The issue of how words are stored and organized as well as how they are accessed and processed has been at the core of studies on the mental lexicon. Among different kinds of words, morphologically complex and compound words have attracted the attention of many scholars doing research on different languages (e.g., Longtin et al., 2003 for French; Rastle et al., 2004 for English; Kazanina et al., 2008 for Russian; among others). Through studying complex and compound words, we can learn about the structure of the mental lexicon in general and how such words are stored (whether as wholewords or their constituting elements or both). We learn also about how they are accessed and which route (whole-word or decompositional) has been taken to arrive at this. On the basis of these questions, different hypotheses have been formulated for complex and compound word processing, which will be discussed in the following section.

Therefore, this chapter is organized as follows. In Section 2.1, there will be a discussion on the prevailing hypotheses of complex and compound word processing. Then the processing of morphologically complex nouns will be discussed in Section 2.2. Within this section, I will first discuss the effect of Stimulus Onset Asynchrony (SOA) on polymorphemic word processing. Then I will narrow down the discussion to compound noun processing. In Section 2.3, the processing of morphologically complex verbs will be discussed. Then, in Section 2.4, I will review related studies on the processing of complex and compound words by patients with aphasia. This is done because investigating studies on the morpheme retrieval in complex words by aphasic patients will provide further evidence as to how constituents in a morphologically complex word are retrieved. I will then compare noun and verb processing in aphasic patients, and subsequently discuss noun/verb prominence in these patients. I will summarize this section by reviewing studies on aphasic patients in Persian, and then end the chapter with Section 2.5, where I will discuss the effect of linguistic factors, such as linearity, and nonlinguistic factors, such as priming technique and frequency on the processing of morphologically complex words.