Empirical Support for the Involvement Load Hypothesis (ILH): A Systematic Review

The Involvement Load Hypothesis (ILH) has become a widely used framework for predicting second language (L2) vocabulary learning from task completion. The purpose of this systematic review was to analyze the predictive ability of the ILH in the acquisition of aspects of knowing a word, its application in different target populations, the effective vocabulary learning task types designed based on the ILH, and the occurrence rate of the ILH components in vocabulary learning tasks. We searched IEEE, ERIC, WOS, Scopus, and ProQuest databases for empirical studies published between 2001 and 2021, using a vocabulary-focused keyword string combined with an ILH-focused keyword string. A total of 78 studies were selected using a set of inclusion and exclusion criteria. The content analysis of these studies showed that researchers have used the ILH to investigate the acquisition of six aspects of knowing a word. Four types of tasks (i.e., fill-in-the-blanks, reading, composition writing, and meaning-inferring) provided more positive evidence for the validation of the ILH. The search component was least present in the vocabulary learning tasks. Researchers have supported the use of the ILH to predict the vocabulary learning potential of tasks completed mainly by adult learners. This systematic review provides direction for future reviews and empirical studies in L2 vocabulary teaching and learning framed by the ILH.