EXCITATION PATTERNS IN THE STARLING COCHLEA - A POPULATION STUDY OF PRIMARY AUDITORY AFFERENTS

The excitatory effect of different test stimuli was quantified in a la rge sample of primary auditory units of the starling. In order to cons truct an excitation pattern, the level of excitation in many single un its in response to a specific test stimulus was plotted as a function of their characteristic frequency (CF). The effects of stimulus freque ncy and stimulus sound-pressure level on the shapes of the excitation patterns were characterized by measuring excitation patterns in respon se 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 cont rast to the mammalian situation, excitation patterns in the starling s howed a systematic asymmetry with the high-frequency side being, on av erage, twice as steep as the low-frequency side. In addition, the soun d-pressure level had no systematic effect either on the symmetry or on the high- and low-frequency slopes of the flanks of the excitation pa tterns. Thus, the nonlinear growth of excitation with increasing sound -pressure level that is typical for the high-frequency flank of mammal ian excitation patterns, was not found in the starling. The difference s in mammalian and avian excitation patterns are probably related to s ystematic differences in tuning characteristics of the respective hear ing organs.