(A) Photoresponse family recorded in normal Ringer. Flash strengths: 425, 848, 1693, 3378, 6739, 13500 Rh*. Data points used to determine τD ranged from 848 to 13500 Rh* (indicated by the horizontal line). (B) Photoresponse family in 25 nM free [Ca2+]o. Flash strengths same as in A. Data points used to determine τD indicated by the horizontal line. (C) Photoresponse family in 25 nM free [Ca2+]o during background illumination producing 640 Rh* s−1. Flash strengths: 425, 848, 1693, 3378, 6739, 13 500, 26800 Rh*. Data points used to determine τD ranged from 3378 to 26800 Rh* (indicated by the horizontal line). (D) Pepperberg plots extracted from A–C. τD increased from 360 ms (▪) to 660 ms (red ○) when retina was switched from normal Ringer to low Ca2+ solution. Background light producing 640 Rh* s−1 decreased τD to 600 ms (blue ).