Relationship between ventral stream for object vision and dorsal stream for spatial vision: An fMRI+ERP study

Recent imaging studies indicated the existence of two visual pathways in hu mans: a ventral stream for object and form vision and a dorsal stream for s patial and motion vision. The present study was motivated by a stimulating question: Supposing shape and motion are processed separately in the two pa thways, how do the respective cortical areas respond to the stimuli of "for ms defined by motion"? fMRI and ERP recordings were combined in order to me asure the spatiotemporal activation pattern in the two pathways responding to forms defined by motion, which were produced solely by coherent movement of random dots against a background of dynamic or static random dots. The fMRI data indicated that the stimuli of forms defined by motion indeed acti vated both dorsal MT/V5 and ventral GTi/GF Furthermore, the RV curves resul ting from fMRI-seeded dipole modeling indicated that each pair of dipoles l ocated at MT/V5 or GTi/GF reached the same best-fit point; a single pair of free dipoles located near the fMRI foci of MT/V5 and GTi/GF could be ident ified at the corresponding best-fit point; and the source waveforms resulti ng from fixed dipole modeling also showed simultaneous activation of MT/V5 and GTi/GF dipoles in the time interval around the best-fit point. The pres ent results, therefore, suggest that MT/V5 and GTi/GF appear to be activate d in parallel and simultaneously responding to forms defined by motion. Suc h findings raise interesting issues about the hierarchical organization and the functional specialization in the two pathways. (C) 1999 Wiley-Liss, In c.