Four ring-tailed lemurs participated in this study. I used one young male (Vide) one young female (Lilly) and two older females (Bi and Ester). 

I presented the lemurs with all the possible binary combinations of 12 foods (apple, melon, sweet potato, carrot, beetroot, cucumber, eggplant, caggage, pumpkin, tomato, meal worm and egg. I presented a lemur with two pieces of different foods and then they made a choice for which one they wanted. I repeated all binary combinations 10 times and this means that each lemur made 660 choices. 

The lemurs learned to come into a smaller corridor in their enclosure and they made a choice from a shelf.