Like wild-type, trp⁹ heterozygous flies carrying trp^S936A.ninaE do not display oscillating voltage electroretinogram response upon constant light stimulation and the frequency response of light-adapted flies to oscillating light of gradually increasing frequencies is comparable to controls at both low and high stimulus frequencies. Dark-adapted flies show no significant changes in the onset of the frequency-locked response to oscillating light of low (10Hz) frequency, but unlike wild-type flies they display a quick (<0.3s) frequency-locked response also at high (70Hz) frequency (wild-type flies take about 8s). Light-adapted flies at high frequency show normal quick onset, same as wild-type.