processing difficulty and principles of grammar

PROCESSING DIFFICULTY AND PRINCIPLES OF GRAMMAR Gisbert Fanselow, Reinhold Kliegl, and Matthias Schlesewsky INTRODUCTION Some words are more difficult to pronounce than others, and, similarly, some sentence types are harder to process than others. Such processing differences are due to properties of the human parser, and these may be responsible for certain laws of natural language syntax is not a new idea: it is a key concept in linguistic typology. This chapter investigates the merits of the proposal that two core principles of current generative syntax, namely the principle that syntactic movement is costly, and the principle that the costs of movement are proportional to the distance covered (Chomsky 1995), can be explained in terms of processing theory. The chapter is not the first attempt of relating abstract syntactic laws to processing facts (cf., e.g., Marcus 1980, Staudacher 1993), but for such an approach to be successful, several requirements must be met: • assumptions concerning processing difficulty must be justified independently • the full range of empirical facts of syntax must be captured, and, • the approach must be explicit about the link between processing difficulty and syntactic laws. After introducing the facts to be explained, this chapter makes a few principled but obvious remarks on the last aspect, to which we return in the final section. The third section sketches the general line of the argument. The fourth section introduces evidence for the claim that movement is cognitively costly, and discusses processing models that predict such costs. Particular attention is given to approaches involving memory load. The fifth section tries to assess to what extent the two key laws of syntax introduced above can be derived from such processing considerations. The paper reports work in progress, so some of the points presently depend more on plausibility arguments than on "hard core data". The conclusion we will arrive at is somewhat different from the one we originally found plausible. We still believe that the processing facts are compatible with the view that processing shapes grammar, but there are too many gaps in the grammaticalization account for it to be likely to be true.

PROCESSING AND SYNTAX: A SURPRISING SIMILARITY Processes by which words or phrases are moved from their canonical position to another belong to the inventory of operations in many if not all natural languages. Thus, in English, direct objects of verbs typically appear in a postverbal position (1a), but in a constituent question, a wh-object needs to be fronted, as in (1b/b').

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(1) a. he saw it b. he saw what ⇒⇒ b.' (guess) what he saw t In on-line processing, local ambiguities involving the grammatical function of such fronted wh-phrases arise frequently. Thus, clause initial what may turn out to be the direct object of a matrix clause (as in (2a)), the complement of a prepositional phrase (as in (2b)), or the subject of a complement clause (as in (2c)). (2) a. what did you sing t b. what did you sing a song about t c. what did you believe t convinced him As was shown by Stowe (1986), among others, the human parser has clear preferences in this domain, which have been described successfully in terms of trace theory. At least according to certain parsing theories (see Pickering & Barry 1991 for a different view), the processing of constituent questions involves the reconstruction of the relation between the actual position of the wh-phrase and its canonical (pre-movement) position, assumed to be filled by a "trace" (represented by "t" in (2)) in many grammatical models (Chomsky 1981). Parsing preferences in the case of local ambiguities involving the grammatical function of wh-phrases are correctly predicted by the assumption that the parser follows an "Active Filler Strategy" (Clifton & Frazier, 1989), which implies that the parser tries to keep the distance between the moved phrase and the canonical position as short as possible. (3) Active Filler Strategy (AFS, non-canonical fomulation) Ceteris paribus¸the parser prefers structure S over structure T if the distance between the wh-phrase α and its trace is shorter in S than it is in T. The AFS predicts standard processing asymmetries for English questions (see Frazier & Clifton 1989), and seems to be responsible for the subject preference in locally ambiguous wh-phrases established experimentally, e.g., for Dutch (Frazier & Flores d'Arcais, 1989), Italian (de Vincenzi 1991), and German (Meng 1997, Schlesewsky, Fanselow, Kliegl, & Krems, in press). Consider (4). (4) a. welche Frau hat t den Mann eingeladen which ambiguous woman has theacc man invited (wh=subject = preferred) "which woman has invited the man?" b. welche Frau hat der Mann t eingeladen which ambiguous woman has thenom man invited (wh=object = dispreferred) "which woman has the man invited?" The grammatical function of the wh-phrase in (4) is not determined by its morphology. The studies mentioned above report evidence that the subject interpretation is preferred by the human parser. This is in line with the AFS: German is a subject-object-verb-language underlyingly, so the distance between the wh-phrase and its trace t is shorter in (4a) than it is in (4b), as one can read off the representations easily. The AFS is thus a well-supported parsing strategy. Quite surprisingly, grammar obeys a principle similar to AFS in similar contexts: it involves a "superiority" condition (Chomsky 1973) or a Minimal Link Condition (MLC) (Chomsky 1995). The AFS expresses a preference for shorter links when there is no clear evidence about the pre-movement position of a phrase. The MLC requires that only the shorter link be formed when two phrases might undergo movement, that is, when there also is a "local ambiguity" of rule application.

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Thus, the grammar of English requires that exactly one wh-phrase is fronted in a constituent question. If the sentence hosts two wh-phrases, only the one that is closer to the landing site may move, as (5) - (6) illustrate. (6) is particularly telling since it also illustrates a subject-object-asymmetry. The observations in (5) and (6) can be reduced to a principle such as (7). (5) a. you persuade who to say what ⇒ b. who did you persuade t to say what c. *what did you persuade who to say t (6) a. you expect who to do what b. who do you expect t to do what c. *what do you expect who to do t (7) Minimal Link Condition (MLC, non-canonical fomulation) Ceteris paribus¸the grammar accepts structure S and rejects structure T if the distance between a moved phrase α and its trace is shorter in S than in T. From the perspective of grammar, the most interesting question about (7) is what is meant by ceteris paribus, but for this chapter, the parallel between the grammar and the parser implicit in (3)/(7) is the most important aspect: whenever the constitution of a chain between a moved element and a trace is not uniquely determined, the parser and the grammar prefer to (re-)construct the shortest chain. Such similarities call for an explanation, and logically, there are three possibilities: principles of grammar might shape the way the parser operates, it may be the other way round, and, finally, the shape of the grammar and of the parser might be influenced indirectly in the same way by a third causal factor. The first alternative is discussed in detail in Fanselow, Schlesewsky, & Kliegl (1998), while the second is in focus in this chapter. A few remarks on potential third factors can be found below and in the other work just mentioned.

PROCESSING AND SYNTAX: HOW LINKS CAN BE CREATED That the form of a grammar is partially determined by processing difficulty is an old idea, but the two domains need a mediator: some sentences are difficult to process but grammatical - multiply center-embedded relative clauses such as (8) are cases in point. Some sentences are easy to process yet ungrammatical - as so-called thattrace-violations (9). Such observations suggest that there is a difference between the grammar and the parser, and that the causal connection between grammaticality and processing difficulty has to be an indirect one. (8) the man the dog the cat the mouse feared chased bit consulted a doctor (9) *who do you think that t loves Mary This indirect link is "grammaticalization" (cf., e.g., Hawkins 1994 for suggestions): By a syntactic change, a process that is unlikely (or difficult) at a given stage in the history of a language is ruled out (ungrammatical) at later stages. Furthermore, there is a consensus that grammars change mainly because they have to be acquired by children. Children do not have direct access to the grammar used by the adult world, rather, they reconstruct a grammar appropriate for their linguistic input. The result need not be identical with the adult model. If there is a likelihood above 0.5 that changes they introduce go in one direction rather than the other, and if languages have gone through a sufficient number of acquisitional cycles (as they have), it is likely that most (or all) languages end up possessing a

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certain property P. Thus, any factor making certain changes even slightly more likely than others can shape grammars quite substantially. Suppose now that processing difficulty plays a significant role in language acquisition. That children replace a difficult option by a simpler one rather than the other way round may be taken to be a default assumption. Thus, processing difficulty may determine the direction syntactic changes take. After a sufficient number of acquisitional cycles, processing difficulty can thus have had a substantial impact on the form of grammar in natural languages. However, this reasoning involves two assumptions that need not be correct. First, it has to be shown that constructions that are hard to process for adults are difficult for children, too (and vice versa) - grammaticalization implies that children's (and not adult's) difficulties are frozen into grammar. Probably, the overlap in processing difficulty between adults and children is substantial, so that this potential problem does not endanger the enterprise. This may be different for the other presupposition: it is not an established fact that the syntactic changes introduced by children simplify the grammatical system in a processing/cognitive/grammatical sense. As Hale (1998) has pointed out recently, syntactic change may be sporadic, and the direction it takes may be accidental. If this is correct, grammaticalization explanations are in trouble. See below for some remarks.

THE COSTS OF MOVEMENT The parallel between the parser and the grammar considered above can be due to a causal link between the two domains. An argument in favor of this view involves at least the following steps: (a) we must establish that movement has a cognitive cost proportional to the length of the path independently of syntax specific heuristic parsing strategies (this section) (b) we must show that what characterizes the parser is sufficiently close to what holds for grammar (We do not need to assume that their laws are identical, however, because the laws of grammaticalization may, e.g., force a form of grammar that does not mirror processing ease in certain subdomains). (c) one needs to be explicit about how grammaticalization works in the domain under consideration. We concentrate on the first issue in this section. Our argument begins with the observation that the human parser prefers syntactic analyses that involve shorter movement links whenever there is a local ambiguity for the grammatical function/ the pre-movement position of a moved wh-phrase. If this behavior of the parser is due to an irreducible heuristic strategy for ambiguity resolution, it is hard to see how it could influence the grammar of a language. What needs to be shown (or made plausible) is that longer movement paths are cognitively more costly in general (not just in the case of an ambiguity), and that this can be linked to the costly nature of movement in terms of grammar. Frazier (1987:548) speculates that subject-object asymmetries as in (4) may be due to the greater complexity of object-initial clauses. According to her, the moved item must be "held in a special memory buffer [...] for longer than is necessary" for the subject initial case. Under this perspective, the validity of her Active Filler Hypothesis (see above) derives from the assumption that the parser minimizes

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cognitive costs in the case of an ambiguity, if the costs of a structure are related to the amount of time for which moved items are kept in memory. The assumption that the AFS reduces to a processing time difference between the two competing structural hypotheses is related to the idea of "race-based" parsing: the faster structural alternative inhibits the computation of the slower ones, a fact that is relevant for our discussion if cognitive load is inversely related to processing speed. The assumptions concerning items held in memory in different construction types follow if a moved item must be kept in memory up to the point at which the pre-movement position can be integrated into the parse tree - which can be done earlier for subjects than for objects (see below). This approach predicts that the additional cognitive load of object initial structures is visible in unambiguous clauses, too. If it is costly to hold a moved item in memory, costs should show up irrespective of whether there is an additional local ambiguity. That this is true is suggested by findings of King & Just (1991), according to which English object-initial relative clauses are harder to process than subject-initial ones. Somewhat clearer evidence can be found in Krems (1984), a study establishing that total reading times are lower for subject initial declaratives (such as (10a)) than for their object initial counterparts (such as (10b)) even when overt case morphology leaves no room for (relevant) local ambiguities. (10) a. der Mann sah den Fisch thenom man saw theacc fish b. den Fisch sah der Mann theacc fish saw thenom man "the man saw the fish" As Schlesewsky, Fanselow, & Kliegl (submitted) point out, subject-objectasymmetries in declarative (and relative) clauses are difficult to interpret because factors independent of movement (pragmatic preferences, etc.) may favor subject initiality. Such extrasyntactic factors play no role in the processing of constituent questions. Therefore, we carried out a set of experiments reported in the article just cited which studied the processing of German constituent question and which are summarized below because they shed some light on the costs of movement. Consider the abstract clausal grids (11) for German embedded questions: (11) a. wh-phrasenominative adverb-1 adverb-2 object verb b. wh-phraseaccusative adverb-1 adverb-2 subject verb c. "whether" adverb-1 adverb-2 subject object verb As in English, complement questions can begin with a wh-phrase (11a-b) or with a question complementizer meaning "whether". This initial element can be followed by adverbs, which in turn may be followed by the subject, the object, or both (depending on what appeared in clause initial position). A series of reading experiments comparing reading times for these (and similar) structures yielded the following results, which are also partially visible in Experiment 1 introduced below (see the appendix). [A] Reading times for unambiguous clause initial wh-phrases are longer for objectinitial questions. Since subject initial questions are not favored pragmatically, the object-initiality disadvantage in questions is a genuine formal effect. [B] A naming task (see Schlesewsky et al. , submitted) showed that the access time of a wh-determiner is shorter if it allows a nominative (subject) interpretation (among others) than if it allows object interpretations only. Thus, it cannot be

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excluded that the reading time difference introduced in [A] is partially due to a difference in lexical access times. [C] However, the reading time advantage for subject-initial questions continues to be visible on the two adverbs following the initial wh-phrase. The effect was always statistically significant for the first adverb, and was so for the second adverb in some experiments, too - high variances in reading times on the second adverb position may have blurred effects sometimes. It is not likely (Schlesewsky et al., submitted) that the object-initiality effect visible on the two adverbs is a spillover of a lexical access problem in the sense of [B]. Therefore, there are additional costs of object-initiality. One might suspect that this additional cost is due to a problem in the processing of sentences in which the subject comes late (as is the case for (11b), as compared to (11a)). That such an interpretation is not unlikely follows from the following observation: [D] Comparing the reading times of subject-initial questions (11a) with those of "whether-initial" questions (such as (11c), in which the subject also comes late), one observes that reading times in the subject initial condition are shorter for the two adverbs. Since no movement is involved in (11c), we conclude that structures with late subjects are difficult per se - because of the position of the subject. [E] However, a comparison of reading times for the object-initial condition (11b) with the "whether"-condition (11c) reveals a further contrast: reading times for the adverb are longer in the object-initial case. Since (11b) and (11c) share the property of having a late subject, this processing difference must be due to yet another factor - that an object is preposed in (11b), but not in (11c) is the only obvious difference. Taking [A] - [E] together, two conclusions may be drawn: the additional costs of object initial structures might be caused by a variety of factors: lexical access and the difficulty of structures with late subjects come into play. But there is also an apparently irreducible cost unit incurred by object fronting itself. It is possible that this pure object-fronting penalty can be explained along the lines suggested by Frazier (1987). Note that the effect disappears as soon as the subject is encountered. German is (underlyingly) a subject-object-verb language, and adverb positions are fairly free. The first position in a German wh-clause at which the trace of a subject wh-phrase can be postulated thus follows the wh-phrase itself: (12) a. wh-subject [tsubject adverb adverb object verb] The object trace needs to follow the subject, though, because all objects do (unless they change position due to processes that need not concern us): (12) b. wh-object [adverb adverb subject tobject verb] Thus, the pure object-initiality-disadvantage disappears when the category immediately preceding the first legal slot for the trace of wh-movement (the category immediately preceding the object's canonical position, if you prefer) is encountered. If parsing is strictly incremental, this means that the object-initiality disadvantage disappears as soon as a position has been reached (viz. the subject) which allows the postulation of the object trace and its integration into the parse tree without violating strict left-to-right incrementality. Arguably, the wh-phrase cannot be removed from memory unless its trace/its canonical position has been reached in incremental left-to-right parsing. The results of our experiments suggest, then, that additional processing time is necessary as long as a wh-phrase is kept in memory. In this sense, movement, a process creating the need of storing phrases up to their canonical position, is costly as such. There is

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a cognitive cost of movement, and the time for which the additional cost arises is proportional to the distance between the moved phrase and the trace. This is a nice result for the general point pursued in this chapter: All current generative models, the Minimalist Program (Chomsky 1995) and Optimality Theory (Grimshaw 1997) take movement to be costly in grammatical terms, in the following sense: phrases must not be moved - unless there are more important factors forcing it. The relation between cognitive and grammatical costs of movement is indirect, however. This is related to, but not identical with, the observation discussed above that grammaticalization must mediate between processing difficulty and grammar. Our results suggest that wh-movement of question phrases is cognitively costly. There is little empirical reason to believe that, say, the movement of a verb from one position to another (as motivated for the grammars of French (Emonds 1978) and German (Bach 1962, Thiersch 1978) creates a cognitive load. We are thus far from having established that movement is cognitively costly as such. The mediating role of grammaticalization may be helpful here, and in a further respect. The notions of "closeness" or "distance" in grammar are hierarchical: they involve relations such as c-command that make crucial reference to an elaborate structural representation. It remains to be shown (and may be false) that the notion of distance relevant for the parser is purely structural as well, and that it is identical with the one used by grammar. This does not, however, necessarily endanger the enterprise of deriving properties of grammar from properties of the parser. Processing difficulty has to be grammaticalized. This grammaticalization is triggered by processing difficulty, but its results must fall within what is expressible in terms of grammar. Suppose, then, (as most linguists do) that there are substantial restrictions on the terms and relations that can appear in a grammar (or, rather, in its mental representation) restrictions that are independent of processing difficulty. Thus, in most if not all approaches to grammar, linear distance does not play role at all. We may thus assume that "linear distance" is not a concept that could appear in a grammar. If the triggering factor involves linear distance, this must be translated into something that makes sense within a grammar: hierarchical relations such as c-command among elements in a structural representation. Anything related to linear distance that ends up being grammaticalized is necessarily translated into a concept involving hierarchical, structural notions of grammar. Even if the AFS crucially involves differences in linear distance (which we do not know), grammaticalization may translate this into the structural relations underlying the MLC. In this context, then, it need not concern us too much whether the details of the AFS and the MLC are identical. This may be different for the grammaticalization of the costs of movement in terms of a ban against unmotivated movement. After all, grammar seems to make a distinction between verb movement and wh-movement, so it is unclear why costs of wh-movement could not be grammaticalized in a form affecting wh-movement only, and nothing else. On the one hand, the grammaticalization process itself might be constrained in a way that prevents specific principles like "Don't move wh-phrases" from arising. On the other hand, it is not obvious at all that there are movement operations other than wh-movement. Verb movement is incompatible with a number of fundamental assumptions of Chomsky (1995), so severel stipulations were necessary to allow the operations. Verb movement is thus not well-founded.

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Similarly, changes in the theory of thematic roles as proposed in Fanselow (submitted) may make so-called NP-movement superfluous as well.

DOES IT HAVE TO BE MEMORY COSTS? And if so, what type of memory? Before we proceed, the role of the recourse to memory load should be clarified, and we should be more explicit about what is understood by "memory". One observation suggests that the "memory component" used above cannot be identified with working memory in a cognitive psychology sense. The work of Kemper and colleagues (Kemper 1992, Norman et al., 1991) has demonstrated an age effect on linguistic performance that can be explained in terms of a reduced capacity of the working memory. If a working memory load is responsible for the additional costs of object-initial clauses, one expects a specific age effect for object initial structures. In Experiment 1 described in the appendix, we confronted young and old adults with sentence material with the structure of (11), that is, we tested for possible age effects on the parameters 'early vs. late subject' and object-initiality. Although there was a significant main effect of age (old adults' reading times are longer), no interaction between age and any of the syntactic factors emerged. The results of Experiment 1 suggest that there is no particular age effect on object-initiality. If the "memory component" causing the costs of movement would be working memory, such an effect should have been visible. Of course, the absence of an effect does not prove a lot, but the results of Experiment 1 are in line with studies described in detail in Kliegl, Fanselow, Schlesewsky & Oberauer (1998), see also Kliegl (this volume). In these studies, accuracy of comprehension was tested for main clauses that contained a single relative clause embedding. There was a significant age by object-initiality interaction, but just for main clause scrambling (different in theoretical terms from wh-fronting), and not for relative clauses (close to wh-fronting in theoretical terms -- but there was an insignificant tendency for an age effect). In follow-up research, Junker, Oberauer & Kliegl (in prep.) show that the age by complexity interaction did not disappear when young adults had to carry out a secondary memory related task (as one would expect if working memory was crucial), but it did so when presentation time was reduced for young adults. Thus, one may at least conclude that the ageing studies have not produced evidence for the idea that working memory in a standard sense is involved in the processing of object-initial structure. If this is correct, the claim that recourse to a syntax-specific memory buffer is costly for the parser is not supported independently. The Frequency Alternative Since the cognitive costs of movement are not likely to be caused by a load on working memory, it is worth while to also consider a further alternative to the idea that there is a special syntactic working memory (not affected by ageing). This alternative to syntax-based accounts of object-initiality is a clause-type frequency explanation. In particular in the light of the many successes of the so-called tuning hypothesis (Cuetos & Mitchell 1988), it seems reasonable that processing speed is related to type frequency in the case of syntactic configurations as well.

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Versions of such approaches which ignore factors different from individual type frequency face the problem of identifying an appropriate level of classification once and for all. Thus, object-initial which-questions seem to be more frequent than their subject initial counterparts (Schlesewsky et al, in press), while subject-initial whquestions seem to be at least as frequent as object initial questions in general (Schlesewsky et al., in press, Meng 1997). Furthermore, given the heavy bias in favor of subject initial declaratives (9:1), the total number of structures that are object initial (disregarding further differences) is much smaller than the totality of subject-initial clauses. Thus, it seems that any experimental result in this domain might find a frequency explanation. In more sophisticated approaches as used in connectionist models, processing ease is not only determined by the frequency of individual cases, since "neighboring" similar structures are also activated. Type frequencies in these neighbor domains therefore play a role as well, in particular if they show a clearer pattern. Thus, MacDonald (1998) argues that the object-initiality disadvantage for relative clauses may be due to the high frequency of neighboring 'regular" subject-initial declaratives. In connectionist systems, the level of classification issue thus disappears. We expect even subject initial which-questions to be easier than object initial ones, due to the strong similarity of the former with the canonical and top frequent standard declarative clause. There is little psycholinguistic evidence that refutes a theory in which frequency and similarity to regular structures account for processing difficulty: the easier alternatives are (in most cases) the more frequent ones, or the ones most similar to top frequent standard types. This is not the fault of the approach: facts of language could have been different. Suppose, for example, that language L has a subject-verb object base order, but that a conspiracy of further constraints forces the preposing of objects in, say, 90 percent of the cases. Connectionist systems and symbolmanipulating grammatical approaches now make different predictions: ceteris paribus, there is no reason for why the subject-initial structure should be easy to parse in the former approaches, while the latter should predict an object-initiality penalty due to the need of keeping preposed objects in memory. The particular example is not likely to arise, but there is a less exotic case: German is a verb-final language underlyingly (this word order shows up in complement clauses), and the finite verb obligatorily moves to second position in main clauses. From a grammatical point of view, embedded clauses should thus be simpler than main clauses (because they involve one movement operation less) while a connectionist model would predict that it is just the other way round (because main clauses are more frequent). We have no evidence that decides the issue (and recall verb movement may turn out to be non-existent), but in principle, a comparison of the two constructions could settle the debate. While overall results are compatible with experience based accounts, one might claim they do not provide an explanation for the internal structure of processing difficulty effects. This may be false, too. It is by no means established that what matters for processing in experience based models is unanalyzable clause patterns. Note that a segment of a clause may itself bear resemblance to a (top frequent) clause pattern. Thus, the object initial sequence (13) resembles the top frequent subject initial pattern from the fourth word on - recall that the object initiality effect disappears when the subject was encountered. (13) wh-object adverb adverb subject .... verb

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The latter observation already leads to the central point: in a sense, experience based connectionist models may be able to predict "costs of movement", too. Suppose Σ=...α..β....γ... is the canonical top frequent pattern. Suppose furthermore β has been fronted so that ∆ = β...α ... ....γ ... arises. The reasoning proposed above implies that ∆ should be more difficult than Σ, up to the point when we reach α. The two models differ, of course, substantially for certain configurations, but we doubt that data have been collected already that allow a decision between the two approaches. Thus, there is a connectionist alternative to our memory based model that could be correct, but if so, this does not affect the major point we wish to discuss, viz., the likelihood of the parser shaping the form of the grammar. The θ-prediction Alternative The experimental findings discussed so far may be related to yet another parsing approach. Suppose a clause c is subject-initial. C need not contain an object - after all, the clause could be intransitive. If the human parser reacts in a conservative way, that is, if it tries to make as few commitments as possible in terms of the number of arguments in the clause, it will initially take subject-initial structures to be intransitive - up to the point when there is evidence to the contrary. If the structure is object-initial, however, it must immediately be processed as being transitive, in order to have a chance to be grammatical at all. Suppose that the human parser is conservative, and suppose that it is costly in cognitive terms to keep unlinked argumental expressions or unlinked argument slots of verbs in memory (or to pass pertinent information through the parse tree). Under such premises, longer reading times for object initial clauses are predicted again. Consider (14) in this respect. (14) α....β.... V If α=subject and β=object, the parser operates with one unlinked argument expression (viz. α) up to the point when it encounters β, and thus finds out that the structure is transitive, that is, that it involves two arguments rather than one. If α=object, two arguments must be assumed from the beginning of the clause on. We thus expect subject initial clauses to be faster to process up to the point when the second noun phrase is encountered - and this is what we found in our experiments. Models based on predictions concerning argument roles and expressions (and the costs of not having them linked) are thus in line with the experimental evidence discussed so far. See Gibson, Hickock & Schuetze (1994) for this approach. As in the case of the connectionist alternative, it may be pointed out that a grammaticalization pattern might arise in response to parsing difficulty as defined by number of unlinked thematic roles that is not much different from what it would be in the memory theory of the costs of movement. The preposing of α creates a difficulty because it will bring costs of (unlinked) argumental expression earlier to bear - as long as movement goes to the left. Consider, however, a sentence type of German exemplified in (15). The examples in (15) involve "long" movement of a wh-phrase out of a complement clause. This complement clause lacks a complementizer, so according to the laws of German syntax, the verb must be preposed to the position that would otherwise be filled by the complementizer (see e.g. Grewendorf 1988, Staudacher 1990). (15) a. welcher Mann denkst Du kennt den Professor whichnom man think you knows theacc professor

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"which man do you think knows the professor?" b. welchen Mann denkst Du kennt der Professor whichacc man think you knows thenom professor "which man do you think the professor knows?" The particular composition of the examples in (15) involves a further aspect. The wh-phrase is immediately followed by the main clause verb in (15). This verb makes it clear that the wh-phrase has undergone long movement: In (15a), the nominative wh-phrase is third person singular, while the verb bears explicit secondperson morphology - but subjects and verbs have to agree in German. Verbs do not agree with objects in German, but they govern case. The verb denken "think" used in (15) is incompatible with an (animate) accusative noun phrase object, so the case clash rules out a matrix object interpretation in (15b). The memory and the θ-role account of object initiality effects make different predictions concerning readings times for these structures. In the memory theory, one expects longer reading times for the initial wh-phrase in the case of (15b): after all, the structure is object initial. The verb following this noun phrase rules out the prediction that the wh-phrase is a matrix constituent in both cases. Given that the parser processes the matrix clause when it copes with the verb, it needs to keep both the wh-subject and the wh-object in memory. Thus, reading times should not differ between (15a) and (15b) for the second element (the matrix verb) and the third element (the matrix subject). The two conditions have a chance of differing in terms of reading times only from the fourth segment (=the complement verb) on - when the complement clause is encountered, the subject may be dropped from memory earlier than the object (see above). Predictions are different in accounts taking recourse to θ-theory. The number of unlinked arguments/thematic roles that a conservative parser assumes in the presence of a clause initial nominative and accusative noun phrase, respectively, is independent of whether this prediction is formulated for the matrix clause or for a complement clause. Thus, the reinterpreation of the wh-phrase as a complement clause constituent that the parser carries out when it is forced by the verb to do so does not affect these predictions. To be more precise, the case difference of the initial wh-phrase in (15) implies that one θ-role/argument is expected when the first element is parsed in (15a), but that two such θ-roles/arguments are expected in (15b). When a matrix verb like denkst is encountered, the parser realizes that the matrix clause has two thematic roles (a subject and a clausal complement), and it now expects one additional θ-role/argument for the complement clause for (15a), but two such roles for (15b). Thus, the difference in the number or predicted arguments/θ-roles is stable (in contrast to the memory account) between the two conditions, it is just shifted to the complement clause. Only when the complement clause verb kennt is encountered is there a chance for the difference to disappear. The difference in load predictions between the two main approaches can thus be summarized as in table 1:

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Table 1 Phrases to be Difference in memorized: Memory Theories a: clause initial SI: 0 1 wh-phrase OI: 1 b:matrix verb SI: 1 0 OI:1 c: matrix SI: 1 0 subject OI:1 d:complement SI: 1? 0-1 verb OI:1? e: 2nd NP in SI:0 0 complement OI:0 clause SI: subject initial; OI: object initial

Unlinked but predicted θroles SI:1 OI:2 SI:3 OI:4 SI:2 OI:3 SI:1 OI:1 SI:0 OI:0

Difference in θ-approaches 1 1 1 0 0

The shaded areas in table 1 mark the segments of the sentences in (15) for which one expects to see a reading time difference between the subject initial and the object initial condition in the two theories. The experiments 2 - 4 described in the Appendix show a clear result: there are reading time differences between the two crucial conditions for segments (a) and (d), but not for the other segments. In this respect, the predictions of the cost of memory theory seem to be borne out, in contrast to what holds for the unsaturated θ-role approach.

DOES GRAMMAR CARE? The preceding sections have summarized some evidence supporting the view that movement is costly in cognitive terms. It is therefore conceivable that a process of grammaticalization has shaped the form of grammars so that they respond to such costs. In this context, the surprising parallel between the grammar and the parser discussed in the initial part of the chapter could find an explanation. Do grammars really care for costs of movement? They specify a (violable) ban against movement, and a Minimal Link Condition. Let us, however, be more explicit about the former aspect. Both minimalist approaches (Chomsky 1995) and Optimality Theory (Grimshaw 1997) assume that movement should be avoided. In the relevant domain of wh-questions, languages should be like Japanese: there is no movement to clause-initial position in complement questions: (16) John-ga dare-o butta ka sirinai Johnnom whoacc hit Q know not "I don't know who John hit" Obviously, Japanese does not represent a universal pattern. After all, wh-phrases are fronted to clause initial position in English (17). Languages such as English might simply have been too lax in responding to processing demands, or there might be other demands that English meets. A consideration of Chinese (18) suggests a candidate for such further demands. (17) what did you say t? (18) Zhangsan zhidao she mai-le shu

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Z know who buy-Asp book "Zhangsan knows who bought books" "who does Zhangsan know bought books" Chinese lacks wh-movement and obligatory scope marking for question phrases. Therefore, (18) is ambiguous: the sentences can be understood as a declarative with an embedded indirect question, or as a question with an embedded declarative complement clause. In contrast, wh-movement in (19) serves the purpose of what Cheng (1997) calls "clausal typing": movement (a) identifies the type of the clause (declarative vs. question) and (b) indicates the scope of the wh-phrase. (19) a. who do you know that she likes b. you know who she likes We have to assume, then, that grammars of natural language do not only respond to cognitive costs of movement (if they do at all) - there are other requirements that have to be met if possible and that may override costs of movement. This in itself does not endanger the project of deriving grammar from processing costs, but the factor counteracting cognitive simplicity must be identified. Note that neither (a) nor (b) can force movement as such, because clausal type can be indicated without movement (as in Japanese (16)), and the same is possible for scope, as constructions with scope markers such as Hindi kyaa may show. (20) a. Raam-ne kyaa socaa ki ravi-ne kyaa kahaa ki kon sa aadmii aayaa thaa Raam-erg what thinks that Ravi-erg what said that which man came? "which man does Rama think that Ravi said came?" b. Raam-ne kyaa socaa ki ravi-ne kon sa aadmii kahaa ki aayaa thaa c. Raam-ne kon sa aadmii socaa ki ravi-ne kahaa ki aayaa thaa If (a) and (b) can be met without movement, and if movement is cognitively costly, it is unclear why movement is tolerated when processing difficulty is grammaticalized. This problem disappears, however, if (only if?) e.g. both [I] and [II] hold, that is, if the scope marking strategy employed in Hindi (20a,b) itself involves cognitive costs, perhaps comparable to the costs of movement. [I] Movement is cognitively costly [II] A construction Σ is cognitively costly if the syntactic scope of α in Σ does not correspond to its semantic scope. Obviously, the only way to respond to both processing demands (if II is correct at all) at the same time (that is, the only way to eat the cake and keep it) is to restrict question formation to subject questions - in which the wh-phrase does not move to the clause initial position indicating its scope, because it already occupies this slot in the base structure. This option seems to characterize Kwakwala (Anderson 1984). Here, the scope of the wh-phrase is identical with its semantic scope without creating movement costs but the price Kwakwala pays is considerable - the language has to provide many grammatical function changing operations such as passive and apply them a considerable number of times, because one still must be able to ask: what do you want? (by saying: what is wanted by you?). Typically, languages rather decide which of [I] and [II] they attribute more weight to - [I] and [II] are two processing demands that cannot be met simultaneously. Reference to two different factors that try to pull grammar in two different directions reduces the attractivity of the processing explanation for grammatical principles substantially, however: recourse to processing difficulty can now simply be dropped. A language has to "decide" whether it indicates the scope of whphrases explicitly or not, and if so, which means it uses for this. If it opts for the

13

latter, it uses what languages always use when something (grammatical function, focussing, topicality) must be marked: morphological means or positional ones. The domain of options seems restricted by the laws of grammar, and it seems that all option do the job equally well. If this picture is correct, processing considerations might come into play in a very indirect way only: if all possibilities are costly in cognitive terms, processing does not restrict the grammars' choice. We will leave it open here whether this is substantially different with the Minimal Link Condition. Chomsky (1995) takes it to be an inviolable constraint of grammar, but there is some evidence (see e.g. Müller 1998) that it can be overriden by quite diverse other types of considerations.

IS GRAMMAR ABLE TO CARE? One additional problem, at least in terms of the empirical foundation of an attempt to derive grammatical costs of movement from processing costs, lies in our complete ignorance of the mechanisms by which languages acquire or lose movement for constituent questions in their history. Ian Roberts (p.c.) suggests that languages acquire the obligatory fronting of wh-words in questions as a reinterpretation of the (less obligatory) preposing of focussed material, in the sense that wh-phrases represent the focus of a question. Historical linguists are less willing to speculate on how language lose whmovement (the crucial part of the grammaticalization explanation), so we have to offer a speculation of our own. If Anoop Mahajan (p.c.) is correct, certain languages like Hindi allow the preposing of topicalized material in front of a preposed wh-phrase in questions. Suppose a language L both has obligatory whfronting and optional fronting of topicalized material to the left of wh-phrases. Then structures such as (21) can arise. (21) [topic: subject1 [wh-object2 [t-1 t-2 verb]]] But the phonetic sequence of (21) allows an analysis without movement as well. This analysis is false for language L (recall that wh-phrases have to be moved), but if the topicalization option is chosen frequently enough, and in conversation with children, the children might not have enough evidence for constructing the more complex structure (21) instead of the simpler alternative (22). By this, the language loses wh-movement. (22) subject object verb If this account of the loss of wh-movement is correct, the processing explanation of the grammatical costs of movement faces two problems: the grammaticalization of the ban against wh-movement in the history of a language presupposes that a language allows massive movement options in the stage immediately preceding the breakdown of the movement analysis. In other words, prior to the loss of whmovement, children would have to go in exactly the opposite direction of what processing difficulty would predict. And note that the final step in the process does not make any reference to processing difficulty at all: the crucial point rather is that the language ceases to offer clear evidence for the application of movement. Things might even be worse. Studies on the acquisition of wh-movement by children learning English or German reveal that children may omit auxiliary inversion or delete the wh-phrase in early acquisitional stages -they do not try to leave a wh-phrase in situ instead of moving it. In languages like French which appear to allow a choice between a movement and an in situ strategy for question

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formation, the preferences of the children are clear: they begin forming wh-question by moving the wh-element (Weissenborn 1993).

CONCLUSIONS The grammar and the parser (understood as a system of strategies and rules for on line syntax processing) resemble each other in many domains. In this paper, we have considered one particular kind of similarity, the costs of movement. Movement can be shown to be costly in cognitive terms, and it is tempting to make such cognitive costs responsible for corresponding aspects of the grammatical system. Such grammaticalization accounts may seem plausible at first glance, but they presuppose the validity of a number of assumptions that may very well be false: (a) In general, it has not been shown so far that processing difficulty plays a decisive role in determining the direction of syntactic changes that shape the overall properties of natural language grammars in the long run. (b) It is not clear whether the cognitive costs of movement are not compensated for by other cognitive costs that arise in structures in which semantic and syntactic scope do not go hand in hand. If so, the "balance of powers" may simply ensure that syntactic change in the domain of question formation can go in any direction. (c) It is not clear whether the actual path of syntactic change in the domain of constituent question formation follows the lines predicted by a processing optimization account. It thus seems mandatory to look for other ways of explaining parallels between the grammar and the parser.

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APPENDIX: FOUR EXPERIMENTAL STUDIES This appendix presents the results of four experimental studies which complement experiments we have reported elsewhere but which are crucial for certain of the points we wish to make. With one exception, the constructional aspects of Experiment 1 are identical with those in one study reported in Schlesewsky et al. (submitted). While the experiments reported there focus on establishing a syntactic object initiality effect, the purpose of Experiment 1 was to control for a possible interaction of age and object-initiality Experiment 1: The processing of wh-questions in old and young adults Method • Subjects Thirty two subjects participated in the experiment: sixteen young adults (mean age: 20) and sixteen old adults (mean age: 69). They were native speakers of German. They had not participated in any previous psycholinguistic experiment, and were not familiar with the purpose of the study. They were paid for participation. • Procedure Subjects read the experimental material in a self-paced reading study with nonstationary presentation and phrase by phrase retrieval. The segments for phrasewise retrieval are indicated in Table 2 below. Sentences ended with a punctuation mark. After the presentation of the punctuation mark, the participants had to carry out a sentence matching task. By pressing a "yes"- or a "no"-button, subjects had to decide whether a control sentence was a verbatim repetition of the preceding sentence. The control manipulation did not involve the proper analysis of the grammatical function of the initial wh-phrase: a negation or an adverb could be missing or be added, or a noun could have been changed. • Material The experimental items were sentences of the type represented abstractly in (11). They consisted of a main clause followed by an indirect "who"-question (nominative or accusative initial) or an indirect whether question, see also (23). (23) es ist egal "it does not matter" a. wer vermutlich glücklicherweise den Mann erkannte whonom presumably fortunately theacc man recognized b. wen vermutlich glücklicherweise der Mann erkannte whoacc presumably fortunately thenomman recognized c. ob vermutlich glücklicherweise der Mann den Dekan whether presumably fortunately thenom man theacc dean erkannte recognized The wh-phrase was followed by two sentential adverbs, which may precede or follow subjects in German. These were in turn followed by a noun phrase explicitly marked for the complementary grammatical function. In the experimental items for the "whether/if" condition, the wh-complementizer was followed by the adverbs, the

16

subject and the object, in that order. There were thus three experimental conditions in the experimental material: subject-initial, object-initial, "whether"-initial. The participants read five experimental items per condition, and were never confronted with two members belonging to a single pair. There were 140 distractor items not involving material analyzable as crucial for the contrast between the two conditions. The segmentation for self-paced reading is given in table 2. Results The data of one participant had to be excluded from the analysis because of the high error rates in the control task. Table 2 summarizes mean reading times in ms, and accuracy in the sentence matching task in percent. Table 2: Results of Experiment 1: All participants Type 1 2 3 4 wh-phrase adv1 adv2 NP compl. wer/wen/ vermutglücklich- der/den ob lich erweise Mann who-nom preforthe-nom who-acc sumably tunately the-acc if man subject 608 600 968 906 initial object 697 761 1092 1073 initial if 593 602 945 982 initial

5

6

NP2

verb

den Dekan the-acc dean

erkannte

-

951

-

1099

856

886

recognized

Accuracy was higher in the object initial condition (85.2%) than in both the subject initial (76.8%) and the if-initial (73.0%) condition. A repeated measures ANOVA showed a reading time difference between the object-initial condition on the one hand and the other two conditions, on the other, with reading times being higher in the object initial condition. This effect was marginally significant on segment 1 (F1(1,30) = 3.74, MSe = 309664.08, p < .07, F2(1,14) = 3.00, MSe = 99900.31, p < .1)), and segment 4 (F1(1,30) = 7.37, MSe = 278107.63, p < .11, F2(1,14) =2.27, MSe = 241826.48, p=.15)). It was significant both in the subject and the item analysis on segment 2 (F1(1,30) = 17.24, MSe =183372.30, p< .01, F2(1,14) = 19.91, MSe =51064.21, p < .05)), and significant on segment 3, but in the subject analysis only (F1(1,30) = 8.95, MSe =253162.34, p< .01, F2(1,14) = 2.50, MSe = 198408.27, p