[ca] En el món globalitzat que ens envolta és cada cop més comú que els adults hagin d'aprendre idiomes a qualsevol edat. Aquest estudi investiga quines són les diferències individuals que tenen impacte en l'adquisició de segones llengües en dos nivells de llengua estrangera, d'un conjunt de quatre diferències individuals: aptitud lingüística, nivell de primera llengua, motivació i orientacions, i edat; a més de les interaccions entre elles. Els participants són dos grups d'estudiants adults d'anglès com a llengua estrangera en dos nivells (nivell inicial, n = 52; nivell intermedi-alt, n = 88). Pel que fa a aptitud lingüística, la hipòtesi planteja que, en nivells inicials, els alumnes que progressen més ràpidament són aquells que tenen un nivell més alt d'aptitud auditiva, mentre que la capacitat analítica és igual d'important a tots els nivells. Respecte al nivell de primera llengua, la hipòtesi suggereix que pot tenir un paper fonamental en els nivells inicials. Els resultats no confirmen que hi hagi un impacte diferent de l'aptitud lingüística global segons el nivell de llengua estrangera. En canvi, si es miren els components, els resultats confirmen el paper primordial que té l'aptitud auditiva per als principiants, i també que la capacitat analítica és important per ambdós nivells. Pel que fa al nivell de primera llengua, els resultats confirmen la hipòtesi que té un paper clau per als principiants. Els resultats per motivació i orientacions també varien en funció del nivell de segona llengua: en el nivell inicial, la orientació professional explica la major part de les diferències; en canvi, en el nivell intermedi-alt la variable més important és la motivació. Finalment, el factor edat en el moment de prendre els tests és la variable més predictiva en el grup inicial. En canvi, no juga cap paper en el nivell intermedi-alt. Tot i així, quan els resultats de desenvolupament de la segona llengua es categoritzen per dimensió lingüística, els patrons són asimètrics: l'edat té efecte en quatre de les cinc dimensions lingüístiques en el grup inicial, mentre en el grup de nivell intermedi-alt només una dimensió mostra els efectes de l'edat: la comprensió oral. Pel que fa a interaccions, en el model PLS del grup inicial, només tres variables tenen valor predictiu: desenvolupament acadèmic, nivell de primera llengua, i edat. En canvi, les variables predictives del model generat pel grup intermedi-alt són motivació, aptitud lingüística, i hàbits de lectura.

[en] In today's globalised world it is becoming increasingly common that adults need to learn new languages at any age. And while the number of foreign language adult learners keeps growing, there is still a dearth of research aiming at elucidating what individual differences explain variation in foreign language learning outcomes in students placed in schools which do not have any entry requirements. This study investigated which individual differences impact second language acquisition at two levels of proficiency out of a set of four IDs: language aptitude, L1 literacy, motivation and orientations, and age; with a special focus on language aptitude and L1 literacy. Finally, the study aimed at explaining the possible interactions amongst the four IDs under scrutiny. Two groups of adult EFL learners at two different levels of proficiency (beginners, n = 52, and upper intermediate learners, n = 88), were tested on a number of variables composing the four constructs, and on five L2 language dimensions. It has been speculated that different IDs may have different impacts at two levels of proficiency; in terms of language aptitude, it has been hypothesised that for low-proficiency students, the faster learning students will exhibit higher levels of auditory ability, while analytic ability is expected to contribute in a similar manner at beginner and advanced levels (Skehan, 1989). Concerning L1 literacy, the hypothesis is that at beginner levels L1 literacy will play a much more prominent role than for advanced learners, providing support for the threshold hypothesis (Cummins, 1979a), and the linguistic coding differences hypothesis (Sparks, 1995; Sparks&Ganschow, 1991, 1993, 1995). Findings did not confirm a differential impact of language aptitude in L2 learning at two levels of proficiency when looking at a global language aptitude score; however, when looking at language aptitude components, results confirmed the hypothesised prominent role of auditory ability for beginners and a role for analytic ability at the two proficiency levels, although the impact of the latter was larger in the upper intermediate learners' group. For L1 literacy, the hypothesis that L1 literacy would play a key role for beginners and not for upper intermediate learners was confirmed. This is consistent with the main tenet of the linguistic coding differences hypothesis that L1 skills serve as the foundation for L2 learning, as well as for the purported existence of a threshold of L1 literacy which learners need to attain for cross-linguistic transfer to occur. Results for motivation and orientations were also different for the two proficiency groups: while professional orientations explained variance in the beginner group, in the upper intermediate learners' group motivation was the variable that correlated with L2 learning. Finally, age at testing was the variable exerting the largest impact on L2 development in the beginner group, while it did not have any impact on the upper intermediate learner group. However, when L2 development scores where disaggregated in five L2 dimensions, findings were asymmetric: while age at testing impacted four out of five dimensions for beginners, there was only one skill which was strongly impacted in the upper intermediate learner group: L2 listening. The study also investigated the interactions amongst variables by applying multiple regression analysis and PLS modelling. In the model obtained for beginners, only three variables were predictive: academic development, L1 literacy, and age at testing. Conversely, the predictive variables in the model for upper intermediate learners were motivation, language aptitude, and reading habits. As a conclusion, findings suggested that different IDs impact L2 learning differently at two levels of proficiency for this participant sample. In addition, the study provided insights as to which were the language aptitude components having an influence at each stage, and what L2 language dimensions were impacted by language aptitude and L1 literacy. Finally, and to the best of the author's knowledge, this is the first study in second language acquisition to use PLS-SEM to explore complex relationships amongst latent constructs.