Opposed to this is the theory of operant conditioning which was fist introduced by the ameri- can psychologist and behaviourist B. F. Skinner in the 1930s. Based on Edward L. Thorn- dike´s “trial-and-error learning” he developed the Skinner-Box to study the behaviour of ani- mals in a controlled environment. This laboratory instrument can be described as a chamber that includes at least one bar or key that the animal can manipulate. Skinner placed a rat in that box and as soon as it accidentally hit the bar food was provided as reinforcement to the animal. After repeating that procedure for several times the rat began to intentionally hit the bar to receive food. The voluntary response was successfully strengthened by reinforcement. Subsequently he did the same experiment with a different rat but instead of reinforcing the response he used punishment (such as electric shocks) to weaken the voluntary response. To describe this phenomena he coined the term operant response (as a contrast to Pavlov´s condi- tioned response) to indicate that the subject operated on its environment in order to produce or reduce a particular effect (Myers 2008: p. 232; Feldman et al. 2005: pp. 162-173).