This study investigated the acquisition of overt morphological case by adult native speakers of
English who were learning Russian or German as a second language (L2). The Russian casemarking
system is more complex than the German system; but it almost always provides the
listener with case inflections that are reliable cues to sentence interpretation. Two approaches to
learning of inflectional morphology were contrasted: the rule-based approach which predicts that
learning is determined by paradigm complexity and the associative approach which predicts that
learning is determined by the cue validity of individual inflections. A computerized picture-choice
task probed the comprehension of L2 learners by varying the cues case-marking, noun
configuration, and noun animacy. The results demonstrated that learners of Russian use casemarking
much earlier than learners of German and that learners of German rely more on animacy to
supplement the weaker case-marking cue. In order to further explore the underlying mechanisms of
learning, a connectionist model was developed which correctly simulated the obtained results.
Together, these findings support the view that adult L2 learning is associative and driven by the
validity of cues in the input.