The contrast sensitivity of fly movement-detecting neurons

Contrast sensitivity functions (CSFs) have been measured for directionally-selective movement-detecting neurons of the lobula plate by using moving sine-wave gratings. At high luminance, the CSF peaks at 0.05 c/deg. Sensitivity is reduced by 40% at 0.02 c/deg and 0.15 c/deg, and by 90% at 0.4 c/deg. At low luminance, the high-frequency falloff shifts toward lower frequencies and the low-frequency falloff disappears. The results point to a number of parallels between the ways in which invertebrate and vertebrate visual systems analyze spatial information.