Learning by aged monkeys on the SOSS 2-Square task across both stimulus manipulation conditions as well as increased ITI conditions. The data represent the last 5 sessions given for each condition. The bold black line is the average performance for the 6 aged animals trained in this manner, represented individually by the narrow black lines. AG7, 11 and 16 received the N/NR condition first and the F/R condition second, whereas AG17, 18 and 19 received the F/R condition first and the N/NR condition second. *, significant difference from the standard 5s ITI condition; †, significant difference from Condition 1 and Condition 2 (all p's < 0.05). Data points are mean ± SEM.