Figure 5: Modeling contributions to rat PII after a light step. Average (±SEM) amplitudes following stimulus offset at a fixed time of 400 ms are modeled with three mechanisms. The two negative components (4 and 5) are modeled with two negative hyperbolic functions (m(4) solid grey line and m(5) dashes grey line), whereas the positive portion (6) is fit with a positive mechanism (m(6) black dashed line). The solid black line represents the summation of the three hyperbolic functions fit to the raw data. (b) The merit functions show that three hyperbolic functions (filled) provide statistically better fit for fixed times >340 ms (grey area, ) compared with two hyperbolic functions (unfilled). (c) and (d) plotted as a function of fixed times.