Fewer studies on trilinguals’ linguistic performance have been conducted than on bilinguals’, concerning cognates vs. non-cognates. The purpose of this study is to investigate whether Spanish-English cognates’ cross-language overlap has any negative effect on sequential trilinguals’ working memory. In order to do so, a verbal picture-naming task was applied to sequential trilinguals whose first language was Persian and had formal exposure to English (L2) and Spanish (L3) respectively. The participants were 36 female students who had learned English in the EFL educational context and were learning Spanish (semester 3, equal to A1 level of International Spanish Test: ELLE) at Allame Tabataba’I University. Learners with behavioral, attention, or learning delays/disorders were excluded from the experiment. At first, the standardized Oxford vocabulary test was given to a large group of trilinguals in order to check their L2 homogeneity, and then students with an upper-intermediate level were selected based on the availability sampling. After that, a timed picture-naming task was applied to test the participants’ lexical access. Also, their cognitive development regarding resistance to inter-linguistic interference was investigated through low- (blocked) and high-competition (mixed) conditions. For this aim, 43 colored pictures including cognate and non-cognate common nouns of both Spanish and English were used in three conditions, two blocked and one mixed. All the nouns were singular. The plural ones like “las gafas” (the glasses) or “las pantalones” (the pants) were omitted from the set of the words. The Spanish articles ‘la’ for the feminine, ‘el’ for masculine, and their plurals ‘las’ and ‘los’ were not included in the conditions. The dependent variable was the number of correct answers in all the three conditions and also for the cognate and non-cognate words in the mixed block. The results showed less accurate responses, more inter-linguistic interference, and lower response times in the mixed condition than in the blocked ones.
