Cognition - The act or process of knowing including both awareness and judgment (Merriam-Webster, Collegiate® Dictionary).

The Cognitive process, includes the ability to perceive the stimuli from world around us through our senses (Vision, hearing, smelling et.), understands the meaning of the stimuli and store it in memory. Retrieve it and combine it with other information, and deciding upon appropriate action.

The traditional basic exercise that is used in research to measure the very basic cognitive function is called Reaction Time.

The person sits in front of a light source, and has a button in front of him, instruction is given to "Press the button as fast as you can when the light turned on".