FUNCTIONAL-ANATOMY OF A COMMON SEMANTIC SYSTEM FOR WORDS AND PICTURES

THE relationship between the semantic processing of words and of pictu res is a matter of debate among cognitive scientists(1,2). We studied the functional anatomy of such processing by using positron-emission t omography (PET). We contrasted activity during two semantic tasks (pro bing knowledge of associations between concepts, and knowledge of the visual attributes of these concepts) and a baseline task (discriminati on of physical stimulus size), performed either with words or with pic tures. Modality-specific activations unrelated to semantic processing occurred in the left inferior parietal lobule for words, and the right middle occipital gyrus for pictures. A semantic network common to bot h words and pictures extended from the left superior occipital gyrus t hrough the middle and inferior temporal cortex to the inferior frontal gyrus. A picture-specific activation related to semantic tasks occurr ed in the left posterior inferior temporal sulcus, and word-specific a ctivations related to semantic tasks were localized to the left superi or temporal sulcus, left anterior middle temporal gyrus, and left infe rior frontal sulcus. Thus semantic tasks activate a distributed semant ic processing system shared by both words and pictures, with a few spe cific areas differentially active for either words or pictures.