Relative to the laboratory and farm setting, it appears that there are a limited number of research articles that have tested cognitive enrichment in zoos with definitive and measurable results. In a review of enrichment in nonhuman primate captivity, there were some mixed conclusions. It was found the puzzle box feeders increased foraging time for various species, a behavior which can be correlated with a decrease in aggressive and abnormal behaviors. However, in some cases there were no observable changes in its effects, and even an increase in aggression over competition for the puzzle box. There is evidence of a successful cognitive enrichment technique in one zoo where the chimpanzees were required to use various tools in feeder contraptions in order to replicate potential instances in their natural environment. The study was set up with different levels so they could slowly learn the techniques, so as to not discourage the chimpanzees. These specially designed feeders increased tool-using behaviors, while reducing abnormal and self-directed behaviors. The authors, however, do admit there were not many abnormal behaviors to begin with from this small sample group (n=5). Research has found that there is a need for additional cognitive enrichment in aquariums for cetaceans and pinnipeds that goes beyond animal training. Examples include encouraging increased choice, allowing additional control over their environment, and promoting more under-water problem solving devices and tasks.