Lexical effects involve learning patterns that are unique ot particular words and not general across all words. These effects arise from two sources: prototype effects and dual-route processes.
Prototype effects: In the area of gender learning, Köpcke (1990) and others have shown that certain core forms may tend to organized gender cues. For example, the fact that the German noun "Schnapps" (distilled liquor) is masculine helps learners understand that most names for alcoholic beverages are masculine. This effect could arise either because of semantic reasons or from frequency effects. In the current study, prototypes were selected that seemed typical for a class.
Dual-route processes: The literature on word learning in both first and second languages often distinguishes between forms that are produced by rote as single units and those that are produced by combination (MacWhinney, 1978; Pinker, 1994). It is usually assumed that regular forms such as "wanted" or "jumped" are likely to be produced by combination of a stem (want or jump) and the regular past tense suffix -ed. At the same time, irregular forms such as "went" or "ran" are likely to be produced as single rote-learned units. However, Stemberger & MacWhinney (1986) showed that high frequency regulars can be produced by rote and some irregular patterns such as bend-bent, send-sent can be viewed as partially rule-governed and combinatorial. In the area of gender learning, dual-route processes are less important than prototype effects.