We have periodically compared the cognitive capacities of adult tamarins to children so that we have a
sense of where the adult monkeys stopped in terms of their development of cognitive capability. We first
tested object permanence (2003), or the ability to represent an object once it has disappeared, and have found through these comparisons that they maintain object permanence once an object has disappeared and can accurately find the object among 3 hiding places.
The next test was to see if the tamarins view local details or can easily group them together to see the global form (2006), an ability that children acquire slowly and end up preferring global shapes by age 6. This quality, a bias toward
global organization, is not one shared by adult tamarins. Tamarin monkeys do not prefer global shape to local
features, rather they look at both levels of object detail equivalently (global-local comparison).
We pursued this idea further to see whether tamarin monkeys readily employ gestalt principles of grouping to make it easier to find an odd item in a set of 4 items (2014). In fact, adult tamarins do not immediately use gestalt grouping principles to organize items into shapes or groups, rather they tend to look at features independently. These two features are comparable to the limitations seen in the perceptual processing of people with autism.
Children at age 3 can learn to sort items into categories utilizing a single dimension but then have trouble switching to sort them by a different dimension. By 5, children show an ability to readily switch between dimensions when sorting cards, a developmental phenomenon that has been studied extensively. We have also found that adult tamarins can form categories and can switch to other dimensions, like first sorting by color and then, with the same cards, sort by shape and ignore color. This indicates that their thinking about rules of organization is comparable to a child over the age of 5 (poster presentation, 2017; recent 2022 publication in Journal of Comparative Psychology).