Figure 2.

Block diagram of a first-order infinite impulse response length (IIR) filter with transfer function H_S(f ) equivalent to (11) or (12). Elements denote a delay of one trial. At the adder element ⊕, updating of the weighted output γ_S·c_S,k(n − 1) of the last trial n − 1 with the weighted input (1 − γ_S)·g_k(n − 1) of the last trial results in the current output c_S,k(n). Note that via γ_S·c_S,k(n − 1), all preceding inputs (and outputs) influence the current output, though for the short-term memory, the influence of trials not in the recent past is negligible.