Colour-coded ganglion cells in the goldfish retina: extension of their receptive fields by means of new stimuli.

1. Receptive fields of colour-coded ganglion cells of the goldfish retina were investigated.2. Only a few cells (5%, Type P) were found to be as simple as those described by Wagner, MacNichol & Wolbarsht (1960, 1963), with an ;on' response to red light in the centre, and an ;off' response to green light over a rather wider area, or vice versa.3. Most cells (49%, Type O) also gave a peripheral response with an ;on' response to green light, and an ;off' response to red light in the periphery, as well as an ;on' response to red light and an ;off' response to green light in the centre (or vice versa).4. When a small spot of light was used to stimulate the periphery of a Type O cell, the peripheral response usually was not obtained. The organization of the periphery is such that a stimulus of large area and low intensity (annulus) is much more effective than a stimulus having equal energy with small area and high intensity (spot). If only small spots are used, the Type O cell is indistinguishable from the Type P cell.5. Spectral sensitivity measurements show that one central and one peripheral process are fed primarily by red-absorbing cones, and the other central and the other peripheral process by green-absorbing cones or rods.6. The diameter of the receptive field as a whole is very large, being 5 mm or more on the retina.7. When red spots in green surrounds, or red/green boundaries are used as stimuli, the response can be predicted by summing the responses to the components of the stimulus.8. This type of receptive field organization is appropriate to mediate simultaneous colour contrast. The ;opponent colour' organization previously reported is appropriate for successive colour contrast, but not for simultaneous colour contrast.9. The component of the response coming from the green-absorbing cones was masked or hidden by the component of the response coming from the red-absorbing cones in 14% of the units (Type Q units). The component from the green-absorbing cones was revealed by using a high intensity of stimulation, or by observing the response after bleaching pigment with an intense red light.