A Checking Account

NPZZ

subject

VPbbb

"

"

"

NPbb

"

"

object_PL V verb

While percolation may be sensitive to the morphophonology of number marking, there is no reason to assume that it is also sensitive to case marking. Attraction may be more effective the stronger or more salient the morphological exponent of number is. Reversely, the determination of the correct number specification of the subject NP might be easier in the presence of unambiguous number marking of the head noun and/or the determiner. Replicating findings from production (Hartsuiker et al., 2003), Severens et al. (2008) found less attraction when the subject NP contained an unambiguous determiner. Since case and number are independently specified—although morphologically realized by a single exponent in inflectional languages like German—percolation of the abstract number feature should be independent of case marking. This prediction will be tested in a series of experiments investigating object attraction (cf. chapter 6).

4.4.3.3 A Checking Account

The Checking Account was first presented in Häussler et al. (2004). Essentially, it attributes attraction to retrieval errors during the checking phase and possibly dur-ing reanalysis as well. The checkdur-ing account relies on the assumption that agree-ment checking is mandatory. Furthermore, it assumes that the checking processes involve subject retrieval rather than the comparison of a predicted verb-number value and the actual verb-number value. Retrieval occasionally fails and deliv-ers the distractor instead of the subject NP. An agreement error results when the two NPs differ in their number specifications. Recently, Badecker et al. (2006) and Badecker and Kuminiak (2007) suggested something similar for language production. For language comprehension, Wagers et al. (2009) propose an attrac-tion account that attributes attracattrac-tion errors to retrieval errors. Their proposal, however, differs from the checking account with respect to the processing phase responsible for attraction. While the checking account assumes that attraction er-rors occur during first-pass parsing, Wagers and colleagues assume that attraction errors occur during reanalysis (cf. 4.4.3.4).

Attributing attraction to the processes responsible for checking subject–verb agreement seems to be discredited by the finding that the linear distance between distractor and verb is not crucial for the incidence of attraction. This argument, however, is only valid if retrieving the subject for purposes of agreement checking involves a linear, backward-search through the sentence conceived of as a string of words. But this is a rather implausible scenario. If retrieving the subject in-volves any search at all, it is unlikely that it is the word string which is searched.

Given what is known about the storage of sentences in working memory, such a search process would have to apply to a hierarchical syntactic representation. Fur-thermore, McElree (2000) and McElree, Foraker and Dyer (2003) have provided evidence that subject retrieval during sentence comprehension is mediated by a di-rect access mechanism, not by a search process. Evidence for cue-based retrieval is not limited to subject retrieval but comes also from experiments demonstrat-ing an impact of similarity-based interference on garden-path recovery (Van Dyke and Lewis, 2003) as well as on processing difficulties in object-extracted rela-tive clauses (Gordon et al., 2001, 2004) and object-clefts (Gordon et al., 2002;

Van Dyke and McElree, 2006). Interference effects arise whenever the cues nec-essary to retrieve a certain item are associated with more than one item in the current memory representation (Lewis and Vasishth, 2005; Van Dyke and Lewis, 2003; Van Dyke and McElree, 2006). Both a hierarchical search through the syn-tactic tree and a direct access mechanism along the lines of McElree et al. (2003) would be compatible with the finding that number attraction is not determined by the linear distance between verb and distractor but by the hierarchical distance between distractor and subject NP.

The checking account in combination with a direct access mechanism of re-trieval predicts that attraction is sensitive to all features that are part of the rere-trieval cue set. A first-hand candidate for being among the retrieval cues is nominative case. Therefore, the checking account, in contrast to the percolation account, pre-dicts that attraction is sensitive to case marking. A distractor which is morpholog-ically compatible with nominative case is more likely to interfere than a distractor which is unambiguously marked for some case other than nominative. At the same time, a subject NP which is case ambiguous may be harder to retrieve than a sub-ject NP which is unambiguously marked for nominative case. This prediction will be tested in chapter 6. Predictions regarding the role of number marking depend on the particular retrieval cues and whether or not number is among them. Prima facie it seems self-evident to assume that number is among these cues. Given that number and case form a natural class, both features may be used together. Fur-thermore, the verb comes with a number specification which has to agree with the subject’s number specification, so why not use it to retrieve the subject? Note first that in such a scenario checking in terms of feature-value comparison would be superfluous since agreement is presupposed. The checking process would be

identical with the retrieval process. Second and more importantly, number is not a genuine subject property. Empirical evidence against the assumption that number is a first-pass retrieval cue comes from studies investigating sentences with local subject–object ambiguities as in (18).

(18) a. Ich

‘I know that the secretary informed the colleagues.’

b. Ich

‘I know that the colleagues informed the secretary.’

The two sentences in (18) are identical up to the clause-final auxiliary. The two NPs in the embedded clauses are both compatible with nominative case as well as accusative case. Therefore, the embedded clause is each locally ambiguous between an SO structure and an OS structure. Number agreement resolves the ambiguity: In (18a) the auxiliary hat is singular, therefore the singular NP die Sekretärin must be the subject; (18b) can only have an OS structure with the plural NP die Kollegen as its subject because the auxiliary haben is plural. Lo-cally ambiguous object-before-subject sentences exhibit strong garden-path ef-fects when disambiguated by number agreement between subject and verb (for recent overviews see Bader and Bayer, 2006; Bornkessel and Schlesewsky, 2006).

Crucially, sentences like (18b) are only rarely reanalyzed successfully as evi-denced by the low percentages of correct judgments in Bader and Meng (1999).

In this experiment using the method of speeded grammaticality judgments, par-ticipants rejected locally ambiguous OS sentences most of the time and reliably more often than corresponding SO sentences (51% versus 15% error rate).¹⁸ Fur-thermore, the garden-path effect is smaller when disambiguation is reached by case (cf. Meng and Bader, 2000a). These two findings are unexpected if num-ber was central for subject retrieval—numnum-ber would unambiguously identify the correct subject. Thus, there are strong arguments against the idea that number is a subject-retrieval cue during first-pass parsing, although number might be help-ful in a second step when recovering from a garden-path effect. If number is not among the retrieval cues the probability of erroneous distractor retrieval is inde-pendent of the number specification. Interference is then equally possible with singular and plural distractors and thus no asymmetry between singular and plural is predicted.

In a way, the percolation account and the checking account are complementary to each other. Modifier attraction and its properties (distance effects, singular–

18Some studies report a slightly better accuracy for OS sentences but still far below the accuracy for SO sentences (e.g., 64% vs. 86% correct judgments in Meng and Bader, 2000a.

plural asymmetry, sensitivity to number marking) are best explained in terms of feature transfer, e.g., by means of percolation. The checking account has some—

although presumably not insurmountable—difficulties to handle these findings.

On the other hand, the percolation account fails to explain object attraction and non-intervening attraction which both can be captured by the checking account.

Furthermore, the two accounts make conflicting predictions concerning the role of case marking. The morphological realization of case should be irrelevant under the percolation hypothesis, whereas retrieval interference may well be sensitive to it.