This is when a stimulus that was previously neutral (meant nothing to you) is paired with another motivating operation and now that stimulus itself creates an MO for the person and has the same value altering and behavior altering effects as the paired MO. In the past when you had to go to the bathroom and you saw a restroom sign you were able to go to the bathroom. Now that restroom sign may evoke your behavior of having to urinate even if you don’t have to in that moment.