Hierarchical visual processing is dependent on the oculomotor system

Using functional MRI and eye movement recordings we studied the processing of hierarchical stimuli. In agreement with others, we Found a minor left he mispheric dominance during local and right dominance during global processi ng. When attention was directed locally, well-known oculomotor cortical are as were activated, and saccades were elicited in 41% of the trials. Their l atencies were similar to pro-saccades. During global processing virtually n o saccades occurred. These results suggest two different operational modes of attention. Attending to local features induces a shift of attention, whi ch simultaneously computes a saccade on any level above the brainstem with a computational burden equal to reflexive saccades. Conversely, attending t o global features induces an expansion of the focus of attention, which rei nforces fixation. NeuroReport 11:241-247 (C) 2000 Lippincott Williams & Wil kins.