Reinhardt, V., Reinhardt, A. 1992. Quantitatively tested environmental enrichment options for singly-caged nonhuman primates: A review. Humane Innovations and Alternatives in Animal Experimentation 6, 374-384.

Compatible companionship has a therapeutic effect on behavioral disorders, providing long- term stimulation of a great variety of species-typical social behavior patterns. Inanimate objects have little impact on behavioral disorders, but some of them provide appropriate means for the expression of species-typical activities. Foraging devices considerably extend foraging times while temporarily ameliorating behavioral disorders. More space is less likely to enrich the environment than are social stimulation and increase in cage complexity. Future research will have to take dependent variables such as age, gender, and the period of time the subject is exposed to the enrichment at the moment of data collection more systematically into account to allow an integrative, comparative evaluation of different enrichment options.