Subject relative clauses are not universally easier to process: Evidence from Basque

Abstract

Studies from many languages consistently report that subject relative clauses (SR) are easier to process than object relatives (OR). However, Hsiao and Gibson (2003) report an OR preference for Chinese, a finding that has been contested. Here we report faster OR versus SR processing in Basque, an ergative, head-final language with pre-nominal relative clauses. A self-paced reading task was used in Experiments 1 and 2, while ERPs were recorded in Experiment 3. We used relative clauses that were ambiguous between an object or subject-gap interpretation and disambiguated later in the sentence. The results of Experiments 1 and 2 showed that SR took longer to read than OR in the critical disambiguating region. In addition, Experiment 3 showed that SR produced larger amplitudes than OR in the P600 window immediately after reading the critical disambiguating word. Our results suggest that SR are not universally easier to process. They cast doubts on universal hypotheses and suggest that processing complexity may depend on language-specific aspects of grammar.

Introduction

Cross linguistic investigations are crucial to discover the source of processing asymmetries, and to differentiate between universal processing mechanisms and the impact of grammatical properties of the languages at play on processing. In order to understand the nature of complexity in language processing, a broad sample of different grammars must be studied; the results of this cross linguistic research will reveal the mechanisms at play in language processing at an adequate level of abstraction.

In the domain of sentence comprehension, relative clause processing has been thoroughly investigated in different languages, with various methodologies. A well-established result of these studies is that subject-gap relative clauses (SR), such as (1a) are easier to process than object relative clauses (OR) like (1b).

The sample of languages where this processing asymmetry has been observed consists of a large group of head-initial (SVO), nominative–accusative languages from the Indo-european family, where relative clauses follow the head noun and are typically headed by a complementizer (typically an interrogative element), as the examples in (1). The languages in this group include English (e.g., Caplan et al., 2002, Ford, 1983, Gibson et al., 1994, Gordon et al., 2001, King and Just, 1991, King and Kutas, 1995, Pickering, 1994, Traxler et al., 2002, Weckerly and Kutas, 1999), Dutch (e.g., Frazier, 1987, Mak et al., 2002, Mak et al., 2006), French (e.g., Cohen and Mehler, 1996, Frauenfelder et al., 1980, Holmes and O’Regan, 1981), German (e.g., Mecklinger et al., 1995, Schriefers et al., 1995) and Spanish (Betancort, Carreiras, & Sturt, 2009). This asymmetry has been found with different methodologies such as self-paced reading, eye movements, event related potentials (ERPs) and functional magnetic resonance imaging (fMRI).

Interestingly, there is a second group of languages that have been recently studied, where relative clauses precede their head noun instead of following it, and where there are no interrogative-like words heading the clause. The languages in this group are Chinese (e.g., Chien-Jer and Bever, 2006, Hsiao and Gibson, 2003; Lin & Bever, 2006; Lin, submitted for publication), Japanese (e.g., Ishizuka, 2005, Ueno and Garnsey, 2008), and Korean (e.g., Kwon, Polinsky, & Kluender, 2006; Kwon, Lee, Gordon, Kluender, & Polinsky, submitted for publication). Results from these languages confirm the SR advantage, with the exception of Hsiao and Gibson (2003) as well as Lin and Garnsey (submitted for publication)¹, who report an OR advantage for Chinese, and Ishizuka, Nakatani, and Gibson (2006) who report a similar result in Japanese. However, their experimental materials and results have been recently contested by Chien-Jer and Bever (2006), Lin and Bever (2006) and Kuo and Vasishth (submitted for publication) who also report a SR preference for Chinese and by Kwon et al. (submitted for publication) that did not find an OR advantage in Korean.

Several hypotheses have been offered in the literature in order to explain the processing asymmetry between subject and object relative clauses. Among them we can differentiate a set of hypotheses that predict this effect to be universal, with no appeal to syntactic structure, and those that predict differences across languages depending on the parametric features of the grammar at stake. It is thus important to determine first whether the SR advantage can be seen in languages with properties that diverge from the language-pool that has been previously studied; if the effect is not present in some of these grammars, the first set of hypothesis would be falsified, but if the effect remains across different types of grammars, these set of hypothesis would gain force. One goal of the present study is to explore SR/OR processing asymmetries in Basque, a head-final language with pre-nominal relative clauses, which unlike all previously studied languages is ergative and highly inflected.

Within the group of hypotheses that predict a universal complexity effect without appeal to syntactic structure, we find the Accessibility Hierarchy (e.g., Dowty, 1991, Hale, 2003, Keenan and Comrie, 1977, Keenan and Hawkins, 1987), and the Perspective Shift Hypothesis (e.g., Bever, 1970, MacWhinney, 1977, MacWhinney, 1982, MacWhinney and Pleh, 1988), both based on the inherent saliency of subjects relative to objects: the Accessibility Hierarchy claims that grammatical functions are universally ordered in a hierarchy that determines the relative accessibility of a given function; since subjects are placed higher than objects in this hierarchy, subject–object asymmetries should always favour subjects. The perspective shift hypothesis argues that subjects determine the perspective of a clause, and perspective shifts employ processing resources; processing a subject relative clause entails no shift, while object relative clauses induce a shift to a new subject, thus creating a complexity effect.

In the group of structure-dependent hypotheses we find working memory (e.g., Ford, 1983, Frazier and Fodor, 1978, Wanner and Maratsos, 1978), integration cost (e.g., Gibson, 1998, Gibson, 2000, Hsiao and Gibson, 2003), syntactic strategies such as Active Filler Strategy and the Minimal Chain Principle (henceforth the AFS and MCP; see Clifton and Frazier, 1989, Frazier and Flores D’Arcais, 1989, Pickering, 1994, Pickering and Barry, 1993, Pickering and Barry, 1991; Stowe, 1989), the simultaneous influence of syntactic and non-syntactic information (e.g., MacDonald et al., 1994, Trueswell et al., 1993), and differences in word-order canonicity (e.g., Bever, 1970, MacDonald and Christiansen, 2002, Mitchell et al., 1995, Tabor et al., 1997). For an extensive review of these proposals, see Traxler et al., 2002, Hsiao and Gibson, 2003.

On the other hand, there are constraint-based approaches, according to which syntactic and semantic structures are hypothesized to be continuously activated in parallel (cf. Boland, 1997, Gennari and MacDonald, 2008, MacDonald, 1994, MacDonald et al., 1994, McRae et al., 1998, Spivey-Knowlton and Sedivy, 1995, Trueswell et al., 1994). Comprehension difficulty in this approach emerges from competition between alternative structures partially activated during comprehension. The frequency of the structures in speakers’ linguistic experience will determine the activation levels of the different structures, so that infrequent structures in a given configuration would be difficult to activate because of competition with more available frequent structures. Thus, according to this approach the relative difficulty in processing relative clauses may depend on the frequency and the extent of the competition that each structure affords.

A common underlying principle to structure-dependent explanations is the appeal to the relative distance between filler-gap dependencies, with increasing distance correlating with increasing complexity. This notion of distance can be characterized in two different ways: in terms of linear distance – the amount of intervening words/terminal nodes, as in the Dependency Locality Theory (DLT, Gibson, 1998, Gibson, 2000), or in terms of structural distance – the amount of intervening syntactic nodes/projections, as in the Structural Distance Hypothesis (SDH, O’Grady, Miseon, & Miho, 2003). Structural distance between filler and gap is always greater in OR than in SR, because objects are embedded deeper in syntactic structure than subjects. This holds both in head-initial (VO) and in head-final (OV) languages, so that both language groups are predicted to display the same complexity effect by the SDH. Syntactic representations in (2) and (3) schematically illustrate the different predictions made by DLT and SDH for head-initial and head-final grammars. Structures (2a) and (2c) represent a SR in a head-initial and head-final language respectively. Structures (2b) and (2d) illustrate an OR in a head-initial and a head-final language. The subject-gap is higher than the object gap in both types of grammars, regardless of head direction, since the object gap is always embedded deeper in the structure, inside the VP²:

A complexity metric in terms of linear distance, as the DLT, predicts inverse asymmetries depending on the value of the head-parameter: in a head-final language, the linear distance between the gap and the filler of a SR (3a) is greater than the linear distance between the gap and the filler of an OR (3b). However, in a head-initial language, both linear and structural distance between filler and gap is greater in OR (3c) than in SR (3d):

Both notions of distance make similar predictions in head-initial languages, so that it is not possible to distinguish between them by studying only this parametric specification. However, in head-final languages each metric yields inverse predictions: the linear gap-filler distance is longer in SR than in OR, but structural distance is greater in OR than in SR. An account based on structural distance (like the SDH) predicts SR to be simpler and easier to process – subjects are higher in the structure of known natural languages (e.g., Baker, 2001, Chomsky, 1957, Clifton and Frazier, 1989, Keenan and Hawkins, 1987; O’Grady, 1997). However, a processing account based on linear distance – intervening material – between filler and gap (like the DLT) predicts SR to be easier than OR only in languages with post-nominal relative clauses, but OR to be easier than SR in languages with pre-nominal relative clauses (e.g., Gibson, 1998, Gibson, 2000, Hsiao and Gibson, 2003). It is therefore important to clarify what the relative clause processing complexity is in languages with pre-nominal relative clauses to properly adjudicate between these two conceptions of distance.

A second goal of this paper is therefore to contribute to determine the relevance of linear and structural distance for the processing of long distance dependencies across languages. We investigate the relative complexity of OR versus SR in Basque in three experiments. A self-paced reading task was used in Experiments 1 and 2, while ERPs were recorded in Experiment 3. Relative clauses in Basque, as in Chinese, Korean and Japanese, are temporally ambiguous, and speakers might not know a RC is coming until they find the inflected verb of the RC, the last word before the head noun. There are no interrogative pronouns, only a complementizer morpheme -(e)n attached as a suffix to the inflected verb, like the form ditu-en shown in (4), where ditu is an auxiliary verb, and -en is the complementizer that indicates the presence of a RC. Experimental sentences were constructed using the -ak ending, which yields an ambiguity between singular transitive subject and plural object, so that the relative clauses were ambiguous between a SR or OR reading until the last word of the main sentence ((4a) and (4b), respectively).

The -ak ending illustrated in the examples in (4) is ambiguous between two morphological classes: (i) a plural absolutive Noun Phrase (i.e. a plural object or a plural intransitive/thematic subject), or (ii) a singular ergative Noun Phrase (i.e. a transitive/agentive subject). In each of these two cases, the -ak sequence has a different morphological structure. When interpreted as belonging to (ii), the class of singular ergative NPs, it consists of a determiner -a “the” and an ergative case marker -k attached, as illustrated in (4b) for instance, where the singular transitive subject irakasleak “the teacher” consists of the noun irakasle “teacher”, plus the singular determiner -a and the ergative case marker -k (irakasle-a-k “the teacher”). When interpreted as belonging to (i), the class of absolutive plural NPs, there is only one morpheme, the plural determiner -ak “the_pl”, and no case marker attached, for absolutive is morphologically unmarked. This can also be seen in (4b), where the plural intransitive (hence absolutive) subject ikasleak consists of the noun ikasle “learner, student” plus the plural determiner -ak (ikasle-ak), and no overt case marker. Similarly, in (4a), irakasle-ak is a plural object (hence also absolutive) “the teachers”, whereas ikasle-a-k is a transitive subject “the student” (see Laka, 1996, for details on case morphology).

Match or mismatch between the case-marking on the head noun of the RC and the gap inside the RC has been argued to have an effect in processing difficulty between the two types of RCs (Sauerland & Gibson, 1998). There is no potential for a case-mismatch confound in our experimental sentences, because they always involve a case-match configuration: on the one hand, OR sentences have absolutive case-marked subjects as head nouns, so both the gap and the head noun carry absolutive case, as in (4b), where the object gap corresponds to an absolutive case-marked NP, and the head noun also carries absolutive case; on the other hand, SR sentences have ergative-marked subjects as head nouns, so both the gap and the head have ergative case, as in (4a), where the subject-gap corresponds to a NP that would carry ergative case, the same case as its head noun in the main clause. That is, in both types of experimental sentences the similarity of the case borne by the gap and head NP is absolute.

There are no differences between the two RCs in terms of storage resources (Gibson, 2000), because the number of unresolved dependencies is the same in the two clauses. Both in the OR (4b) and in the SR (4a), only one head needs to be postulated to generate a grammatical sentence: an inflected verb that would yield a well-formed intransitive main clause, because given the ambiguity of the first overt phrase, a grammatical intransitive sentence can be completed by simply adding a verb: ikasle-ak datoz “the students arrive”. Secondly, we can also discard the effect of word-order canonicity (MacDonald & Christiansen, 2002) because the relative clauses do not follow the SOV canonical order of the language; (4b) presents a SVO order, and (4a) an OVS order, so that a processing asymmetry cannot be explained by the canonicity hypothesis. The structural distance between the subject-gap and the filler is shorter than the structural distance between the object gap and the filler, because the later is lower in syntactic structure (cf. structures (2c) and (2d)). Thirdly, linear distance or integration cost is higher for SR than for OR in these sentences: in the OR (4b), the number of intervening words is two (verb and inflected auxiliary), whereas in the SR (4a) the number of intervening words is three (object, verb and inflected auxiliary). Finally, similarity or differences in frequency of use for the two relative clauses will be measured in a corpus analysis to investigate whether frequency of use can account for processing differences.

In sum, if an object relative clause preference is obtained it will suggest that (a) SRs are not universally, inherently easier to process than OR, so that accounts based on the inherent or universal properties of subjects would be ruled out, and that (b) integration cost in terms of structural distance does not explain processing preferences across grammars. Moreover, if an OR advantage were to obtain, given the SR advantage results in Japanese and Korean, the explanatory role of linear distance between filler and gap would require further scrutiny.