The auditory algorithms discussed above are based on extensive physiological data accumulated over decades of physiological and psychoacoustical experiments. While clearly much remains to be discovered in the auditory system, there are certain physiological experiments that are critical for the further development of the auditory cortical models. These experiments address: (1) the physiological bases of the multiscale representation in the cortex and midbrain structures; (2) the nature of the cortical microcircuits that give rise to the selective amplification of perceptual features.