Unseen qualities such as states of mind (any condition which is significantly different from a normal waking state e.g. as a result of fear or anxiety) were not used in this type of study even though we know that the mind plays a part in all advanced animals' behaviors. Behaviourism states that behaviour can be studied without knowing what the physiology of an event is, and without using theories such as that of the mind. By definition, all behaviour can be observed.