Excitation patterns in the starling cochlea: a population study of primary auditory afferents.

The excitatory effect of different test stimuli was quantified in a large sample of primary auditory units of the starling. In order to construct an excitation pattern, the level of excitation in many single units in response to a specific test stimulus was plotted as a function of their characteristic frequency (CF). The effects of stimulus frequency and stimulus sound-pressure level on the shapes of the excitation patterns were characterized by measuring excitation patterns in response to 33 different test stimuli which covered a range of frequencies (0.125 to 2.0 kHz) and sound-pressure levels (20 to 90 dB SPL). In contrast to the mammalian situation, excitation patterns in the starling showed a systematic asymmetry with the high-frequency side being, on average, twice as steep as the low-frequency side. In addition, the sound-pressure level had no systematic effect on the symmetry or on the high- and low-frequency slopes of the flanks of the excitation patterns. Thus, the nonlinear growth of excitation with increasing sound-pressure level that is typical for the high-frequency flank of mammalian excitation patterns, was not found in the starling. The differences in mammalian and avian excitation patterns are probably related to systematic differences in tuning characteristics of the respective hearing organs.