Computational cognitive modeling of predictive sentence processing in a second language (2022)

Abstract: We propose an ACT-R cue-based retrieval model of the real-time gender predictions displayed by second language (L2) learners. The model extends a previous model of native (L1) speakers according to two central accounts in L2 sentence processing: (i) the Interference Hypothesis, which proposes that retrieval interference is higher in L2 than L1 speakers; (ii) the Lexical Bottleneck Hypothesis, which proposes that problems with gender agreement are due to weak gender representations. We tested the predictions of these accounts using data from two visual world experiments, which found that the gender predictions elicited by German possessive pronouns were delayed and smaller in size in L2 than L1 speakers. The experiments also found a “match effect”, such that when the antecedent and possessee of the pronoun had the same gender, predictions were earlier than when the two genders differed. This match effect was smaller in L2 than L1 speakers. The model implementing the Lexical Bottleneck Hypothesis captured the effects of smaller predictions, smaller match effect and delayed predictions in one of the two conditions. By contrast, the model implementing the Interference Hypothesis captured the smaller prediction effect but it showed an earlier prediction effect and an increased match effect in L2 than L1 speakers. These results provide evidence for the Lexical Bottleneck Hypothesis, and they demonstrate a method for extending computational models of L1 to L2 processing.

## introduction although the world population is quickly becoming bilingual, there are very few computational models of bilingual sentence processing. because most of these models were developed for technological applications-e.g., automatic translation-, this results in a scarcity of models that are cognitively realistic or even evaluable with human data @xcite @xcite . however, such models are crucial to develop computational research that is informed by state-of-the-art psycholinguistic work. with this goal, we propose a computational cognitive model of bilingual processing built in an architecture, act-r, which is designed to model human cognition and can be evaluated with human data @xcite . the act-r architecture has also been used to model a number of linguistic phenomena, such as retrieval interference effects in linguistic dependency resolution @xcite , the influence of prominence on pronoun resolution @xcite , the effect of memory load on sentence processing @xcite , sentence processing in patients with aphasia @xcite , the interaction of sentence processing and eye movements @xcite , and incremental formal semantic processing @xcite . accounts of bilingual processing can be divided in terms of how they explain differences between native (l1) and non-native (l2) processing. here we focus on two different explanations of l1-l2 differences. the first, the interference hypothesis (ih), makes reference to the cue-based retrieval theory @xcite . the interference hypothesis stipulates that memory retrieval is key for different parts of sentence processing, including the processing of non-local pronoun-antecedent dependencies like "john noticed that richard i had cut himself i with a knife". when "himself " is encountered, speakers attempt to retrieve an antecedent matching the pronoun features. retrieval success requires suppressing interfering elements that match some but not all of the relevant features (e.g., "john" has the appropriate gender and number features but not the syntactic ones, because it is outside the clause of the pronoun). the interference hypothesis proposes that l1 and l2 speakers are similar in their likelihood of initiating retrieval operations, but that l2 speakers are more prone to interference, yielding more misretrievals (e.g., wrongly recovering "john" as the pronoun's antecedent). by contrast, the lexical bottleneck hypothesis (lbh) is framed within so-called capacity-based accounts, which propose that l1-l2 differences arise because speakers process an l2 in a noisier cognitive architecture, resulting in slower and more error-prone parsing @xcite @xcite . the lexical bottleneck hypothesis proposes that l1-l2 parsing differences are due to variability in the bilingual lexicon. specifically, because lexical processing "precedes and feeds into syntactic processing, key characteristics of bilingual lexical processing may cause aspects of non-target parsing" @xcite . with regard to grammatical features like gender-the focus of this paper-the claim is that l2 speakers fail to use this information for syntactic processing because l2 words have weaker or more unstable gender representations, making the retrieval of gender information less robust in l2 than in l1. an additional factor-not modeled here-is l1 transfer, such that l2 gender processing may be harder in syntactic contexts that differ between the l1 and the l2. we evaluate the interference hypothesis and the lexical bottleneck hypothesis by using their claims to modify an act-r model that was previously shown to capture l1 predictive processing @xcite . the predictions of the modified act-r models are evaluated against the results of two eye-tracking experiments that examined how l1 and l2 speakers use gender features to do memory retrieval and to predict upcoming referents @xcite . we show that the act-r version that implements the lexical bottleneck hypothesis does a better job at capturing l2 gender predictions. our results-although currently limited to gender-suggest that the lexical bottleneck hypothesis provides a suitable framework to model the predictive use of morphosyntactic information in l2, and could be extended to other features such as number, case and animacy. ## human data the human data was taken from two visual world eye-tracking experiments with the same materials and design but two different groups of participants: 74 l1 german speakers @xcite , experiment 2) and 132 l2 german learners @xcite @xcite . the l2 group comprised native speakers of spanish and english. because they did not differ behaviorally, the comparisons below consider a unified group of l2 participants. we reanalyzed the two experiments to directly compare l1 and l2 processing. in the experiments, l1 and l2 participants were asked to help find the belongings of two fictional characters, martin and sarah. they were told that they would see images and hear instructions, and that their task was to select the object mentioned by the instruction. the instructions always contained a possessive pronoun doubly-marked for gender: the gender of the pronoun stem (sein-/ihr-) agreed in gender with the antecedent (martin or sarah). the gender of the pronoun suffix agreed in gender with the upcoming noun, which allowed participants to predict the identity of the target object prior to hearing it in the instruction, e.g.: 'click on his. masc blue. masc button. masc '. the experimental trials showed 2 colored objects: a target object (e.g. a blue button. masc ) and a competitor of a different gender (e.g. a blue bottle. fem ). the 96 items were distributed in two conditions (1). in the match condition, the possessor and target noun had the same gender, i.e., both masculine or both feminine. in the mis-match condition, the possessor mismatched the gender of the target object but matched the competitor's. the results of the experiments showed that the gender of the pronoun was used predictively, such that participants showed a target-overcompetitor looking preference prior to hearing the noun. in addition, there was a "match effect", with predictions starting earlier in the match than in the mismatch condition (figure 1 ). we examined whether the size and onset of predictions and/or the onset of match effects differed between l1 and l2. the size of predictions was quantified as the target-over-competitor looking preference in the entire time-window before the target noun was heard (i.e., from pronoun onset to noun onset plus 200ms to account for saccade planning). the onset of prediction was quantified as the earliest point in time at which fixations to the target object significantly differed from fixations to the competitor. this timepoint, together with a 95% confidence interval, was taken as the prediction onset @xcite . our l1-l2 comparisons revealed the following differences: (i) the size of predictions was approx-imately 9 percentage points smaller in l2 than in l1 (henceforth smaller-prediction). the target-over-competitor advantage was 58 [56, 60] % in the l2 group vs. 67 [65, 69] % in the l1 group. (ii) the onset of predictions was always later in l2 than l1 (later-prediction). in the match condition, the difference in l1-l2 onsets was 211 [60, 320] ms. in the mismatch condition, the difference in l1-l2 onsets was 108 @xcite ms. (iii) the match effect-the difference between mismatch vs. match onsets-occurred in both groups: l1 match effect 303 [160, 400] ms and l2 match effect 200 [120, 280] ms. the match effect in onset times was numerically smaller in the l2 group (smaller-match), but the betweengroup difference was not statistically reliable (as evidenced by the 95% ci crossing 0): 103 [-40, 220] ms. ## discussion we proposed computational cognitive models of two main theories of l2 processing -the interference hypothesis and the lexical bottleneck hypothesis. both are verbally stated theories of processing differences between l2 and l1 speakers, and ours is, to our knowledge, the first computational cognitive realization of those theories. the theories were implemented by extending an existing l1 processing model @xcite . we used visual-world eye-tracking data from a predictive sentence processing task to test the models. the results showed that the lbh performed better than ih in capturing the three key effects observed in the data. with the exception of one effect, the ih predicted effects that were opposite to the ones observed in human speakers. overall the lbh appears to be a more likely explanation of l2 sentence processing as far as the predictive use of gender in processing is concerned. therefore, we propose that the well-attested difficulty shown by l2 speakers in using gender predictively (as compared to l1 speakers) is more likely attributable to problems in how l2 speakers represent gender information in a non-native language @xcite @xcite and/or to difficulties in using this information as quickly as l1 speakers @xcite . an important qualification is that the two implementations evaluated here did not model the potential effect of l1 transfer. recall that the l2 group consisted of both spanish and english learners of german. because the majority of nouns used in the human experiments had the same gender across spanish and german, and because there was no evidence of between-group differences, we think that the current dataset is not suitable for modeling l1 transfer effects. research using other datasets will be relevant to address the role of l1 transfer, which is hypothesized to play a role in the lexical bottleneck hypothesis @xcite . the role of l1 transfer in the ih is less clear, but it may affect the current implementation if, for example, both l1-and l2-based gender features are available for retrieval in the memory chunks corresponding to the objects on-screen. the effects reported in the l1 and l2 data were possibly born out of retrieval interference during predictive processing @xcite . hence we expected the ih account to capture the effects better as the ih is rooted in the cue-based retrieval framework of sentence processing, and cue-based retrieval theory has rendered explanation to various psycholinguistic phenomenon through retrieval interference. a possible reason for the ih predicting opposite patterns to the ones observed in the data could because retrieval interference as per the cue-based retrieval theory can lead to two opposite processing phenomena -inhibitory vs. facilitory processing -depending on the context @xcite @xcite . the precise nature of the interference effect in a given context can only be predicted through an actual implementation of the model. our results emphasize the importance of computationally formalizing the predictions of the cue-based retrieval theory in particular @xcite , and of verbal theories in cognition in general @xcite . although the lbh model captured crucial patterns in the differences between l2 and l1 processing, one serious limitation of the model (and also of the ih model) was in terms of capturing the effect of delayed prediction onsets (later-prediction) in the mismatch condition for l2 speakers. since both the l2 models failed at capturing this effect, we think it is also unlikely that a combination of the two models would be able to capture this effect. this also implies that the gender prediction in l2 speakers possibly also involves a process that cannot be explained by either of the hypotheses. we think a computational implementation of another l2 processing hypothesis, in combination with the lbh model, might help capture this effect.