Figure 3. Responses from P347L rod to repeated dim flashes

Observations of individual responses to repeated dim flashes reveal two distinct type of single photon responses. A: Three types of responses could be easily identified by examining the individual responses to a series of 200 flashes. "Blanks" were those in which no response was observed (bottom trace); "Singles" were where the response resembled the typical wild type single photon response (middle trace); and "Steps" were those in which the rising phase of the response continued beyond the time required for the singles to peak, followed by a plateau of variable duration and a rapid return to baseline (upper trace). The baseline for each trace is indicated by a dashed line. The maximum response, I_max, was 8.5 pA for this cell; the stimulus strength was 20.4 photons/μm², or 2.8 Rh* per flash, 36 °C, DC to 50 Hz. B: Sorting and averaging the singles and blank responses reduces the noise, but does not change the underlying shape of the response.