Abstract: Objective Categorizing external stimuli in cognitive processing is a basic principle in the brain mechanism. Numerous studies have suggested different brain mechanisms in processing natural vs. artificial objects. However, few studies have explored the difference in brain mechanism in processing animals and plants, although they play different roles in human evolution. To examine the difference in their processing mechanisms, we employed neuropsychological approach to compare the speed of judgment on nouns belonging to animals or plants. We also examined the relationship between functional lateralization of the brain and the difference in processing animals and plants. Methods Twenty-five right-handed participants (healthy college female subjects, 20~25 years old) were asked to categorize 120 single-character nouns belong to either animals or plants. The subjects were instructed to respond with speech in one session, and response with button presses in the other two. In the first button-press session, left hand corresponded to animals, and right hand corresponded to plants. The correspondence was switched in the last session. Results In the speech-response session, the reaction time (RT) in responding to animals was significantly shorter than that to plants (t=-3.77, P<0.001). In the button-press sessions, a significantly faster RT for animals than plants (t=-3.98,P<0.001) was observed with the right-hand response. Conclusion Our study provided primary but initial evidence showing the brain mechanisms in processing animals and plants are different. Relationships between the functional lateralization of the brain and the processing mechanisms for animals and plants were also observed.

Key words: categorization, speech response, button-press response, animals, plants, functional lateralization, reaction time