Dynamics and sensitivity of the pupillary system in the eyes of noctuid moths

Abstract

Infrared reflectometry was used to study the pupillary response in the superposition eye of noctuid moths while presenting incremental (light-on) and decremental (light-off) light stimuli. The stimulus intensity was kept within the range where the luminous pseudopupil was seen during constant illumination. After a latency period the response gradually (dynamic phase) attained an upper (light-off) and a lower (light-on) asymptotic level, respectively. The response to both increments and decrements changed exponentially with time towards asymptotic levels that were determined the stimulus intensity. The mean latency period ± SD of light and dark adaptation was 12.1 ± 3.0 and 6.2 ± 1.2 min, respectively. The time constant (at the 90% level) of the dynamic phases were 13.3 ± 4.6 min for light adaptation and 56.1 ± 10.5 min for dark adaptation. Steady state responses plotted against light intensity defined sigmoid-shaped intensity-response curves that were fitted by Lipetz equations with n-values nearly equal to 1. The curves, extending from about 10 6 to 10 10 photons × cm 2 × s −1, had a linear segment covering about 1 log unit intensity to either side of a midpoint located at about 10 8.2 photons × cm −2 × s −1. Spectral response curves for pupillary and electroretinogram responses were closely similar, suggesting that the aperture size in noctuid moth eyes is controlled by retinula cell activity.