Receptive Fields of the Visual System of the Squid

Abstract

IN an octopus some second order visual cells that receive synapses in the plexiform layer from the optic nerve fibres have dendritic fields with an oval orientation lying in the horizontal plane¹. It has now been shown that in a squid there are cells with several distinct types of receptive field, which are suitable to act as detectors of visual contours of differing size, shape and orientation. The largest have oval dendritic fields, several millimetres long, predominantly orientated along the vertical (dorso-ventral) axis of the optic lobe (Figs. 1 and 2). Each makes contact with the endings of many thousands of optic nerve fibres and therefore they are probably activated only by very large visual contours. Their large axons reach deep into the optic lobe, from which the axons of third order cells reach direct to the first order giant cells. This may therefore be the pathway for escape reactions from large objects, perhaps also for schooling responses to other squids. The cell bodies of these second order visual neurones lie at the base of the inner granule cell layer and their trunks bend over in the second tangential layer of the plexiform zone to make recurrent axons (Figs. 1 and 3).