Efeitos paramétricos do atraso do reforço sobre o responder de ratos submetidos a esquemas de razão e intervalos variáveis

This study examined the effects of introducing different delays of reinforcement on the rate of lever pressing by eight rats under variable interval and variable ratio schedules (VI and VR, respectively). Following baseline conditions under immediate reinforcement, unsignaled and non-resetting delays of reinforcement were introduced upon each of these schedules. In different conditions, delays of 2 s, 5 s and 8 s were presented in both increasing and decreasing sequences. The results showed negative correlations between rate of responding and delay of reinforcement for most subjects and delays. By analyzing the frequency distribution of the delays actually obtained in each single reinforcer delivery, it was possible to verify a higher concentration of 0.5-s delays when a 2-s delay was programmed. In contrast, actual delays concentrated around 5 s and 8 s when the programmed delays were 5 s and 8 s, respectively. Such differential effects generated by the delays of reinforcement on responding can be understood by analyzing how the delay affected the ongoing contingencies in each particular schedule. Keywords: delay of reinforcement; schedules of reinforcement; variable interval; variable ratio; rats.