1.1 Prominence, definiteness marking, and information status

An influential approach to referent management has been Centering Theory (Brennan et al. 1987; Gordon et al. 1993; Brennan 1995; Grosz et al. 1995; Strube & Hahn 1999). This theory assumes that (a) new discourse referents are added to a list of already existing referents and that (b) all referents are ranked according to their activation level or prominence (see also von Heusinger 2000). It is important to note that this ranking of referents is not at all rigid or fixed. It rather changes and is updated continuously as discourse unfolds. Now, while Centering Theory states that the prominence of the referents in an utterance is by and large determined by the referents’ grammatical role, more recent research has shown that grammatical role is only one factor among many, including thematic role (Stevenson et al. 1994; Ferretti et al. 2009; Fukumura & van Gompel 2010; Schumacher et al. 2015), topic-hood (Kaiser 2011), focus (Crawley 2001; Kaiser 2011), aspect (Kehler et al. 2008; Kehler & Rohde 2013), implicit causality (Stevenson et al. 1994; Arnold 2001; Fukumura & van Gompel 2010; Hartshorne & Snedeker 2013), and discourse goals (Jasinskaja et al. 2015).

But how can we measure a referent’s prominence or activation status? There have been several approaches in the literature. Centering Theory focuses on the local coherence between two adjacent sentences and uses the ranking of the discourse referents to determine which anaphoric expression will be used for re-mentioning. The claim is that speakers use a pronoun to refer to the most prominent, i.e. the highest ranked, referent, and a definite noun phrase to refer to less prominent, i.e. lower ranked, referents. This approach reflects the more general idea that the prominence level of a discourse referent can be assessed by testing which type of referring expression a speaker uses to refer back to that referent (cf. Ariel 1988; Gundel et al. 1993). The more prominent a referent is, the more likely it is that a speaker will use a reduced expression, such as a pronoun, to refer back to it.

Another approach is to test ambiguous pronoun resolution, such as the resolution of a personal pronoun (Crawley & Stevenson 1990; Stevenson et al. 1994; Bosch et al. 2007; Bouma & Hopp 2007; Kaiser & Trueswell 2008; Kaiser 2011; Kurczek et al. 2013; Rohde & Kehler 2014). In this approach, the prominence level or accessibility of a referent is measured by the degree to which a subsequent ambiguous pronoun is resolved to that referent. For example, it has been shown that comprehenders more often resolve an ambiguous personal pronoun to the preceding subject than the preceding object referent (Arnold 2001).

In the present study, we assess the prominence level and accessibility of discourse referents of descriptive noun phrases. We measure a referent’s accessibility at the point the referent is newly introduced in discourse, using event-related brain potential (ERPs, Experiment 2), and at the point a following ambiguous pronoun needs to be resolved (Experiment 1). The central claim is that the introduction of a new discourse referent through a descriptive noun phrase and the accessibility of that referent at later re-mentioning involve two separate processes. One process relates to the noun phrase’s descriptive content, the other to the referential choice a speaker or hearer needs to make. While these two processes have been attested for noun phrase processing in previous studies, we extend these studies by also testing for contextually induced pragmatic inferences emerging at the sentence level, i.e. after the noun phrase has been retrieved and integrated. Indeed, such inferences are predicted to occur following considerations from more theoretical accounts. Our aim, then, is to provide a comprehensive model of descriptive noun phrase processing that builds on empirical data and goes beyond noun phrase retrieval and integration.

The descriptive content of a noun phrase provides the comprehender with a concept, which contributes most of the noun phrase’s semantics. What is important for the present study is the observation that the concept of a noun phrase can establish a relation to an already activated concept, the concept of the anchor. According to Prince (1981; 1992, more recently Baumann & Riester 2013), the concept or information status of a newly introduced noun phrase can be given, inferred (inferable) or brand-new, although in the present study, we will only test referents with inferred and brand-new information statuses.

For example, in (1a), the concept of the noun phrase the pretty boy next to the window is brand-new, as the concept PRETTY BOY cannot be inferred from the concept of any noun phrase in the preceding context. In contrast, the concept of the trainer next to the window in (1b) is already available at noun phrase encounter, as the concept TRAINER can be inferred from the concept GYM. Or, put differently, the concept of the noun gym pre-activates the concept of the noun trainer.

While the descriptive content of a noun phrase can activate a concept that delimits or determines the set of potential referents, the definite and indefinite article lead the comprehender to select a matching referent from that set. Since Frege (1892) and Russell (1905), the semantics of the definite and indefinite article is one of the main research topics in formal semantics and analytic philosophy. While most researchers agree that the semantics of the indefinite article comes with an existential entailment, such that it signals to the comprehender that a referent exists without introducing an individual referent, the semantics of the definite article is subject to some debate (see Elbourne 2013 for an overview). Russell (1905) and Neale (1990) propose that the definite article is a quantifier that expresses an existence and uniqueness entailment of an entity that satisfies the descriptive material. Frege (1892), Strawson (1950), Heim (1991), and Elbourne (2013) assume that definite noun phrases are referential expressions with a uniqueness presupposition, such that definite noun phrases always introduce an individual referent. Finally, Heim (1982), Kamp (1981), and Roberts (2003) suggest that the definite article expresses a familiarity presupposition, such that definite noun phrases can only felicitously be used when they can be linked to an antecedent. In line with Heim (1991), Strawson (1950), and Elbourne (2013), we assume that the definite article contributes a uniqueness presupposition and that the indefinite article triggers an existential entailment.

Based on the examples presented in (2)–(5) below, we further propose that a noun phrase’s information status (inferred or brand-new) and definiteness marking (definite or indefinite) interact in interesting ways and that they do so at the level of a sentence’s proposition. For brand-new definite noun phrases like the pretty boy next to the window in (2) the contribution of the definite article is to license a unique set, which is described by the noun phrase. For example, in (2) we assume that there is exactly one pretty boy in the described event.

For inferred definite noun phrases like the trainer next to the window in (3), on the other hand, the definite article licenses the uniqueness of the associated concept. Unlike for brand-new definites, the concept of inferred noun phrases, TRAINER in (3), is pre-activated by an anchor, gym, and therefore the referent must be related to the anchor concept, GYM. We might then say that the main difference between referent uniqueness in (2, the pretty boy) and referent uniqueness in (3, the trainer) is that only in (3) does a comprehender identify a unique referent within a pre-activated set of referents.

More interesting, and perhaps more controversial, is the way indefinites can introduce discourse referents. As stated above, we agree that the indefinite article triggers an existential entailment. That is, indefinite articles express that the set of potential referents is non-empty. The particular type of referent that is assigned to the concept, then, depends on the linguistic context and additional pragmatic inferences, which, we argue, are linked to the information status of the noun phrase. For brand-new indefinites and in the absence of any contextual information (e.g., a domain restriction or common frame/event knowledge), sentences like the one in (4a) have the same truth conditions as sentences like the one in (4b). Nevertheless, in a situation where we know that more than one trainer lives in the building, uttering (4a) is pragmatically infelicitous (Heim 1991).

The indefinite noun phrase a trainer in (4a) leads to a uniqueness implicature that follows from the Maxim of Quantity: (4b, one or two trainers) and not (4a, a trainer) should be uttered if there is reason to believe that more than one trainer lives in the building. Thus, the uniqueness implicature of (4a) makes a trainer very similar to the trainer in (4c), where uniqueness is presupposed (see Heim 1991 for a discussion).

Turning to the inferred indefinites, we first note that, given specific context information, a speaker often knows whether there must be a unique referent that fits the concept or not. For example, in the context of a gym class, a comprehender presumably knows that there is exactly one trainer. In the context of a gym, on the other hand, the comprehender might assume that there are multiple trainers although it is also plausible that there is only one trainer. To make this point more explicit, consider the trainer in (5a) and a trainer in (5b).

The anchor gym in the first sentence activates a number of concepts, including TRAINER, PARTICIPANT, WORK OUT, SWEAT, etc. By virtue of belonging to the pre-activated set of referents, the concept associated with the descriptive noun phrase, i.e. TRAINER, is already activated at the point the noun phrase (the trainer in (5a) and a trainer in (5b)) is encountered. Just like for the inferred definites, the pre-activated concept delimits the set of potential referents.

However, unlike for the definites cases, the indefinite article expresses that there is at least one trainer in the described event, which is coherent with the pre-activation of the concept TRAINER. Under these conditions, i.e. when additional information or a domain restriction is available, the indefinite article additionally expresses a non-uniqueness condition, namely that there is more than one trainer. In such cases, the indefinite article does not contrast with one and more, but instead with the definite article, which expresses uniqueness. In line with the principle of Maximize Presupposition discussed in Heim (1991; 2011) if a speaker knows for a particular setting that there is only one trainer, she or he is urged to use the definite article. Thus, if she/he uses the indefinite article, she/he is likely to signal that there is more than one trainer. As an illustration, consider the statement Bill has a bicycle. He’s cleaning a saddle. This statement seems infelicitous, as it contrasts with our knowledge that a bicycle has exactly one saddle.

It then seems that the indefinite article can interact with the immediate linguistic context in very different ways: When there is no domain restriction and no pre-activation by the previous context, a uniqueness implicature emerges. When there is a domain restriction or pre-activation through previous linguistic context, a non-uniqueness condition is triggered (see Heim 1991 for an extensive discussion of this apparently paradoxical behavior).

Following from the considerations above, we propose that the prominence and activation status of definite and indefinite noun phrases with brand-new concepts is likely to be very similar. For both noun phrases, a brand-new concept is introduced and the associated referent is identified either via a uniqueness presupposition (for definite articles) or a uniqueness implicature (for indefinite articles). For definite and indefinite noun phrases with inferred concepts, we suggest that the former are more prominent and should come with a higher activation status than the latter. This is because comprehenders can select or activate a uniquely identifiable referent for inferred definites but not for inferred indefinites. Indeed, it is possible that comprehenders remain with the concept, e.g., the concept of trainer in (5b, a trainer in the context of a gym) without even activating a referent.

1.2 Experimental approaches to information status and definiteness marking

The idea that the introduction of a referent with a descriptive noun phrase involves two processes is based on the semantic analysis that descriptive noun phrases consist of a discourse referent and some descriptive content. Karttunen (1969), Kamp (1981), Heim (1982; 2011), and Farkas (2002) have long pointed out that a descriptive noun phrase has two essential parts: a referent that licenses anaphoric links in the subsequent discourse, and a descriptive part that is associated with the concept that undergoes interpretative variation, depending on the particular context of interpretation. What is missing, however, is a systematic empirical investigation of these two parts in moment-by-moment comprehension. We are also not aware of a comprehensive model that implements the two processes and aims at accounting for noun phrase processing, including referent access and integration, as well as for additional inferences that may be obtained at the sentence level.

The lack of more empirically driven data is partly due to the fact that most studies in the field used proper names for the introduction of new discourse referents – presumably because proper names carry little conceptual information that could potentially interfere with the parameters under investigation (e.g., grammatical role, thematic role, implicit causality, etc.).

Two exceptions, both of which used event-related brain potentials (ERPs), are Burkhardt (2006) and Schumacher (2009). For ERPs at the noun, both studies found that inferred referents were accessed more easily than brand-new referents (see also Schumacher & Hung 2012), which is fully compatible with the notion of concept pre-activation in the case of inferred referents. Schumacher (2009) also found that definite articles yielded stronger processing costs than indefinite articles, suggesting that the uniqueness condition of definite articles was computed at article encounter. Interestingly, for ERPs elicited at the noun neither Burkhardt (2006) nor Schumacher (2009) found any effect of definiteness marking. In other words, nouns of definite marked noun phrases behaved very similarly to nouns of indefinite marked noun phrases. This might suggest that, while unique vs. non-unique identifiability of a referent is triggered at the article, it is only fully computed at the sentence level and does therefore not significantly affect the retrieval or integration of the referent at the point that referent is encountered, i.e. at the denoting noun. Thus, if brand-new indefinites trigger a uniqueness implicature and inferred indefinites a non-uniqueness implicature, these additional pragmatic inferences do not seem to be found at the noun phrase but rather at the sentence level.

Additional support for separate effects of information status and definiteness marking and some preliminary support for the claim about pragmatic inferences at the sentence level come from Brocher et al. (2016). The authors created short stories consisting of a context sentence that provided an anchor (e.g., gym), a second sentence that introduced two human referents, one in subject and one in direct object position, and a third sentence that included an ambiguous personal pronoun. The manipulation of interest pertained to the referent in object position of the second sentence, which was always a descriptive noun phrase.

Monitoring eye fixations time-locked to the onset of the pronoun, Brocher et al. found that participants looked more at the picture of inferred definite than the picture of inferred indefinite referents. No differences in fixation times were observed for brand-new definite and brand-new indefinite referents. These data are compatible with the view that for both brand-new definite and indefinite descriptions, comprehenders identified and activated a unique referent, either through presupposition or through implicature. Brocher et al.’s (2016) data are also compatible with the view that comprehenders did not select and activate a unique referent for inferred indefinites, presumably because these expressions triggered a non-uniqueness implicature.

In interpreting their results, Brocher and colleagues proposed a Dual-Process Activation Model, which is summarized in Figure 1. The model states that the introduction of a new discourse referent with a descriptive noun phrase involves two processes, concept activation and referent activation. Concept activation is linked to a noun phrase’s information status: Concepts of inferred noun phrases are pre-activated by an anchor expression in preceding context, while concepts of brand-new noun phrases are not pre-activated. This explains why discourse referents of inferred noun phrases were accessed more easily than referents of brand-new noun phrases in Burkhardt (2006) and Schumacher (2009). Referent activation is linked to the definite and indefinite article of the noun phrase. Definite articles lead the comprehender to uniquely identify a referent, whereas indefinite articles lead the comprehender to assert referent existence. This distinction is in line with the data reported in Schumacher (2009), who found differences in the ERP signature between definite and indefinite articles.

Figure 1

Illustration of the Dual-Process Activation Model.

Thus, the findings from previous studies on descriptive noun phrase processing (retrieval and integration) are compatible with the assumption that there are two distinct processes in referent management, namely concept activation and referent activation. The more novel part of the Dual-Process Activation Model, then, is that it predicts the integration of specific pragmatic inferences at the sentence level. The claim is that when referent activation triggers an existential entailment and the concept of the associated noun phrase is brand-new, comprehenders can identify a referent through a uniqueness implicature. If, in contrast, referent activation triggers an existential entailment and the concept of the associated noun phrase is already activated, comprehenders draw a non-uniqueness implicature, which does not lead to the activation of an individual referent. This part of the model explains why brand-new indefinites patterned with their definite counterparts in Brocher et al. (2016). Under both conditions, the referent was uniquely identified. It also explains why inferred definites were more accessible than inferred indefinites. Inferred definites not only led to unique identifiability of a referent, but also allowed comprehenders to directly access that referent from the pre-activated set. Inferred indefinites, finally, led to a non-uniqueness implicature so that there was no dedicated referent that the noun phrase could refer to, promoting the competing subject referent to an even stronger candidate for pronoun resolution.

Indeed, Brocher and colleagues speculated that inferred indefinites might not introduce an individual discourse referent, but rather a role, i.e. a complex functional structure that itself can be filled with individual referents (cf. Zwarts 2014), similar to weak referential items that are introduced by bare nouns and weak definites (Carlson et al. 2013). In other words, when a noun phrase is encountered that can be linked to a previously activated concept and its designated set, the definite article uniquely identifies one element, i.e. the unique element of the set, while the indefinite article might merely assert that the set is non-empty. This can lead to some processing costs when an individual needs to be identified, which was the case at pronoun encounter in Brocher et al. (2016).

Although the Dual-Process Activation Model is the first model of descriptive noun phrase processing that goes beyond the noun phrase level and extends to discourse-level processing, and although the results of Brocher et al. (2016) largely converge with previous findings (Burkhardt 2006; Schumacher 2009), there are two shortcomings to their materials. First, Brocher and colleagues used potentially different sources of uniqueness for inferred and brand-new referents and, as a consequence, also used different nouns in the inferred conditions and the same noun in the brand-new conditions. In the inferred definite condition, the authors used referents whose concept was unique by virtue of anchor encounter, such as the trainer in the context of a gym class. In the inferred indefinite condition, they used referents whose concept was non-unique by virtue of anchor encounter, such as a participant in the context of a gym class. For brand-new referents, in contrast, referent uniqueness was signaled to the comprehender solely by the article of the critical noun phrase (a pretty boy vs. the pretty boy in the context of a gym class). We might then argue that Brocher et al. (2016) investigated different sources of uniqueness in their inferred and brand-new conditions. In the former, they tested uniqueness triggered by the anchor and the world knowledge associated with it (knowing what a gym class looks like means knowing that there will be exactly one trainer). In the latter, they tested uniqueness triggered by the article of the noun phrase. Because Brocher et al.’s most critical finding pertains to the fact that (non-)unique identifiability differently affected the accessibility of inferred and brand-new referents, it is important to rule out the possibility that their findings were due to the kind of unique identifiability tested in the materials.

Second, Brocher et al.’s study was about pronoun resolution, measuring the competition between the object and the subject referent. In their study, listeners encountered the ambiguous pronoun after critical referents had already been introduced and therefore after processing of the critical descriptive noun phrase. Although this design allowed the authors to test for the integration of specific pragmatic inferences, it did not allow them to test concept activation and referent activation at the very point the noun phrase was retrieved and integrated in discourse.

1.3 Overview of experiments

In the two experiments we report here, we addressed both shortcomings in Brocher et al.’s (2016) study discussed above and further tested the validity of the Dual-Process Activation Model. We created short stories consisting of three sentences. The first sentence included a noun phrase that served as anchor providing the concept of the inferred referents. No such anchor was provided for brand-new referents. The second sentence introduced two (human) referents. While the subject referent was always a proper name, the concept of the critical object referent could either be inferred from preceding context (inferred) or not (brand-new). Furthermore, the object noun phrase was a noun phrase with either a definite or an indefinite article. Crucially, except for the object noun phrase, all materials were identical across conditions.

In Experiment 1, we tested whether, at the sentence level, comprehenders integrate the various pragmatic inferences discussed above and reflected in the Dual-Process Activation Model (cf. Figure 1) when source of uniqueness is held constant between inferred and brand-new referents. We used a visual world eye tracking experiment that closely followed the design and procedure of the eye tracking study presented in Brocher et al. (2016): We measured eye fixations while participants resolved the ambiguous pronoun in the final sentence of the stories. If Brocher et al.’s results in their inferred conditions extend from anchor-triggered uniqueness (gym class – the trainer) to article-triggered uniqueness (gym – the trainer), we should find more looks to the object picture in the inferred definite than the inferred indefinite condition. This would be in line with the assumption that comprehenders activate a unique referent when they encounter a definite noun phrase with an inferred concept, while they do not activate an individual referent when they encounter an indefinite noun phrase with an inferred concept. No large differences should be obtained between the brand-new definite (gym – the pretty boy) and the brand-new indefinite condition (gym – a pretty boy). Both these conditions should lead to unique identifiability of the associated referent.

Experiment 2 used ERPs and tested specific neurophysiological markers of referent access and integration at the very point the noun phrase and associated referent were mentioned for the first time in the discourse. This experiment, therefore, addressed the second shortcoming in Brocher et al.’s study discussed above. Because Experiment 2 tested noun phrase processing directly (while Experiment 1 tested referent accessibility at re-mention), this study, unlike the eye tracking study, used the same noun in the inferred and brand-new conditions. It therefore tested the same concepts across these conditions. Experiment 2 is important because the two processes incorporated in the Dual-Process Activation Model, i.e. concept and referent activation, are expected to also affect the retrieval and integration of definite and indefinite noun phrase. Referent activation is tightly linked to the processing of the article, while concept activation is linked to the processing of the noun. As will become clearer below, we expected nouns with inferred concepts to be accessed and integrated more easily than nouns with brand-new concepts.

2.2 Results

For the discussion of fixation times at pronoun encounter, we will continue to speak of inferred and brand-new referents although, of course, at pronoun encounter referents are no longer inferred or brand-new. Changing the terminology between first (full noun phrase) and second encounter (pronoun), though, would be rather confusing and all critical manipulations (information status and definiteness marking) pertain to the first encounter of the referents.

Mean accuracy to comprehension questions was 84% and all participants performed above 80%. Before statistical analyses, we excluded 7.4% of the data due to blinks and an additional 1.7% of data points because no picture on the screen was fixated within a specific time frame (see below). For the remaining data, we analyzed all fixations between pronoun onset and 1400 ms post pronoun onset. We then divided the resulting 1400 ms into a baseline time frame, consisting of the first 200 ms post pronoun onset, and an additional four time frames, each consisting of 300 ms. Note that the first frame of interest ranged from 200 ms to 500 ms post pronoun onset, because it takes around 200 ms for the eye to launch a saccade as response to a stimulus (Matin et al. 1993). We calculated mean fixation times to the picture of the subject referent, object referent, and look-away object per participant, trial, and time frame. Whenever a fixation within a frame landed on one of the three pictures, the associated referent received a score of 1, while the two non-fixated referents received a score of 0.

Statistical analyses were conducted in R (R version 3.2.2), using the lme4 package (Bates et al. 2014). We used the same analytic plan as Brocher et al. (2016). We conducted nested hierarchical generalized linear regression models with looks to the object picture relative to the sum of looks to all three pictures as dependent measure. To that end, all data points were included in the analysis as a vector containing the looking time to the object referent and the sum of looking time to the object picture, subject picture, and look-away picture. For example, given a particular time frame of 300 ms, if 90 ms of looks within that frame fell on the object picture, 150 ms on the subject picture, and 50 ms on the look-away picture, the dependent measure for this particular frame and condition would be (90, 290). We opted for this statistical approach because it directly reflects the binomial distribution of the data (i.e. given a particular frame, a participant either looks at a picture of interest, 1, or not, 0), while acknowledging that conditions might also differ with respect to the looks that did not fall on the target object picture (by including the sum of looks to all pictures on the screen in the dependent variable).

We modeled the influence of the two predictors information status (inferred or brand-new) and definiteness marking (definite or indefinite article) and their interaction on mean fixation times within a time bin. Both predictors were sum-coded prior to analyses. Models were then fitted for each time frame individually. They included by-participants and by-items intercepts as well as by-participants and by-items random slopes. The random slopes for the two earlier time bins (200–500 ms, 500–800 ms) included the linear combination of information status and definiteness marking in the by-participants slope and definiteness marking in the by-items slope. For the two later time bins (800–1100 ms, 1100–1400 ms), both random slopes included the linear combination of information status and definiteness marking. P-values for the analysis of fixation times were corrected for multiple testing, applying the Bonferroni procedure (for five comparisons) and corrected p-values will be reported for each time frame.

The time course of the proportion of looks to the picture of the object referent is plotted in Figure 3. Results of the inferential statistics are summarized in Table 2. Because predictors were sum-coded, the intercepts reflect the grand average of looking time across all four conditions. The coefficients present deviations from that average. A positive coefficient for definiteness marking reflects an increase and a negative value a decrease in looking time to the object picture in the definite conditions. Likewise, for information status, a positive coefficient reflects an increase and a negative value a decrease in looking time to the object picture in the inferred conditions.

Figure 3

Looks to the picture of the object referent (in%) along with standard errors per time frame and condition; the beginning of the x-axis marks the onset of the pronoun; the numbers represent ms post pronoun onset; inferred = referents with inferred concepts; brand-new = referents with brand-new concepts; definite = noun phrases with definite article; indefinite = noun phrases with indefinite article.

As can be seen in Figure 3, while mean looking times are somewhat disparate within the 200 ms within pronoun encounter, conditions start to diverge at 500 ms post pronoun onset. Although there is a general tendency for pictures of definite referents to attract more looks than pictures of their indefinite counterparts, this difference seems stronger for inferred than brand-new referents. The difference between inferred definite and inferred indefinite referents is most pronounced between 500 ms and 1100 ms post pronoun onset.

Results of the regression models confirm this observation. The two models fitted for the time frames 500 ms–800 ms and 800–1100 ms, respectively, revealed a significant Information status × Definiteness marking interaction. Resolving this interaction for the 500 ms–800 ms frame confirmed that inferred definite referents attracted more looks than inferred indefinite referents, b = 0.50, SE = 0.01, t = 3.63, p < .001, with no significant difference between brand-new referents, b = 0.61, SE = 0.62, t = 0.98, p = .652 (p-values Bonferroni-corrected for two comparisons). Resolving the interaction for the 800 ms–1100 ms frame revealed the same pattern. Inferred definite referents continued to be fixated more than their indefinite counterparts, b = 1.50, SE = 0.61, t = 2.46, p = .028. For brand-new referents, again, no reliable difference was obtained, b = 0.74, SE = 0.51, t = –1.44, p = .302 (p-values Bonferroni-corrected for two comparisons). We also fitted a model for the time frame that included the very onset of the pronoun plus the subsequent 200 ms to test for baseline effects. There were no statistically reliable differences between definite and indefinite or inferred and brand-new referents, nor was there an interaction, all zs < 1, all ps > .6.

2.3 Discussion

Experiment 1 replicates the data reported in Brocher et al. (2016) and renders it unlikely that their results were due to the testing of different sources of uniqueness in the inferred and brand-new conditions, namely anchor-triggered and article-triggered uniqueness. Data from Experiment 1 are also not compatible with the key assumptions of accessibility scales, which predict definite descriptions to be generally more accessible than indefinite descriptions, and Functional Centering Theory, which predicts inferred referents to be generally more accessible than brand-new referents.

Instead, our data suggest that comprehenders used both the information status of a referent as well as the definiteness marking of the associated noun phrase to integrate specific pragmatic inferences at the sentence level, i.e. at a point in discourse at which the referent had already been accessed and integrated.

This is in line the Dual-Process Activation Model as well as with more theoretical approaches in the field (Karttunen 1969; Kamp 1981; Heim 1982; Farkas 2002): In contexts where a noun phrase and its associated concept are brand-new, both the definite and indefinite article lead to the activation of a discourse referent. The definite article leads to referent activation (or identification) through a uniqueness presupposition. The indefinite article, on the other hand, leads to the activation of a discourse referent through the combination of its primary function to express existence together with a uniqueness implicature, which then leads to the referent. As a consequence, no significant differences were obtained when a referent needed to be assigned to a later occurring pronoun, because a referent was equally activated in both conditions (brand-new definite and brand-new indefinite).

Now, the referential choice prompted by the article and the additional pragmatic inferences differ in contexts where the concept of a referent had been pre-activated by an anchor. The pre-activated concept provides knowledge common to both the speaker and hearer and thereby restricts the choice of which referents to activate. Under these conditions, the definite article leads to the restriction that one unique element needs to be accessed from the pre-activated set of elements, while the indefinite article expresses non-uniqueness and does not activate a particular referent, but rather acknowledges the existence of a set of referents.

For example, in the context of a gym, the noun phrase a trainer simply affirms that there are typically trainers at a gym, without pointing the hearer to the identification of a specific trainer. The inferred indefinite referent is then best represented by a role (Zwarts 2014) and its referential properties similar to the properties of bare nouns and weak definites (Carlson et al. 2013). It is this very assumption of the Dual-Process Activation Model that explains the observed differences between inferred indefinite and brand-new indefinite referents. Only for the latter, but not the former, do hearers infer that there is a referent that can be uniquely identified.

Note that one might argue that the experimental design we used favored referents of definite over referents of indefinite descriptions. That is, one might argue that participants linked the pronoun to the picture of the object referent more quickly when that referent could be uniquely identified than when it could not because the corresponding picture showed one instance of, for example, a trainer. Although generally plausible, we believe that a direct link between picture and definiteness marking has not (significantly) affected our results. First, if presenting a picture of a single person made definite noun phrases more quickly available than indefinite noun phrases, we should have found more looks to the picture of definite than indefinite noun phrases also in the brand-new conditions, which is not what we observed. Second, while it is possible that participants’ gazes moved more quickly to the picture of the object referent at article encounter when that article was the rather than a, the dependent measure in Experiment 1 was the mean looking time at pronoun encounter, which was considerably later in the stories than the onset of the object noun phrase.

Finally, our data do not allow us to determine whether the observed differences in pronoun resolution between subject and object antecedent were due to differences in next mention bias, differences in pronoun preference, or both. Considering that the preference of specific referring expressions has mostly been associated with grammatical and thematic role (as well as recency, see Arnold 2010 for a brief review), and also considering that all our target referents appeared in (non-preferred) object position, we suspect that our results are most likely due to differences in next mention bias, rather than to differences in pronoun preference.

3.2 Results

Analyses were conducted for various windows of interest. All windows were time-locked to the beginning of the respective word of interest, i.e. to the onset of the article and noun, respectively. For the article, we conducted an ANOVA on mean amplitudes in the 300 ms–700 ms window post article onset (Anderson & Holcomb 2005; Schumacher 2009). For the noun, we performed separate ANOVAs for mean amplitudes in the N400 window, ranging from 300 ms to 500 ms post noun onset, and the late positivity window, ranging from 500 ms to 800 ms post noun onset. All windows of analysis are based on previous studies in the field and were determined prior to data collection.

ERPs on article. Grand averages of the ERPs time-locked to article onset (a/the) are depicted in Figure 4. The output of the corresponding ANOVA is presented in Table 4. Results of the supplemental analysis on midline electrodes can be found in the Online Supplement, Appendix B. Inspection of Figure 4 reveals that definite articles yielded larger negativities than indefinite articles in frontal channels, while indefinite articles led to larger negativities than definite articles in posterior electrodes. Both these observations pertain more to the electrodes on the left than to the electrodes on the right side of the scalp. The ANOVA, then, registered a significant ROI × Definiteness marking interaction. Follow-up analyses confirmed that definiteness marking was significant in the left frontal, F(1, 23) = 5.41, p = .029, and left posterior ROI, F(1, 23) = 4.77, p = .039.

Figure 4

Grand averages for ERPs time-locked to article encounter. Averages are provided for the definite (blue) and indefinite article (red).

ERPs on noun. Grand averages of ERPs time-locked to noun onset (trainer) are provided in Figure 5. Results of the statistical analyses on N400s and late positivities are provided in Table 5. Results of the analyses on central electrodes can again be accessed in Appendix B of the Online Supplement. As predicted, and replicating previous studies, we found overall smaller N400s for inferred than for brand-new referents, although it is important to note that visual inspection of Figure 5 suggests that this difference was mainly driven by brand-new indefinite referents. Nevertheless, only the main effect of information status reached statistical significance. In addition, we found smaller positivities for inferred than brand-new referents, which is compatible with previous findings showing that concept pre-activation can ease referent integration in non-topic positions (Hung & Schumacher 2012; Schumacher & Hung 2012). Information status interacted with ROI. Resolution of the ROI × Information status interaction revealed that the effect of information status was only reliable in the right posterior ROI, F(1, 23) = 4.38, p = .048.

Figure 5

Grand averages for ERPs time-locked to noun encounter. Averages are provided for inferred definite noun phrases (green), inferred indefinite noun phrases (yellow), brand-new definite noun phrases (red), and brand-new indefinite noun phrases (blue).

3.3 Discussion

Data from Experiment 2 are compatible with the various claims of the Dual-Process Activation Model and broadly line up with previous studies on noun phrase processing. As predicted, both definiteness marking, which we link to referent activation, and information status, which we link to concept activation, affected the very introduction of a new discourse referent with a descriptive noun phrase.

Definite articles elicited larger negativities than indefinite articles in frontal electrodes on the left side of the scalp, replicating Schumacher (2009), while indefinite articles elicited larger negativities than definite articles in posterior electrodes also located at the left side of the scalp, which replicates Anderson & Holcomb (2005). Thus, the data of Experiment 2 are compatible with both Schumacher (2009) and Anderson & Holcomb (2005). We argue in line with these studies that the larger negativity for definite rather than indefinite articles in frontal electrodes reflects the fact that the definite, unlike the indefinite, article instructs the comprehender to search for an individual referent in previous context (Schumacher 2009). The larger negativity for the indefinite compared to the definite article, in contrast, reflects the fact that the indefinite unlike the definite article leads the comprehender to anticipate new information, more specifically a new discourse referent. What is important with respect to the notion of referent activation, as is reflected in the Dual-Process Activation Model, is that only the definite article initiates a process of referent identification.

Turning to the ERPs elicited at the nouns, we found that inferred noun phrases were accessed with more ease than their brand-new counterparts, as indicated by significant differences in N400 magnitude. This finding is fully compatible with Burkhardt (2006; 2007), Schumacher (2009), and Schumacher & Hung (2012), as well as with the idea that a noun’s information status can be used to establish coherence. Our data also show that the pre-activation of a referent’s concept leads to easier referent integration in discourse. This finding adds to the evidence that the availability of an inference relation (e.g., between GYM and TRAINER) affects referent integration, at least when the noun phrase of that referent appears in canonical, non-topic position (Burkhardt 2007; Schumacher & Hung 2012).

Finally, the retrieval and integration of the noun in object position were unaffected by definiteness marking. These findings, which corroborate the data reported by Schumacher (2009), suggest that comprehenders did not compute referent uniqueness vs. non-uniqueness when processing the noun of the descriptive noun phrase. Instead, and as we proposed in our discussion of the Dual-Process Activation Model above, uniqueness and non-uniqueness of a referent seem to be fully computed via presupposition and implicature at a sentence level. When accessing and integrating the critical noun phrase in our stories, participants were still in the process of generating the proposition of the respective sentence. Thus, at this point, they seem not to have derived the associated presuppositions and implicatures associated with the referents.