Perception is the only way for subject to know external world. Different from traditional philosophy of perception that treats perception as a mysterious veil between subject and external world, perception in Floridi＇s philosophy of information is the interface between them and data provider. Floridi develops a praxical model of perception by integrating the method of levels of abstraction and action-based semantics. However, this model cannot solve the problem how causality and normativity can be bridged in perception process. With replenishment of Ruth Millikan＇s naturalistic sign theory, which divides function of sign into proper function, actual function, and intended function, we can explain how normativity emerges from perception process, and provide foundation for knowledge by combining naturalistic and constructivist approach.