1. Action-Sentence Compatibility Studies
In this category of studies, the compatibility of a body action with the metaphoric meaning of a verb is examined. Studies on action-sentence compatibility effect have been conducted on both literal and metaphoric sentences. Here, only studies that have investigated metaphoric action-sentence compatibility effect are reviewed, as this type of work is relevant to the content. In the past two decades, results of many action-sentence compatibility studies have suggested that when a body action is compatible with the literal or metaphoric meaning of a verb, it is easier for people to make a judgment on the sensibility of the metaphoric verb by that body action, e.g., 
. This can be taken as an evidence that the meaning of metaphoric verb is simulated in the mind when a sentence that includes that verb is processed. In one of the most well-known action-sentence compatibility studies 
, participants made judgments on the sensibility of a set of sentences that described the directed transfer of abstract entities, such as, ‘The policeman radioed the message to you’, and ’You radioed the message to the policeman’. The participants made such judgments by moving their hands toward or away from their bodies. The results showed that when a sentence referred to a metaphoric action in one direction, the participants had difficulty in making a sensibility judgment by making a response in the opposite direction. This has been called the action-sentence compatibility effect. For example, it was easier for the participants to give a positive answer to the sentence you radioed the message to the policeman
by a movement away from the body than by a movement toward the body. This suggests that the action of sending a message from the sender to the receiver was simulated when the participants were processing the sentence. In other words, the action of sending a message was metaphorically simulated in terms of sending a concrete object from the sender to the receiver. This is why the participants were faced with difficulty in making a sensibility judgment that required an action in the opposite direction. In an extension, Borreggine and Kaschak 
used the same sentences that described the metaphorical transfer of abstract entities and found that the action-sentence compatibility effect arose only when participants were given the opportunity to plan their motor response while they were processing the sentence. The results of this study again suggested that the metaphorical action of transferring abstract entities is mentally simulated or embodied when such sentences are processed.
In a recent study 
, the action-sentence compatibility effect was examined for a set of abstract verbs with low motor associations and a set of novel words. In the learning phase of the first experiment, motor features of a set of abstract verbs with low motor features were strengthened. In the learning phase of the second experiment, motor features of a set of novel words were strengthened. After adding the motor experiences in the learning phases, a significant degree of action-sentence compatibility effect was observed in the test phases of experiments. The interesting point about the findings was that when some motor experiences were associated with even novel words, action-sentence compatibility effect was observed. The results of all such studies suggest that simulation of actions takes place not only for literal verbs but also for metaphoric verbs, which supports they key idea of metaphorical embodiment.
One study reported that metaphoric action-sentence compatibility effect has an impact on discourse comprehension 
. Participants of this read a text describing an individual making metaphoric forward movements. In the first experiment, participants’ body movements were manipulated to be compatible or incompatible with metaphoric actions. In the second experiment, participants’ body postures were manipulated to be compatible or incompatible with the metaphoric actions. The results of both experiments showed that compatibility of body movement and body posture with metaphoric action enhanced participants’ comprehension of discourse. This means that compatibility of body movement or even body posture with the metaphoric action described in a discourse affects global understanding of the discourse, while incompatibility of body movement or body posture with the metaphoric action described in the discourse can negatively affect discourse comprehension. The results of all studies suggest that performing an action that is not compatible with a metaphoric action and maybe even having the intention to perform an action that is not compatible with a metaphoric action disrupts the process of sentence comprehension and discourse comprehension.
2. Eye-Tracking Studies
In this category of studies, traces of eye movements during metaphor processing are examined. The results of some of these studies have shown that when a metaphoric or a literal sentence is processed, the direction of eye movement is compatible with the direction of the movement that is described by the metaphoric or literal verb, e.g., 
. For example, in the metaphoric sentence he rose up in the hierarchy of the company
, promotion is metaphorically described in terms of an upward movement. The literal sentence the sun rose up
describes the upward movement of the sun. The results of many eye-tracking studies have shown that processing such metaphoric and literal sentences is accompanied by upward eye movement. This has been taken as evidence suggesting that metaphoric and literal verbs are mentally simulated and are realized in upward eye movements.
Richardson and Matlock 
examined eye movements of a group of participants when they were looking at pictures that were being described by metaphoric fictive motion sentences (e.g., the road goes through the desert). In some cases, the contextual information indicated that the terrain was difficult to pass, while in other cases the context indicated that the terrain was easy to pass. The results showed that the length of time of inspections and eye movements scanning along the path increased during fictive motion descriptions that had been initially described as difficult (the desert is hilly) as compared to easy (the desert is flat). Interestingly, the difference in inspection times and eye movements was not observed when the pictures were described without fictive motions. This suggests that fictive motions are mentally simulated and these mental simulations are realized in eye movements. Castaño and Carrol 
examined patterns of eye movements of a group of participants during processing literal sentences that described actual physical motions (e.g., the curtain is rising) and metaphoric sentences that described changes in quantity or emotional states in terms of motion (e.g., prices are rising). The results showed that eye movements were mostly compatible with the direction implied by the verb, regardless of whether the verb had been used in a literal or metaphorical sense.
Mishra and Singh 
examined fixational eye movements of a group of participants looking at images that were described by either fictive motion sentences or nonfictive motion sentences. The results showed significant gaze durations and number of fixations during comprehension of fictive motion sentences compared to nonfictive motion sentences. This suggests that the mode of visual processing of a picture described by a fictive motion sentence is somehow different from the mode of visual processing of the same picture described by a nonfictive motion sentence. In a related study, Singh and Mishra 
found that comprehenders gazed for a longer period of time at visual scenes when hearing metaphoric fictive motion sentences compared to literal sentences. This indicates that when a static image is metaphorically/fictively described in terms of a motion event, that motion is mentally simulated and realized in the patterns of eye movements.
All these studies suggest that when a static concept is metaphorically described in terms of a motion event (e.g., time is a moving) or in terms of a fictive motion (e.g., the road passes through the jungle), the motion is mentally simulated. This mental simulation may be physically realized or embodied in various parts of the body, such as hand gestures or eye movements. However, there is an important difference between the embodiment of metaphoric actions in eye movements and other parts of the body such as hand gestures. While hand gestures can have an active communicative role, eye movements do not have such a function. People may use hand gestures to communicate more information and emphasize something, but eye movement cannot have such a communicative function. Patterns of eye movement during processing metaphoric sentences can be the reflection of a mental simulation. In other words, they are the physical realizations or the embodiment of a fully mental simulation. Therefore, patterns of eye movements can be taken as strong evidence that supports metaphorical embodiment.
3. Hand-Prime Studies
In this category of studies, the impact of a hand gesture on the understanding of a subsequent metaphor is investigated. The hand gesture, which is produced or imagined by the comprehenders or is visually presented to them, functions as a prime. In the first major study of this category, Wilson and Gibbs 
conducted an experiment to find out how producing a real body movement or imagining a body movement affects the process of understanding a subsequent metaphor. In each item of one experiment, a metaphor that described a concept in terms of a metaphoric action was used. Participants produced a body movement that depicted the metaphoric action and then immediately read the metaphor. For example, they produced a pushing movement and then read the metaphorical phrase push an argument
. In each item of another experiment, the participants imagined the metaphoric action and then immediately read the metaphor. The results of these experiments showed that performing or even imagining a body movement that depicted the metaphoric action of a subsequent metaphor could enhance the process of understanding the metaphor. This suggests that a metaphoric action such as pushing is simulated or embodied when the metaphorical phrase push an argument
is processed. In other words, the motor system, which guides the action of pushing, plays an active role in grounding the target of this metaphor in the metaphoric action. Therefore, when the motor system is activated by performing or imagining a pushing movement, it is more prepared to contribute to the processing of this metaphorical phrase. In fact, the motor system, as one of the cognitive resources involved in the processing of this metaphorical phrase, facilitates and enhances the process of comprehending this metaphorical phrase.
If a gesture that depicts the metaphoric action of a metaphor can facilitate the process of understanding the metaphor, it can be predicted that a gesture that is incongruent with the metaphoric action can disrupt the process of understanding the metaphor. This question was investigated by two recent priming studies on metaphorical embodiment. In one study 
, different groups of participants made sensibility judgments on a set of 20 metaphors. One group made judgments in congruent gesture-prime conditions, while the other group made judgments in incongruent gesture-prime conditions. Another group made judgments in no-prime conditions. In the congruent gesture-prime conditions, each metaphor was preceded by a gesture that depicted the schema of the subsequent metaphor. That is, it depicted a metaphoric action or something related to the base of the subsequent metaphor. In incongruent gesture-prime conditions, each metaphor was preceded by a gesture that was incongruent with the schema of the subsequent metaphor. The results showed that in congruent gesture-prime conditions, a higher proportion of sentences were judged to be sensible and sensibility judgments were made faster compared to those in no-prime and incongruent gesture-prime conditions. Since metaphor schema is a depiction of the metaphoric action or depicts something that is related to the metaphoric action, it can be concluded that the metaphoric action or schema of a metaphor is simulated in the mind of the comprehender during metaphor processing. Therefore, when the schema of a metaphor is presented to the comprehenders just before processing a metaphor, their comprehension of the metaphor is facilitated. In another related study, Khatin-Zadeh 
examined three groups of participants’ interpretations of a set of metaphors in three different conditions: congruent gesture-prime conditions, opposite gesture-prime conditions, and no-prime conditions. In congruent gesture-prime conditions, the written version of each metaphor followed a gesture that was congruent with the gestural representation of the metaphor schema. In opposite gesture-prime conditions, the written version of each metaphor followed a gesture that was incongruent with the gestural representation of the metaphor schema. The results showed that the best interpretations were given in the congruent gesture-prime conditions, while the weakest interpretations were given in opposite gesture-prime conditions.
4. Gesture-in-Learning Studies
The role of gesture in enhancing the process of learning has been demonstrated by a large number of studies, e.g., 
. In these studies, the contributions of iconic and metaphoric gestures have been at the focus of research. Iconic gestures present an illustration of the shapes of objects they refer to and have a direct relationship with the semantic content of their referents 
, while metaphoric gestures present an illustration of the base of a metaphor and have an indirect relationship with the semantic content of the target of the metaphor. This section of the review focuses on studies that have investigated the role of metaphoric gestures in enhancing the process of learning and emphasizes that this function of metaphoric gesture supports metaphorical embodiment. In various branches of science, many concepts are metaphorically described in terms of easy-to-understand representations. For example, in mathematics, the arithmetic operations of addition and subtraction are metaphorically described in terms of rightward movements (or right space) and leftward movements (or left space) on an axis, respectively, e.g., 
. These rightward and leftward movements can be illustrated by metaphoric gestures. It has been demonstrated these metaphoric gestures can play an active role in enhancing the process of learning these arithmetic operations, e.g., 
Results of these studies can also be taken as a support for metaphorical embodiment, because they suggest that abstract concepts can be mentally simulated, reflected in gestures, and grounded into concrete environment through the mediation of sensorimotor systems. In fact, metaphoric gestures are reflections of mental processes. Gestures are concrete realizations of these mental processes. Therefore, it can be said that the contribution of metaphoric gestures to learning processes can be taken as supporting evidence for metaphorical embodiment, because it supports the idea that metaphoric gestures are physical realizations of mental processes that take place through the active involvement of sensorimotor systems. Hostetter and Alibali 
propose the gesture-as-simulated-action theory and argue that using iconic gestures along with literal language and using metaphoric gestures along with metaphoric language show that concepts and actions are simulated. Importantly, this happens for both literal and metaphoric language. For example, a pushing gesture that co-occurs with the literal sentence push the table
is an iconic gesture. Using this iconic gesture shows that the action described by this literal sentence is mentally simulated and reflected in co-speech gestures. Furthermore, a pushing gesture that co-occurs with the metaphoric sentence push the idea
is a metaphoric gesture. Using this metaphoric gesture indicates that the metaphoric action described by this metaphoric sentence is also mentally simulated and reflected in the accompanying gestures. In other words, using co-speech metaphoric gestures, which is very common in daily language, is evidence that even metaphoric actions are mentally simulated and embodied in co-speech gestures. In fact, metaphorical embodiment is supported by the highly common phenomenon of using co-speech metaphoric gestures with metaphoric language.