In psycholinguistic studies, with regard to cognitive models, conceptual preparation, lexical concepts, lemmas, morphemes, phonological words and phonetic patterns have been proposed as different levels of lexical processing. In previous studies, some theories have suggested the sequencing and the simultaneity of the processing modules; however, the contribution of each specific processing level has not been determined. In this study, with the participation of eighty-six undergraduate students of English Literature, picture naming task was used to determine the differences in contribution of lexical processing levels in second language (L2) noun and verb processing. According to this research, in L2, noun processing is mostly under the influence of the conceptualization stage and verb processing is mostly under the influence of the formulation stage. Therefore, it may be concluded that in language teaching, emphasizing the visual codes of concrete nouns and the morphological features of verbs, specifically facilitate learning. Moreover, with respect to the findings of this research, it may be proposed that nouns have longer retention in comparison with verbs; however, verbs are more subject to incidental learning.