Plesker, R., Herzog, A. 2001. Prima hedrons, puzzle feeders and television as environmental enrichment forcaptive African Green Monkeys. Primate Eye 74, 4 (Abstract).

The prima hedrons had no significant effect on any of the behaviours investigated. These were infrequently used as objects for playing, resting or observation. In contrast, the puzzle feeders were frequently used by the youngsters and avoided by the adult males. The access to television (mainly nature films) enhanced the observation behaviour of the whole group for a short time. Again, the adult males, but also the youngest offspring did not appear to be interested. Stereotype movements in one adult male increased during the offer of objects.