Figure 4. Temporal characteristics of the electroretinogram responses. In A, the peak latencies of the electroretinogram (ERG) ON (left) and OFF (right) transients are presented, obtained with 2 s stimuli under dark adaptation (black squares) and under background illumination of 5.66 log quanta s⁻¹ μm⁻² (green triangles). The results obtained in wild-type flies (empty symbols, dashed lines) and in hclB^T2 mutants (filled symbols, solid lines) are represented. In the inset, original curves of a wild-type (black) and hclB^T2 mutant (red) ON response are superimposed. The beginning of the records corresponds to the stimulus onset. Stimulus intensity=6.73 log quanta s⁻¹ μm⁻². Peak latency is delayed in the hclB^T2 mutant (two way analysis of variance [ANOVA], 10⁻⁹<p<0.05 for different stimulation conditions). The delay is small in the dark-adapted responses, being well pronounced under light adaptation. In B, the results of low-pass filtering of the ERG ON transients are presented, obtained using 2 s stimuli in a wild-type fly (black squares) and hclB^T2 (red circles) mutant. The amplitudes are normalized to the amplitudes of the nonfiltered signals (raw signals recorded at a bandpass of 0–1000 Hz). Stimulus intensity=6.73 log quanta s⁻¹ μm⁻². On the left, the results obtained under dark adaptation (DA) are presented. On the right, the results obtained under a background of 6.66 log quanta s⁻¹ μm⁻² (light adaptation, LA) are presented. The amplitudes of the mutant responses are decreased to a lesser extent by low-pass filtering. The difference is greater under light adaptation. This is indicative of the slower kinetics of the hclB mutant responses and implies that HCLB receptors may contribute to the high-pass filtering of the visual signal during light adaptation.