of David Ausubel (1968). The fundamental idea in Ausubel’s cognitive psychology was that learning takes place by the assimilation of new concepts and propositions into existing concept and propositional frameworks held by the learner. This knowledge structure as held by a learner is also referred to as the individual’s cognitive structure. Out of the necessity to find a better way to represent children’s conceptual understanding emerged the idea of representing children’s knowledge in the form of a semantic map. Thus a new tool was born not only for use in research, but also for many other uses (Novak & Gowin, 1984).
So, semantic map have its roots in Ausebel’s theories and research on advance organizers. Ausebel (1968) also, advanced the belief that a learner’s existing knowledge, which he referred to as cognitive structure, greatly influences student learning. When the cognitive structure expands by incorporating new information, learning occurs. To facilitate this process, semantic maps provide students with the required framework to relat existing knowledge to the new information learned (Ausebel, 1968). Prior to 1969 advance organizers had been presented as prose passages. Baron (1969: 113) changed them to tree diagrams that utilized vocabulary of the concepts to be learned. Baron called his modification of Ausubel’s semantic organizers “the structured overview”. A structured overview was a “diagrammed representation of the basic vocabulary of a unit so as to show relationships among the concepts represented by those words”. Structured overviews were referred to as graphic organizers (Hawk, 1986: 81). The semantic organizer, like its predecessor the advance organizer, was originally intended as a readiness activity. Research and classroom practice, however, has shown that graphic organizers are equally useful as assimilation or follow-up activities (Griffin & Kammenui, 1995).
Knowledge gained about the brain processes information has been instrumental in the development of teaching techniques and learning strategies. Several cognitive theories in particular lend support to the use of graphic organizers in helping students process and retain information. Schema theory, dual coding theory, and cognitive load theory provide the basis for explaining the characteristics of graphic organizers that support the learning process (Hawk, 1986).

۲.۳. Theoretical Section
This review of literature covered, in detail, the studies related to semantic mapping strategies.
Novak developed the semantic mapping technique in 1970s at Cornell University. Novak and his research team based their work on David Ausuble’s cognitive assimilation theories and the constructive movement (1968); both of which stress the importance of assimilating new information into previously learned structures. They acknowledged that, to learn meaningfully, individuals must choose to relate new knowledge to relevant concepts and propositions they already know (Novak & Gowin, 1984). It is noteworthy that Novak & Gowin (1984) directly stated that semantic mapping could be used for extracting meaning from textbooks and literary texts. In 1984, he specifically proposed semantic mapping as a tool for improving reading comprehension.
Heimlich & Pittelman (1986) explained that a semantic map is one type of graphic organizers. It helps students visually organize and graphically show the relationship between one piece of information and another. This strategy has been identified by researchers as an excellent technique for increasing vocabulary and improving reading comprehension. As a pre-reading activity, semantic mapping can be used to activate prior knowledge and to introduce key vocabulary words. As a post reading activity, words, categories, and new concepts can be added to the original maps to enhance understanding.
Williams (1994) said that semantic mapping enables students not only to visualize relationships, but to categorize them as well. As a direct teaching strategy that includes brainstorming and teacher-led discussions, it provides opportunities for schema development and enhancement, as well as prediction, hypothesizing and verification of content when used as a pre-reading activity. It is also referred to as a web or concept map. The teacher can introduce semantic maps to the class in different appearances. They can be shown as circles, squares, or ovals with connecting lines. The students read an assigned text. Through class discussion, the teacher writes the main idea of the text in the middle of the top circle. The students share the supporting details of the main idea and place them in circles that are connected to the main idea by lines. This activity can also be used by students in cooperative groups or individually.
Estes (1999) explained semantic mapping as a strategy for graphically representing concepts. Semantic maps portray the schematic relations that compose a concept. They assume that there are multiple relations between a concept and the knowledge that is associated with the concept. Thus, for any concept there are at least three types of associations:
۱. Associations of class; the order of things the concept falls into.
۲. Associations of property; the attributes that define the concept.
He continued that the major purpose of a semantic map is to allow students to organize their prior knowledge into these formal relations, and thus to provide themselves a basis for understanding what they are about to read and study. Comprehension can be thought of as the elaboration and refinement of prior knowledge. What the semantic map provides is a graphic structure of that knowledge to be used as the basis for organizing new ideas as they are understood.
Harvey and Goudvis (2000) mentioned that semantic mapping strategies are valuable instructional tools. Unlike many tools that just have one purpose, semantic mapping is flexible and endless in application. One common trait found among this strategy is that they show the order and completeness of a student’s thought process strengths and weaknesses of understanding become clearly evident. Many semantic maps show different aspects of an issue in close and also the big picture, since many maps use short words or phrases, they are ideal for many types of learners, including English Language readers with intermediate proficiency. Tree maps can be used to show classifications, analysis, structures, attributes, examples, and brainstorming.
Ajideh (2003) argued that failure to activate the prior knowledge is the main problem of learners in reading classes. Pre-reading activities can provide a reader with necessary background to organize activity and to comprehend the material. These experiences involve building a knowledge base for dealing with content and the structure of the material. He noted that pre-reading activities elicit prior knowledge, build background, and serve to focus attention. In other words, second language readers need to draw on appropriate schematic knowledge to reach satisfactory interpretation of the text. In fact, schematic knowledge has textual representations which are represented by lexical choices made by the discourse producer in the encoding process. Thus one of the teacher’s duties is to help the reader recognize these lexical choices. Any lexical element in a text is the textual representation of an abstract mental concept. He suggested that prior to reading the instructor can highlight those lexical elements in a text that seems to be in close relationship with the topic of the text and by making them transparent, the relevant schemata can be activated in reader’s mind. He dealt with the question of semantic mapping activities in ESP textbooks which were written for Iranian students as university books by SAMT.
Dehnad (2005) provided a paper on teaching reading through graphic organizers. She asserted that graphic organizers, when used as a pre-reading activity, could
facilitate learning by promoting the learners to guess and develop ideas and learn new concepts related to the study topic. Graphic organizers enable students to show a huge amount of information by a single picture, providing a “big-view” of the topic after encountering the material. Moreover, they encourage the students to think about information in a new way which removes the words and let them think about connections. Graphic organizers depict the relationship between main ideas, subordinate ideas, and supporting information and thus help learners improve their reading skills. They show the new words in a novel way which provides an efficient ground for recalling the meaning of words through schematic branches.
Raymond (2006) added that semantic mapping can be a helpful reference for students to use in clarifying confusing points as they are reading. Once students are familiar with the nature of the semantic maps, they can create their own as a during-reading or post-reading activity.
Rahimi (2007) offered an article on the effect of using computer-assisted semantic mapping on the Iranian EFL students’ reading comprehension achievement. He explains that the achievement of students in learning English will grow when they use some computer semantic maps before reading the text. Actually these maps which are conducted by computer programs have positive effects and improve the comprehension of the text before the reading action.

۲.۴. Practical Section
This section covered the studies which have investigated and reported the impact of using semantic mapping strategies on learning or reading process of a defined population as follows.
To identify the empirical basis for using graphic organizers, Moore and Readence (1984) conducted a meta-analysis of graphic organizer research with non-disabled students. Twenty-three studies were included. Overall, 161 effect sizes were computed, and an average effect size of .22 was computed. However, the effect size varied depending on the treatment or the criterion variables examined. For example, a large effect size (.57) was found when graphic organizers were used after reading text, but a much smaller effect size was reported when graphic organizers were presented before the task. Similarly, an effect size of .68 was reported when the dependent measure was vocabulary in contrast, when the test measured comprehension, the effect size was .29. Moore and Readence also analyzed the 23 studies qualitatively. The results indicated that the teachers who used graphic organizers in the studies reported feeling more competent while leading students through content material. The placement of the graphic organizer activity in the instructional sequence of the lesson differs depending upon the study. The meta-analysis by Moore and Readence (1984) indicated a larger effect size for graphic organizers when they were introduced as a post organizer (.57) than as an advance organizer (.27).
A study by Hawk (1986) involved average students in sixth and seventh grade life science classes, and examined the effectiveness of graphic organizers as an advance organizer on student achievement. A total of 455 students from

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