ACQUISITION OF STIMULUS-CONTROL WHILE INTRODUCING NEW STIMULI IN FADING

After establishing a discrimination between red positive stimulus and green negative stimulus [in pigeons], the lowest intensity colors that restricted all responding to positive stimulus were determined. Then, 2 new white lines differing in line orientation were each superimposed on one color and were increased in intensity. The color intensity was decreased and eventually eliminated. Probe stimuli consisting of lines against dark backgrounds were presented before each stimulus intensity change, and probe responding was used to assess control acquired by various dimensions of new stimuli during fading. The lines acquired control of responding while being introduced, and control was strenghthened as the colors were attenuated. Such an acquisition locus was attributed to starting intensity of the original controlling stimuli and was explained in terms of stimulus blocking. Using probes while introducing new stimuli enhanced the acquisition of control by new stimuli.