilitates the overtaking or the lead “human-vehicle” empties the lane. A sequence of illocutionary acts in drivers’ communicative interactions is in this thesis modelled as a "Conversation" using the Linguistic Model of Drivers’ communicative Interactions (LMDI). In such an interaction, drivers use and interpret certain communicative acts or cues at the illocutionary level as "Directives", for example "requests" or "commands", and other acts or cues as "Commissives", for example "acceptances" or "rejections" of the "Directives". Regarding the non-verbal "locutionary" acts, the communication of intent between drivers can be mediated by different, formal and informal, communicative acts or cues. It is argued in this thesis that drivers collect information to anticipate the intent of other "human-vehicles" from two levels: a) the social level, which includes the explicit, intentional communicative acts emitted by a driver, and b) the physical level, which includes communicative acts emitted intentionally or cues used to interpret intent based on the observed motion of a "human-vehicle" on the road.Chapter 7 presents a first empirical verification of the LMDI based on observations of natural drivers’ interactions in real traffic conditions. The observations took place in the Hymettus ring road, a road with at least two lanes per direction and a central barrier. The drivers were asked to drive normally their own vehicle while in parallel commenting aloud about their observations in the surrounding traffic and any action undertaken by themselves as a result of any such observation. During the route one observer was seated in the passenger seat and recorded with two cameras the traffic scene in front and behind the vehicle and the driver’s commentary. The observations of 25 experienced drivers, 17 men and 8 women, were analysed. The findings support the argument that in many cases, drivers consider other vehicles as social units, as "animate human-vehicles", and largely base their expectations for the evolution of the traffic scene by observing and interpreting the behaviour of these social units. Indeed, on average in 38.7% of the uttered periods drivers referred to observations and interpretations of social behaviour of "animate human-vehicles". From the 360 periods referring to observations of social behaviour, 90 referred to anticipation of others’ intent. According to the analysis, in order to predict the future trajectory of a moving vehicle, a driver uses the physical geometry of the road and the physical limitations, assuming a smooth motion of the vehicles in the future. Any observed deviation of a vehicle from its expected smooth motion, is considered as a possible result of an intentional action by its particular driver and is used to anticipate intent of this “human-vehicle". These cues, which are created by observing inanimate objects, are supplemented by the cues emitted by the animate human drivers, and contribute to the anticipation of intent. In addition, the observer anticipates intent based on stereotypes. Furthermore, according to the analysis, the illocutionary force of acts within the observed interactions could be modelled as a "discussion" with a series of illocutionary acts, as represented by the LMDI. Empirical findings also support the argument that in cases of uncertainty, when the underlying Common Ground is not enough for safe prediction of the evolution of the traffic scene, drivers consciously seek to interact with other drivers, so as to communicate their intent, to update and repair their Common Ground and to agree on a safe future motion plan. Indeed, the analysis showed that most of the communicative interactions were initiated when one driver wished to change lane in the presence of another “human-vehicle” in the target lane or when one driver wished to drive faster than a lead “human-vehicle”. Finally, the observations were analysed separately for older and younger drivers. According to the analysis, older drivers face driving as a social phenomenon at the same level as younger drivers. However, the communicative acts and communicative interactions clearly tended to be less for older drivers. These findings support the argument that older drivers may adopt a strategy that allows them to avoid frequent communicative interactions, in order to compensate for their degraded abilities.Chapter 8 presents a first assessment of the effects from the integration of a manoeuvring negotiations unit based on the LMDI in DSAS. The assessment was based on an experiment using a dynamic driving simulator. Four different driving scenarios were algorithmically developed and four driving support systems were simulated, a system warning about collision risk during lane change on highways, a system warning about crash risk with the oncoming car in case of left turn on bi-directional urban road, a system warning about collision risk while entering a highway, and a system warning about crash risk with the oncoming car in case of overtaking on a rural road. For each system, two conditions were simulated. In the first condition, the warning was provided according to the calculated Time To Collision with the other vehicle involved in the manoeuvre, at two levels, high and medium risk. In the second condition, a manoeuvring negotiations unit, based on the LMDI, was additionally simulated. More precisely, the software simulated the “acceptance” by the other “driver” of the participant’s manoeuvring “request”, which was supposedly signalled by the activation of the turn indicator by the participant. The "acceptance" was signalled by an additional icon besides the collision risk icons which were displayed according to the Time To Collision value. The study revealed some effects on parameters relevant to traffic efficiency due the possibility of such negotiations. More specifically, in three of the four scenarios the participants started their manoeuvre earlier and at conditions of greater objective risk when there was the "explicit" consent of the other “driver” to their intended manoeuvre. This suggests that participants felt more confident when the system was providing the explicit "consent" of the other "driver" than when the warning was provided only in accordance to the laws of physics (i.e. the Time To Collision value). The found effects on driving behaviour and the subjective assessments of drivers as regards the functionality of the systems in both conditions support the argument that drivers feel more certain when there is the possibility of communicating with other drivers, i.e. when there is an explicit "consent" by others to their intended manoeuvre. The findings support the argument that the functionality of DSAS after the integration of a manoeuvring negotiations level is more in accordance with human assessments and expectations.Finally, Chapter 9 summarizes the general conclusions of this thesis, and specifies directions for further research. The results of this thesis show that: (i) social interactions are and will remain an important component of the driving task and (ii) DSAS can be enriched by the integration of a social interactions level based on a model such as the LMDI. Such an endeavour, if successful, will ensure that the performance and functionalities of DSAS are more in accordance to that of the human driver and the human driver’s expectations. In the future, it will be necessary to collect further empirical data from communicative interactions through natural observations of more manoeuvre types in different traffic environments, so as to validate or expand the issues identified. Furthermore, future studies of such negotiations modules should involve two or more interacting human drivers and should record and analyse full cycles of communicative interactions in a more naturalistic setting, while experiments including automated vehicles should be also conducted. Future studies should also focus more specifically on the design of the manoeuvring negotiations module, i.e. how to handle cases when there will be no “response” to the manoeuvring “request” or when the observed behaviour of the vehicle is not in line with the expected one according to the “response” given to the manoeuvring “request”, so as to protect the whole system from any malicious or irresponsible use.Αντικείμενο της παρούσας διατριβής είναι οι επικοινωνιακές αλληλεπιδράσεις οδηγών, οι οποίες αποτελούν μια απαραίτητη συνιστώσα της οδήγησης. Οι αλληλεπιδράσεις αυτές βασίζονται σε διαδοχικές στοιχειώδεις επικοινωνιακές πράξεις. Είναι κοινή παρατήρηση ότι, όταν οι οδηγοί προβλέπουν ότι το όχημά τους θα βρεθεί στο μέλλον σε επικίνδυνη εγγύτητα με κάποιο άλλο όχημα, τείνουν να επικοινωνούν σκόπιμα εκ των προτέρων την πρόθεση κίνησής τους στους λοιπούς εμπλεκόμενους οδηγούς, ώστε από κοινού να προγραμματίσουν και να πραγματοποιήσουν ένα ασφαλές μελλοντικό σχέδιο κίνησης. Σε θεωρητικό επίπεδο, ο στόχος της παρούσας διατριβής ήταν να μελετηθεί το διαδραστικό τμήμα της οδήγησης, φωτίζοντας το φαινόμενο της επικοινωνίας πρόθεσης των οδηγών και συμφωνίας τους σε ένα μελλοντικό κοινό σχέδιο κίνησης. Σε πρακτικό επίπεδο, στόχος της διατριβής ήταν να αναπτυχθεί ένα μοντέλο των επικοινωνιακών αλληλεπιδράσεων οδηγών το οποίο θα μπορεί να ενσωματωθεί, ως επίπεδο διαπραγμάτευσης ελιγμών, σε συστήματα υποστήριξης και αυτοματοποίησης οδήγησης (ΣΥΑΟ), ώστε να είναι η λειτουργικότητά τους περισσότερο σύμφωνη με τις ανθρώπινες προσδοκίες. Στο κεφάλαιο 2 παρουσιάζεται αναλυτικά η σημασία του υπό μελέτη φαινομένου των επικοινωνιακών αλληλεπιδράσεων οδηγών και πώς οι αλληλεπιδράσεις αυτές μπορούν να αναλυθούν σε στοιχειώδεις φάσεις με τη μορφή λογικού διαγράμματος και να περιγραφούν με τη μορφή συζήτησης μεταξύ των εμπλεκομένων οδηγών. Για μια πρώτη εμπειρική επιβεβαίωση της συχνότητας αλλά και της σημαντικότητας των αλληλεπιδράσεων αυτών, χρησιμοποιήθηκαν οι καταγραφές βίντεο πραγματικών προσπεράσεων σε οδό ταχείας κυκλοφορίας, δύο κατευθύνσεων, χωρίς κεντρικό διάζωμα. Η ανάλυση 82 περιστατικών προσπέρασης έδειξε ότι η πρόθεση προσπέρασης μπορούσε να αναγνωρισθεί πριν την έναρξη του ελιγμού στο 45,12% των περιπτώσεων, μέσω τυπικών και άτυπων νύξεων. Σε 6 από τις 22 περιπτώσεις όπου η πρόθεση αναγνωρίσθηκε και υπήρχε επερχόμενο όχημα, ο οδηγός αυτού άλλαξε την τροχιά του οχήματός του ώστε να διευκολύνει τον ελιγμό. Στο κεφάλαιο 3 γίνεται βιβλιογραφική επισκόπηση των νοητικών μοντέλων οδήγησης, όπως το ιεραρχικό μοντέλο Michon, το μοντέλο του Wilde, το μοντέλο COCOM, τα επίπεδα επίγνωσης της κατάστασης του Endsley, το μοντέλο ECOM και το μοντέλο Joint Action Control. Όλα, εκτός από ένα, αυτά τα μοντέλα οδήγησης είναι προσωπικά μοντέλα, δηλαδή εστιάζουν σε ένα μεμονωμένο οδηγό και αναλύουν πώς αυτός επιτελεί τις διάφορες δραστηριότητες που απαιτούνται για την οδήγηση. Δε γίνεται σαφής αναφορά ούτε μοντελοποιείται η σκόπιμη επικοινωνιακή αλληλεπίδραση των οδηγών πριν την υλοποίηση ενός ελιγμού, με στόχο την εξασφάλιση της κοινής κατανόησης για την ασφαλέστερη και περισσότερο άνετη υλοποίηση του ελιγμού.Στο κεφάλαιο 4 παρουσιάζονται οι έως τώρα προσπάθειες σχεδίασης και ανάπτυξης ΣΥΑΟ, καθώς και συστημάτων αναγνώρισης πρόθεσης του οδηγού του οχήματος. Αρχικά η σχεδίαση των ΣΥΑΟ βασιζόταν σε παραμέτρους όπως ο χρόνος σύγκρουσης με το εμπλεκόμενο όχημα. Η πρακτική έδειξε ότι οι προειδοποιήσεις των ΣΥΑΟ δεν ήταν σύμφωνες με τις προσδοκίες των οδηγών. Έτσι, οι μετέπειτα οδηγίες σχεδίασης του οργανισμού National Highway Traffic Safety Administration προτείνουν ο χρονισμός των προειδοποιήσεων των ΣΥΑΟ να βασίζεται στον αναμενόμενο χρόνο απόκρισης του οδηγού και στο επίπεδο επιβράδυνσης που θα επιλέξει ο οδηγός. Αρκετά ΣΥΑΟ προειδοποιούν για κίνδυνο σύγκρουσης βάσει της προβλεπόμενης μελλοντικής τροχιάς των οχημάτων, την οποία εκτιμούν με χρήση μοντέλων κίνησης. Όμως, οι αποστάσεις προειδοποίησης που υπολογίζουν τα ΣΥΑΟ είναι μεγάλες και μη σύμφωνες με την εκτίμηση κινδύνου ενός τυπικού οδηγού. Πράγματι, αρκετές μελέτες δείχνουν ότι η αποδοχή των συστημάτων προειδοποίησης από τους οδηγούς είναι μάλλον περιορισμένη, και ένας πιθανός λόγος είναι ότι οι προειδοποιήσεις των ΣΥΑΟ δε συμφωνούν με τις εκτιμήσεις και προσδοκίες των οδηγών. Στην παρούσα διατριβή υποστηρίζεται ότι αυτό συμβαίνει επειδή τα ΣΥΑΟ δε λαμβάνουν υπ’όψιν στη σχεδίασή τους τις επικοινωνιακές αλληλεπιδράσεις των οδηγών. Στο κεφάλαιο 5 επιχειρείται η διασαφήνιση κάποιων όρων που χρησιμοποιούνται κατά την περιγραφή του φαινομένου, όπως ο συντονισμός, που μπορεί να θεωρηθεί ως η ενορχήστρωση συμπεριφορών για την επίτευξη κάποιου κοινού στόχου και υποστηρίζεται ότι λαμβάνει χώρα σε προ-συνειδητό επίπεδο, και η συνεργασία, που μπορεί να θεωρηθεί ως μια παρατηρούμενη κοινωνική αλληλεπίδραση με θετικό αποτέλεσμα για καθέναν από τους εμπλεκομένους σε αυτήν. Κοινωνική είναι η συμπεριφορά που είναι προσανατολισμένη προς άλλα άτομα, ενώ κοινωνικές αλληλεπιδράσεις είναι οι πράξεις, δράσεις ή πρακτικές δύο ή περισσοτέρων «εαυτών», αμοιβαία προσανατολισμένων ο ένας προς τον άλλο, δηλαδή οποιαδήποτε συμπεριφορά προσπαθεί να επηρεάσει ή να λάβει υπ’όψιν τις υποκειμενικές εμπειρίες ή τις προθέσεις ενός άλλου εαυτού. Στην παρούσα διατριβή υποστηρίζεται ότι η οδήγηση είναι σε πολλές περιπτώσεις κοινωνική δραστηριότητα, ότι οι οδηγοί αντιμετωπίζουν τα άλλα οχήματα ως κοινωνικές μονάδες, ως «έμψυχους οχηματ-ανθρώπους», και σε μεγάλο βαθμό βασίζουν τις προσδοκίες τους για την εξέλιξη της κυκλοφοριακής σκηνής στην παρατήρηση και ερμηνεία της συμπεριφοράς αυτών των κοινωνικών μονάδων. Στη συνέχεια του κεφαλαίου αναλύεται πώς η οδήγηση μπορεί να θεωρηθεί ως συλλογική δραστηριότητα, με Βασική Συμφωνία την ασφαλή και εύρυθμη κυκλοφορία στους δρόμους για όλους τους χρήστες του οδικού δικτύου. Για την οδήγηση ως συλλογική δραστηριότητα απαιτείται επίσης η ύπαρξη Κοινού Νοητικού Υποβάθρου, το οποίο υποστηρίζεται στην παρούσα διατριβή ότι βασίζεται στους ρητούς κανόνες του Κ.Ο.Κ., αλλά και σε κοινά αποδεκτές συμβάσεις. Επίσης υποστηρίζεται ότι σε περιπτώσεις όπου προκύπτει κίνδυνος κατάρρευσης του Κοινού Νοητικού Υποβάθρου, όταν οι οδηγοί είναι αβέβαιοι ως προς την πρόθεση των άλλων, οι οδηγοί συνειδητά επιδιώκουν να επικαιροποιούν και να ανασκευάζουν το Κοινό τους Νοητικό Υπόβαθρο, προσπαθώντας να αλληλεπιδράσουν με τους άλλους οδηγούς, έτσι ώστε να επικοινωνήσουν την πρόθεση κίνησής τους και να συμφωνήσουν σε ένα ασφαλές μελλοντικό σχέδιο κίνησης.Στο κεφάλαιο 6 αναλύεται πώς μια συμπεριφορά που μπορεί ο παρατηρητής να περιγράψει με σημασιολογικούς όρους, μπορεί να θεωρηθεί ως γλωσσική συμπεριφορά. Στη συνέχεια παρουσιάζεται η θεωρία Γλωσσικών Πράξεων του Austin (1962) και η κατάταξη των προσλεκτικών γλωσσικών πράξεων του Searle (1975), η οποία μπορεί να χρησιμοποιηθεί και για τη μοντελοποίηση μη-λεκτικών επικοινωνιακών πράξεων, όπως αυτές των οδηγών. Έτσι, οι επικοινωνιακές αλληλεπιδράσεις των οδηγών μοντελοποιήθηκαν χρησιμοποιώντας τη λεκτική / προσλεκτική / απολεκτική τυπολογία του Austin. Κάθε τέτοια επικοινωνιακή πράξη υποστηρίζεται ότι περιλαμβάνει τρεις τύπους πράξεων, μια «λεκτική», μια προσλεκτική και μια απολεκτική πράξη. Η «λεκτική» πράξη μεταδίδει την έννοια και την αναφορά κατά τον Austin. Τέτοια πράξη μπορεί να είναι η χρήση της κόρνας, το οπτικό σήμα, η πλευρική μετατόπιση του οχήματος προς την κεντρική διαγράμμιση ή η σκόπιμη

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