The present behavioural study explores the cognitive processing of primary and complex conceptual metaphors during the first step of the translational process: comprehension. According to Lakoff and Johnson (1980), primary and complex conceptual metaphors are based on different conceptual architectures, a simpler one for primary conceptual metaphors, and a more sophisticated one for complex conceptual metaphors. As far as we know, there is no empirical evidence that understanding primary conceptual metaphors requires less cognitive effort than understanding complex conceptual metaphors. In order to know whether primary conceptual metaphors are easier to understand than complex conceptual metaphors, a psycholinguistic experiment was designed and run to investigate processing speed and conceptual clarity during comprehension. Among other interesting results, our study provides evidence that conceptual clarity is greater with primary conceptual metaphors than with complex conceptual metaphors. Therefore, a translator will not be challenged in the same way depending on the type of metaphor s/he has to understand. As a first step towards understanding the mechanisms of comprehension, this study paves the way for further investigations on how comprehension influences the subsequent stages of translation, especially regarding how conceptual clarity may vary during comprehension and help determine the quality of the translation.