Affect is the displaying and experiencing of emotion. It includes positive dimensions such as joy, interest, and contentment, as well as negative dimensions of emotion such as disgust, fear, and anger. Affect is a very rapid response to internal (e.g., thoughts, memory) or external stimuli (e.g., other people). It is different from mood, in that it is more momentary and observable by others, whereas mood is longer lasting and constitutes a symptom that patients may report (e.g., depression). Affect can be observed from facial expression, gestures, posture, and speech (e.g., word choice, tone, rate).