Activity in the Optic Nerve of Pecten Maximus in Response to Changes in Light Intensity, and To Pattern and Movement in the Optical Environment

1. In the eye of Pecten maximus there are two functionally independent retinae. The proximal retina contains receptors which respond to increase of illumination, those of the distal retina respond to decrease. 2. The activity of each retina was investigated by recording from the optic nerve, which contains the axons of both types of receptor. Visual stimuli used included changes in overall illumination, pattern and movement. Dark adaptation was also studied. 3. The ‘off’ response is generated by cells which are anatomically primary receptors. Two light dependent processes are involved: a slow development of excitability and a simultaneous inhibition of action potentials. 4. The reflected image is important in movement perception. Only the distal cells lie in the image plane, and they can respond to moving objects, as these cause dimming of successive cells when their images cross the retina. Dark objects subtending 2° or more at the eye, and moving through more than 2°, are effective stimuli. Light objects are also effective, provided they have remained stationary for several seconds before moving. There is no response to stationary pattern. The proximal cells respond only to increase in overall light intensity. 5. These findings are discussed in relation to the behaviour of Pecten.