The cortical network processing contextual, semantic and physical relationships between visual objects

Human imaging studies of visual representations have so far focused on objects that belong to the same category (e.g., flowers, chairs, etc.). However, objects can relate to each other along multiple dimensions. They may share physical features (e.g. a hairdryer and a drill), the same basic-level name (e.g. two different lamps), or the same context (e.g., an oven and a refrigerator). How are these different relationships represented in the brain? Using fMRI to address this question (12 subjects; 3T magnet; TR=2sec; 33 slices, 3mm each), we presented subjects with blocks of pictures, where each block contained objects that shared properties along a single dimension (i.e. appearance, basic-level name, or context). In addition, we included control blocks with pictures of meaningful objects that were unrelated to each other. We compared the cortical activation that was elicited by each of the experimental blocks with the cortical activation elicited by the control blocks. The results revealed a unique activation pattern in the temporal cortex, which was dependent on the relationship between the objects. Contextually related objects elicited activation that focused in the collateral sulcus and in the anterior tip of the fusiform gyrus. Different exemplars, on the other hand, showed primarily a decrease in activation compared with control objects. This activation concentrated in the mid-fusiform gyrus and in the lateral-occipital sulcus. Finally, perceptually related objects activated regions in the fusiform gyrus and in the posterior lateral-occipital sulcus. These findings indicate that the representation of objects and their intricate relations is subserved by a cortical network involving at least five distinct regions. The relative role of each component of this network in orchestrating our comprehensive perception of objects in the environment, ranging from physical features to conceptual properties, will be discussed.