Hearing develops through the last trimester, and near-term fetuses can tell frequencies apart and remember sounds that recur. The ceiling on the evidence was the retention interval: a few days after birth and no further. So one team played a descending piano melody twice daily through weeks 35 to 37 of gestation, then came back six weeks later with that melody and an ascending one. Would anything still register?
Six weeks later the heart gave it away. All the infants showed a significant heart rate change to the melodies. In the exposed infants, the descending melody produced a twice as large as the one produced by the ascending melody, and twice as large as either melody produced in the 25 . Three weeks of prenatal exposure was still measurable at one month old.
Human hearing develops progressively across the last trimester of gestation. Near-term fetuses can discriminate acoustic features such as frequencies and spectra, process complex auditory streams, and remember sounds that recur often. The limit in the literature was not whether they remember but for how long, since existing data reached only a few days past birth.
This study set out to extend that interval. Experimental fetuses were given precisely controlled exposure to a descending piano melody twice daily during the 35th, 36th and 37th weeks of gestation. Six weeks later, with the infants a month old and in quiet sleep, the researchers recorded cardiac responses to that melody and to an ascending control melody.
The pair of melodies is the design’s strength. Their contours were precisely inverse while their spectra were similar and their duration, tempo and rhythm identical, which left their almost the same. Any difference in response therefore had to come from the direction of the tune.
All infants showed a significant heart rate change. In the exposed infants the descending melody evoked a cardiac deceleration twice as large as the one produced by the ascending melody. It was also twice as large as those produced by both melodies in the 25 control infants. So three weeks of prenatal exposure to one was still affecting the autonomic nervous system six weeks later, extending the known retention interval from a few days to six weeks. Read the measure for what it is: a tuned bodily response in twenty-five infants, not a memory anybody could recall.
wat. A descending piano melody heard in the womb still slowed a one-month-old’s heart twice as much as the same tune played upward.
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The control melody is what makes it convincing. Inverting the contour while holding spectrum, duration, tempo and rhythm nearly identical means the infants were responding to the shape of the tune and not to its sound in general.
How do we know?
Granier-Deferre and colleagues gave fetuses controlled exposure to a descending piano melody twice daily in weeks 35 to 37. Six weeks later they recorded cardiac responses of 25 exposed and 25 naive infants in quiet sleep, to that melody and an inverted control.
What is still unknown
Twenty-five infants per group, with a measure that is a change in heart rate rather than anything the infant does. A tuned autonomic response is not a memory the child could ever recall.
Learn something?
Where to next
Is there a shape a melody has to have to get stuck?music
How does one word in a question plant a memory of something that never happened?memory
Why do we remember a long experience by only two moments of it?memory