This paper reviews some aspects on the perceptual processes involved in the categorization of natural sounds, especially in birdsong. Different models have been proposed to account for the simple filtering observed at the peripheral level to the recognition processes, revealed through behavioural responses. Some studies have shown that neurons in some of the motor nuclei (high vocal center) in the brain are specialized towards precise species-specific characteristics, even the bird's own song. These results indicate a high level of integration, but little is known about intermediate levels. Studies of the perception of natural songs by starlings show that many neurons in field L are selective towards particular features of the songs. Neighbouring neurons tend to show complementary or similar selectivities, determining areas of response. Such studies emphasize the importance of combining ethology and neurophysiology, and of the use of natural sounds to test neuronal selectivity.