Which factors determine the choice of a plural allomorph for a new singular form? Are regular mappings stored differently from irregular mappings? Do native speakers only rely on analogical mappings to inflect novel word forms or do they use rules? To answer these questions we used data from Maltese, a language with a split morphology, which has a rich and variable set of concatenative and non-concatenative plural patterns.We conducted a production experiment, in which we investigated the mapping of a singular onto a plural. We show that this is driven by an interplay between the similarity of novel singular forms with existing singular words and their corresponding plural forms. Moreover, knowledge of the frequency of the plural patterns in the mental lexicon serves as a basis for generalization to novel words. Our results support an analogical model of morphological processing. We do not find evidence that native speakers use default rules.

Word-based models of morphology propose that complex words are stored without reference to morphemes. One of the questions that arises is whether information about word forms alone is enough to determine a noun's number from its form. We take up this question by modelling the classification and production of the Maltese noun plural system, using models that do not assume morphemic representations. We use the Tilburg Memory-Based Learner, a computational implementation of exemplar theory and the Naive Discriminative Learner, an implementation of Word and Paradigm, for classification. Both models classify Maltese nouns well. In their current implementations, TiMBL and NDL cannot concatenate sequences of phones that result in word forms. We used two neural networks architectures (LSTM and GRU) to model the production of plurals. We conclude that the Maltese noun plural system can be modelled on the basis of whole words without morphemes, supporting word-based models of morphology.

We discuss what factors influence the acquisition of morphophonemic alternations. What mechanisms are available to the learner; what is the basis for grammatical generalizations? Using the Artificial Language Paradigm we compared the acquisition of three alternations differing in phonetic substance, locality, and amount of exposure: one alternation was substantively based and structurally l ocal, another one was structurally local but not substantively based, and the last alternation was neither substantively based nor structurally local. Within each alternation we exposed the experimental groups to a greater or smaller number of instances. Results show a clear advantage for the substantively based alternation during acquisition. In addition, the local dependency has an advantage over the non-local one and alternations that are presented frequently have an advantage over those that are presented infrequently. We show that all three factors influence the acquisition of morphophonemic alternations, but they do so to a different d egree. Phonetic substance causes the strongest boost in the acquisition process and builds on locality, which also plays a role, and amount of exposure influences the acquisition process independent of the nature of the alternation. We argue that acquisition models should take the interaction of these factors into account.

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Using the artificial language paradigm, we studied the acquisition of morphophonemic alternations with exceptions by 160 German adult learners. We tested the acquisition of two types of alternations in two regularity conditions while additionally varying length of training. In the first alternation, a vowel harmony, backness of the stem vowel determines backness of the suffix. This process is grounded in substance (phonetic motivation), and this universal phonetic factor bolsters learning a generalization. In the second alternation, tenseness of the stem vowel determines backness of the suffix vowel. This process is not based in substance, but it reflects a phonotactic property of German and our participants benefit from this language-specific factor. We found that learners use both cues, while substantive bias surfaces mainly in the most unstable situation. We show that language-specific and universal factors interact in learning.