How effective is second language incidental vocabulary learning? A meta-analysis

L2 proficiency

Research indicates that learners who know more L2 words are likely to learn more words incidentally through reading (e.g., Webb & Chang, Reference Webb and Chang2015a; Zahar et al., Reference Zahar, Cobb and Spada2001) and watching television (Feng & Webb, Reference Feng and Webb2020; Peters & Webb, Reference Peters and Webb2018). This may occur because students who know more words have better reading (Laufer, Reference Laufer, Lauren and Nordman1989; Schmitt et al., Reference Schmitt, Jiang and Grabe2011) and listening comprehension (Van Zeeland & Schmitt, Reference Van Zeeland and Schmitt2013b), which may allow them to attend more to unknown language features that are encountered. Research indicates that the degree to which learners attend to unknown L2 words during reading is positively related to learning those words (Godfroid et al., Reference Godfroid, Ahn, Choi, Ballard, Cui, Johnston, Lee, Sarkar and Yoon2018; Pellicer-Sánchez, Reference Pellicer-Sánchez2016).

Institutional level

Although research tends to provide details indicating participants relative age, age itself, and place of study (primary or secondary school, university), age has not been explicitly examined in intervention studies as a variable. However, two recent meta-analyses indicate that older learners may make greater incidental vocabulary learning gains than younger learners. De Vos et al.'s (Reference de Vos, Schriefers, Nivard and Lemhöfer2018) meta-analysis of incidental vocabulary learning through encountering spoken input revealed that age had a positive effect on learning; participants who were university students made greater gains in vocabulary knowledge than children in elementary school and kindergarten. Uchihara et al.'s (Reference Uchihara, Webb and Yanagisawa2019) meta-analysis provides some justification for this result. They found that older learners were better able to make use of frequency effects to learn words incidentally than younger learners.

Text type

Gardner's (Reference Gardner2004) corpus driven analysis of narrative and expository text written for children indicated several differences that may affect incidental vocabulary learning. Narrative text was found to include a higher proportion of high frequency words than expository text, while expository text consisted of a much larger number of different word types than narrative text. Gardner concluded that narrative text provided better conditions for incidental vocabulary learning than expository text. Because text type in studies of incidental vocabulary learning consist of both narrative (e.g., Brown et al., Reference Brown, Waring and Donkaewbua2008; Rodgers & Webb, Reference Rodgers and Webb2020) and expository text (e.g., Peters & Webb, Reference Peters and Webb2018; Vidal, Reference Vidal2011), there is value in investigating the degree to which it moderates learning.

Text audience

The materials in studies of incidental vocabulary learning may be primarily targeted towards first language (L1) or L2 learners. Materials created for L1 learners include novels (e.g., Pellicer-Sánchez & Schmitt, Reference Pellicer-Sánchez and Schmitt2010), songs (Pavia et al., Reference Pavia, Webb and Faez2019), and television programs (e.g., Peters & Webb, Reference Peters and Webb2018; Rodgers & Webb, Reference Rodgers and Webb2020). Materials aimed at L2 learners include graded readers (e.g., Horst, Reference Horst2005; Waring & Takaki, Reference Waring and Takaki2003), teacher speech (Jin & Webb, Reference Jin and Webb2020), and textbook passages (e.g., Teng & Reynolds, Reference Teng and Reynolds2019). Materials such as novels and television shows created for native speakers of English are typically designed to inform and entertain. In contrast, materials aimed at L2 learners may be designed to promote the learning of language features that are encountered, as well as inform and entertain. Thus, it is useful to examine text audience as a variable to determine whether materials created for L2 learners enhance vocabulary gains.

Spacing

Incidental vocabulary learning is hypothesized to occur through repeated encounters with unknown words where knowledge is gained in small increments over time (Nagy et al., Reference Nagy, Herman and Anderson1985; Webb & Nation, Reference Webb and Nation2017). This suggests that the interval between encounters with unknown words may affect the degree to which they are learned. Most studies of incidental vocabulary learning have had very little spacing between encounters with all learning occurring through encounters in a single text in a single learning session (e.g., Peters & Webb, Reference Peters and Webb2018; Waring & Takaki, Reference Waring and Takaki2003). However, more recently there have been longitudinal studies of incidental learning over many sessions (e.g., Horst, Reference Horst2005; Rodgers & Webb, Reference Rodgers and Webb2020; Webb & Chang, Reference Webb and Chang2015a, Reference Webb and Chang2015b). Research on the spacing of encounters has revealed that spaced learning consistently leads to greater retention of vocabulary knowledge than massed learning (learning without an interval between repeated encounters) (e.g., Kim & Webb, Reference Kim and Webb2022; Nakata, Reference Nakata2015).

Mode of input

Many studies have revealed that words can be learned incidentally through reading (e.g., Pigada & Schmitt, Reference Pigada and Schmitt2006; Waring & Takaki, Reference Waring and Takaki2003). An increasing number of studies have begun to show that words can also be learned incidentally through listening (e.g., Pavia et al., Reference Pavia, Webb and Faez2019; Van Zeeland & Schmitt, Reference Van Zeeland and Schmitt2013b), reading while listening (e.g., Brown et al., Reference Brown, Waring and Donkaewbua2008; Webb & Chang, Reference Webb and Chang2012), and viewing (e.g., Peters & Webb, Reference Peters and Webb2018; Rodgers & Webb, Reference Rodgers and Webb2020). Several studies have compared learning across different modes of input. However, the results have been inconsistent. Brown et al. (Reference Brown, Waring and Donkaewbua2008) found that reading and reading while listening contributed to greater gains in vocabulary knowledge than listening. In contrast, Webb and Chang (Reference Webb and Chang2012) found that reading while listening led to greater gains in word learning than reading, while Feng and Webb (Reference Feng and Webb2020) found that reading, listening, and viewing all contributed to similar gains in vocabulary knowledge.

Control of prior knowledge of target words

Most studies of incidental vocabulary learning have used target single word items that were real words (e.g., Horst, Reference Horst2005) and used pretests to control for prior knowledge of target items. However, pseudowords (e.g., cader, denent) are also used as target items (e.g., Van Zeeland & Schmitt, Reference Van Zeeland and Schmitt2013a; Waring & Takaki, Reference Waring and Takaki2003) to ensure that participants have no knowledge of their forms and allow researchers to forgo the inclusion of pretests of vocabulary knowledge (Nation & Webb, Reference Nation and Webb2011). Justification for the use of pseudowords is thus methodological. However, Uchihara et al. (Reference Uchihara, Webb and Yanagisawa2019) found that the use of pseudoword target items contributed to larger frequency effects in incidental vocabulary learning studies. Thus, examining the effects of pre-knowledge control in studies of incidental vocabulary learning is warranted.

Test format

Research indicates that the degree to which learners are able to demonstrate their knowledge of words may depend on the test format that is used to measure learning. Laufer and Goldstein (Reference Laufer and Goldstein2004) found that the form recall test format in which test takers must produce the L2 forms of words when presented with their meanings was the most demanding test followed by meaning recall tests (test takers are presented with the L2 forms of items and must produce their meanings), form recognition (test takers are presented with the meanings of target items and must select the correct L2 word from several choices), and meaning recognition (test takers are presented with L2 words and must select their corresponding meanings from among several choices), in that order. Because incidental vocabulary learning gains tend to be relatively small, it is important to use tests that are sensitive to knowledge, and so meaning recognition tests are perhaps used most frequently in research while form recall tests are used less often. Other test formats that are occasionally used are Wesche and Paribakht's (Reference Wesche and Paribakht1996) Vocabulary Knowledge Scale (VKS) and a second type of form recognition test that involves indicating whether target words were encountered in spoken or written text (e.g., Peters & Webb, Reference Peters and Webb2018). Examining the degree to which test formats moderate incidental learning gains may shed light on the degree to which gains vary across test types.

The present study

The present meta-analysis investigated the effects of meaning-focused learning through reading, listening, reading while listening, and viewing on incidental vocabulary learning. The following research questions were posed:

• 1. What is the overall effectiveness of L2 incidental vocabulary learning through exposure to L2 meaning-focused input?

• 2. What is the overall rate of incidental vocabulary learning in: (a) measures of form recognition, meaning recognition, and meaning recall, and (b) through reading, listening, reading while listening, and viewing?

• 3. To what extent do variables related to learners, materials, comprehension activities, and methodological differences moderate L2 incidental vocabulary learning gains?