Figure 2. Incomplete mean subtraction and deviations from matching behavior.

(A) The probability of choice as a function of fractional income. Each point corresponds to one simulation of the model, Eq. (4), in a concurrent VI reward schedule with fixed baiting probabilities. The level of deviation from matching behavior (black line) depends on the level of incomplete mean subtraction, γ and synaptic saturation stiffness, ρ. Red squares, γ = 0.05, ρ = 1; blue diamonds, γ = 0.5, ρ = 1; gray triangles γ = 0.5, ρ = 4; colored lines are the analytical approximations, Eq. (7). (B) Susceptibility of behavior as a function of γ. In order to quantify the effect of γ on deviation from matching behavior, we repeated the simulations of A for many values of γ and measured the susceptibility of behavior (the slope of the resultant curve, see text and Materials and Methods). Blue dots, ρ = 5; red dots, ρ = 1; black dots, ρ = 0.2. Lines correspond to the expected slope from the analytical approximation, Eq. (7).