Changes of Acuity during Light and Dark Adaptation in the Dragonfly Compound Eye

Intracellular recordings o f angular sensitivity from the photoreceptors o f Aeschnid dragonflies (Hemianax papuensis and Aeschna brevistyla) are used to determine the magnitude and time course o f acuity changes follow ­ ing alterations o f the state o f light or dark adaptation. Acuity is defined on the basis o f the acceptance angle, A q (the half-width o f the angular-sensitivity function). The maximally light-adapted value o f A q is half the dark-adapted value, indicating greater acuity during light adaptation. Following a change from light to dark adaptation, A q increases slowly, requiring at least 3 min to reach its dark-adapted value. In contrast, the reverse change (dark to light) induces a rapid reduction o f A q , and at maximal adapting luminances, this reduction takes place in less than 1 0 sec.