Effect of use on the elective appearance of an instrumental reaction in dogs.

Dogs were used to elaborate two instrumental reactions – flexing the left or right forepaw respectively to pull a dish of food within reach of its mouth. If both paws were simultaneously fixed to levers, dog was faced with a choice between two reactions. In preliminary trials right paw preference was strong despite equal effectiveness of the left paw in obtaining the food. The aim of the experiment was to alter this right paw preference by forcing the use of the left paw. Each ten training trials were followed by a test with free choice of paws. According to the probabilities PL = 0.8 and PR = 0.2, a random table was used to determine the order of forced use of the right or left paw. In all, 1,000 training trials and 100 tests with free choice were carried out on each of three dogs. According to the training program in every 100 training trials the left paw was made to display the reaction a total 80 times, the right paw, 20 times. Absolute alteration in the preference occurred even though in all trials with free choice both forepaws were equally effective in obtaining food. Thus, use as well as condition of reinforcement is important in instrumental conditioning.