POLARIZATION SENSITIVITY IN THE CRAYFISH OPTIC LOBE - PERIPHERAL CONTRIBUTIONS TO OPPONENCY AND DIRECTIONALLY SELECTIVE MOTION DETECTION

1. Polarization sensitivity (PS) was examined in nonspiking interneuro ns, tangential cells, of the crayfish optic lobe. Stationary PS profil es were measured with pulses of illumination at fixed intensity and va ried e vector orientation (theta). Dynamic polarization responsiveness was examined with a rotating polarizer. The dynamic response was asse ssed with variations in rotation velocity and direction and for variat ions in intensity. 2. Eighty percent of the cells tested were polariza tion sensitive. These were divided into two types. Type I cells exhibi ted PS magnitudes comparable with those of photoreceptors and lamina m onopolar cells in the same species. Most type I cells exhibited a dire ctionally selective response to a rotating polarizer, 3. Type IT cells exhibited PS magnitudes substantially higher than those observed in l amina neurons. These cells also revealed evidence for a polarization o pponency mechanism. 4. The results are interpreted in terms of a gener al hypothesis for polarization feature detection, on the basis of four principles. 1) Most or all tangential cells are subject to inhibition . 2) The inhibitory pathway is polarization sensitive. 3) If the theta producing the maximum response at fixed stimulus Intensity (theta(max )) of the inhibitory input is similar to theta(max) - 90 degrees of th e excitatory input, then the inhibition forms the basis of a polarizat ion opponency mechanism. 4) If theta(max) of the inhibitory input is s imilar but nor identical to theta(max) of the excitatory input, then t he inhibitory input provides a basis for directionally selective polar ization vision.