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Production of Demonstratives in Dutch, English and Portuguese Dialogues

A data elicitation study on the type of demonstratives and determiners selected to denote objects in English, Dutch and Portuguese dialogues is presented. Participants were given a scenario and a scripted dialogue in which a furniture seller identifies target objects to a buyer. They were then asked to choose a combination of a determiner or demonstrative and a referring expression to be uttered by the seller and told that the agent would point at the targets while uttering the chosen linguistic descriptions. The study was conducted with native speakers and rendered a total of 920 demonstratives and determiners. It focused on accessibility of the target referents and distance between agents and target referents. Results show that the three language groups largely agree in their preferences and, in contrast to previous work, align with a nearby/far away distinction.


Introduction
This paper investigates the use of indexical determiners (i.e. determiners employed for direct references to objects and that include a pointing gesture) by Dutch, Portuguese and English speakers. A comparison of the use of Dutch and English demonstratives in terms of the accessibility of the target by Piwek and Cremers (1996) suggested that English and Dutch speakers follow opposite strategies in their use of indexical demonstratives. Dutch speakers use proximal demonstratives for referents that are relatively difficult to access (deze), while English speakers use proximals (this, these) for referents that are relatively easy to access. Piwek et al.(2008) present an explanation for these differences in terms of the use of pointing gestures (Clark and Bangerter, 2004;Bangerter, 2004), suggesting that a pointing gesture functions as a "labelling" of the target object as being relatively accessible. Hence, where proximals require a pointing gesture, distal demonstratives (dat/that and die/those, which are more similar to definite determiners) can also be used nonindexically. This model corresponds to the 'folkview' of demonstratives that considers distals to indicate objects far away from the speaker and proximals to indicate objects near the speaker (Bühler, 1934;Clark, 1996). Byron and Stoia (2005) present a motivation for choosing either a proximal or a distal demonstrative based on three dimensions (i.e. spatial, temporal and task performance). Their analysis of a corpus of collaborative dialogues between participants solving a treasure hunt problem in a virtual space, shows that, in English: (1) distals are used both for objects located close to and far away from the speaker, whereas proximals are only used for objects located near the speaker; (2) proximals are used for objects that relate to the current time and to the future, while distals are used for past events; and (3) distals are less sensitive to the space and time dimension and more sensitive to the task than proximals.
While we acknowledge that these are important dimensions in the analysis of demonstratives, in the present paper we restrict ourselves to an elicitation study and analyse the use of indexical determiners in terms of accessibility and distance, in line with the model developed by Piwek et al. (1996;2008).
In addition to the languages compared by Piwek et al. (Dutch and English), we also analyse the use of demonstratives in Portuguese. The dialogue context designed for this study fits a discursive context in which the distal/proximal distinction is appropriate for Portuguese (Cavalcante, 2002), and thus enables us to compare the use of demonstratives across these three languages. Another difference between this study and those conducted by Piwek et al. is the data gathering method. While those authors relied on corpora collected from free task-based dialogues between participants, we employed scripted dialogues (André et al., 2000;Williams et al., 2007) presented to individual participants who were explicitly asked to choose among demonstratives.

Production Study
The study presented below originated from an investigation into the perception of multimodal referring expressions (REs) in a virtual world by Japanese an English speakers (Van der Sluis and Luz, 2011b; Van der Sluis et al., to appear). In this paper, the materials from a production study initially conducted for Japanese to validate our Japanese translation of a dialogue written in English, have been translated and further adapted to Dutch and Brazilian Portuguese. We draw on the results of this study to analyse the use of demonstratives in English, Dutch and Portuguese. The REs considered in this study are embedded in a scripted dialogue between two agents in a furniture sales setting. The study focuses on 'firstmention' REs which identify objects that have not been talked about earlier in the discourse.
A dialogue script was written for two agents in a furniture shop. The layout of the shop and the positions of the agents and furniture items is shown in Figure 1. The shop contains 26 objects, comprising distractors as well as target referents. The dialogue consists of 19 utterances and features a conversation between a female agent purchasing furniture for her office, and a male shop-owner describing some furniture items. The furniture seller agent refers to objects in the domain by uttering each scripted RE combined with a pointing gesture directed to the target object. Validation showed that the dialogue was acceptable to English speakers. Van der Sluis and Luz (2011a) describe the setting in greater detail.
B: Yes, that would be great.

S:
The These Those

(4)
large chairs chairs in the middle large chairs in the middle red chairs in the middle large red chairs in the middle large red chairs red chairs would go well with the office chair I showed you earlier.
[pointsto (4) small chairs chairs next to the red ones small chairs next to the red ones green chairs next to the red ones small green chairs next to the red ones small green chairs green chairs To match them with your own office chair we could order them in a different colour.
B: Yes, I do like the red colour better. So if you can order them in red that would be great. S: Certainly, that would be no problem.
(e) (d) Figure 1: Screenshot of the application in which participants were asked to choose their preferred REs. Utterances by the Seller and Buyer are marked with "S:" and "B:", respectively. Options were presented as shown in the DE-boxes marked (d) and (e), and RE-boxes marked (4) and (5).
The dialogue was used as a template in which five first-mention referring expressions (REs) could be varied. The REs used to fill out these slots were chosen to cover various aspects of REs as are currently being studied in NLG: (1) cardinality, the REs targeted three singular objects and two larger sets of items; (2) locative expressions, the REs included three absolute locative expressions and two relative locative expressions; and (3) the position of the referent, the targets were distributed in the domain of conversation such that one referent was located near to the stationary agents, two referents were located far away from the agents, and two sets of referents were located somewhere in between those two extremes. Figure 1 shows 14 furniture items that are used for assessing multimodal GRE output: labelled (1) to (5), as well as a number of distractors. It was assumed that the agents would stay stationary and point in the direction of the targets.
The text was translated into Dutch and Brazilian Portuguese so as to adapt the dialogue to the normative, communicative and inferential rules of the respective cultures, but we attempted to keep the REs as close to the English originals as possible. The translations and localisations for Dutch and Portuguese followed a similar pattern as the process for Japanese described in (Van der Sluis and Luz, 2011b). Validation of the translated dialogues was conducted by three native speakers in the respective languages and revisions were made accordingly.
Although the study was also conducted for Japanese, we will restrict our discussion in this paper to Dutch, English and Portuguese because the Japanese system for demonstratives differs from the ones discussed in this paper. It is a ternary, person-oriented system (Anderson and Keenan, 1985, p.282-286), in contrast to distance-oriented system such as the ones that seem to govern the use of demonstratives in Portuguese, English and Dutch. Although the Portuguese system also incorporates three classes of demonstratives, namely: este(a)/s, isto, (proximal), esse(a), isso (medial) and aquele(a)/s (distal), these often operate as a binary system where the este and esse classes are used interchangeably as proximals whereas aquele is used as a distal (Cavalcante, 2002;Jungbluth, 2005).
Linguistic preferences were elicited through a web-based application. After being introduced to the scenario and task, participants were shown a screen similar to Figure 1. A picture of the domain was displayed at the top and kept visible throughout the dialogue. The bottom part of the screen contained the dialogue, through which the participants could scroll and select the REs and determiners or demonstratives from a set of options, all of which were simultaneously available to the participant while reading the sentence. The five REs were each presented with two boxes as illustrated in Figure 1: the DE-box, for determiner or demonstrative selection and the RE-box, for referring expressions. After each RE-box, it was stated that the agent's utterance would be combined with a pointing gesture in the direction of the target. The REs collected with the study are analysed elsewhere (Van der Sluis and Luz, 2011a) and will not be further considered in this paper. The DE-box included three options for Dutch, English and Portuguese: a definite determiner and a proximal and distal demonstrative.

Hypotheses
Two hypotheses, denoted H1 and H2 and summarised in Table 1, were tested for the five REs pro- duced in the dialogue with respect to the use indexical demonstratives. H1 is related to the accessibility of the target (Gundel et al., 1993) and H2 concerns the physical distance between the speaker and the target object. Compared to the targets of RE2 and RE4, objects identified by RE1, RE3 and RE5 are relatively easier to access because they are located in the 'focus area' of the discourse (RE3 and RE5) or set visibly apart from the other objects in the domain (RE1). Hence, RE1, RE3 and RE5 call for demonstratives that indicate easy access. According to Piwek and Cremers (1996), Dutch speakers prefer proximal demonstratives for objects which are relatively hard to access, while English speakers apparently follow the opposite strategy. Portuguese speakers appear to follow a strategy which is similar to the latter (Cavalcante, 2002). In order to test these claims we set the accessibility hypothesis, H1, so that it predicts opposite strategies for Dutch, on the one hand, and Portuguese and English on the other. Hypothesis H2 relates to the distance between target object and speaker. It predicts that participants will prefer distals over proximals to indicate objects further away (i.e. a proximal for RE1 and RE4 and distal demonstratives for the other REs). Since the dialogue script includes an explicit pointing gesture for all REs, we expected participants to choose either a proximal or an (indexical) distal demonstrative. We had no hypotheses about the use of definite determiners and exclude them from further analysis.
age groups: 71% between 20 and 30, 26% between 31 and 40, and 2% over 41 years old; occupations: 29% students, 57% academics and 14% other) and 51 native Dutch speakers (female: 55% female, 45% male; age groups: 21% between 20 and 30, 33% between 31 and 40, and 26% between 41 and 50 and 20% over 50 years old; occupations: 4% students, 14% academics and 82% other). Figure 2 presents the percentages of definite determiners, proximal and distal demonstratives selected per RE per language. Results show that native speakers of Portuguese, Dutch and English roughly agree in their choices. However, for RE3 we found some disagreement. The majorities of the English and Dutch participants, did not select a demonstrative, but selected a definite determiner for RE3 (i.e. 'the small desk next to it'). In contrast, the Portuguese speakers preferred a distal demonstrative. Table 2 shows the frequencies of the demonstratives selected, determiners excluded. Again, Portuguese, Dutch and English speakers mostly agree in their choices. The majorities chose a proximal demonstrative for RE1 (i.e. 'this red chair'), a distal demonstrative for RE2 (i.e. 'that large desk'), a distal for RE3 (i.e. 'that small desk next to it'), a proximal demonstrative for RE4 (i.e. 'these red chairs') and a distal demonstrative for RE5 (i.e. 'those green chairs next to the red ones').

Demonstratives
We computed χ 2 statistics to assess whether the data borne out the differences hypothesised (Table 1) and if those differences were statistically significant (i.e. whether the null hypotheses that no difference exists could be confidently rejected). The results of these tests are also summarised in Table 2. Portuguese, where differences are indicated with * = p < .05 and ** = p < 0.01. Where the null hypothesis is rejected, a + sign indicates a difference that agrees with the alternative hypothesis (H1, H2), and a − sign indicates a difference that disagrees with the alternative hypothesis.

Discussion and Conclusion
The Distance Hypothesis (H2) appears to be a better fit to the preferences of native speakers of the three languages than the Accessibility Hypothesis (H1). It agrees with the majority of choices for RE1, RE2, RE4 and RE5 in all language groups. Expression RE3, however, proved to be something of an exception, specially for Dutch and English, in that participants of those languages preferred to use a definite determiner in this RE rather than a distal or proximal demonstrative. It seems that in this case the increased accessibility of object (3), caused by the previous reference to 'the desk next to it', was transferred to the definite determiner rather than the distal demonstrative for Dutch and the proximal demonstrative for English, as predicted by H1.
In contrast to previous work, the data collected in our study show that the majorities of the three languages agree in their choices of demonstratives. This may be explained by the fact that pointing gestures were an explicit part of the REs that we tested, and therefore could be evidence for the post-hoc analysis presented by (Piwek et al., 2008), aligning with the folk view of a nearby/far away distinction.
Finally, this study introduced some methodological innovations. Unlike studies where data are collected from naturalistic conversations, we explicitly asked participants to make a judgement as to which demonstrative to use. This was done in a context which, although arguably still open to subjective interpretation, is much more tightly controlled and therefore better suited to cross-linguistic comparison. However, it could be argued that better control comes at the cost of naturalness. By asking the participants to respond from a third person's perspective and imagine the effects of communicative acts (including gestures) the study might have favoured reflective answers over spontaneous production. Such trade-offs seem to be characteristic of this sort of study, and getting them right is one of the many challenges in language generation research.