Publication Date


Advisor(s) - Committee Chair

James Craig, Leroy Metze, Elsie Dotson

Degree Program

Department of Psychology

Degree Type

Master of Arts


The purpose of this experiment was to determine if stress, induced by intraperitoneal (IP) injections of epinephrine, influenced rats' preference to freeload (drink sucrose solution from a drinking tube) or to work for a liquid reinforcer (obtain sucrose solution by barpressing). Furthermore, the order in which stress was introduced was investigated.

Following two weeks of water deprivation, 6 female and 6 male Hooded rats approximately 90 days old were divided into two experimental groups. The first group (S-N) was stressed the first and second experimental testing days in which a choice was presented between barpressing and freeloading for a 10% sucrose solution. The choice was presented the third and fourth testing days in the absence of stress. The second group (N-S) was given the choice of barpressing or freeloading the first and second experimental testing days in the absence of stress, and was presented with the same choice the third and fourth days in the presence of stress. Two dependent variables were measured: the ratio of the amount of solution earned by barpressing to the total amount of solution consumed and the amount of solution earned by barpressing.

The results of the study indicated that rats in the stress condition preferred to freeload. Furthermore, the order in which the stress was introduced affected work versus freeloading preference. When permitted to make the initial choice between barpressing or freeloading in the absence of stress, all rats chose to barpress. When the stress was subsequently introduced on the third experimental testing day, all rats preferred to freeload. Results of the (S-N) group were not as significantly conclusive because of the large variance of choice in both the stress and nonstress conditions.


Applied Behavior Analysis | Experimental Analysis of Behavior | Psychology | Social and Behavioral Sciences