Usability is a beautiful concept, more than the term and its use, or abuse, make us think.
The word comes from the Latin uti use, simple then.
Not really, because the meaning of this term is often neglected or reduced to its daily meaning of using something, the habit of the act or being the usual thing itself.
How is cognitive load monitored? Skin conductance (GSR), eye-tracking and electroencephalography (EEG) investigate the balance between usability of the interface and information complexity.
From the facial expressions Ekman and Friesen have outlined the basic emotions, and by reading them with Face Reading it is possible to have marketing ideas.