Applied Psycholinguistics 25 (2004), 603–634 Printed in the United States of America DOI: 10.1017.S0142716404001298 Morphological insensitivity in second language processing

Two competing explanations exist regarding the nature of morphological difficulty in adult second language acquisition: competence deficit versus performance deficiency. This study tested these ex-planations by examining English as a second language (ESL) learners ’ morphological performance in reading comprehension tasks. Chinese ESL speakers were asked to read English sentences for compre-hension in three self-paced word by word reading experiments. Their reading times were measured to determine if they were sensitive to idiosyncrasies/disagreement in sentences that do and do not involve the number morpheme. The results show that they are not sensitive to number disagreement, but sensitive to other idiosyncrasies tested. This insensitivity to the number morpheme suggests that their morphological knowledge is not an integrated part of their automatic second language competence. Inflectional bound morphemes of English, such as third person singular-s, plurals, and past tense, are notoriously difficult for adult learners of English as a second language (ESL). Even very advanced ESL speakers who are otherwise consid-ered highly proficient and effective users of the language often have difficulty in using these morphemes correctly in spontaneous communication. Such difficulty has been well documented in the second language acquisition (SLA) literature. First, a large number of studies have shown a low accuracy rate in the use of inflectional morphemes by adult ESL users in spontaneous communication across different first language (L1) backgrounds and different second language (L2