OBJECT-RELATED ACTIVITY REVEALED BY FUNCTIONAL MAGNETIC-RESONANCE-IMAGING IN HUMAN OCCIPITAL CORTEX

The stages of integration leading from local feature analysis to objec t recognition were explored in human visual cortex by using the techni que of functional magnetic resonance imaging. Here we report evidence for object-related activation. Such activation was located at the late ral-posterior aspect of the occipital lobe, just abutting the posterio r aspect of the motion-sensitive area MT/V5, in a region termed the la teral occipital complex (LO), LO showed preferential activation to ima ges of objects, compared to a wide range of texture patterns, This act ivation was not caused by a global difference in the Fourier spatial f requency content of objects versus texture images, since object images produced enhanced LO activation compared to textures matched in power spectra but randomized in phase, The preferential activation to objec ts also could not be explained by different patterns of eye movements: similar levels of activation were observed when subjects fixated on t he objects and when they scanned the objects with their eyes, Addition al manipulations such as spatial frequency filtering and a 4-fold chan ge in visual size did not affect LO activation, These results suggest that the enhanced responses to objects were not a manifestation of low -level visual processing, A striking demonstration that activity in LO is uniquely correlated to object detectability was produced by the '' Lincoln'' illusion, in which blurring of objects digitized into large blocks paradoxically increases their recognizability. Such blurring le d to significant enhancement of LO activation, Despite the preferentia l activation to objects, LO did not seem to be involved in the final, ''semantic,'' stages of the recognition process, Thus, objects varying widely in their recognizability (e.g., famous faces, common objects, and unfamiliar three-dimensional abstract sculptures) activated it to a similar degree. These results are thus evidence for an intermediate link in the chain of processing stages leading to object recognition i n human visual cortex.