Reduction of Sucrose Reward to Smaller and Nonreward Levels without Contrast Effects

Five groups of albino rats were trained in a straight runway for 44 pre-shift trials, 2 trials per day with a 3- to 5-min intertrial interval (ITI). Two of the groups (30-0 and 30-3) received 1 ml of 30% sucrose solution as a reward, two groups (3-0 and 3-3) received an equal volume of 3% sucrose, and one group (0-0) received no reward. During 20 postshift trials, three groups (0-0, 3-0, and 30-0) received no reward, and two groups (3-3 and 30-3) received 3% sucrose. Postshift trials were massed (10/day) with the same ITI as in preshift. The reward shift produced a direct relationship between the amount of preshift reward and resistance to extinction and no evidence of successive negative contrast whether the shift was to smaller or non-reward levels.