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Abstract Metaphors are, not only frequently used in daily communication, but more importantly,also a critical element in human cognition and thinking processes.Research on the cognitive processes for metaphor comprehension is of great significance to cognitive psychology and psycholinguistics.The main question investigated here is where there is a unique cognitive process underlying metaphor comprehension,compared to literal language.Or,what is the specific cognitive processing in metaphor comprehension and brain network concerned? Existing research on this question has produced inconsistent results,leading to different theories about metaphor processing. We propose that metaphors can be divided into two different categories,namely derived metaphors and evoked metaphors, associated with different cognitive processes and neural mechanisms. Controversies among theories and empirical data may possibly be due to non-differentiation between different types of metaphors.Using both behavioral methods and fMRI techniques,the present study was intended to compare the cognitive processes and neural mechanisms of these two types of metaphors at the sentence level. Results showed that,reaction times of derived metaphoric sentences and evoked metaphoric sentences were both longer than that of literal sentences.More importantly,compared with literal sentences,there was more activation in both left middle temporal gyrus and superior temporal gyrus and left inferior frontal gyrus for derived metaphoric sentences.For evoked metaphoric sentences, left inferior frontal gyrus was more activated compared with literal sentences.The results indicate that cognitive processes and neural mechanisms of derived metaphoric sentences are different from those of evoked metaphoric sentences. For derived metaphoric sentences,the process involves activating several word meanings and selecting proper meaning to make sentence semantically integrated. Given that contexts in sentence are complicated,it is more difficult to inhibit the literal meaning of metaphoric words.Therefore, increasing competition between the literal meaning and the metaphoric meaning of metaphoric words leads to deep semantic processing and longer reaction time for derived metaphoric sentences. More importantly,complex processing results in specific activation in left middle temporal gyrus and superior temporal gyrus reflecting competition between multi-meanings,and activation in left inferior frontal gyrus reflecting depth of semantic processing.As a contrast,with support from sentence contexts,semantic searching in evoked metaphoric sentences is a directed search process,and it is not necessary for a nondirective search in a much broader semantic field like that in evoked metaphoric words. Similarly, compared to literal sentence processing, evoked metaphoric sentences need to extend meanings to related information rather than to directly select word meanings,which resulted in longer reaction time and also specifically activated left inferior frontal gyrus. The findings as a whole show that metaphor comprehension involves unique cognitive processes different from literal language comprehension. However, cognitive processes and neural mechanisms of metaphor do not operate in a single mode,as the type of metaphors can modify metaphor processing and associated brain activities.The present study indicates that distinguishing cognitive processes and neural mechanisms of different metaphors can resolve some conflicts in metaphor processing studies and help to integrate different empirical studies for a deeper understanding of metaphor comprehension.
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