Incidental Vocabulary Learning: Evaluating the Predictions of the Involvement Load Hypothesis Plus

Abstract

Incidental vocabulary learning is a fundamental way to develop L2 learners’ vocabulary knowledge. The Involvement Load Hypothesis Plus (ILH Plus) offers a refined model of the earlier ILH on incidental vocabulary learning, yet its predictions remain largely unverified. This study evaluated the predictions of the ILH Plus regarding the contribution of the search component and examined whether word length and working memory (WM) contribute beyond the model or moderate its predictions. In a quasi-experimental design, 87 female university EFL learners completed a reading task either with or without search (dictionary consultation). Vocabulary learning was assessed using immediate and delayed meaning-recall tests, and WM was measured using digit-span tasks. Results showed that both tasks produced comparable immediate vocabulary learning which supports the predictions of the ILH Plus whereas similar delayed retention does not. Word length significantly predicted both immediate and delayed vocabulary learning whereas phonological WM was only positively associated with immediate learning. Neither word length nor WM moderated the predictions of the ILH Plus. The findings suggest that there is a threshold for task effectiveness to be measurable when compared to another task. They also emphasize the importance of considering lexical characteristics alongside task effectiveness index when evaluating incidental vocabulary learning.