Like wild-type, trp⁹ heterozygous flies carrying trp^S936D.ninaE do not display oscillating voltage electroretinogram (ERG) response upon constant light stimulation. The electroretinogram response of light-adapted trp⁹/+;trp^S936D.ninaE flies to oscillating light of gradually increasing frequencies is comparable to controls at lower stimulus frequencies, but mean oscillation amplitude of the response drops significantly at higher frequencies relative to controls. Dark-adapted flies show no significant changes in the onset of the frequency-locked response to oscillating light of either low (10Hz) or high (70Hz) frequency compared to wild-type flies. However, there is no difference in the timing of the onset of frequency-locked response between dark-adapted and light-adapted flies as both take about 8s to show response (similar to the onset time of dark-adapted controls), whereas in light-adapted wild-type flies it takes less than 0.3s until they display frequency-locked response.