Figure 6. Weber–Fechner relations for lamprey rods and cones.

Backgrounds and flashes were at 500 nm for rods and 600 nm for cones; intensities are given separately in units of Rh^* or Rh^* s⁻¹ for rods and P^* or P^* s⁻¹ for cones. Sensitivity (S _F) was calculated by dividing the peak amplitude of responses within the linear range (r < 0.3r _max) by the flash intensity in Rh^* or P^*. Data have been fitted with eqn (4) with values of I ₀ of 67 Rh^* s⁻¹ for rods and 7070 P^* s⁻¹ for cones.