Scotopic responses and bipolar cell-mediated activity emerge at P9. Emergent bipolar cell activity shapes the ERG waveform at P9 and P10. (A and C) Normalized a-waves from P9 (A) and P10 (C) retinas to short (1–10 ms) green flashes presented at t = 0 s. Flashes delivering 0.19–117 photons µm⁻² elicited scotopic responses (first row), 234–495 photons µm⁻² elicited mesopic responses (second row), and those flashes delivering 13,280 photons µm⁻² elicited photopic responses (bottom row). Synaptic blockers (see Materials and methods) were then perfused to eliminate any bipolar cell contribution, and subsequent recordings were repeated in the same retinas using identical flashes (red traces). Arrows in A represent a positive going pull on the waveform. (B and D) A Pepperberg analysis (see Materials and methods) on P9 (B) and P10 (D) data reveal the effect of bipolar cell-mediated activity on the waveform. Response recovery time (Δt to 40% recovery after the emerging nose component—dashed horizontal line) to the five brightest green flashes used in Fig. 2, plotted as a function of the first three (P9) and the middle three (P10) brightest flash intensities. The dominant time constant of recovery (τ_D) was significantly greater in retinas perfused with blockers (P9: n = 5 and 6, P = 2.6789 × 10⁻⁵ and became more obvious at P10 (P10: n = 10 and 9, P = 7.0149 × 10⁻¹¹). Error bars = mean ± SEM. Asterisks indicate a P value of <0.001.