Neural Representation of Natural Kinds and Artifacts.

Abstract:
Selective impairment in naming natural kinds or man-made artifacts suggests separate neurological representation of these semantic categories. It has been hypothesized that distinguishing among natural kinds involves fine-grained visual-perceptual processing, with lexical access requiring recruitment of visual-perceptual brain areas, while distinguishing among artifacts entails knowledge about function as well, with lexical access also recruiting motor-kinesthetic brain areas. Previous studies were confounded by the use of tasks involving different decision-making processes for each category. This study used fMRI to compare cerebral activity during semantic processing of words for animals and household implements, with pseudowords as baseline stimuli. Ten subjects judged visually presented animal and implement terms for pleasantness, a task that ensured a common cognitive process for all semantic and baseline stimuli. Words were presented every four seconds, in 40 second word-category blocks, for a total of six blocks per category and twelve blocks of pseudowords. We observed activation in the left posterior temporal lobe (BA 22) during the animals condition. In contrast, the implements condition produced left occipital activation (BA 18), along with bilateral striatal activity. These results confirm the distinction in neural representation of the two semantic categories. The involvement of the striatum in judging implements suggests additional recruitment of motor-related areas in the semantic processing of terms for manipulable objects.