Research task. Deaner et al. (2006) have performed one of the most complete literature revisions on intelligence study in non-human primates. In the review, the authors differentiate between nine paradigms and within the paradigms up to thirty various procedures. It is also widely accepted that the types of problems may be i) well defined vs. ill defined and ii) novel vs. familiar. A combination of these two oppositions provides four types of possible problems: well defined and novel, ill defined and familiar and so on.

We suggest to also differentiating between a "task to solve a problem" and a "research task". We are not going to say that the two task types are mutually exclusive. Still there are somewhat different notions that underlie the task types.

The core of a typical task to solve a problem is, a problem that is clearly and unambiguously given. To take an example from experiments with apes, a chimpanzee is hungry (often because of the will of the experimenter), and it has to get the food that is out of its reach. There is here a problem (hunger) and, what is very important, the reward for solving of the problem.

At the basis of a typical research task, there is a need to understand, to grasp, to discover a principle of work, of functioning of something. Thus, a research task by the very nature of it has to include an element of discovering something what earlier was subjectively unknown.

Many experiments that have become classics of behavioral science included a research task into the experimental plan. In the experiments of E. Thorndike (1911) with his puzzle box, a cat was tested if it can understand the functioning of the box to solve the problem (to get out of the box), although it did not come to understanding of the box functioning and showed a sort of trial and error learning. R. Yerkes (1916) forced the apes and monkeys understand according what principle they can get food. The animals have to grasp an abstract idea "first at the left end" to solve the problem (to get the food). The famous DONALD+GERALD problem (Newell, Simon, 1972) contains much of research task in its structure because a subject has to not only discover unknown numerical