Conditioned suppression as a function of the number of stimuli that precede shock

Abstract

The conditioned suppression of a previously trained lever pressing response was observed in hooded rats. One group of rats received pairings of one 60-sec stimulus followed by shock. The remaining two groups received two consecutive 3D-sec stimuli with the second stimulus followed by shock. It was found that the one-stimulus group suppressed lever pressing strongly during every presentation of the stimulus. Both of the two-stimuli groups suppressed lever pressing in both stimuli on early trials. On later trials. both groups showed less suppression of lever pressing in the first stimulus than in the second stimulus. indicating the development of a discrimination of the time of shock delivery.When pairings of a stimulus, followed by brief electric shock, are presented several times to a rat emitting operant responses, the operant response rate decreases during the stimulus and returns to the pre-stimulus rate after the shack is presented and the stimulus is withdrawn. The decrease in operant response rate during the stimulus is a demonstration of conditioned suppression.A large number of experiments (e.g., Brady, 1955;Annau & Kamin, 1961) have studied the conditioned suppression of operant behavior in a single stimulus that preceded shock. In the present experiment, which is similar to an experiment reported briefly by Kamin (1965), the suppression of operant behavior was obselVed when two stimuli preceded shock. A control group of rats received delayed conditioning trials composed of a single 6D-sec stimulus that ended with shock. Two experimental groups of rats received trials composed of two 3Q-sec stimuli in succession, and the second stimulus ended with shock. One of the experimental groups received the trials according to a trace conditioning procedure, and the other group received the trials according to a compound (successive cue) conditioning procedure. The two experimental groups provided a comparison of response suppression in two pre-shock stimuli when the second stimulus and the intertrial stimulus were either the same (trace procedure) or different (successive cue procedure). METHOD SubjectsThe Ss were 15 male hooded rats, 13S days old at the beginning of the experiment. Before training the lever pressing response, Ss were allowed free access to Purina Lab Chow pellets and water. Each S was tested at SO% of its ad lib weight, which was maintained during the experiment by feeding an appropriate amount of Purina Lab .Chow after the daily experimental session. ApparatusThe Ss were tested during daily 6O-min sessions in a standard Lehigh Valley Electronics (LVE) operant conditioning chamber (Model 1417 c). Reinforcement for lever pressing was a 4S mg Noyes rat pellet. A 1.0 mA shock was presented through the grid floor of the chamber by a LVE shock supply"(ModeI153l) and a scrambler (Model BliSS). A light stimulus was provided by the illumination of two 7-W lamps mounted in a wall-of the chamber, and a tone (2000 .cps, 80 dB) was delivered to the . .chamber by a Hewlett-Packard oscillator (Model 200cD). ...

Effects of component training and subsequent sequencing of stimuli on shuttlebox avoidance responding of rats

“…One strategy sought to enhance the associative strength of individual components by conditioning them separately prior to combining them into a compound (Kamin, 1969;Wagner, 1971). Another approach attempted to provide a careful analysis of response topographies during training to determine whether differential responding to components could be detected (Brahlek, 1968;Levis, 1970). The intent of the present research was to determine the effects of a component-training procedure on modifying the topography of avoidance responding elicited by stimuli ordered in a serial sequence.…”