Introduction

There is widespread agreement that successful text comprehension involves constructing a mental representation of the situations described in the text (Johnson-Laird, Reference Johnson-Laird1983; Kintsch, Reference Kintsch1988; Zwaan & Radvansky, Reference Zwaan and Radvansky1998). This representation includes concepts which appeared in the text plus elements of prior knowledge that were activated by these concepts. As such it represents more than just a verbatim record of the text. A core feature of written and spoken text is the use of pronouns – for example, “he” or “she” – which provide reduced forms of expression to refer to protagonists in a text. Successful adult comprehenders rapidly resolve these co-references to achieve a cohesive and coherent mental model of the situation (Fukumura & van Gompel, Reference Fukumura and van Gompel2015). An influential account of adults’ pronoun resolution, The Event Structure Hypothesis (Rohde et al., Reference Rohde, Kehler and Elman2006; see also Kehler, Kertz, Rohde & Elman, Reference Kehler, Kertz, Rohde and Elman2008) suggests that the temporal characteristics of events influence adults’ resolution of a subsequent pronoun. This paper examines a previously untested but interesting prediction of this account in a sample of adults – specifically, whether the presence/absence of an inherent endpoint influences adults’ resolution of a subsequent pronoun. It also examines whether the temporal characteristics of events influence adolescents’ and children’s pronoun resolution.

In this paper, our focus is on events, which we define as verbs and their predicates. Events can differ in their temporal characteristics in two ways. The first is the inherent temporal properties of the events themselves: this determines their lexical aspect. Specifically, events can differ according to whether or not they have: (a) a specific endpoint (telic events) or no inherent endpoint (atelic events) (Comrie, Reference Comrie1976; Dowty, Reference Dowty1979); (b) duration (durative events) or not (punctual events) (Vendler, Reference Vendler1967); and (c) require a continual effort to be maintained or not (Vendler, Reference Vendler1967). Vendler (Reference Vendler1967) classified events on the basis of these properties resulting in four categories of lexical aspect: states, achievements, accomplishments and activities. The study reported here focuses on anaphoric pronoun resolution (hereafter referred to as pronoun resolution) following events from the latter two lexical aspect categories. Accomplishments (e.g., pass a biscuit) are durative, require input of energy for them to take place, and they are telic: they have an inherent endpoint (when the biscuit is passed) involving a change of state, after which the particular action cannot continue. Activities (e.g., run) also have duration and require energy but, in contrast to accomplishments, they are atelic: they do not have an inherent endpoint (i.e., they can be terminated and begun again at any time).

The second way in which events can be temporally differentiated is by morphological inflection of the event verb itself. This is the grammatical aspect of an event and it primarily distinguishes between describing the event as an ongoing process (with imperfective grammatical aspect) or as a completed event (with perfective grammatical aspect) (Madden & Ferretti, Reference Madden and Ferretti2009; Moens & Steedman, Reference Moens and Steedman1988). Grammatical aspect differs from tense: tense describes how events are sequenced with reference to some narrative timeline, whereas grammatical aspect describes the temporal characteristics of individual events within this time frame. Thus grammatical aspect distinctions can be achieved within different tenses. For example, in English, imperfective aspect is expressed using the auxiliary “is” and the verb infection “–ing” (e.g., is passing, is running) in the Present Progressive tense and using the auxiliary “was” and the verb inflection “–ing” (e.g., was passing, was running) in the Past Progressive tense. Similarly, perfective aspect is expressed using verb inflections “–es” or “–s” (e.g., passes, runs) in the Present tense and the verb inflection “–ed” or an irregular past participle (e.g., passed, ran) in the Simple Past tense. In this study we expressed imperfective aspect using the Past Progressive tense (e.g., was passing, was running) and perfective aspect using the Simple Past tense (e.g., passed, ran) to align with the majority of adult research investigating the effect of grammatical verb aspect on adults’ mental representation of events (Becker, Ferretti & Madden-Lombardi, Reference Becker, Ferretti and Madden-Lombardi2013; Ferretti, Rohde, Kehler & Crutchley, Reference Ferretti, Rohde, Kehler and Crutchley2009; Madden & Zwaan, Reference Madden and Zwaan2003; Magliano & Schleich, Reference Magliano and Schleich2000; Morrow, Reference Morrow1985).

The Event Structure Hypothesis (Rohde et al., Reference Rohde, Kehler and Elman2006) proposes that adults combine two probabilities when determining the referent of a pronoun. The first is the likelihood that a pronoun would be used to refer to a particular protagonist given their grammatical status in the preceding context. The second is the likelihood that a particular protagonist will be re-mentioned. It is argued that this re-mention probability is influenced by the temporal characteristics of an event (critically because this influences the type of coherence relation adults expect to follow and different coherence relations have different protagonists as their Subject; Kehler et al., Reference Kehler, Kertz, Rohde and Elman2008; Rohde et al., Reference Rohde, Kehler and Elman2006).

Support for the proposal that adults’ pronoun resolution is influenced by the grammatical status of protagonists comes from studies where adults have been asked to provide continuations without and with pronoun prompts. For example, adults are more likely to begin a continuation following the stimulus “John _source handed a book to Bob _goal.” with a reference to the previous Object protagonist (Bob) rather than the Subject protagonist (John). However, providing a pronoun at the start of the continuation increases the frequency with which adults provide continuations with John as the Subject (Stevenson, Crawley & Kleinman, Reference Stevenson, Crawley and Kleinman1994). This finding shows that, for adults, pronouns themselves confer a Subject bias interpretation. It is important to note that this bias does not in itself imply that adults will demonstrate an absolute Subject interpretation of the pronoun; only that the presence of a pronoun inclines adults more towards providing continuations starting with Subjects than if a pronoun was not present.

In the Event Structure account, adults’ Subject bias interpretation of pronouns is explained as a consequence of their tendency to more frequently pronominalize re-mentions of Subject protagonists than Object protagonists in bare prompt conditions (Fukumura & van Gompel, Reference Fukumura and van Gompel2010, Reference Fukumura and van Gompel2015; Rohde, Reference Rohde2008; Stevenson et al., Reference Stevenson, Crawley and Kleinman1994). Importantly, this bias towards pronominalizing Subject re-mentions occurs regardless of which of the protagonists (John or Bob) is more frequently re-mentioned (Arnold, Reference Arnold2001; Ferretti et al., Reference Ferretti, Rohde, Kehler and Crutchley2009; Fukumura & van Gompel, Reference Fukumura and van Gompel2010; Kehler & Rohde, Reference Kehler and Rohde2013a; Rohde & Kehler, Reference Rohde and Kehler2014; Stevenson et al., Reference Stevenson, Crawley and Kleinman1994). Thus it is argued that, when adults encounter a pronoun, their production bias to more frequently pronominalize Subject re-mentions leads them to infer that the previous Object is less likely to be the referent of the pronoun than the previous clause Subject (Kehler & Rohde, Reference Kehler and Rohde2013a; Rohde & Kehler, Reference Rohde and Kehler2014).

The idea that adults have a re-mention bias for particular protagonists involved in an event has been suggested and evidenced several times (Arnold, Reference Arnold2001; Stevenson et al., Reference Stevenson, Crawley and Kleinman1994). The evidence supporting the Event structure claim that adults’ re-mention bias is influenced by the temporal characteristics of events comes from studies in which adults are asked to produce a continuation for sentence stimuli. In these studies, the grammatical status of protagonists is maintained across stimuli but the grammatical aspect of the event is manipulated, as in examples 1a and 1b (Ferretti et al., Reference Ferretti, Rohde, Kehler and Crutchley2009; Rohde et al., Reference Rohde, Kehler and Elman2006).

1. 1a. John _source handed a book to Bob _goal. He…

2. 1b. John _source was handing a book to Bob _goal. He…

As noted above, when adults are asked to provide continuations following Source-Goal transfer events without pronoun prompts, they are more likely to refer to the Object protagonist (Bob) than the Subject protagonist (John) at the start of their continuations. Providing a pronoun at the start of the continuation (1a) increases the frequency with which adults begin the continuation with reference to the Subject protagonist to 51%. Expressing the event with imperfective aspect (1b) further increases the frequency with which adults begin the continuation with reference to the Subject protagonist (John) to 70% (Rohde et al., Reference Rohde, Kehler and Elman2006). In the Event Structure account, the grammatical aspect with which transfer events are expressed influences pronoun resolution because it influences the re-mention bias for the Goal protagonist. It does this because transfer events are telic, they have duration and a natural endpoint and the Goal protagonist is central to this endpoint. The 51% resolution to the Source in the perfective condition (1a) found by Rohde et al. (Reference Rohde, Kehler and Elman2006) indicates that, despite a strong next mention bias towards the Goal, as found in bare prompt conditions, adults’ Subject interpretation bias for ambiguous pronouns is strong enough to rival this Goal re-mention bias (Ferretti et al., Reference Ferretti, Rohde, Kehler and Crutchley2009; Rohde et al., Reference Rohde, Kehler and Elman2006; Stevenson et al., Reference Stevenson, Crawley and Kleinman1994). In addition, the 70% resolution to the Source in the imperfective condition (1b) found by Rohde et al. (Reference Rohde, Kehler and Elman2006) indicates that, for adults, expressing telic events with imperfective aspect invokes a substantial reduction in their re-mention bias for the Goal protagonist. An eye-tracking study supports the claim that adults demonstrate a higher expectation for a re-mention of the Goal protagonist following perfectively rather than imperfectively expressed transfer events, before a pronoun is encountered (Grüter, Takeda, Rohde & Schafer, Reference Grüter, Takeda, Rohde and Schafer2018)

Previous research has not examined whether the temporal characteristics of events influence children’s pronoun resolution. This may explain why a contradictory pattern of performance has been observed: whilst some research has shown that participants from 3-year-olds through to adults demonstrate a Subject interpretation of an ambiguous pronoun (Hartshorne, Nappa & Snedeker, Reference Hartshorne, Nappa and Snedeker2015; Song & Fisher, Reference Song and Fisher2005), other work reports that 3- to 5-year-olds do not demonstrate this tendency (Arnold, Brown-Schmidt & Trueswell, Reference Arnold, Brown-Schmidt and Trueswell2007, experiment 2). All of these experiments tracked participants’ eye movements as they viewed a picture while listening to sentences. It is important to note that in these experiments the presence of a Subject interpretation of the pronoun is assumed only if the Subject protagonist is selected on greater than 50% of the critical trials. Hartshorne et al. (Reference Hartshorne, Nappa and Snedeker2015) presented 5-year-olds and adults with stimuli such as 2a and 2b.

1. 2a. Emily ate dinner with Hannah. She skipped her salad and only ate dessert.

2. 2b. Emily and Hannah are going to Disneyland. Emily has never been to Disneyland. She is really excited about going to Disneyland.

In 2a and 2b, the protagonists are described performing a joint action and in 2b the Subject protagonist is repeated in the sentence prior to the pronoun. Children and adults demonstrated a Subject interpretation of the pronoun “She” for both 2a and 2b but the effect occurred sooner for adults. Other work shows that 3-year-olds resolve an ambiguous pronoun to the Subject protagonist when the Subject’s name has been repeated in prior context sentences as in 2b above (Song & Fisher, Reference Song and Fisher2005).

In contrast, Arnold et al. (Reference Arnold, Brown-Schmidt and Trueswell2007) did not find a greater than 50% Subject interpretation of an ambiguous pronoun for the 3- to 5-year-old children in their study (experiment 2). Their stimuli differ from those used by Hartshorne et al. (Reference Hartshorne, Nappa and Snedeker2015). An example is provided in 3 below.

1. 3. Donald is bringing some mail to Mickey while a big rain storm is beginning. He’s carrying an umbrella and it looks like they’re both going to need it.

This type of event has an inherent endpoint and the second mentioned protagonist is central to this. It has been argued that children’s failure to demonstrate a greater than 50% Subject interpretation of the pronoun (“He” in the example) in Arnold et al. (Reference Arnold, Brown-Schmidt and Trueswell2007) arose because the proximity of the pronoun and the disambiguating information limited the time available for children to demonstrate a Subject interpretation in the looking task used to measure performance (Hartshorne et al., Reference Hartshorne, Nappa and Snedeker2015). This argument is supported by the findings of Hartshorne et al. (Reference Hartshorne, Nappa and Snedeker2015) where, when no disambiguating information was provided, children demonstrated a Subject interpretation of the pronoun.

However, there are other explanations for the Arnold et al. (Reference Arnold, Brown-Schmidt and Trueswell2007) finding. As noted previously, when adults are asked to provide continuations for events with endpoints such as Source-Goal transfer events (Donald _source brought some mail to Mickey _goal) they show a bias towards re-mentioning the second (Goal) protagonist (Stevenson et al., Reference Stevenson, Crawley and Kleinman1994). This re-mention of the Goal protagonist is reduced when adults are asked to provide continuations beginning with pronouns (Stevenson et al., Reference Stevenson, Crawley and Kleinman1994). Indeed, adults only demonstrate a Subject (Source) interpretation of a subsequent pronoun when Source-Goal transfer events are expressed with imperfective aspect. Thus, the failure of young children to demonstrate a Subject interpretation of the pronoun in Arnold et al. (Reference Arnold, Brown-Schmidt and Trueswell2007) may indicate that the presence of an endpoint is an important influence on children’s resolution of a subsequent pronoun. Specifically, Arnold et al.’s (Reference Arnold, Brown-Schmidt and Trueswell2007) finding may indicate that a re-mention bias for particular protagonists in events with endpoints develops prior to a Subject interpretation of pronouns. Another explanation for the Arnold et al. (Reference Arnold, Brown-Schmidt and Trueswell2007) result is that expressing a telic event with imperfective aspect does not lead children to revise their expectation for a re-mention of the protagonist focused by the endpoint to the same extent as it does for adults.

Young children are sensitive to the lexical and grammatical aspect of events. For example, pre-schoolers are more likely to use imperfective markers with atelic events and perfective markers for telic events (Shirai & Andersen, Reference Shirai and Andersen1995). According to Tomasello’s (Reference Tomasello2003) usage-based theory of language acquisition (Distributional Bias hypothesis), this pattern of development is the result of the frequent association between particular verbs and particular inflections in the input (language environment). An alternative explanation for the development of verb tense marking is the Aspect First Hypothesis (Shirai & Andersen, Reference Shirai and Andersen1995; Wagner, Reference Wagner2001, Reference Wagner2009), which claims that children’s sensitivity to aspect is the result of their mental representation of events. There are various forms of this hypothesis: some assume a primary role for lexical aspect distinctions (in particular event telicity) in children’s event construal (Shirai & Andersen, Reference Shirai and Andersen1995), whilst others assume a primary role for grammatical aspect distinctions (the ongoing or completedness of events) in children’s conceptualisation of events (Wagner, Reference Wagner2001).

From either the Distributional Bias (Tomasello, Reference Tomasello2003) or the Aspect First (Shirai & Andersen, Reference Shirai and Andersen1995; Wagner, Reference Wagner2001, Reference Wagner2009) accounts of language acquisition, it is clear that children have to learn to generalise their use of aspectual morphemes to express the ongoing nature of a telic event – for example, “closing a window” – and the perfective expression of an atelic event – for example, “played with blocks” (Wagner, Reference Wagner2009). A number of studies have examined the development of children’s understanding of aspect in cross-sectional designs with young children between 2 to 6 years. In general, these studies have used a picture matching task to examine whether children associate events expressed with perfective aspect to depictions of completed events and events expressed with imperfective aspect to ongoing events.

In this regard, there are mixed findings in the research concerning the age at which children can reliably distinguish between the perfective/imperfective expression of events: some research shows this is achieved by 3 years of age (Weist, Atanassova, Wysocka & Pawlak, Reference Weist, Atanassova, Wysocka and Pawlak1999; Weist, Lyytinen, Wysocka & Atanassova, Reference Weist, Lyytinen, Wysocka and Atanassova1997; Zhou, Crain & Zhan, Reference Zhou, Crain and Zhan2014), whilst other research shows this is not achieved until 5 years of age and is not as reliable as adults’ performance (Wagner, Reference Wagner2009). In addition, whilst 3-year-olds can distinguish between the perfective/imperfective expressions of telic events, they are less sensitive to a difference between the perfective/imperfective expressions of atelic events (Weist et al., Reference Weist, Atanassova, Wysocka and Pawlak1999). Young children’s difficulty with perfective atelic items may simply reflect a difficulty in representing such a situation pictorially – for example, the distinction between played/playing with blocks is arguably more difficult to portray than the telic version painted/painting a flower. Alternatively, children’s difficulty may reflect that distinctions between the ongoing/completed expressions of atelic events are just less significant than distinctions between the ongoing/completed expressions of telic events.

There is some support for the latter argument from studies with adults. Using the N400 ERP as a measure of semantic difficulty, Becker et al. (Reference Becker, Ferretti and Madden-Lombardi2013) contrasted events from the lexical category of accomplishment with activity events. For accomplishments, adults had less difficulty reading concepts which had been previously expressed in imperfective sentences than perfective sentences. In contrast, for activity events there was no difference in mean N400 ERP between the two grammatical aspect conditions. The authors suggest that grammatical aspect influences adults’ concept integration for accomplishment events because their mental representations of the two aspect manipulations differ. In contrast, they suggest that expressing activity events – for example, talk as “was talking” or “talked” – results in similar representations of the event.

Another reason for determining whether the temporal characteristics of events influence children’s pronoun resolution is that it may provide insight into children’s reading comprehension difficulties, in general. Seven- to 11-year-old children with poor reading comprehension have difficulties with pronoun resolution (Ehrlich & Remond, Reference Ehrlich and Remond1997; Elbro, Oakhill, Megherbi & Seigneuric, Reference Elbro, Oakhill, Megherbi and Seigneuric2017; Engelen, Bouwmeester, de Bruin & Zwaan, Reference Engelen, Bouwmeester, de Bruin and Zwaan2013; Francey & Cain, Reference Francey and Cain2014; Megherbi & Ehrlich, Reference Megherbi and Ehrlich2005; Oakhill & Yuill, Reference Oakhill and Yuill1986; Yuill & Oakhill, Reference Yuill and Oakhill1991), which contributes unique variance in reading comprehension (Elbro et al., Reference Elbro, Oakhill, Megherbi and Seigneuric2017). Of note, some research finds that poor comprehenders have particular difficulty identifying the referents of personal pronouns when these are co-referential with the Subject protagonist (Megherbi & Ehrlich, Reference Megherbi and Ehrlich2005): whereas 7- to 8-year-old good comprehenders demonstrate an advantage for Subject antecedents, same age poor comprehenders demonstrate an Object advantage.

These, and other, findings have been interpreted to reflect a difficulty in a backwards search for appropriate referents when the pronoun is encountered (Ehrlich & Remond, Reference Ehrlich and Remond1997). However, Engelen et al. (Reference Engelen, Bouwmeester, de Bruin and Zwaan2013) found that 6- to 11-year-old good and poor comprehenders differed in their expectancy for a re-mention of particular protagonists when listening to a narrative. In their study, children listened to a narrative while viewing a display containing line drawings of the four characters. Throughout the story, the characters were re-mentioned either by name (e.g., “squirrel”) or using a personal pronoun (“he”). Differences in the pattern of eye movements between the good and poor comprehenders were evident at the onset of a pronoun rather than after hearing a referring expression. Specifically, good comprehenders were more likely to fixate a pronoun’s referent than were the poor comprehenders, indicating that the good comprehenders anticipated the re-mention of the referent. The Engelen et al. (Reference Engelen, Bouwmeester, de Bruin and Zwaan2013) study is the first to show that good and poor comprehenders may differ in their processing of sentences prior to the pronoun.

In summary, the Event Structure account of pronoun processing claims that the temporal characteristics of events influence pronoun processing but to date this has only been tested in adults through the manipulation of the grammatical aspect of events with inherent endpoints (accomplishments). To examine this claim in more detail, this study examines adults’ pronoun resolution following events without inherent endpoints (activities) as well as those with inherent endpoints (accomplishments). Specifically, we test the prediction of the Event Structure hypothesis, that adults will be more likely to resolve a pronoun towards the previous Subject protagonist for events without inherent endpoints (activities) than for events with inherent endpoints (accomplishments). We also examine the influence of grammatical aspect on adults’ pronoun resolution within these two types of event. We test the reproducibility of the finding that the grammatical aspect of events with endpoints (accomplishments) influences adults’ pronoun resolution and test the Event Structure claim that the grammatical aspect of events without endpoints (activities) will not influence adults’ resolution of a subsequent pronoun (Kehler & Rohde, Reference Kehler and Rohde2013b). There is indirect evidence supporting this claim in the findings of the effect of grammatical aspect on adults’ concept integration, but it has not previously been directly investigated (Becker et al., Reference Becker, Ferretti and Madden-Lombardi2013).

There are contradictory findings in the literature regarding the age at which children demonstrate a Subject interpretation of an ambiguous pronoun and it is possible that this may be explained as a result of differences in the lexical and grammatical aspect of stimuli used in these studies. To examine this hypothesis, this study examines the influence of lexical and grammatical aspect on younger (7- to 11-year-old) and adolescent children’s (13- to 14-year-old) pronoun resolution and compares the performance of these two groups to adults’ performance using the same materials. Previous research has established that young children are sensitive to the thematic roles of protagonists in their pronoun resolution (Pyykkönen, Matthews & Järvikivi, Reference Pyykkönen, Matthews and Järvikivi2010) and can discriminate between events expressed with alternative grammatical aspects (Weist et al., Reference Weist, Lyytinen, Wysocka and Atanassova1997, Reference Weist, Atanassova, Wysocka and Pawlak1999; Wagner, Reference Wagner2009; Zhou et al., Reference Zhou, Crain and Zhan2014). However, to date, there have been no investigations of whether the lexical or grammatical aspect of events influences children’s pronoun resolution. The younger age range was included to establish whether or not there is an influence of lexical and/or grammatical aspect on the pronoun resolution in an unselected sample of children in this age range, which may identify a potential source of difficulty for children of this age with poor reading comprehension (Ehrlich & Remond, Reference Ehrlich and Remond1997; Elbro et al., Reference Elbro, Oakhill, Megherbi and Seigneuric2017; Engelen et al., Reference Engelen, Bouwmeester, de Bruin and Zwaan2013; Francey & Cain, Reference Francey and Cain2014; Megherbi & Ehrlich, Reference Megherbi and Ehrlich2005; Oakhill & Yuill, Reference Oakhill and Yuill1986; Yuill & Oakhill, Reference Yuill and Oakhill1991). The older age range was included to establish developmental trends in the influence of lexical and grammatical aspect on pronoun resolution. It was predicted that both groups of children would demonstrate the same pattern of influence as adults, but that adolescents’ performance would be more similar to adults’ than younger children’s.