Abstract
The present research study aimed to investigate the psycholinguistic aspects of interlanguage (IL) variability in English as a second language learners from Iran. Three morphological forms were specifically examined in this study: the plural "-s," past tense forms, and present tense forms. In order to investigate the learners' cognitive processes, the researchers used a mixed-method approach, combining qualitative semi-structured interviews with quantitative analysis of written task performance. Under various task conditions, learners exhibited two opposing patterns of IL variability (increasing and decreasing) in their morphological forms. Various degrees of accuracy were noted for every kind of morpheme. Different students allocated their attention differently to form and meaning in both under pressure and relaxed task environments. The observed variations could have been caused by limited working memory and attention capacity in addition to L1 transfer. The research indicated that the field of second language acquisition could benefit from an explanatory approach to comprehend IL variability from the learner's perspective. It provides recommendations for larger-scale research projects in a variety of educational contexts, along with pedagogical implications.