The goal of readers is to comprehend texts coherently. There are substantial individual differences in reading comprehension ability, which can be attributed to individual differences in the ability to integrate propositions coherently. Recently, studies focusing on individual differences in language comprehension have increased, and most use the concept of working memory to explain this phenomenon. Although only a few studies have examined individual differences in languages besides English (e.g. Osaka & Osaka, 1994), there are nevertheless a few studies exploring whether there are differences of individual differences across various languages.
Since Daneman and Carpenter (1980) developed the reading span task, several studies have revealed that readers with large working memory capacities have better comprehension abilities than those with small capacities. Working memory is composed of processing and storage modules (Baddeley, 1986) and the reading span task was designed to demand both components. For example, a participant reads aloud several sentences, memorizing the final word of each sentence. When instructed to recall the final words, high-span participants have a greater capacity than their low-span counterparts to memorize more words while reading sentences. Daneman and Carpenter's study has been often cited as representative of individual difference studies because of the value of the reading span task as a measurement tool for working memory capacity.
Many studies using the reading span task revealed that high-span participants differ from low-span participants in several domains, such as ambiguous-word processing (Miyake, Just & Carpenter, 1994), vocabulary learning (Daneman & Green, 1986), syntactic processing (King & Just, 1991), syntactic ambiguity resolution (MacDonald, Just & Carpenter, 1992), and pronoun resolution (Daneman and Carpenter, 1980).