Hydrophones implanted inside the intact amniotic sac recorded sounds available to fetal lambs. Unlike recordings made from outside the intact amnion in human subjects, sounds produced at levels similar to normal conversation from outside the ewe were picked up without masking by maternal cardiovascular sounds. Noises from inside the mother were intermittent and linked to her activity.
Summary. The midbrain areas that yielded calling with the smallest currents were within the nucleus intercollicularis and isthmi complex. Natural calls were evoked, but they could not be localized. Rather, some calls were more easily evoked than others.Calling has been elicited with small currents from the midbrain of a variety of birds such as redwinged blackbirds J 4A getaius phoeniceus , chickens, Java sparrows Padda oryzivora 5 and in Japanese quail Coturnix coturnix japonica 6'7. However, a detailed threshold survey of the midbrain of the latter species is lacking. To date, there is general
Two experiments were carried out to test the hypothesis that prenatal sound stimulation has postnatal effects in sheep. In the first, a group of domesticated ewes was stimulated with an alien sound and their lambs' response to the same sound was compared with that of lambs born to unstimulated mothers. In the second experiment a group of Soay ewes was stimulated with an alien sound and a comparable group stimulated with a series of bleats. Lambs born to these ewes were tested with both sound stimuli. Lambs tested with sound patterns which they had not heard before birth showed more heart rate acceleration during or after stimulation than did lambs tested with sounds which could already have been familiar. This difference was much greater in the response to alien than to species sounds, and it was less consistent on the first than on subsequent trials. There was also a tendency for a marked change in the respiratory pattern, evidenced as a sigh, to occur in response to familiar sound.
The sound environment of the foetal lamb was recorded using a hydrophone implanted a few weeks before term in a small number of pregnant ewes. It was implanted inside the amniotic sac and sutured loosely to the foetal neck, to move with the foetus. Results differ from those reported earlier for the human foetus: sounds from the maternal cardiovascular system were picked up only rarely, at very low frequencies and at sound pressures around, or below, the human auditory threshold. Other sounds from within the mother occurred intermittently and rose to a high sound pressure only at frequencies above about 300 Hz. Sounds from outside the mother were picked up by the implanted hydrophone when the external sound level rose above 65-70 dB SPL, and the attenuation in sound pressure was rarely more than 30 dB and, especially at low frequencies, usually much less. However, attenuation due to the transmission of sound through the body wall and other tissues tended to change from time to time. It is concluded that the foetal lamb's sound environment consists of (1) intermittent low frequency sounds associated largely with the ewe's feeding and digestive processes and (2) sounds such as vocalisations from the flock, human voices and other sounds from outside the mother.
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