Final answer:
The false belief test is used to assess theory of mind in both humans and primates, indicating the understanding that others may have beliefs different from one's own.
Step-by-step explanation:
The type of test used to determine if a person or primate possesses theory of mind (ToM) is known as the false belief test. This test is a cornerstone in developmental psychology, especially when studying the cognitive development of children and the potential for cognitive abilities in non-human primates. In children, the false belief test allows researchers to assess whether they understand that others can hold beliefs about the world that are incorrect, which signals a development in theory of mind. Similarly, such tests are applied to primates to see if they display a rudimentary understanding of others' mental states. A classic cognitive experiment by Wolfgang Köhler with chimpanzees demonstrated their capabilities for abstract thought by showing they could problem-solve by stacking boxes to reach a banana, showcasing a level of insight and planning.