The MAC cell

The MAC recurrent cell consists of a control unit, read unit, and write unit, that operates over dual control and memory hidden states.

The control unit successively attends to different parts of the task description (question), updating the control state to represent at each timestep the reasoning operation the cell intends to perform.

The read unit extracts information out of a knowledge base (here, image), guided by the control state.

The write unit integrates the retrieved information into the memory state, yielding the new intermediate result that follows from applying the current reasoning operation.