Response errors in conditioned discrimination

White rats were trained to escape an electric shock by jumping to one of 4 platforms, indicated by a white card. Then a tone was paired with the presentation of the shock. This resulted in the appearance of errors and an increase in time, which again showed a practice effect on repetition. The use of the tone alone again resulted in a slight increase in time and errors, reduced by repetition. In early extinction trials the time and the number of traversals of the grid before jumping increased, but errors did not. The animals eventually failed to jump. "The addition of the stimulus to-be-conditioned and the withdrawal of the conditioned stimulus seem to disorganize the learned response and to make relearning necessary. The need for relearning and certain difficulties in applying conditioning terminology indicate the hierarchical nature of the habit and the essential similarity to habits studied with the usual discrimination methods."