This is a study from 1986 on this topic:

Objective evaluation of a behavioral enrichment device for captive chimpanzees (Pan troglodytes)

M. Bloomstrand1,*,

K. Riddle3,

P. Alford3,

T. L. Maple2

Zoo Biology Volume 5, Issue 3, pages 293–300, 1986

There are many articles on chimpanzee enrichment and I hope this is a good place for you to start.

You can also have a look at this paper:

Tool use task as environmental enrichment for captive chimpanzees

Maura L. Celli, Masaki Tomonaga, Toshifumi Udono, Mikagu Teramoto, Kunimaru Nagano

Applied Animal Behaviour Science

Volume 81, Issue 2, 19 April 2003, Pages 171–182

Moreover, this journal -Applied Animal Behaviour Science-contains a lot of papers on the enrichment topic.

Thank you very much :)

Bloomsmith and her colleagues have done much work in this area, as noted above, and there are a large number of papers on this topic.

Bloomsmith, M. A., Alford, P. L. and Maple, T. L. (1988), Successful feeding enrichment for captive chimpanzees. Am. J. Primatol., 16: 155–164. doi: 10.1002/ajp.1350160206

There is also a nice literature on the effects of cognitive challenge as a form of enrichment. For example:

Yamanashi, Y. and Hayashi, M. (2011), Assessing the effects of cognitive experiments on the welfare of captive chimpanzees (Pan troglodytes) by direct comparison of activity budget between wild and captive chimpanzees. Am. J. Primatol., 73: 1231–1238. doi: 10.1002/ajp.20995

CLARK, F. E. and SMITH, L. J. (2013), Effect of a Cognitive Challenge Device Containing Food and Non-Food Rewards on Chimpanzee Well-Being. Am. J. Primatol., 75: 807–816. doi: 10.1002/ajp.22141

There is a huge literature on the subject, as earlier comments have made clear, but some of it is problematic, methodologically. For example, the usual design is the simplest: Before-After comparison (A-B), but better is A-B-A, to see if return to baseline or not. Further, most studies don't use comprehensive ethograms or activity budgets, but concentrate on a few (e.g.) dissipation of bad habits or enhancement of good habits. This does not allow for trade-off complications, e.g. increase in foraging may come at cost of socialising. Further, few studies consider the possibility that 'enrichment' may be stressful, e.g. adding food-vending devices that may increase rates of agonism. Finally, although the main independent variable (usually introduced objects) may be clear, the dependent variables may be less so. Are rates of behavioural output validated with regard to natural behavioural patterns?

there is a research conducted in Malaysia National Zoo on the effect of the enrichment activities.. the enrichment activities significantly impact the foraging behaviour, nest-building and observing.. refer to the link attached..

http://www.scopus.com.www.ezplib.ukm.my/record/display.url?eid=2-s2.0-40749151021&origin=resultslist&sort=plf-f&src=s&st1=md-zain%2cB.M&nlo=&nlr=&nls=&sid=796A576643BE9142B77A06FFE3920893.iqs8TDG0Wy6BURhzD3nFA%3a20&sot=b&sdt=b&sl=24&s=AUTHOR-NAME%28md-zain%2cB.M%29&relpos=20&relpos=20&citeCnt=5&searchTerm=AUTHOR-NAME%28md-zain%2CB.M%29