How can we tell when someone is deep in thought, or concentrating hard? How can we tell when they are not interested, or not paying attention? How does the body respond to a negative thought?
The eyes are key to understanding this category. When we are interested in something, often the eyes will widen to take in more information. Conversely, they narrow if the object is not quite understood and the mind is working to make sense. Whatever the response, an essential element is sharp focus. We go through our lives not fully focusing on things around us. When we do focus, it is because the unconscious brain registers the object as meaningful.
Other signs of cognitive engagement include: nodding of the head, quick (saccadic) eye movement, head tilt to hear more clearly and stroking of the lips, or the chin.