E-vector discrimination by the goldfish optic tectum

Abstract

1. Because behavioral evidence indicates that fishes can perceivee-vector direction in plane polarized light, intracellular recordings were made on bipolar cells, ganglion cells, amacrine cells and horizontal cells in the goldfish retina. In flattened retinal fragments stimulated with polarized flashes no evidence for significante-vector sensitivities was found. 2. Dichroism could not be demonstrated in the cornea, lens or other dioptric elements of this fish eye. 3. Finally extracellular spike recordings of single units in the goldfish optic tectum were made to determine whethere-vector discrimination could be measured in the output of the intact eye in the living fish. 500 msec test flashes were presented to the retina with narrow band spectral red, green and blue light (quantum equalized) as well as with white light over a 4–5 log unit range of intensities. 4. Practically all tectal cells of the 47 successfully recorded showed some sensitivity toe-vector direction. The response function was roughly sinusoidal with maxima and minima 90° apart. Maximal responses to polarization plane orientation were found in all sixe-vector directions tested. Consequently an analyzer without discrete channels for particular polarization planes must be present quite different from that present in many rhabdom bearing eyes. 5. E-vector direction influenced various parameters of the tectal responses (on, off, sustained, etc.) in some cases in the same direction and in other cases in the opposite direction. Both excitatory and inhibitory components, as well as color coded ones, were affected. 6. Intensity response curves indicate polarized light sensitivity ratios ranging from 1.4 to 31.7, with a mean of 8.2 for 13 cases.