Anderson, J. R., Visalberghi, E. 1991. Primate psychological well-being: A comparative approach to environmental enrichment for captive primates. Applied Animal Behaviour Science 30, 195 (Abstract).

The presence of woodchips and especially the introduction of [unspecified] objects, reduced general locomotor activity in the capuchins; however, the objects had no such effect on the lemurs, and the provision of woodchips plus grain almost doubled their rates of locomotion. ... 'Foraging' behavior occurred in the woodchips condition and peaked when grain was added in both species, but the capuchins foraged up to 20 times more than the lemurs. Object-manipulation was 7-20 times more frequent in the capuchins than the lemurs. Both species showed less interest in dull-coloured objects than bright coloured objects.