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 hemispheric dominance during local and right dominance during global processing. When attention was directed locally, well-known oculomotor cortical areas were activated, and saccades were elicited in 41% of the trials. Their latencies were similar to pro-saccades. During global processing virtually no saccades occurred. These results suggest two different operational modes of attention. Attending to local features induces a shift of attention, which simultaneously computes a saccade on any level above the brainstem with a computational burden equal to reflexive saccades. Conversely, attending to global features induces an expansion of the focus of attention, which reinforces fixation.
Weber
B
B
Department of Neurology, Universitätsspital, Zürich, Switzerland.
Schwarz
U
U
Kneifel
S
S
Treyer
V
V
Buck
A
A
D001288:Attention / Q000502:physiology*; D005403:Fixation, Ocular / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008959:Models, Neurological; D009801:Oculomotor Muscles / Q000502:physiology; D010296:Parietal Lobe / Q000502:physiology; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D012044:Regression Analysis; D012438:Saccades / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*