Extinction of a Discrete-Trial Bar-Press as a Function of Percentage Reinforcement,Reinforcement Cue,and Manipulandum Condition

6 groups of 12 albino rats received 80 acquisition trials, defined as 12 bar-presses, with sucrose reward. Two groups received 100% reward; four groups received 50% reward, half with a dipper click on all trials (50C), half with a dipper click only when reinforced (50C-NC). 3 of the 6 groups had the bar present during the ITI, 3 did not. During extinction half of each group received the dipper click, half did not. During extinction the 50C-NC groups were significantly more resistant to extinction than the other 100% and 50% groups, which did not differ significantly. Results were discussed in terms of a discrimination hypothesis of secondary reinforcement.