Journal of the experimental analysis of behavior
-
After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response-shock interval, delaying shock, and the second component differed only in that four bar-presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. ⋯ Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio-avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non-drug) periods.
-
Is a conditioned aversive stimulus necessary in avoidance conditioning? Or is a reduction in the rate of aversive stimulation alone sufficient to generate and maintain an avoidance response? Rats were subjected to an avoidance procedure in which shocks occurred randomly in time, but a response could reduce the overall rate of shock. Fifteen acquisition curves, obtained from 16 animals, showed both immediate and delayed, rapid and gradual increases in response rate; there was no representative acquisition curve. ⋯ Responding on this procedure shows that avoidance conditioning can occur without benefit of either classical exteroceptive stimuli or covert stimuli inferred from the temporal constancies of a procedure. It also shows that reduction in shock rate is alone sufficient to maintain avoidance.