SECOND LANGUAGE Vol. 15 (2016, pp. 5–28) The Japan Second Language Association 

http://www.j‐sla.org/ 

Missing the Trees for the Forest:

Morphology in Second Language Acquisition 森を見て木を見ず: 第二言語習得における形態論

Donna Lardiere Georgetown University ドナ ラディエレ ジョージタウン大学

Abstract By nearly all accounts, the mastery of morphology in a second language (L2) is difficult, especially for adult learners. This paper provides an overview of recent research investigating the kinds of challenges L2 learners face in acquiring and spelling out morphosyntactic features, including the extent to which L2 morphology can be successfully acquired, the extent to which morphological errors accurately reflect underlying knowledge of those features (and how we might assess this), and the role of L1 influence in ultimate attainment of the L2.

要旨 ほとんどすべての研究において，第二言語における形態素の習得は，特に大人の学習者の場合，

困難であることが示されている．本研究では，第二言語学習者が形態素を習得する際やスペルア

ウトする際に直面している以下のような問題を扱っている最近の研究を概観する．どの形態素が

習得できるのか，どの形態素の誤りがその素性の元となる知識を反映したものであるのか，第二

言語の最終到達点に対する母語の役割はどのようになっているのか． 1 Introduction By nearly all accounts, the mastery of morphology in a second language is difficult, especially for adults. Slabakova (2006, p. 324) refers to it as the “bottleneck” of L2 development, and DeKeyser (2005, p. 6) writes that “the problem of L2 users’ failing to use morphology, even in comprehension, is so fundamental that it has by itself spawned entire bodies of literature.” The learning challenge can indeed be daunting, if one thinks about it: not only must the learner

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acquire knowledge of exactly which morpholexical forms express which (combinations of) syntactic and semantic features, but also knowledge of a constellation of potential conditioning factors that may be phonological, syntactic, lexical, semantic, and/or pragmatic, including the conditions under which such forms are obligatory, optional, or prohibited. The features in question may be interpretable or not; the forms (in theory) may be overt or not. Of course, young children acquiring their native language(s) face the same requirements and almost always eventually succeed. However, nativelike attainment is fairly atypical among adult L2 learners, who bring to the learning task an already fully developed, psychologically-entrenched prior-language system of features, categories, and conditioning factors that may differ dramatically from those of the target language1. Moreover, even if such complex L2 knowledge were completely attained, language processing routines among adult L2 acquirers might be slower or somehow less efficient, leading to performance variability under certain real-time conditions.

Not surprisingly, therefore, second language acquisition (SLA or L2A) research has tended to focus on learners’ persistent divergence from nativelikeness, attempting to account for it and to model learner knowledge of the target grammar. Unlike very young children, whose ability to conceptualize the various meanings associated with morphological distinctions is still developing alongside their linguistic development, adults are cognitively mature. On the one hand, this should make language learning easier, in the sense that the cognitive categories that are expressible in language are already available for mapping to morphological forms. On the other hand, because these categories are obviously grammaticalized differently across languages, and learners already know how the categories are grammaticalized in their native language(s), second language learning requires (possibly radically) reorganizing and redistributing such categories and features among the morpholexical items of the L2. In general, the more complex such grammatical distinctions are, and the more differently they are lexicalized in the target language from those of the native language(s), the more difficult we expect this task to be. Furthermore, because second language phonology poses well-known problems for late language learners, the extent to which morphological realization in the L2 is subject to complex allomorphy or to prosodic constraints that differ from those of the L1 is also likely to affect the ultimate outcome of morphological acquisition. (We return to the issue of prosodic transfer from the L1 in section 2.7.)

Some key (and highly interrelated) questions that arise, then, for SLA research in morphology are the following, around which the remainder of this paper has been organized: 1 Birdsong (2006, p. 20) observes that the findings of over 20 studies (and there are undoubtedly many more now) investigating the rate of nativelike L2 attainment among late age-of-acquisition (AoA > 12) learners suggest that nativelikeness is “not typical but neither is it exceedingly rare” depending on AoA, L1-L2 pairing, task type, amount of formal training and L2 use, among other factors. Birdsong (1999, pp. 14–15) argues for an overall nativelike attainment rate of 10–15% among the relevant population, defined as learners with exogenous circumstances favoring acquisition (e.g., immersion for a substantial length of time), as opposed to “any and all who have had some exposure to an L2 or who have tried to learn a foreign language.”

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(1) To what extent does variability in morphological performance (e.g., instances of

omission or reliance on an underspecified form in an obligatory context), particularly for inflectional morphology, reflect a lack of knowledge of corresponding syntactic and/or semantic features and categories (such as tense, aspect, case, number, gender, definiteness, etc.)? Because mature learners have the cognitive capacity to compute the conceptual distinctions such categories grammaticalize, there is seemingly no conceptual barrier to their acquisition. As we shall see, much work in SLA has been devoted to trying to determine whether or not adult learners have underlying knowledge of grammatical categories even if the morphology that expresses them is only variably produced.

(2) What counts as evidence for morphosyntactic knowledge and how should morphological variability be modeled (e.g., as a competence or performance issue)? Most generative SLA studies assume some version of the separation hypothesis (Beard, 1995), according to which underlying morphosyntactic features are abstract and distinct from their morphophonological exponents; thus, in principle, knowledge of abstract features even in the absence of mastery of their associated inflectional forms is possible. Many of these studies rely on a Distributed Morphology (DM) framework (Embick & Noyer, 2007; Halle & Marantz, 1993) to model learners’ grammatical representations. This is an approach in which the outputs of syntactic derivation are terminal strings consisting of abstract feature bundles; the feature bundles are then matched as closely as possible with those of phonological exponents referred to as vocabulary items. More recently, a few researchers have also adopted a Feature Geometry model (Harley & Ritter, 2002), which attempts to predict which forms will be underspecified or used as a default at progressive stages of development. We return to representative examples of these approaches in section 2.5. Various aspects of morphological performance have also been explored in studies of L2 processing, to which we turn in section 3.

(3) What is the role of L1 transfer? In practice, this question broadly boils down to the extent to which L1 knowledge is deterministic; that is, whether or not learners can (eventually) acquire morphological contrasts that are required in the L2 but not instantiated in the L1. One type of account, ultimately rooted in some form of the critical period hypothesis, has argued that nativelike attainment of certain categories and features not activated during primary language acquisition is simply not possible for late learners. Other studies, however, focusing on learners at near-native L2 proficiency levels, argue that nativelike attainment is eventually possible. We explore both positions in sections 2.3–2.4 and again in section 3.

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2 Morphological Variability in SLA Like children acquiring their native language, adult learners exhibit variability in their use of functional morpholexical items such as determiners, copulas, auxiliaries, classifiers, and markers for tense, aspect, agreement, case, gender, number, etc. In other words, these items might be omitted where required in obligatory contexts, or replaced by an incorrect form—often an underspecified form, such as an infinitive or participle instead of a finite verb form specified for person, number and/or gender agreement. Children, though it might take them awhile, typically converge on the correct forms of their native language(s) and eventually produce them invariably (that is, within the variability norms of their target language community). Adults, though it may not be impossible for them to do so, often do not, sometimes even after long periods of immersion in the target language environment. Consider the following examples of ‘fossilized’ naturalistic speech from two case studies of L2 English acquirers who had lived in an English-speaking environment for many years and whose grammatical knowledge had likely reached a developmental end state—Patty, a native speaker of Hokkien and Mandarin Chinese (Lardiere, 2007) and SD, a native speaker of Turkish (White, 2003a): (4) a. Yeah, front tooth a little bit black. [Patty (Lardiere, 2007, p. 182)] b. You would amaze, how he know so many thing. [Patty (Lardiere, 2007, p. 74)] c. But then after a while he just give up. [Patty (Lardiere, 2007, p. 82)] d. And she cleans ... the house. And wash the dishes. [SD (White, 2003a, p. 134)] e. And, woman wear hat. [SD (White, 2003a, p. 138)]

Within formal approaches to SLA, an enduring and much-debated question that arises from the variable omission of functional elements, as shown in the examples above, is what such variability indicates about the nature of the learners’ mental representation of the grammatical properties associated with these elements. In other words, do syntactic functional categories such as Determiner Phrase (DP) or Tense Phrase (TP) fail to be projected in the learner’s syntactic structure in those instances where determiners or tense/finiteness morphemes have been omitted from an utterance? And another (more methodological) question: What criteria must be met in order to conclude that a learner has acquired (or not) knowledge of a particular morphosyntactic feature such as definiteness or past tense? We address these issues in the following subsections. Let us turn to the latter question first for a brief look at a few key methodological concerns. 2.1 Some Methodological Issues in the L2 Acquisition of Morphology Since Brown’s (1973) groundbreaking study of morpheme order acquisition in English L1 acquisition, one criterion for determining whether a morpheme (and by hypothesized implication, its associated morphosyntactic feature) has been acquired is suppliance in obligatory contexts. Brown’s own criterion, adhered to in much child language acquisition

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research, was 90% suppliance across at least three speech samples (p. 258). For SLA, various criterial percentages of obligatory morpheme suppliance have been applied across the literature. Tsimpli and Mastropavlou (2008, p. 163) adopted Brown’s 90% criterion as indicating ‘mastery’ of article suppliance in L2 Greek. In a study of the acquisition of verb-raising and subject-verb agreement in L2 German, Vainikka and Young-Scholten (1994) required the naturalistic production of a correct agreement suffix in at least 60% of raised main verbs, and at least two correct instances each of at least four different suffixes of the inflectional agreement paradigm, as the criterion for concluding that knowledge of agreement (and the corresponding morphosyntactic functional category Agr) had been acquired. Similarly, Eubank and Grace (1998, p. 77) classified native Chinese speakers acquiring L2 English as “having agreement” if they supplied 70% correct overt agreement affixation (3sg -s) on thematic main verbs on an oral translation task. Such criteria, obviously arbitrary, are best used primarily as a rough measure for grouping learners by proficiency level or developmental stages. As Lardiere (1998) demonstrated, however, they are unreliable as independent measures for determining whether or not knowledge of a particular morphosyntactic feature has been acquired. And as R. Hawkins (2001, p. 46) further points out, even 100% suppliance of a morpheme in obligatory contexts does not necessarily entail that the L2 learner has assigned the same interpretation to that morpheme as native speakers of the target language.

Many experimental SLA studies, especially those of the L2 endstate grammar, use the criterion of nativelikeness, as determined by a specific range of performance among native speaker controls. Learners whose performance falls outside the native-speaker range are considered non-nativelike, but as pointed out by Birdsong (2005, p. 324), not all departures from nativelikeness should be taken to indicate defective language learning mechanisms. For example, bilingualism itself, whether early or late, is known to result in language processing that is slower and/or less efficient than that of monolingual speakers, which can affect word segmentation and lexical retrieval (e.g., Birdsong, 2006; Carroll, 2006; Sorace, 2011).

One of the trickiest methodological problems in SLA, and yet one of the most commonly encountered, is deciding how to ascribe knowledge of a morphosyntactic category to a learner in cases where suppliance of morphemes is persistently non-nativelike but also non-negligibly high. A study by Hawkins and Liszka (2003) offers an illustrative case in point. Hawkins and Liszka compared rates of L2 English past-tense marking in spontaneous oral production among native Chinese (n = 2), Japanese (n = 5) and German (n = 5) speakers all matched for generally high L2 English proficiency. They found that the native Chinese speakers were significantly less likely than the Japanese or German groups to inflect verbs for past tense in English. They attributed this to a morphosyntactic deficit—specifically, the inability of Chinese speakers to acquire a [+past] feature in their L2 English grammar because this feature is absent from their L1 and therefore (according to the grammatical deficit view to be discussed in the following section), no longer accessible. In contrast, Japanese and German both have a [+past] feature. The methodological dilemma is that, although indeed statistically different from the Japanese and German speakers (who inflected 92.8% and 95.6% of verbs in past-tense contexts for past, respectively), the Chinese informants nonetheless correctly inflected 76.7% of verbs in past-

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tense contexts for past tense (from Hawkins and Liszka’s Table 3 (p. 30)). This proportion is significantly higher than chance, and many researchers would thus hesitate to conclude that native Chinese speakers are unable to acquire this feature.

An even more striking example comes from Franceschina (2001), who looked at suppliance of gender and number marking in obligatory contexts for Martin, a native English speaker who had proficiently acquired L2 Spanish. Although gender and number marking on nouns was perfect (100%), gender and number agreement marking on adjectives, articles, pronouns and demonstratives was not, leading Franceschina to claim that her informant’s L2 Spanish DP was not fully or correctly specified for gender or that this feature was “altogether absent from the subject’s L2 syntactic representations” (p. 243). Yet the correct suppliance of such agreement morphology in obligatory contexts was 92.2% for adjectives, 91.07% for articles, 90.49% for pronouns and 85.16% for demonstratives (from Franceschina’s Table 4 (p. 236)). These percentages, while not perfect and not nativelike, would nonetheless be too high for many researchers to comfortably conclude that the features in question are ‘altogether absent.’ In this sort of case, deciding whether the methodological glass is half-empty or half-full depends to a large extent on the theoretical assumptions that inform the study. It is to some of these differing views that we next turn. 2.2 Tracking Down the Source of Morphological Variability The key theoretical debates in formal generative research on L2 morphological variability take place within a broadly-shared context of assumptions about the nature of the language faculty, including a hypothesized knowledge vs. performance distinction and a role for abstract morphosyntactic features in driving syntactic and semantic computations. Within the widely-adopted minimalist program framework (Chomsky, 1995, 2001), grammatical representations consist of hierarchically-merged constituents including functional categories, such as Tense (T), Determiner (D), and Number (Num), that comprise sets of abstract morphosyntactic feature-values, such as [±past], [±definite], and [±plural], respectively. The number and composition of such categories vary crosslinguistically, as do the various types of language-specific (morpho)lexical items whose features in some sense must ‘match’ those of the category in question. For example, the regular suffix -/d/ (abstracting away from its phonetically-conditioned allomorphs) and the words was, went, gave, got, brought, taught, found, etc. all contain a feature [+past] that matches the feature value [+past] of T in an English grammatical representation that meets the discourse/contextual or formal conditioning criteria for selecting this particular value.

A major task of the language learner, therefore, is to learn, or as Chomsky (2001, p. 4) puts it, to ‘assemble’, the lexicon of a language, by associating its lexical items with whatever morphosyntactic features that language selects. As mentioned earlier, the various conditioning criteria for selecting a particular feature value must also be acquired, including knowledge of its degree of obligatoriness and any allomorphy. For both L1 and L2 acquisition, then, there are multiple points along the ‘computational path’ at which a breakdown resulting in a morphological error or omission could conceivably occur. One possibility is that the abstract

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morphosyntactic feature value or category in question has simply not (yet) been acquired and is thus not available as part of the syntactic representation. Another possibility is that it has been acquired, but the complete set of various conditioning factors under which it must (or may) be introduced into the syntactic representation has not (yet) been mastered. Yet another possibility is that the morphosyntactic feature has been acquired and is appropriately represented in the syntactic structure but the learner has not (yet) acquired the complete set of lexical items with which that feature (or constellation of features, such as person, number and/or gender agreement for a particular tense or case paradigm) is associated. Or the learner may have acquired the corresponding lexical item(s), but cannot access or process the right one quickly enough in real time, or may not be able to construct a targetlike phonological representation or otherwise establish the correct phonological linearization (spell-out) procedure for it. Of course, some combination of these conditions may co-occur, or different ones for different features, depending, for example, on factors such as input salience, or allomorphic, paradigmatic or pragmatic complexity. For adult L2 acquisition, in particular, there is the additional possibility that cognitive changes or limitations imposed by a hypothesized critical period for language acquisition or other age- or L1 experience-related effects may negatively affect one or more of the possible loci of morphological computation outlined above.

Considering the complexity of the L2 acquisition task, it is not surprising that different formal approaches to accounting for morphological variability have focused on one or another of these different possible sources of non-convergence. Two main schools of thought, initially divided roughly along competence vs. performance lines of inquiry, have predominated in the field within the past two decades: one is a representational deficit view, in which one or more formal features are completely missing from the syntactic representation; the other is a morphological deficit or missing surface inflection view, in which knowledge of the feature in question has been acquired and is available in the syntax but fails to be appropriately or consistently realized in the morphology. Over the past several years, though, it has become apparent that this original dichotomy may be a bit too coarse and various refinements and alternative approaches have been proposed. These accounts are sketched in the following sections. 2.3 Incomplete Grammatical Representations It is to be expected that L2 learners at beginning through intermediate stages of development will exhibit variable omission of inflectional morphology; children acquiring their native language do as well, and accounts that have looked at early stages of L2 development have broadly followed similar theoretical accounts for L1 acquisition. For earlier L2 developmental stages, a primary research question has been whether learners represent morphosyntactic functional categories such as tense and agreement at a point when they are not consistently producing the associated morphemes for these, or even not producing them at all. The answer to this question will be shaped by one’s views of the relationship between morphology and

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syntax, especially the role of morphosyntactic features in triggering various syntactic operations such as movement.

Recall, of course, that L2 learners already have knowledge of some set of functional categories from their native language, so that, unlike L1 acquisition, the knowledge of these could in principle be used to construct syntactic representations for at least the same categories in the L2 grammar. However, some researchers argue that knowledge of such L1 morphosyntactic categories is not initially available for the L2, because the abstract categories in question (e.g., T, D, Num) cannot be constructed until the actual L2 morpholexical items (e.g., -ed, the, -s for L2 English) associated with their features have been learned and are produced consistently (or to some criterial percentage of suppliance in obligatory contexts, as mentioned earlier). This approach, following along the lines of similar L1 acquisition theories (e.g., Radford, 1995; Vainikka, 1993/94) is best exemplified by the work of Vainikka and Young-Scholten (1994, 1996), who tied the productive L2 acquisition of the German subject-verb agreement paradigm to syntactic finiteness and V2 word order. More generally, this hypothesis (often referred to as the Minimal Trees Hypothesis and more recently as Organic Grammar) is supported within this theoretical framework to whatever extent researchers find that the posited syntactic effects associated with the categories, such as subject-raising, verb-raising, and case valuation within TP, or wh-movement in CP, or noun-raising over adjectives in DP, etc., do not occur before the relevant morphemes are acquired. It is likewise disconfirmed to the extent that such syntactic effects are evident despite associated morphological variability. Both outcomes have been reported (see the following section and R. Hawkins (2001), Herschensohn (2001), Lardiere (1998, 2000, 2007, 2008), Schwartz and Sprouse (1996, 2000), White (2003b), among others, for more extensive discussion).

The minimal trees hypothesis, although it posits missing functional categories and features in early stages of L2 development, does not preclude eventual nativelike ultimate attainment. However, much recent work has turned toward addressing non-nativelike endstate outcomes of SLA, and more specifically, whether it is even possible for mature L2 learners to acquire certain formal morphosyntactic features, particularly those required by the target L2 that are not already part of their L1 grammar. One approach that predicts it is not possible is a representational deficit or feature deficit model (e.g., Franceschina, 2001, 2005; R. Hawkins, 2003, 2009; Hawkins & Chan, 1997; Hawkins & Hattori, 2006; Hawkins & Liszka, 2003; Tsimpli & Dimitrakopoulou, 2007; Tsimpli & Mastropavlou, 2008). More specifically, this type of account proposes that, for mature L2 learners in cases where a particular morphosyntactic feature was not previously selected in the learner’s native language(s), that feature will no longer be accessible in the L2, due to maturational or critical period effects. Following developments in minimalist syntactic theory, this claim has been further refined to preclude only uninterpretable features from being acquirable—that is, only purely formal features with no inherent semantic content, such as those that trigger movement and/or enter into agreement relations. (This revised version is sometimes referred to as the Interpretability Hypothesis.)

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An example of this approach is the Franceschina (2001) study mentioned earlier. Recall that her L2 Spanish informant, Martin, was able to perfectly produce correct gender marking on Spanish nouns. Because gender on nouns is considered an inherently lexical feature, it is expected to be completely acquirable given sufficient exposure to input. However, gender agreement on adjectives, articles, pronouns and demonstratives must be computed and is considered an uninterpretable feature. The representational deficit view predicts that the gender agreement feature cannot be acquired by a native speaker of a language that has no grammatical gender, such as Martin, who was a native speaker of English. As pointed out earlier, Martin’s gender agreement marking, although quite accurate (ranging from roughly 85–92% suppliance in obligatory contexts), was less accurate than his gender selection on nouns—a difference that Franceschina attributed to the absence of an uninterpretable gender (agreement) feature in Martin’s underlying syntactic representation. Similar results were obtained by Franceschina (2005) in another, cross-sectional L2 Spanish study that compared gender accuracy between native speakers of L1s with and without grammatical gender. Although gender agreement by the [–gender] L1 group across a range of tasks reached high levels of accuracy, this group was nonetheless outperformed by the [+gender] L1 group, leading Franceschina to conclude that the [–gender] learners do not encode an uninterpretable gender feature in their L2 Spanish syntactic representations.

Another example of a study that argues for a representational deficit account is that of Tsimpli and Mastropavlou (2008), who investigated the L2 acquisition of pronominal clitics in Greek by six adult Russian and Turkish early bilingual native speakers who lived in Greece and had been using Greek on a daily basis for at least 8 years, and whose L2 grammatical knowledge was suggested by the authors as having reached a developmental end state (p. 158). According to the authors’ morphosyntactic analysis, first- and second-person clitics in Greek bear an interpretable [+person] feature, whereas third-person clitics, analyzed as clusters of uninterpretable case and agreement features only, do not. Moreover, in regard to case, genitive clitics are analyzed as bearing an interpretable [+person] feature that renders them referential, whereas accusative clitics do not. The authors’ prediction then, according to the Interpretability Hypothesis, was that the third-person accusative clitic should be more problematic than the other forms (p. 152). More specifically, the production of first- and second-person clitics should lag behind third-person ones, and the performance on third-person accusative clitics should be even lower than that of third-person genitive clitics. The following table, adapted from Tsimpli and Mastropavlou (2008:149), summarizes the relevant featural properties:

Table 1. Interpretable and uninterpretable features of Greek pronominal clitics Accusative Clitics Interpretable Uninterpretable

1st/2nd Person [+person] [case], [agreement] 3rd Person Ø [case], [agreement]

Genitive Clitics Interpretable Uninterpretable 1st/2nd/3rd Person [+person] [case], [agreement]

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Tsimpli and Mastropavlou found that, overall, their informants produced first- and second-person clitics significantly more often than third-person ones, as expected, and genitive clitics significantly more often than accusative ones, also as expected. They therefore concluded that the (grouped) findings supported their hypothesis. A look at the individual data, though, provides a slightly more complicated picture: the advantage for first- and second-person over third-person clitics was significant for only four out of the six participants, and the advantage for genitive over accusative was significant for only three out of the six. Moreover, for some learners, including two for whom there was a significant difference between first-/second-person vs. third-person clitics, the latter were still produced at quite high rates—for example, 65.5%, 75% and 80%.2 These individual results are somewhat unexpected on a maturational account that renders uninterpretable features inaccessible to learners. Additionally, there may be no need to resort to an interpretability/uninterpretability distinction to account for the findings of this study: it is simply possible that third-person accusative clitics in Greek are somewhat harder for adult L2 learners to learn because there are more distinct forms—six as opposed to only two in the first- and second-person accusative case and genitive case paradigms and only three in the third-person genitive paradigm, as shown in Table 2, adapted from Tsimpli and Mastropavlou (2008, p. 146).

Table 2. Paradigm of pronominal clitics in Greek, accusative and genitive case

ACCUSATIVE GENITIVE 3rd Person MASC FEM NEUT MASC FEM NEUTSINGULA ton tin to tu tis tu PLURAL tus tis ta tus tus tus

2nd Person SINGULA se su PLURAL sas sas 1st Person SINGULA me mu PLURAL mas mas

More generally speaking, the learning difficulty for adults appears to increase with the

number of inflectional contrasts to be acquired. DeKeyser (2005, pp. 5–6) remarks that “Difficulty of language form is largely an issue of complexity. ... [and] could be described as the number of choices involved in picking all the right morphemes and allomorphs ...”. Similarly, J. Hawkins (2004, p. 38) considers formal complexity from the perspective of language processing (which in general is less efficient for late language learners): “The

2 Tsimpli and Mastropavlou report only percentages of use vs. omission of clitics in obligatory contexts (their Table 9, p. 163). Tsimpli (personal communication, Aug. 12, 2011) clarifies that substitution errors were included under ‘use’ rather than ‘omission’ and that the most frequent substitution error was neuter for other genders.

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processing of linguistic forms and of their properties requires effort. This effort is minimized by reducing the set of units in a form that need to be articulated and processed ... [i]t is also minimized by reducing the number of conventionalized properties that are assigned to forms in the grammar or lexicon and that need to be activated in processing.” In cases involving greater formal complexity, both L1 and L2 learners in earlier developmental stages often rely on a default or overgeneralized form to represent a particular morphosyntactic feature such as gender or case. In adult SLA, however, morphological variability involving the underspecification of forms may well persist into the grammatical end state, an issue to which we return in section 2.5. 2.4 Intact Syntax, Deficient Mapping to Spell-out Recall from above that, within the generative linguistic framework, there are syntactic effects associated with the morphosyntactic features of functional categories; such effects include subject-raising, verb-raising, nominative case valuation within finite T, wh-movement to CP, or noun-raising over adjectives in DP, and others. The precise formulation of the theory is constantly undergoing revision, but the general idea is that there is a relationship between the presence of certain kinds of morphosyntactic feature values and certain kinds of syntactic operations. For example, the presence of a ‘strong’ or so-called Extended Projection Principle (EPP) feature in finite T triggers the raising of a subject from within a VP to T, where it is assigned nominative case. In English, for example, where case marking appears suppletively on pronouns, child L1 utterances such as her gone school and me driving are often interpreted as indicating that the child lacks the morphosyntactic functional category T or, alternatively, that a finite T is ‘mislicensing’ incorrect case marking on the subject (Radford, 1995, p. 503). For adult SLA, however, there is some evidence of a persistent dissociation between acquired knowledge of abstract morphosyntactic features and (the production of) their inflectional exponents. Lardiere’s (1998, 2007) case study of Patty revealed perfectly accurate suppletive case marking on pronominal subjects as a function of finiteness, indicating Patty’s acquisition of a finiteness distinction in English, as well as the accurate placement of verbs with respect to adverbs, negation, and auxiliaries (including use of do-support), despite her frequent omission of tense and agreement verbal inflectional morphology. Similarly, Prévost and White (2000) found that adult L2 learners of French and German variably omitted finite verbal inflections in finite contexts but did not oversupply them in non-finite contexts. Moreover, the finite inflectional forms that were supplied were largely correct, leading the authors to conclude that these learners had tacit knowledge of syntactic finiteness, despite not always being able to come up with the correct inflection (in which case they defaulted to an underspecified nonfinite form rather than produce an incorrect finite agreement morpheme). Similar results were found for two native English-speaking L2 learners of French by Herschensohn (2001).

Within DPs, White (2003), in her case study of SD, found evidence for knowledge of definiteness-effect constraints in existential sentences in SD’s L2 English even though her overall production of definite articles in required contexts was variable, and White, Belikova,

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Hagstrom, Kupisch and Özçelik (2012) likewise found nativelike knowledge of definiteness-effect constraints among learners of L2 English whose native languages were Turkish and Russian (neither of which has articles or observe definiteness restrictions in negative existentials). Regarding the acquisition of number and gender agreement inflection within DPs, Bruhn de Garavito (2008) reported that native French speakers learning L2 Spanish acquired (or transferred) the correct noun-adjective word order of Spanish DPs thus indicating the presence of the syntactic (‘strong’) feature hypothesized to trigger N-raising over adjectives, while at the same time failing to produce plural inflection approximately 40% of the time at early stages, even though French, like Spanish, includes a functional NumP category in its DP and expresses plurality on nouns and their agreeing determiners and adjectives (we return to this study in section 2.7). 3 White, Valenzuela, Kozlowska-Macgregor, and Leung (2004) similarly found that lower-proficiency L2 Spanish learners whose L1s were either French or English also acquired the correct post-nominal position of adjectives, yet produced errors in noun-adjective gender agreement.

More generally then, the learners in these studies often exhibit the hypothesized correct syntactic reflexes of the abstract features in question at the same time that they may fail to accurately or consistently produce the associated morphological exponents, especially in their spoken production. This ‘morphological deficit’ approach to probing learner L2 knowledge has been labeled the Missing (Surface) Inflection Hypothesis (Haznedar & Schwartz, 1997; Prévost & White, 2000) and the problem with morphology has been characterized as a breakdown in the linking or mapping between the morphosyntax and the morphophonology, possibly (or especially) under performance pressure to access the correct form in real time.

Although these morphological deficit studies provide support for learner knowledge of the hypothesized syntactic reflexes of abstract feature values and functional categories, they still face the problem of having to account for the morphological deficit itself. Under syntactic or representational deficit accounts (discussed in the previous section), such variability receives a fairly straightforward account: inflection is not reliably produced because the associated morphosyntactic features have simply not been acquired. Researchers of each persuasion—syntactic vs. morphological deficit approaches—in some sense represent opposite sides of the same coin. Representational deficit proponents must explain how so many adult L2 learners perform as well as they do (e.g., significantly better than chance) on accurately producing and interpreting functional morphology and/or its syntactic reflexes if the associated morphosyntactic syntactic feature in question has not been (and moreover cannot be) acquired. Morphological deficit proponents, on the other hand, must explain why functional morphology so often fails to be reliably produced or interpreted if the morphosyntactic feature in question is present in the L2 grammar. We turn next to some proposals that address the latter issue. 3 A reviewer points out that, aside from suppletive plurals such as cheval/chevaux ‘horse/horses’ and determiners, French plurals and agreeing adjectives have no distinct phonological form. We return to a brief discussion of some phonological aspects of L1 transfer in this study in section 2.7.

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2.5 Morphological Underspecification Recall from above that Prévost and White (2000) found that adult L2 learners of French and German sometimes produced nonfinite verb forms for finite forms in finite contexts. Nonfinite forms were also used correctly in nonfinite contexts, but overextended as a default form in finite (e.g., raised-verb) contexts. The reverse pattern—using finite-marked forms in nonfinite contexts—occurred only rarely. Moreover, when finite verb inflections were supplied, they were largely accurate. In other words, when inflectional errors occurred, these were systematically, rather than randomly, incorrect. For the L2 French learners, Prévost and White also examined the forms of subject clitics in clitic-doubling constructions with a co-referring subject NP. They found that clitics agreed in person, number and gender with the subject NP “to a large extent” (p. 124), but where errors occurred, it was the 3SG.MASC form il ‘he’ that was used as the default and overgeneralized to other contexts.

Learners’ reliance on a default or underspecified morphological form is a developmental hallmark of both child and adult language acquisition, though it may persist to a much greater degree in the latter. Prévost and White modeled the tendency of learners to produce underspecified forms within a Distributed Morphology framework (Halle & Marantz, 1993), in which each inflectional form (Vocabulary Item or VI) is associated with a morphosyntactic feature bundle. Lexical insertion legitimately consists of the selection of a form whose features comprise a subset of those on the corresponding syntactic terminal node. Prévost and White assumed that the learners in their study acquired the syntactic terminal node features but had not yet learned the complete specifications of the associated VIs. More specifically, they proposed that nonfinite forms are underspecified for finiteness ([αfinite]) and can be inserted in either finite or nonfinite contexts, whereas finite forms are fully specified and cannot be inserted into nonfinite contexts, accounting for the observed asymmetry. They similarly concluded that the French default subject clitic il is underspecified for phi features ([αperson], [αnumber], [αgender]) and may be inserted in more fully-specified agreement feature contexts without inducing a feature clash. As learners’ morphological knowledge develops, they gradually acquire the more fully-specified forms; however, it is possible that language processing or communication pressure continues to result in an underspecified default form occasionally re-surfacing in production.

There is a large literature on the L2 acquisition of noun class/gender agreement by native speakers of L1s with and without grammatical gender. A robust finding has been that learners rely, at least initially, on an underspecified default form; among L2 Romance language studies, for example, the overextended agreement form on determiners, adjectives and/or participles is typically masculine in place of feminine in required feminine contexts, but not vice versa (e.g., Alarcón, 2011; Bruhn de Garavito & White, 2003; Dekydtspotter & Renaud, 2009; Franceschina, 2005; McCarthy, 2008; Montrul, Foote, & Perpiñán, 2008; Renaud, 2010; White et al., 2004).

In an interesting set of studies of the processing of gender agreement on past participles in L2 French by native English speakers, Dekydtspotter and Renaud (2009) and Renaud (2010) found that the shortest reaction times occurred for learners’ responses to (mis-matched)

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masculine forms in feminine contexts, whereas latencies were actually longer for (matching) masculine forms in masculine contexts and feminine forms in feminine contexts, and even longer still for (mis-matched) feminine forms in masculine contexts. The authors concluded that these results point to the underspecification of masculine gender as a default gender that incurs the lightest computational cost, and surmised that learners require such a default feature value as part of a domain-specific mental feature structure.

Attempts to account for the particular underspecification patterns observed in the data have sometimes led to what might be termed a ‘depth-of-embedding’ approach to morphological computation. Lardiere (2000, p. 123–124) adapted Beard’s (1995) model (for case marking in Russian) of an algorithmic mapping—from grammatical function to syntactic context to morphosyntactic case to person/number features to noun class features to phonological spell-out—to account for why her case-study informant Patty had no trouble producing correct L2 English pronominal case-marking (or person/number-marking) but occasionally faltered on correct 3SG gender-marking (e.g., substituting he for she or vice versa). The latter involved an additional calculation under real-time communicative pressure; Patty only made this type of error in her speech but not in her writing. A similar type of proposal, the Contextual Complexity Hypothesis of Hawkins and Casillas (2008), more explicitly predicts within a Distributed Morphology framework the probability with which an inflectional VI will be omitted in the speech of early-stage L2 English learners, as a function of the number of contextual dependencies to be calculated. For example, an early L2 English speaker’s vocabulary entry for nonpast 3SG subject-verb /-s/ agreement might consist of the following statement: ‘insert /s/ in the context of a verb which is in the context of a non-past T, itself in the context of a 3rd person, singular N’ (p. 602). The complexity of the terminal node-chaining in this case predicts that 3sg nonpast -s will fail to be retrieved more often than a form with a less complex entry, say, -ing or - (= a bare verb), for which the only context that needs to be specified is ‘verb’.

Perhaps the most explicitly worked-out ‘depth-of-embedding’-type model is that of McCarthy (2008), who relies on Harley and Ritter’s (2002) hierarchical feature geometry to predict which forms will be developmentally underspecified in her study of gender and number agreement in L2 Spanish. In Harley and Ritter’s model, the absence of a particular feature within an entailment hierarchy of features simply triggers the default value of the next-higher feature in the hierarchy. For acquisition, this predicts that learners’ knowledge of any given feature rests to some extent on whether that feature is further partitioned (i.e., has dependent features) in a particular language; a given node must be acquired before its dependents. For Spanish, McCarthy assumes that [masculine] is encoded as the unmarked default feature value of a bare [gender] feature node, whereas [feminine] requires further partitioning of that node. Similarly, the feature [plural] is dependent on the existence of a higher [number] node, the unmarked value for which is [singular]. The developmental prediction for Spanish, therefore, is that masculine inflection will be used in feminine contexts but not vice versa, and that singular forms will be used in plural contexts but not vice versa, at least until the required

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dependent feature structure has been added. As we have seen, this is the error pattern most widely attested among studies of L2 agreement in Spanish (and French). 2.6 Feature Reassembly Recall from earlier sections that a major task of the language learner (following Chomsky (2001, p. 4)) is to ‘assemble’ the lexicon of the target language by associating its lexical items with whatever morphosyntactic (and semantic and phonological) features are selected by that language. Of course L2 learners, especially mature learners, already possess a fully developed and entrenched system of features, categories, and conditioning factors for the realization of formal contrasts in the L1. If we assume, following Schwartz and Sprouse’s (1996) Full Transfer/Full Access Hypothesis, that the knowledge of one’s L1 constitutes the departure point for acquiring the features of the L2, then the acquisition of the L2 grammar will require learners to seek out, reorganize and redistribute features among the new lexical items of the L2—a process Lardiere (2008, 2009) has dubbed ‘feature reassembly.’ In other words, learners need to acquire knowledge of how features are assembled (or bundled together) on functional category feature matrices and lexical items in the L2, along with the particular language-specific conditions under which they are phonologically realized. The more complex the formal contrasts are and the more differently they are lexicalized in the L2 from the way they are in the L1, the more difficult this task will be and the later such distinctions will be reliably encoded. In practice, the notions ‘difficult’ and ‘late-acquired’ can be operationalized as appearing at higher levels of L2 proficiency, if at all.

The feature-reassembly approach implicates a prominent role for L1 transfer in L2 grammatical development. Unlike the Interpretability Hypothesis and other representational deficit views discussed earlier, however, the role of the L1 is not completely deterministic, in the sense that features (regardless of interpretability) that are not present in the L1 can nonetheless be acquired in principle in the L2 (following the ‘full access’ part of Schwartz and Sprouse’s proposal), as long as there is some detectable evidence for a formal contrast in the linguistic environment that is paired with some difference in interpretation. But the most challenging part of morphological acquisition will be the (re-)building of new feature matrices for the lexical entries of vocabulary items and functional categories of the L2, especially in cases where these differ considerably from those of the L1.

To illustrate, consider studies by Lardiere (2009) and Hwang and Lardiere (2013), which examined the acquisition of plural marking in L2 Korean by adult native English speakers. Number-marking in Korean provides a good test case for feature-reassembly, as the features associated with the Korean plural marker (-tul) partly overlap in some respects with those of the English plural but differ strikingly in others, especially in regard to specificity, numeric vs. non-numeric quantification, classification, animacy, distributivity and interaction with case-marking. Moreover, the insertion of the plural marker in Korean is optional under some conditions, whereas it is either strongly preferred or dispreferred in others, depending on the particular syntactic, semantic or discourse context(s). Finally, although it is quite infrequent in the input, the plural marker may optionally appear under certain conditions with a distributive

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meaning (in a sense, ‘pluralizing’ events by distributing them over the members of a referentially-plural set denoted by a c-commanding subject) on sentential elements other than count nouns, such as manner adverbs, locative postpositions and other non-nominal categories.

Hwang and Lardiere tested 77 native English-speaking learners of L2 Korean at four different proficiency levels on various aspects of Korean plural marking and found indiscriminate acceptance of plural marking at lower proficiencies, as expected (because plural marking in English is obligatory on plural-referent count nouns), but that knowledge of the complex restrictions on its use, as well as of the preferred contexts for its use, were gradually acquired (to within nativelike ranges by at least some learners) as proficiency increased. Moreover, in line with the underspecification observations discussed earlier, there was some evidence that the most advanced group, while correctly rejecting unacceptable plural marking in quantified contexts at a significantly higher rate than lower-proficiency groups, incorrectly overextended that restriction to human nouns—that is, to nouns bearing the ‘next feature down’ ([+animate]) on a hypothesized DP feature hierarchy of contextual conditions on plural marking in Korean.

In another study with findings very amenable to a feature-reassembly analysis, Papadopoulou et al. (2011) investigated the acquisition of case and verbal tense and agreement marking in L2 Turkish by native Greek speakers, as well as the interaction between Turkish accusative case marking, specificity, and object scrambling. The authors found that verbal inflection was reliably acquired by higher-proficiency learners, whereas the requirement for accusative case marking on scrambled specific objects was not. They attribute their findings to the particular morphological differences between Greek and Turkish with respect to case, i.e., the richer case system of the latter but especially the specificity feature associated with accusative marking in Turkish but not Greek, and conclude that features that are grammaticalized or encoded differently in the L1 than the L2 will be more difficult to acquire. 2.7 The Role of Phonology in the Acquisition of Morphology As remarked by DeKeyser (2005, p. 2), “The meaning of morphemes and the distribution of their allomorphs cannot be acquired without the phonological capacity to extricate them from the flood of sounds in every sentence.” This is true, of course, for both L1 and L2 acquisition, but the latter appears to be profoundly influenced by adult learners’ prior knowledge of the phonology of their native language. An illustrative example of L1 phonological transfer affecting L2 inflectional morphology comes from a study by Bruhn de Garavito (2008) of the acquisition of plural marking in L2 Spanish by L1 French speakers. As mentioned in section 2.4, this study reported the rather surprising finding that the omission rate for plural inflection in L2 obligatory contexts by native French speakers at early stages of acquisition was approximately 40%, even though French has similar morphosyntactic plural marking on nouns. Further analysis revealed that French learners appeared to acquire Spanish plural marking in stages corresponding to their acquisition of aspects of Spanish syllable structure, e.g., knowledge that obstruents are allowed as part of the rhyme in Spanish and then that affixes to

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final consonants in Spanish require epenthesis. In other words, the author argues, the high rate of plural omission was likely due to differences in syllable structure between the two languages.

The most detailed analyses of the effect of L1 phonology on the acquisition of L2 functional morphology have been carried out in an extensive set of studies by Goad and White (e.g., 2004, 2006, 2008a, 2008b, 2009; Goad, White & Steele, 2003; White, 2008). Their Prosodic Transfer Hypothesis proposes that constraints on prosodic structure in the L1 play an important role in accounting for the omission of functional morphology such as tense, number and determiners in the L2, particularly in spoken production, if the prosodic representations required by the L2 are disallowed or not instantiated in the L1. Assuming the prosodic hierarchy framework of Nespor and Vogel (1986) and Selkirk (1996), Goad and White observe that languages differ as to whether, say, functional material is represented internal to the prosodic word (PWd), adjoins to the PWd to form another PWd, or attaches directly to the prosodic phrase (PPh), as shown in (5) (from White (2008, p. 309)): (5) a. PWd internal b. PWd adjunction c. PPh attachment

PWd PWd PPh base func PWd PWd

base func func base

Aspectual inflection in Mandarin Chinese, for example, is claimed to be represented PWd-internally (as in (5a)) whereas nominal and verbal suffixation in English is represented via PWd adjunction (5b), predicting that Mandarin native speakers will have difficulty producing English suffixes. Because irregular past tense marking in English is PWd-internal, however, its prosodic representation can be easily accommodated by a native Mandarin speaker, consistent with studies showing that irregular past tense is produced at much higher rates than regular past inflection in L2 English by native Mandarin speakers. In both French and English, determiners attach to the PPh, but determiners are lacking in Mandarin, for which the representation in (5c) is argued to be unavailable. Therefore, although the correct morphosyntactic representation for determiners may be acquired in, say, L2 English, they may not be able to be produced (correctly) by Mandarin native speakers, though they should cause no difficulty to a native French speaker. Eventually, new prosodic structures can be built in the L2, although L1 effects may still be observed (e.g., both Turkish and Mandarin native speakers produced stressed articles in their L2 English). Goad and White (2009, p. 23) suggest that phonological development lags behind morphosyntactic development, presumably because learners must acquire the syntax of new functional material before they can prosodically organize it.

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3 Target-like L2 Morphological Attainment? There have been many studies by now that have provided indisputable evidence that at least some late L2 acquirers’ morphological knowledge, as measured by performance on some tasks, falls within nativelike ranges or is statistically indistinguishable from that of native monolingual speakers. Much of the data in support of this conclusion has come from several kinds of ‘offline’ tasks such as acceptability judgment, truth value judgment, cloze, preference, or various elicited production tasks. Because some of these tasks allow for the possibility of metalinguistic reflection or ‘non-automatic’ responses based on explicit L2 knowledge, researchers have turned to online processing tasks to probe further for discrepancies between native and non-native sensitivity to morphological errors, and indeed, in some cases have found them. Jiang (2004, 2007) probed native Chinese learners’ sensitivity to L2 English number agreement violations and reported that, in contrast to English native speakers whose reading times increase in the ungrammatical condition, the nonnative learners failed to significantly differentiate between grammatical vs. ungrammatical agreement conditions even though they performed accurately on an untimed written agreement test. In a related study, Jiang, Novokshanova, Masuda and Wang (2011) compared native Russian or Japanese speakers’ sensitivity to plural agreement violations in L2 English, finding that the Russian participants (whose L1 has a grammaticalized plural) showed a reliable sensitivity to plural errors, whereas the Japanese participants (whose L1 does not have a grammaticalized plural) did not. The authors concluded that the data supported their Morphological Congruency Hypothesis, according to which only morpheme-congruent learners—those whose L1 has a corresponding grammaticalized morpheme—are able to reach nativelike proficiency in acquiring a particular L2 morpheme. Morpheme-incongruent learners, on the other hand, “will find it extremely difficult, if not impossible, to develop nativelike competence with respect to the same morpheme” (p. 943). Another experimental study that shows L1 effects in L2 processing is that of Hopp (2010), who tested L1 speakers of Dutch, English or Russian grouped into advanced and near-native levels of proficiency in L2 German on their knowledge and processing of scrambling, case and subject-verb agreement inflection in German. Hopp found that all three L1 near-native groups showed nativelike convergence on an offline grammaticality judgment task and self-paced reading task, suggesting that they had acquired nativelike representations of morphological marking as a means to correctly assign syntactic functions to scrambled sentences in German. On a speeded grammaticality judgment task, however, only the L1 Russian near-native group demonstrated nativelike performance on reliably detecting case-marking violations; the L1 English and Dutch near-native groups did not. Hopp attributed this result to persistent L1 influence affecting L2 processing efficiency; that is, the processes used to access and compute grammatical features are less automatized than those of native speakers. (Neither English nor Dutch has case marking on full DPs, whereas Russian does.) It is important to note, however, that the Hopp (2010) and Jiang et al. (2011) studies draw completely different conclusions from what appear to be similar types of results: For Jiang and

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colleagues, a lack of automaticity in processing reflects a true representational deficit, whereas for Hopp, a lack of automaticity reflects slower and less efficient processing that is not necessarily qualitatively distinct from that of native speakers. In support of this view, Hopp demonstrated that even the German native speaker controls in his study evinced degraded performance when presentation speed was increased. In other words, the types of morphological inflection that posed processing difficulties for the L1 Dutch and English near-native groups also posed “equal degrees of difficulties in native performance at increased task demands” (pp. 923–924). It is, however, persistent L1 influence that renders the L2 system less computationally efficient, according to Hopp. In fact, taking into consideration a wider range of studies that have investigated L2 processing sensitivity to L2 morphological errors (e.g., Foote, 2011; Gillon Dowens, Vergara, Barber & Carreiras, 2010; Sagarra & Herschensohn, 2010; Wen, Miyao, Takeda, Chu & Schwartz, 2010), the answer to whether nativelike attainment in this domain is possible appears to be a qualified ‘Yes, but ...’. Gillon Dowens et al. (2010, p. 1885) observe that their results “add to the growing body of evidence indicating that native-like language processing in late learners is possible at high levels of proficiency under some conditions.”

The conclusions one can draw from the extensive literature on L2 morphological acquisition may appear at times to resemble those of the proverbial blind men feeling an elephant. One sees obvious L1 transfer effects (and some researchers see them as permanently deterministic, others not), L2 proficiency effects, developmental effects, language complexity effects, and task effects. Some see underlying morphosyntactic deficits, or nativelike knowledge (or the potential for such knowledge) of morphosyntactic features but deficits in purely morphological and/or phonological domains, or performance problems with lexical retrieval, especially under the demands of communicative pressure or timed tasks. For any given learner, it is likely that multiple factors interact in accounting for morphological knowledge at any particular developmental moment or at different stages of development. For some late learners, some researchers have observed target-like knowledge and performance; however, this is not the typical outcome for most late learners, indicating that the acquisition of morphology in a second language remains an enduring challenge for both learners and researchers. Acknowledgements I would like to thank the organizers and participants of the 15th Annual Meeting of the Japan Second Language Association, particularly Makiko Hirakawa, Miki Shibata and Shigenori Wakabayashi.

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