Psychology

The study of Robert A. Rescorla entitled Probability of Shock in the Presence and Absence of CS in Fear Conditioning aimed to test his two ideas regarding Pavlovian conditioning. His first assumption focused on the importance of the number of pairings of CS and US in the formation of CR while the second dealt with the importance of contingency between CS and US in the formation of the CR.

Rescorla tested his first hypothesis by subjecting 24 male Sprague-Dawley rats, which were grouped into three and were categorized as Group R-1, Group G, and Group R-2, into VI training sessions and then a 5-day Pavlovian fear conditioning session. After conditioning, subjects went through two 2-hr VI sessions followed by ten test sessions. Result of the experiment indicates that the equal probability of a shock in the presence and absence of a tone produced no CR suppression to CS and that the same probability of US was given only when CS produced substantial conditioning. These results attest to the previous conclusions by Rescorla. The results favored the inadequacy of the notion that states the importance of contingency of US on CS.

The second experiment examined the second assumption by subjecting 80 male Sprague-Dawley rats which were 100 days old into five Pavlovian conditioning sessions. The subjects were grouped into 10 and each group received different probability of shock every 2-min interval during the presence and absence of CS. After conditioning, the subjects underwent two 2-hr VI training sessions and 6 days of test sessions. Results of the experiment showed no consistency in the differences among the 10 groups in their reaction to the absence of CS on both the 2-hr VI training sessions and the 6-day test sessions. The experiment tested four probabilities of US in the presence and absence of CS and three important points were derived from the second experiment 1) There was little or no suppression if US came with equal probability in the presence and absence of CS 2) Having a fixed probability of shock during CS, when the probability in the absence of CS was increased, suppression is reduced among the subjects and 3) Having a fixed probability of shock in the absence of CS, when the probability of shock in increased in the presence of CS, suppression among subjects was intensified. The last statement affirms that the number of coordinated occurrences of CS and US is important in conditioning.