1. A neurophysiological investigation of hearing in herring (Clupea harengus) has been undertaken. Gross nervous or multi-unit activity and single unit activity have been recorded from the acoustic region of the medulla oblongata, using 5–20 μ dia. metal electrodes and micropipettes, respectively. 2. Nervous responses to pure tone stimulation were obtained for sound frequencies from 30 c/s to 4000 c/s at moderate intensities (up to 35 dB above 1μBar) and up to 8000 c/s at high sound pressure levels (50–60 dB). 3. Single units can be divided into two groups (a) units responding to frequencies up to 500 c/s, (b) units responding to frequencies up to 2000 c/s or higher. The response of the first group consisted of an increase in discharge rate above the “spontaneous” level. In the last group acoustic stimulation caused either an increase in discharge rate for high sound frequencies and a decrease for low frequencies, or vice versa. 4. The most sensitive single units had thresholds of -20 to -25 dB at their optimal sound frequency which for different units ranged from less than 100 to 1200 c/s. The threshold increased for higher frequencies. 5. A tentative audiogram is suggested. This indicates that the herring has a uniformly low threshold of -20 to -25 dB for frequencies of 30–1200 c/s, with a sharp increase in threshold to +20 dB for 3000 c/s, +35 dB for 4000 c/s.
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