Figure 4. Recovery of responses to bright and dim flashes following a full bleach.

Superimposed responses to bright flashes (left) and dim flashes (right), at a succession of times following a full bleach, for subject TDL. The upper panels show the method of rod isolation, and illustrate averaged responses to blue flashes (blue traces), together with the mean cone signal obtained with red flashes (red traces). A, bright stimuli. The blue traces were obtained with single flashes (400 μs in duration) delivering 4·05 × 10⁴ Td s, presented at intervals of roughly 4 min. The red trace is the mean response to five photopically matched red flashes delivered during the first 12 min following extinction of the bleaching exposure. B, dim stimuli. The blue traces are averaged from groups of 8-10 flashes (50 μs in duration) delivering 135 Td s, and presented at intervals of 5 s. The red trace is averaged from 34 responses to photopically matched red flashes presented throughout the recovery period. C and D, rod-isolated responses (black traces) to bright flashes and dim flashes, obtained by subtracting the red trace (in A or B) from each of the blue traces. The post-bleach time (min) is indicated to the right. The red traces plot the theory curves fitted using the first approach (iterative fitting; see Methods). The dashed vertical lines at 5·5 ms and 14 ms in the two panels indicate the respective times at which the bright and dim flash responses were measured using the second approach (measurement at fixed times). To avoid crowding, only representative traces are plotted in this figure, but in Fig. 5 the extracted parameters are plotted at all post-bleach times tested. For this subject the pupil diameter was 7·2 mm. The difference between the maximal dark-adapted response amplitude in this experiment and in the experiments of Fig. 2 (on the same subject) presumably arose from different positioning of the DTL electrode on different days.