Learning a new language is not easy and requires a lot of time and effort from the learner. Although researchers and language teachers have applied various strategies, techniques, methods, tools, and technologies to ease this convoluted learning process, it seems that so many areas of language teaching and learning still remain unexplored. One area that demands further improvement is technology and its impact on language learning. Indeed, “language teachers today are faced with so many fascinating options for using technology to enhance language learning that it can be overwhelming” (Kessler, 2018, p. 205). Due to the continual growth of technology and its vast popularity among people, some researchers and language teachers focus on video and consider it a teaching and learning tool that can facilitate the process of second/foreign language learning and teaching.

Technology can be integrated into the teaching process as a medium of instruction or it can be used by language teachers to provide language learners with supplementary support that they might need for learning inside and outside of the classroom. In other words, technology can render the language learning process easier and more productive by providing activities, tasks, and experiences in an authentic language spoken by native speakers in real contexts and settings (Egbert, Hanson-Smith, & Chao, 2007). According to Kessler (2018, p. 207), providing a “variety of learning contexts” is one of the most important benefits of technology to teaching and learning. Language teachers and educators need to be aware of the influences of technology on language teaching and learning in order to utilize them efficiently in their classroom activities and practices.

Since the use of technology is widespread, it seems that the presence of technology is a must in today's language classrooms for teaching language skills and subskills. For example, vocabulary is one of the most demanding areas of a language that requires teachers to implement new teaching tools and ideas. Technology can provide an answer to these requirements and can accelerate the process of learning the words of the target language (L2). In fact, technology can have positive effects on language learning generally and vocabulary acquisition specifically. Schmitt (2008) stated that a large number of words are required “to function in English: 8000–9000-word families for reading, and perhaps as many as 5000–7000 families for oral discourse” (p. 329). This huge number of words can be difficult for some language learners to acquire and might demotivate them or eventually cause them to abandon learning the new language.

Vocabulary plays an important role in language learning and development. Some researchers (Harmon, Wood, & Keser, 2009; Linse, 2005) believe that the development of a language highly depends on the development of words in that language. Schmitt (2000) focused on the importance of vocabulary in communication and stated that “lexical knowledge is central to communicative competence and to the acquisition of a second language” (p. 55). This area of language needs to be highlighted and emphasized more by researchers, language teachers, and educators to make the process of second/foreign language vocabulary acquisition easier and more enjoyable for language learners.

Since vocabulary acquisition has gained a lot of attention among researchers so far and resulted in many research studies in this field, it seems that there needs to be one study that organizes these findings and results in one review article. This will help researchers and language educators to easily access the findings of these studies to track progress in this field. To do this, the current literature review focuses on video as a technology tool that is often used in second/foreign language classrooms to teach vocabulary of the target language. This literature review begins with a focus on incidental vocabulary learning as a vocabulary teaching strategy bringing its theoretical basis into consideration. Then, it advances to the most recent research studies that were conducted in this area. Thus, this literature review answers the following questions:

• Does watching a video, as an incidental vocabulary learning strategy, meet the theoretical and practical criteria to be used in second/foreign language classrooms?
• What areas of incidental vocabulary learning strategy need to be improved to cover the requirements of a successful vocabulary instruction?

Incidental Vocabulary Learning

The history of vocabulary teaching shows that vocabulary was first deemphasized by language teachers and researchers (Meara, 1980). Krashen (1989) introduced the notion of comprehensible input to emphasize the important role of vocabulary in language learning. Based on this view, vocabulary needs to be learned incidentally and language learners must be exposed to an abundant number of words from the target language in meaningful contexts. The idea of comprehensible input helped researchers to locate a theoretical basis for this exposure in the target language in such a way that they introduced incidental learning strategy in second/foreign language learning. Incidental vocabulary learning strategy focuses on incidental acquisition of words without dedicating too much attention to them. This strategy became popular because different researchers reported positive results from its implementation in second/foreign language classrooms. For example, Schmitt (2008) championed the importance of incidental vocabulary learning and stated that “It is a commonsense notion that the more a learner engages with a new word, the more likely they are to learn it” (p. 338).

Incidental vocabulary learning has always been compared with intentional vocabulary learning. In the former there is no intention of learning vocabulary while in the latter the main purpose is doing so. Hulstijn (2003) defined intentional vocabulary learning as a method of vocabulary learning in which the learner is aware of the purpose of the instruction and knows what he/she is going to learn in advance. In other words, intentional vocabulary learning is a method of vocabulary learning in which the language learner wants to learn vocabulary intentionally by focusing and paying attention to it (Hulstijn, 2001). Intentional vocabulary learning strategy is based on the Schmidt's (1990) Noticing Hypothesis. According to this hypothesis, second language learners need to notice the features of a language in order to learn it.

Schmidt (1990) claimed that “conscious processing is a necessary condition for one step in the language learning process and is facilitative for other aspects of learning” (p.131). Based on this concept, the language learner's awareness can have positive effects on the language learning process. According to this hypothesis, the more attention paid by language learners to the features of a language, the better the learning of that language.

Researchers have found intentional vocabulary learning strategy to be both positive and negative. For example, the results of some studies (Laufer & Nation, 2012; Nation & Chung, 2009; Sonbul & Schmitt, 2010) highlighted the effectiveness of intentional vocabulary learning strategy over an incidental strategy among adult language learners while some others such as Nation (2011) reported the negative effects of intentional vocabulary learning when overemphasized.

On the other hand, incidental vocabulary learning is defined as a kind of vocabulary learning strategy in which there is no direct intention of doing so (Bruton, Lopez, & Mesa, 2011). However, the difference between intentional and incidental vocabulary learning “cannot lie only in the presence or lack of attention” (Arndt & Woore, 2018, p. 125). Craik and Lockhart (1972) stated that the deeper the level of processing, the better the learning. Ellis (1999), as cited in Arndt and Woore (2018, p. 125), differentiated between intentional and incidental learning by the level of attention paid to the concept and stated that “in intentional learning, the focal attention is on the linguistic forms, whilst peripheral attention is given to understanding the overall message, and vice versa in incidental learning”. Although intentional and incidental vocabulary learning is mostly defined by the researchers with respect to the learner's attention and intention, “operationalising attention-based definitions is problematic” (p. 125). It is problematic because all the processes, which are unclear and inaccessible, happen in the language learner's mind (Arndt & Woore, 2018).

This disagreement among researchers on the key points in the definition of intentional and incidental vocabulary learning strategies can be answered by referring to their theoretical basis. Since intentional vocabulary learning strategy is based on Schmidt's (1990) Noticing Hypothesis, the learner needs to notice the word which indicates the necessity of attention in this strategy. So, the word “attention” is crucial to the definition of the intentional vocabulary learning strategy. On the other hand, incidental vocabulary learning is based on Vygotsky's sociocultural theory (1978) whereby language development occurs through interaction with peers, friends, family members, and so on. Since the interaction between people requires more than just attention, the word “attention” is not acceptable on its own. So, other variables must be included in the definition of incidental vocabulary learning strategy as well.

Sociocultural Theory

Incidental vocabulary learning is based on the sociocultural theory of Vygotsky (1978). According to this theory, a child learns his/her native language through interaction and collaboration with others. The more collaboration and cooperation with other people such as family members, peers, and friends, the better and faster will be the learning of that language. Incidental vocabulary learning, when taking this concept into consideration, focuses on the unintentional learning of the students and states that language learners can learn vocabulary without intending to do so. It must be mentioned that other factors such as learner's prior knowledge and experience, learner's interest, learning styles, and other conditions need to be present for words to be learned. This implicit vocabulary learning can take place by reading a text, communicating with others, watching a video, and so on.

One of the most important concepts of sociocultural theory is the matter of scaffolding. Based on this concept, learners can benefit from supports and extra bits of help that are provided for them during the process of language acquisition. For example, teachers can use scaffolding to teach vocabulary incidentally without providing learners with direct meaning or translation of words. In other words, the scaffolding that is provided by the teacher will help the learner to move within his/her Zone of Proximal Development (ZPD) to reach their potential level of development.

Zone of Proximal Development (ZPD) in the sociocultural theory of Vygotsky (1978) refers to “the distance between the actual developmental level as determined by the independent problem solving and the level of potential development as determined through problem solving under adult guidance or in collaboration with more capable peers” (p. 86). The better the scaffolding, the closer the language learner is to the potential level. The development of the learner is said to be achieved whenever the potential level of the learner in ZPD was reached. This is a time of independence for the learner. In other words, the potential level is a point at which the language learner would be able to act individually and independently without further help and without further need for external support and scaffolding.

The level of scaffolding and support necessary for language learners is not necessarily provided by the teacher. Collaboration with peers and having communication with other language learners can create a good opportunity for language learners to improve their vocabulary knowledge. Some other resources such as textbooks, dictionaries, worksheets, and self-teaching materials can act as scaffolding. In fact, they can provide the necessary support for language learners to reach their potential level. Ohta (2005) took this a step further and mentioned the effects of internal scaffolding. This researcher stated that it would be more beneficial to look at the ZPD from a different point of view rather than just considering it as an interpersonal space. This differentiation would help language learners to focus more on their internal resources such as language and linguistic awareness. This will also help them to exert more control over their ZPD and to be able to provide the necessary scaffolding and support for themselves.

Language teachers can choose from various options of technology and use them in their classrooms to accelerate the process of language learning and to improve opportunities for these learners (Kessler, 2018). Since the use of technology such as social media has become a very important part of our daily life, the absence of technology “in our classroom is quite noticeable” (Kessler, 2018, p. 206). Arndt and Woore (2018) highlighted the role of media and audio-visual input in second language learning. They stated that the freedom of language learners to choose between a variety of audio-visual resources in their desired time can facilitate language learning “because the user's inherent interest in the content and desire to understand it leads to deep engagement with that input” (p. 124-5).

Language teachers try to implement technology more than before in their language classrooms due to its growing popularity among people. On the other hand, researchers are also trying to explore the advantages of these tools to improve learning opportunities and to enhance the acquisition of words, phrases, and sentences in the target language. For example, Kacetl and Frydrychova-Klimova (2015) decided to use video clips to teach travel and tourism vocabulary to students in the Management of Travel and Tourism program at the University of Hradec Kralove in Czech Republic. They focused on the outcomes of using more than 80 English video clips with 40,000 words used in them. The authors analysed the most frequently used words, phrases, and idioms in these video clips to provide a dictionary “of professional collocations and terms in the field of travel and tourism” (Kacetl & Frydrychova-Klimova, 2015, p. 364).

1.1 Video

One of the technology tools that can be applied to language teaching and learning is video. Watching TV programs and videos in the target language can have a great impact on language learning because of the repetition and exposure that learners gain in the classroom (Webb & Rodgers, 2009). Peters and Webb (2018) highlighted the great impact of TV on language learning and stated that “TV provides learners with authentic, spoken input and creates opportunities for incidental vocabulary learning” (p. 557). Webb and Rodgers (2009) argued that watching L2 programs are helpful for learning lessfrequently spoken words because of the number of times that these words are repeated in L2 programs.

Videos and video segments produced for native speakers are one of the most beneficial language teaching and learning resources. Videos such as these can help language learners to see the authentic use of language in sentences produced by native speakers. These videos can help language learners to realize the passion and the rationale behind the words and sentences. In other words, context authentic to native speakers can be simulated by playing videos in the classroom because they can provide all the necessary information such as the pronunciation of words in the target language, their usage, meaning, and so on. Videos are a rich resource that can cover some language skills and sub-skills, such as grammar, pragmatics, listening, and speaking.

It is important for language learners to learn a new language in an authentic and real-like setting through interaction and cooperation with native speakers. Providing this opportunity for language learners is not always feasible due to the fact that native speakers are not always available or the target language is taught in an EFL setting. So, there might be insufficient resources of the target language inside and outside of the classroom for language learners. This unavailability of learning resources for second/foreign language learners can be supplemented by incorporating technology such as TV programs into classroom instruction. Webb (2015) argued that watching L2 programs can be an extra help for vocabulary acquisition alongside the other sources such as extensive reading. “One of the biggest influences that technology has had on teaching and learning contexts is the increasing variety of learning contexts” (Kessler, 2018, p. 207).

Some researchers (Neuman & Koskinen, 1992; Perez, Peters, Clarebout, & Desmet, 2014) emphasized the positive role of watching videos in vocabulary learning. They also highlighted the positive effects of watching videos on incidental vocabulary learning. Since dual coding takes place while watching L2 programs, the chance of vocabulary learning enhances. “Dual Coding Theory assumes that cognition occurs in two independent but connected codes: a verbal code for language and a nonverbal code for mental imagery” (Sadoski, 2005, p. 221).

McKeown, Crosson, Moore, and Beck (2018) argued the effects that videos can have on learning different aspects of vocabulary knowledge, and stated that a “word's meaning becomes generalized across encounters so that it loses connection to specific contexts, allowing it to be applied flexibly to new contexts” (p. 576). In other words, videos can provide the necessary meaningful context, which is absent in the EFL setting, for second language learners. Native speakers demonstrate the real use of target words in videos and help language learners to acquire flexibility in their communication and speech production. This flexibility in the language learner's word knowledge allows the “learner to integrate the meaning of a word into a novel context so that the learner can make sense of the context as a whole” (McKeown et al., 2018, p. 576).

The other benefit of using technology, in general, and videos specifically is that by watching authentic videos learners can learn about the target culture and some of its related aspects such as pragmatics. The role of culture in second/foreign language learning is undeniable. In fact, teachers, researchers, and educators believe that “without the study of culture, teaching L2 is inaccurate and incomplete” (Genc & Bada, 2005, p. 73). Not only are language teachers concerned with teaching the target culture to the students, but also language learners have concerns about learning the target culture and how to make culturally accepted communication as well. In fact, “For L2 students, language study seems senseless if they know nothing about the people who speak the target language or the country in which the target language is spoken” (Genc & Bada, 2005, p. 73). This emphasis on the teaching and learning of the target culture occurs due to the importance of culturally accepted forms of communication between language learners and native speakers. This can be very difficult or even meaningless if they know nothing about the target culture (Bada, 2000).

This section includes three different research studies conducted in 2018. The researchers of these studies have explored the use of videos and their impacts on second/foreign language vocabulary acquisition. The articles, cited in this literature review, were chosen from three different international, peer-reviewed journals in the field of second/foreign language teaching and learning based on Scopus, SJR, Elsevier's abstract citation database, and Clarivate websites. Vocabulary acquisition, audio-visual input, technology and vocabulary acquisition, and incidental vocabulary learning strategy were the keywords used in the Google search bar to find the scholarly articles. Three articles related to the topic of this literature review were found. Each research study has been summarized and the results have been mentioned briefly in this section.

2.1 Study One

In a research study by Perez, Peters, and Desmet (2018), the authors investigated the impact of two techniques of vocabulary teaching on language learners' vocabulary acquisition. The first technique was the implementation of four different captioning modes: full, keyword, glossed, and no captioning. Test announcement through watching audio-visual materials was the second technique in this study. In fact, the researchers tried to stimulate "learners' noticing and form-meaning mappings of novel words" (p. 2). To explore the most effective technique, the researchers provided eight different teaching conditions and divided the participants into eight groups. Participants of the study watched three videos in French in one of the eight different teaching conditions of the experiment. The study materials were three authentic short clips produced for native speakers and accompanied with some supplementary materials such as interview excerpts.

The number of participants was 227 in this study. This quantitative study had one dependent variable and two independent variables. The researchers considered participant's vocabulary uptake as the only dependent variable of the study and assigned three levels to this criterion variable: form recognition, clip association, and meaning recall. The first independent variable of the study was various subtitling modes, such as full captioning, keyword captioning, glossed keyword captioning, and no captioning. The second was test announcement.

The results of the study showed that the group with glossed keyword captions outperformed the other groups in terms of form-recognition and meaning recall tests. Although the authors reported positive effects of word searching “in the glossed keyword captioning group,” test announcement was insignificant when compared to word searching. The authors found test announcement to be insignificant in terms of learning some intended words and changing participants' behaviour in word searching.

2.2 Study Two

Incidental vocabulary acquisition of EFL learners was investigated by Arndt and Woore (2018). The researchers compared video blogs and written blog posts as two different forms of online media. Different aspects of vocabulary knowledge, such as orthography, semantics, and grammatical function was also a part of this study. The researchers investigated which vocabulary teaching strategy (reading blog posts or watching video blogs) leads to better vocabulary acquisition.

The authors considered two levels (YouTube videos and reading blog posts) as their independent variables. Vocabulary acquisition was the only dependent variable of this study. Researchers used authentic videos, YouTube videos, and their scripts in this research. These videos and their scripts had the same linguistic content, but were arranged in two different formats. The number of 84 people were selected and divided into two experimental groups.

The results of the study showed that incidental learning of vocabulary occurred in both groups. The authors reported that both reading blog posts and watching YouTube videos were two successful techniques of vocabulary teaching. The findings of the study also showed that each treatment (whether reading or watching online) can contribute to different aspects of the learner's vocabulary knowledge. For example, the orthographic knowledge of the learners improved by reading blog posts while “greater recall of the target words' grammatical functions and greater recognition and recall of their meanings” (p. 124) was achieved by watching the videos.

2.3 Study Three

While most studies have investigated the effects of watching short video clips on vocabulary acquisition, Peters and Webb (2018, p. 557) explored watching fulllength TV program and its impact on vocabulary acquisition of EFL learners. Four different variables, including “ frequency of occurrence, relevance, cognateness, and prior vocabulary knowledge” were identified by the researchers. The authors did a comprehensive study by conducting two different experiments and having an experimental and control group for each experiment. A total of 125 participants were involved in this study and exposed to an authentic fulllength TV program about a Business English course. Word learning was the only dependent variable of the study. Vocabulary learning strategy was the only independent variable. This study had four covariates, including frequency of occurrence, cognateness, relevance, and the learners' prior vocabulary knowledge.

The authors reported that a full-length TV program can lead to incidental vocabulary learning “at the level of meaning recall and meaning recognition” (p. 551). The authors of the study conducted two experiments. The first experiment investigated the effects of watching a full-length L2 program on form recognition and meaning recall of the participants while the second experiment explored the effects of the viewing L2 program on the participants' meaning recognition. The results highlighted that learner's prior knowledge, word's frequency of occurrence, and cognates are three effective variables for incidental vocabulary learning. Table 1 shows a brief summary of the results of the studies.

Table 1. The Summary of the Research Studies

The critical analysis of the theoretical basis for incidental vocabulary learning strategy shows that vocabulary can be learned incidentally through different ways, including interaction, cooperation, watching, repeating, and so on. Incidental vocabulary learning strategy is also based on the view that words can be learned naturally by using different individual senses such as hearing and vision. Listening to somebody speak, reading a text, or watching a TV program are some situations where listeners are able to hear the words in context and meaningful sentences.

Based on these findings, it seems necessary for language learners to learn words in natural settings and for teachers to provide them with real-life opportunities that give them the chance for natural acquisition of the target language. Technology can help teachers to provide language learners with this opportunity. To do so, teachers and educators may use certain applications that let native speakers participate in the learning process. This participation will allow learners to acquire words naturally by cooperating and collaborating with each other.

The results of the most recent studies, as indicated above, highlight the significant role that watching videos can have in vocabulary acquisition of a second/foreign language. It is obvious from the results of different research that videos ease the burden of vocabular y acquisition for second/foreign language learners. Videos make vocabulary more comprehensible for language learners by providing additional information about different aspects of the words. Teachers can do this by putting learner's prior knowledge and experience into the learning process.

It is also clear that researchers tend to focus more on the effects of watching videos on learning different aspects of vocabulary rather than just focusing on the word itself. They believe that knowing a word means having knowledge about different aspects of that word. Although the abovementioned research studies have a paramount contribution to the field of second/foreign language acquisition, it seems that there is still much to do in this field. For example, further research must be conducted to investigate the effects of videos (including short clips, fulllength videos, or any other type of audio-visual materials) on young learners' vocabulary acquisition. This can be done to see whether there are any differences between vocabulary acquisition of language learners in different ages by different learning styles and attitudes towards learning the target language.

Although the above-mentioned research studies were conducted in different EFL settings, it seems that there is still a need for more research to focus on culturally and linguistically diverse students. More research will help to find the differences in terms of vocabulary acquisition strategies between students with a completely different cultural and linguistic background knowledge.

The most recent research studies have focused on authentic videos as their research materials, while the use of instructional videos has been deemphasized in these studies. Instructional videos that are produced for educational purposes can provide language learners with basic knowledge of the target language. In fact, these graded materials can act as scaffolding and prepare the language learners to interact in real situations. It seems that researchers also need to investigate the effectiveness of the instructional videos on meaning recall, word recognition, vocabulary knowledge, and so on. Since it is not possible to use authentic videos in lower levels of language learning due to low language proficiency level of the learners, instructional videos can be a good substitute.

Some techniques have also been introduced by researchers to improve the outcome of using videos in the classroom. For example, adding subtitles to the videos is one of these techniques that seems to influence vocabulary acquisition. Some studies (Danan, 1992, 2004; Garza, 1991; Neuman & Koskinen, 1992) reported positive effects of watching videos with subtitles on incidental vocabulary acquisition. Mousavi and Gholami (2014) used flash stories as a technique for improving the outcome of watching video and reported positive effects of watching flash stories in English on Iranian young learners' incidental vocabulary acquisition. The flash stories that were used in this study was a narration about social and moral issues. To conduct the research, participants were divided into three groups: watching flash stories with subtitles, watching them without subtitles, and reading the subtitles as the main text without watching the flash stories. The results of the study emphasize how vocabulary development takes time and needs patience. It had positive effects, however, and the researchers reported improvement in the participants' comprehension skills overtime.

Since language learning, and vocabulary acquisition in particular is a process-oriented approach rather than product-oriented, it seems that the field suffers from a lack of qualitative study to evaluate the learner's real perception and feelings of the incidental vocabulary learning. Language teachers need to know more about the learner's perceptions, attitudes, beliefs, and individual differences in the classroom to change their teaching strategy if necessary. Language learners are one of the most important parts of the learning process in classrooms: if they feel confused or ignored in the classroom, the instruction would be fruitless and the outcome would be nothing but a waste of the time. By putting various factors, such as learner's perceptions, feelings, attitudes, appropriate teaching strategy, and so on into consideration, the teachers can provide an impeccable teaching strategy “which surely eventuates in steady improvement on teaching pedagogy and skills as well as the enhancement of implacable teaching and learning process” (Karami, 2016, p. 246).