 According to Dretske, an experience has its content fixed by the biological, phylogenetically determined function of the system (or combination of systems: (1995), 22) of which it is a state. The function of the system is to provide information: for instance, the function of the auditory system is to provide information about pitch, intensity, timbre, and direction of sound, and it does this by occupying different states corresponding to different values for each of these properties. The different states are all the different auditory experiences that a given system is capable of being in. The same main idea is developed by Ruth Millikan, who focuses on mental content generally rather than on experience content per se.