Figure 4.

Coefficient of variation R_T against noise amplitude σ_l of layer l in isolation. In (A) and (B), we have the R_T curves of weak and strong electrical synaptic strengths κ_l,e, respectively, for short, intermediate and long synaptic time delays τ_l,e. In (C) and (D), we have the R_T curves of short and relatively long synaptic time delays τ_l,e, respectively, for weak, intermediate and strong synaptic strengths κ_l,e. Increasing (decreasing) the electrical synaptic strength κ_l,e or the length of its time delay τ_l,e, deteriorates (enhances) SISR by increasing (decreasing) the values of R_T and by shrinking (extending) the interval of the noise amplitude in which R_T can achieve very low values. For example, in (D), for κ_l,e = 1.0 and τ_l,e = 10.0, the red R_T-curve lies entirely above the line R_T = 1.0 with a lowest value of R_Tmin = 1.24 occurring at just one point ${\sigma }_l=4.6\times 10^{-4}$, indicating the non-existence of SISR. Parameters of layer l: N = 25, n_l,e = 1, β = 0.75, ε = 0.0005, α = 0.5.