Distance modulated neuronal activity in the cortical visual areas of cats.

During previous studies in cats and monkeys, it was found that in some neurons, responses to visual stimuli of the same angular size were dependent on the absolute distance to these stimuli. To study how widely this peculiarity of visual responses is distributed among cortical visual areas, we recorded activity of neurons in areas V4A, V2, V1, and frontal visual area on the lower bank of the cruciate sulcus. Neuronal activity was recorded at near (20 cm) or far (3 m) distances from a 3D stationary visual scene. Visual scenes were vertically corrugated light gray screens. Angular dimensions of the screens were the same at short and far distances. Eye movements were free during the test procedure. It was found that about 20% of neurons in areas V4A, V1, and frontal visual area had significantly different levels of activity, while animals were looking at the visual scenes located near or far from the eyes. No neurons with depth modulated activity were found in area V2.