Aiming to improve the human-likeness of natural language generation systems, this study investigates different sources of variation that might influence the production of referring expressions (REs), namely the effect of task demands and inter-intra-individual variation. We collected REs using a discrimination game and varied the instructions, telling speakers that they would get points for being fast, creative, clear, or no incentive would be mentioned. Our results show that taskdemands affected REs production (number of words, number of attributes), and we observe a considerable amount of variation among the length of REs produced by single speakers, as well as among the REs of different speakers referring to the same targets.

In a production experiment (Experiment 1) and an acceptability rating one (Experiment 2), we assessed two factors, spatial position and salience, which may influence the production of relational descriptions (such as “the ball between the man and the drawer”). In Experiment 1, speakers were asked to refer unambiguously to a target object (a ball). In Experiment 1a, we addressed the role of spatial position, more specifically if speakers mention the entity positioned leftmost in the scene as (first) relatum. The results showed a small preference to start with the left entity, which leaves room for other factors that could influence spatial reference. Thus, in the following studies, we varied salience systematically, by making one of the relatum candidates animate (Experiment 1b), and by adding attention capture cues, first subliminally by priming one relatum candidate with a flash (Experiment 1c), then explicitly by using salient colors for objects (Experiment 1d). Results indicate that spatial position played a dominant role. Entities on the left were mentioned more often as (first) relatum than those on the right (Experiments 1a–d). Animacy affected reference production in one out of three studies (in Experiment 1d). When salience was manipulated by priming visual attention or by using salient colors, there were no significant effects (Experiments 1c, d). In the acceptability rating study (Experiment 2), participants expressed their preference for specific relata, by ranking descriptions on the basis of how good they thought the descriptions fitted the scene. Results show that participants preferred most the description that had an animate entity as the first mentioned relatum. The relevance of these results for models of reference production is discussed.

In this study, we ask whether references to paths and landmarks in route directions (RDs) are influenced by environmental complexity, zooming in on two aspects of the visual surroundings, namely intersection structure and visual clutter. Speakers are asked to produce (Experiment 1), understand (Experiment 2) and evaluate (Experiment 3) turn-by-turn RDs in a naturalistic setting (Google Street View panoramic pictures). We find that increased levels of visual clutter and intersections with complex structures trigger more references to landmarks and paths when participants produce RDs, longer decision times to determine what the next correct step in a route is and increased preference for landmarks. Finally, we discuss possible implications for automatic RD generation.

There is a general agreement that landmarks in route directions should be perceptually salient and stable objects. Yet, other attributes, such as (animated) motion, can also attract visual attention and make entities salient. In the present study, we investigate if and when speakers refer to moving entities in route directions and how listeners evaluate such instructions. We asked speakers to watch short videos of different crossroads with and without moving landmarks and give directions to listeners, who in turn had to choose a street on which to continue (Experiment 1) or choose the instruction they most preferred among three route directions (Experiment 2). Results reveal that speakers mentioned moving entities, especially when the trajectory was informative for the place where a turn should be taken (Experiment 1). Listeners had no problem understanding instructions with moving landmarks (Experiment 1). Yet, participants chose instructions with stable landmarks more often (Experiment 2). These results are discussed in relation to automatic route directions generation.

Although communicative purposes are an important element in language production, few studies investigate the extent to which they might affect referential choices. In this study we contrast two tasks with different purposes: identification and route directions giving. In Experiment 1 speakers referred to a target building nearby or further away so their addressee would distinguish it from other buildings (identification) or give route directions and use the same building as a landmark (instructions). Our results showed that irrespective of the speaker's purposes, referring expressions consisted of the same types of attributes, yet the attribute frequency and formulation differed. In the identification task the referring expressions were longer and contained more locative and more postnominal modifiers. In addition, referential choices were influenced by the visual distance between the speaker and the target: When speakers observed the target from afar, their references were longer and contained more often locative modifiers. In Experiment 2 a different group of participants had to evaluate references produced in Experiment 1 while assessing descriptions of objects or descriptions of objects extracted from route directions. Neither task, distance, nor the length of the phrases influenced their choice, indicating that addressees consider references produced in both conditions equally adequate in both uses.