The Five Khandhas - Perception is one khandha

Saññākkhandha (perception) is real; it can be experienced whenever we remember something. There is saññā with every moment of citta. Each citta which arises experiences an object and saññā which arises with the citta remembers and 'marks' that object so that it can be recognized. Even when there is a moment that one does not recognize something citta still experiences an object at that moment and saññā which arises with the citta 'marks' that object. Saññā arises and falls away with the citta; saññā is impermanent. So long as we do not see saññā as it really is: only a mental phenomenon which falls away as soon as it has arisen, we will take saññā for self.
Topic 175