Figure 5.

The relative retrograde gradient remains unaffected by manipulation of item difficulty. (Illustration with self-generated data points. (A) Example forgetting curve (white dots) and Ribot gradient (black dots), generated with the model using μ₁ = 2, a₁ = 0.04, μ₂ = 0.01, and a₂ = 0. (B) Distorted curve where μ₁ has been multiplied with (from left to right) 1, 1.4, 1.8, 1.4, and 2. (C) Relative retrograde gradient for the undistorted curves. (D) Relative retrograde gradient for the distorted curves.