Intracellular recordings in the medulla of the locust optic lobe reveal units showing u.v. sensitivity and spectral opponency. Previously only a single population of photoreceptors had been recorded in the locust retina, with peak sensitivity from 450–480 nm. Behavioural measurements show that the dorsal light response is elicited only by u.v. light, unlike the optomotor response whose spectral sensitivity is probably attributable to inputs from the green-sensitive cells. The possibility that the cells described may be involved in maintenance of level flight is discussed.

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