Receptive field organization and response properties of visual neurons in the pigeon nucleus semilunaris

The present study provides the first electrophysiological evidence that the nucleus semilunaris is a visual center in the pigeon midbrain. The receptive field of E-type cells is either an excitatory field alone or an excitatory center with an inhibitory periphery, which in most cases is surrounded by a disinhibitory region. Cells of I-type possess only an inhibitory receptive field. Semilunar cells are selective for fast (30-160 degrees/s), intermediate (40 degrees/s) and slow (10-20 degrees/s) velocities of motion, with directional cells mainly preferring forward and downward motion. About 40% of cells prefer a white stimulus moving against a black background, and 60% of cells prefer a black stimulus against a white background. The physiological significance of these properties is discussed. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.