In research on the neural mechanisms for the processing of biologically important sounds such as species-specific sounds and sounds produced by prey and predators, it is necessary to study responses of central auditory neurons to biologically important sounds, information-bearing elements (IBEs) in them, and tone bursts. The tone bursts or constant-frequency (CF) components can be an IBE in many species of animals. Information-bearing parameters characterizing these sounds must be systematically varied, and tuning of neurons to individual parameters must be studied. The measurement of a tuning curve must be performed not only for excitatory responses, but also for inhibitory and facilitative responses, if any. The selectivity of a neuron to a particular type of sound must be tested for whether it is level-tolerant. Responses to complex sounds can probably be explained on the basis of those to IBEs and tone bursts, so that the use of the tone bursts, even though they are not IBEs, is as essential as that of the biologically important sounds.