ACOUSTIC STRUCTURE OF VOCALIZATION AND STAPEDIUS MUSCLE-ACTIVITY DURING VOCAL DEVELOPMENT IN CHICKENS (GALLUS-GALLUS)

The link between stapedius muscle activity and acoustic structure of v ocalization was analysed in cocks of age 20-30 to 90-100 days old. The results show that stapedius muscle activation depends on the acoustic structure of vocalization and changes during vocal development. This dependence was observed in spontaneous calls and in vocalizations elic ited by stimulating the mesencephalic ''calling area''. In 30-day-old cocks stapedius muscle EMG response is never associated with vocalizat ions with an acoustic energy content which is always distributed at fr equencies higher than 2000 Hz. The coupling between vocalization and s tapedius muscle activity begins later, when birds produce vocalization s with acoustic energy shifted towards lower frequencies. Overall, sta pedius muscle activity is related to a bird's production of high ampli tude low frequencies. These results support the hypothesis that the pr imary role of the stapedius muscle during normal vocal development is to dampen the amplitude of low frequency energy that reaches the cochl ea during vocalization.