Depiction of the input of retinal bleaching (RB) to the startle habituation, using simulated data. In the classic decay model (blue) described by Beppi et al.³⁵, the amplitude (A_C) corresponds to the magnitude of the locomotor response to the first stimulus (d₁) minus the offset (O_C), namely the steady-state responsivity (constant). The decay pattern with RB accounts for the effect of retinal bleaching with decay to an asymptotically increasing offset (O_RB). Habituation is a high-pass filter [A_C × exp(Dc × n)], where Dc is the decay constant and n the stimulus number minus 1. The bleaching effect is instead a low-pass filter [A_RB × exp(–n / Rc)] where Rc is the rise constant and is larger than Dc (in this example Dc = 1 and Rc = 3), while A_RB (= d₁ – O_RB) is considerably smaller than A_C. The habituation with bleaching effect can hence be described as [A_C × exp(Dc × n) + A_RB × exp(–n / Rc) + O_C].

When trying to fit a classic first-order exponential into such a decay pattern with retinal bleaching, a “fictitiously” high average (i.e., constant) offset (O_err) and a “fictitiously” smaller amplitude (A_err = d₁ – O_err) would be obtained, as we can observe in Figure 2 (see offsets and amplitudes in the highest lux-levels).