The study of conditioning using experiments on animals is an important part of the learning theory. Classical and operant conditioning belong to the areas of learning theory which were explored in detail by empirical researchers. The research in classical and operant conditioning is highly important both from theoretical and practical perspectives; these experiments provide insight into the mechanisms of learning and extinction in animals, and also create background for new learning and training approaches for human beings, such as associative learning. There are several variables the study of which has particular impact on human learning theories: these are reinforcement schedules (type and intervals) and extinction. The timing and repetition of schedule has a direct impact on the effectiveness of the learning process, and one of the significant problems of modern learning theory is the combination of schedules which leads to optimal learning. The studies of human extinction and its mechanisms are used in learning theory, and are also important for psychotherapy (e.g. fear-related disorders and fear extinguishing). In this research, the interaction between two variables ”“ the type of the reinforcement schedule (fixed-ratio or variable-ratio) and overtraining time (low, medium and high) is analyzed, and the effect of both variables on the resistance to extinction is considered.
1. Literature review
The research in operant conditioning was initiated by B.F. Skinner, who used rewards and punishments to study behavioral patterns of animals. He coined the following concepts: reinforcement ”“ the events strengthening the following behavior of the animal (which can be classified as positive and negative reinforcement), punishment ”“ the events leading to the decrease of the desired behavior (also divided into positive and negative), and schedules of reinforcements ”“ the rules guiding the reinforcement for the instances of behavior. Nowadays the following types of schedules can be identified: continuous reinforcement (when the reinforcement is applied every time when the desired behavior occurs) and partial reinforcement (when the reinforcement is presented only in certain occasions of the desired behavior). There are four types of partial reinforcement: fixed ratio schedule (the reinforcement emerges after a specified number of responses), variable ratio schedule (the reinforcement emerges after a random number of responses), fixed interval schedule (when the reinforcer is applied first time only after a given period of time) and variable interval schedule (when the reinforcement is applied after a non-predictable period of time).
The researchers have explored different aspects of the impact of fixed and variable schedules in operant conditioning. In the work of Suboski & Indiana (1965), the effects of fixed-ratio and variable-ratio scheduled reinforcement on rats were compared. 8 rats in the experiment were on fixed-ratio schedule 16:1 and 8 rats were on variable-ration schedule 16:1 during 21 days. 60 reinforcements per day were provided for both groups for bar pressing. Suboski & Indiana determined that there were no significant differences between the response rates, post-reinforcement pauses, inter-responses pauses and rates while responding between these two groups. The researchers also applied switching schedules, which led to quick increase of overall response rates and to decrease in post-reinforcement pauses for the group which switched from fixed-ratio to variable-ratio schedule (Suboski & Indiana, 1965). For variable-ratio group, switching to fixed-ratio led to negative correlation between post-reinforcement pause and the number of bar presses required in the preceding ratio (Suboski & Indiana, 1965).
An in-depth research was performed by Mazur (1986), who explored the indifference point in choosing fixed or variable schedule of reinforcement for pigeons with the help of adjusting the schedule of reinforcement and delays between stimuli to the conditions and choices of the pigeon; the equivalence rule describing the trends of indifference points with regard to schedule ratio and delay conditioned was formulated (Mazur, 1986).