I believe that there is no easy answer to this question. Rather I suppose that intelligent behavior emerges from many simple, modular processes.
I just wrote my current model of intelligence down. "current", because I evolve it continuously and adept it to newly gained knowledge. Even if I have some basic knowledge of artificial intelligence; I may not have the deepest knowledge of theories of mind, yet. Therefore I do not claim that my model has to be correct. However, it might be thought-provoking impulse. Particularly because I try to show the totality instead of grabbing one exact area and saying that this all what there is to intelligence.
The picture gives a first overview over the elements which I think are crucial. The connections show the collaboration between the elements and the information flow. It might look a little bit chaotic, but as already said, I do not think you can reduce intelligence to one simple formula.
In the following I will begin with the central part, the representation. In my opinion some form of representation is needed for intelligent behavior, because it is the only way one can try what the result of some actions might be without doing this actions physically. I would divide the representation into an internal and an external representation. For example if you close the eyes you will always have a vague idea where which objects were before you closed the eyes. But in general you will not be able to remember all the details. With closed eyes (excluding other senses) you can use only the internal representation which is already highly abstract. This internal representation will be supplemented with many details, which are the external representation, if your eyes are opened.
This leads us directly to sensory inputs. These are all sensory perceptions which the body perceives. Probably the external representation will be build up by these. Because everything we sense is coded in neuronal signals, the external representation is in fact also internal. But I call it external representation, because without the information from the environment it cannot reach it full detail level. The abstraction of these sensory inputs creates the internal representation, which can persist without continuous input of senses and may be manipulated in your mind to explore different possible actions.
Another important part of intelligence seems to be abstraction. Not only the sensory perceptions will be abstracted, but also it is possible that new abstraction are made based on the internal representation. Probably is the memory important for this, because the skill to abstract makes uses of experiences.
The memory means for me the totality of all information which is stored for some time span. It makes learning and remembering possible.
Another important point is the operation search. This "module" searches based on the current representation for different possibilities to act and rates them. Afterwards it will causes a appropriate action to be executed.
These actions will be executed by the output. These are in general all muscle movements: grasping something, going somewhere, speaking something.
To make it possible to evaluate the consequences of operations or actions, some form of prediction is needed. For such an operation the internal representation will be changed to reflect the most probable consequences based on the current representation and the memory of earlier experiences. In this way it is possible to explore action possibilities. Of course, the memory is very important here, because the prediction of action consequences depends heavily on experiences.
By calculating the difference between such a prediction and the real changes in the external representation it is possible to learn. Either by abstracting these differences or may be also with some other method. It might be reasonable to introduce an own module learning for this. Moreover, because learning itself is a wide area in which research is done.
Least, but not last, we have the point motivation. Without the motivation to achieve something no goal-oriented acting is possible in my opinion. Therefore I believe this point to be very important.
This is my current thought model in a nutshell. I would appreciate critics, additions and agreement in the comment. May be this article is also some food for thought for one or another.