Habituation is the earliest and the simplest type of learning. It has been observed in the youngest of infants and across the animal kingdom. Learning can be defined as an enduring change in the behaviour of a subject that is attributable to a specific experience. Habituation describes the decrease in intensity of a subject’s response to an experience, or stimulus, when repeated. Habituation is a learned regulation of behaviour and must not be confused with the diminished response of a subject due to sensory adaptation or motor fatigue.