You most likely paid attention to this question based on which stage of the perception process?

Selection

Explanation:

The perception process is a series of steps that include the selection of stimuli, the organization of that data, and the interpretation of it.

Selection is the first step, and it refers to deciding what to attend to, eventhough if that decision is unconscious or intentional.  

The attended stimulus refers to that one specific thing in the environment, such as this question, that we can choose to attend.

because the early people found out about it.