The field of second language phonology has typically focused on the effect of the native language at the level of phonetic categories, with the implicit assumption being that the accuracy of phonetic category perception directly translates to accuracy of these sounds in the lexicon. However, research on second language lexical encoding has shown that learners with accurate discrimination often still do not have target-like lexical representations, suggesting that factors beyond perception may be at play.

Thus, this dissertation investigates not only the relationship between lexical encoding and perception, but also the relationships between lexical encoding and phonological short-term memory, inhibitory control, attention control, and second language vocabulary size. English-speaking learners of Spanish were tested on their lexical encoding of the Spanish /tap-trill/, /tap-d/, /trill-d/, and /f-p/ contrasts through a standard lexical decision task and a forced choice lexical decision task. Perception ability was measured with an oddity task, phonological short-term memory with a Russian serial non-word recognition task, attention control with a flanker task, inhibitory control with a retrieval-induced inhibition task, and vocabulary size with the X_Lex vocabulary test.

Findings indicate that the factors that affect lexical representations depend on which sounds are being encoded. When representations contain sounds that are differentiated along a dimension not used in the native language (i.e., /tap-trill/), learners with higher phonological short-term memory have an advantage, likely because they are better able to hold the relevant phonetic details in memory long enough to be transferred to long-term representations. Differences in perception ability matter most for sounds that are perceptually difficult to distinguish (i.e., /tap-d/). Finally, second language vocabulary size is the strongest factor in predicting lexical encoding across almost all contrasts, such that a larger vocabulary predicts greater accuracy. This is presumably because knowing more words entails the presence of more phonological neighbors, which puts pressure on learners’ phonological system to differentiate these minimally different words with more detailed representations. In addition, a larger vocabulary is indicative of more experience with the language, and exemplars for words that are based on more input are likely better defined.