Fetal Development

Historical Development of Research

One of the earliest books about fetal development in the context of music was published by the German psychologist William Preyer in 1885: Specielle Physiologie des Embryo (Special Physiology of the Fetus), with a separate chapter on “Die Fünf Sinne vor der Geburt” (“The Five Senses Before Birth”). Preyer was certain that the fetus could not hear sounds. However, in 1925, Albrecht Peiper conducted experimental studies with an automobile horn and refuted the thesis of the fetus's “deafness.” However, in recent decades, technical developments such as ultrasound, photography in utero, and medical instruments that can measure body movement and the heartbeat of the fetus have improved research into the behavior of fetuses and newborns (mainly conducted by developmental psychologists, behavioral neurobiologists, and music psychologists).

Methodologically, it is difficult to distinguish between a direct reaction from the fetus and indirect reactions through the mother, because the fetus is connected to her anatomically although not sharing all of her physiological states. Furthermore, it may be that the fetus perceives sounds but does not react to them. Sophisticated research about correlations between fetal acoustic experiences and musicality or acquisition of language is still required.

Characteristics of Acoustic Perception

Starting with the 20th week of pregnancy (of a total of 40 weeks), fetal reactions to acoustic stimuli are traceable, but with a latency. With 25 weeks, reactions begin immediately. At this time, the fetus reacts to sounds, detectable via fetal body and breathing movements or changes in heartbeat. Amniotic fluid inside the middle ear before birth transmits the sounds. By the 28th week of pregnancy, the inner ear is fully functional. From this stage onward, acoustic stimuli lead to consistent responses. Thus, the fetus can hear during the last trimester of gestation but is not able to localize sound sources. The ability to distinguish between different sounds continues to develop during this time. In the 36th week, the fetus is able to distinguish between two tones with an interval of an octave.

Noises from eating and drinking, the stomach and bowel, the cardiovascular system, heartbeat, and body movements such as walking, dancing, or running are acoustic signals from inside the mother's body that can be heard by the fetus. The loudness of these noises has not been clearly defined. Some authors describe it as very noisy (72–96 decibels [dB]); others measured approxmiately 30 to 50 dB in nonpregnant women and after delivery. Acoustic stimuli transmitted from outside the uterus are attenuated by about 30 dB because of the abdominal wall and the womb: high frequencies beyond about 2 kilohertz (kHz) are inaudible; moderate frequencies, which are relevant for speech and music, are slight; and low frequencies [Page 466]below about 300 hertz (Hz) are attenuated only very slightly. The mother's voice is the best-heard stimulus because the sound is transmitted via her bones; in contrast, a newborn cannot recognize its father's voice.

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