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methods for delivering sound to fetus (three of them)?
Airborne technique: Sounds
created at some distance from the mother, Sound waves travel through air
to reach mother (and fetus!), Typically, sound created with loud
speakers within a few feet of mother
Air-Coupled technique: Stimulation applied directly to mother's abdomen
through speaker, Speaker usually isolated from mother's abdomen by
foam/rubber ring, Advantage over airborne is that it transmits sound
more directly to mother and minimizes sound pressure loss
Vibroacoustic technique: Device like tuning fork or voice simulator
(electronic larynx) transmits vibrations directly to the mother's
abdomen. Designed to propagate sound pressure more efficiently through
tissue and fluids
What are the methods for Determining Detection of Sound by Fetus (two of them)?
Look for MOTOR response:
Startle responses, other changes in fetal movement corresponding to onset of sound.
ly measure through visual or tactile methods, but can now be measured through
ultrasound. Reports of mother not generally used - mother's reports are
less reliable, and mother is less sensitive to movement than newer
Look for PHYSIOLOGICAL changes:
Typically, changes in heart rate are observed
ly used stethoscope and watch, but can now use cardiotocography (electronic fetal monitor).
IN AMPLITUDE: When sound waves
pass from air to liquid medium there is a loss of strength of
vibrations, this occurs because the sound wave reaching the fetus are
lower in intensity than they were originally - they've been attenuated.
What are the frequency differences in attenuation?
FREQUENCY: LOW frequency sounds below about 300 Hz will have little or no attenuation (little or no loss of sound energy)
HIGH frequency sounds have much more attenuation and are much less
likely to make it to fetus with enough energy to be heard over internal
Clarity of Sound Reaching Uterus through Speech and is it clearly heard?
Querleu et al (1988)
Participants asked to recognize various phonemes (vowels and consonants) from intra-uterine recordings
Both male and female voices clearly heard, though voices lost
"crispness," making many phonemes (especially consonants, which contain
higher frequencies than vowels) unrecognizable.
Participants recognized 30% of phonemes, and only 22% of the consonants
Most of the time it is not clearly heard
Clarity of Sound Reaching Uterus through Orchestral Music and is it clearly heard?
Studies performing intra-uterine
recordings of orchestral music. Attenuation of higher frequencies made
music sound more muffled and less bright or brilliant than original
recording. However, for music played at normal listening volumes, rhythm
and basic timbre come through and tunes are generally easy to identify.
Fetuses respond with faster movements to more stimulating music and with slower movement to more sedate music.
However, the likely explanation is that the fetus is simply responding
to very broad acoustical differences between music (e.g. loudness,
tempo) and NOT responding to different "styles" of music.
Does maternal response to music affect the fetuses response ?
Played classical/pop songs to mother via headphones
Fetuses showed increase in motor activity and decrease in respiratory
movements when mother listened to 25 minutes of classical or pop music
(compared to control
group with no music). Effects were stronger for genre of music that mother reported she preferred.
Zimmer: the mother's liking of a particular genre may affect her
physical state (e.g. state of relaxation) and this may be causing the
lingering effects of heartbeat sound exposure on infant ?
newborns are COMFORTED by sounds of heartbeat of about 72 bpm because it is a familiar sound from the womb.
Salk: Newborns who heard heartbeat for 4 days after birth cried less and
were likely to gain weight than newborns in control group. However
studies did find like other tools such as the metronome gave the sma
result as the sound of the heartbeat. One possibility is that rhythmic
sounds at that tempo just happen to be comforting to a newborn. Another
possibility is that fetal exposure to resting heartbeat made them
relaxed during prenatal development, and this relaxation has now
generalized to other slow rhythmic sounds as well.
Newborns prefer music they were
exposed to during prenatal development. Newborns became more alert with
decreased heart rate and movement when hearing the theme song of a TV
show their mother watched every day during her pregnancy.
Rauscher et al were cautious in
drawing any conclusions, media got results and concluded that listening
to Mozart highers the infants IQ. Did not mention that this was not true
most of the time and it did not last long at all. Explanations in
findings were ignored. The media GREATLY overextended the original
findings. The popular idea of the "Mozart Effect" has not been
Newborns/infants at orienting sound? accuracy? improvement?
2 to 4-day old newborns will turn
their head toward sound of a rattle. Some can even track and follow a
moving sound (though they aren't too accurate!).By about 6 months, they
can get within 4-6 degrees of sound source location. At 7 months, they
can reach for a sound in the dark using only their sense of hearing to
Newborns/infants at orienting sound compared to adults?
However, infants' ability to
localize sounds not as good as adults. One possibility is that their
small heads make interaural timing and intensity differences hard to
detect. Their head also doesn't make much of a "sound shadow" that
reduces intensity of sound wave at far ear. They also spend a lot of
time on their backs - our head and ears work best at sound localization
when we are STANDING.
Fetuses exposed mostly to low frequencies (due to attenuation characteristics of mother's body)
Newborns are better at discriminating high frequencies. Olsho (1984)
5 month old infants better at discriminating sounds over 4000 Hz than
adults, but are WORSE than adults for lower frequencies (2000 Hz and
IT IS POSSIBLE.
Kessen: Taught infants to sing pitches and judged their pitch accuracy.
On averge infants were on the same pitch 70% of the time and when they
DID miss, it was because they just hadn't transitioned to the next pitch
yet - they were still singing the previous pitch.
EEG/ERP study with infant (2, 3, 4 month olds) vs adult processing of pitch differences
3 and 4-month olds had responses similar to adults, but 2-month olds were very different.
3 and 4-month olds had a "mismatch negativity" (MMN) response 200ms
after onset of oddball tone, followed by a positivity around 300ms.
Infants at 2-months did not.
Explanation: There is a developmental transition somewhere between 2 and
4-months of age in the way pitches are processed in the brain.
Possible explanation: progressive myelination occurs in infants' brain.
The slow-wave response of 2 month old may change to fast adult-like
response as the process of myelination takes place.
What is habituation and how can we use it with infant research on melody perception?
Chang and Trehub:
This is decrease in response to a stimulus after
repeated presentations. We can use it with infant research on melody
perception: When researchers played scrambled version of original
melody, infants' heart rate decreased (i.e. this is a new melody!). When
researchers played an exact transposition of original melody, infant's
heart rate did not decrease (i.e. nothing new here!)
Chang and Trehub
Suggests infants don't pay attention to actual pitches, but instead to
contour of melody, and most infants can detect difference between two
melodies that differ in only one pitch, if it changes the contour.
However, infants usually cannot
discriminate between two melodies with same contour, even if there are 3
or more different intervals between melodies. Suggests that melodic
contour and relative intervals between pitches of melody seem to be much
more important than the absolute pitches of the melody.
Infants process rhythms similar
to how they process melody - they recognize a particular rhythm as being
the same even when the tempo changes. Recognizing a particular rhythm
doesn't rely on the absolute TIME between the rhythmic elements, but
instead on the relative timing between elements.
absolute time differences between beats or relative time differences between beats are important?
Phillips-Silver & Trainor
During presentation of unaccented rhythm, researcher bounced child on
either every second beat or every third beat - allowing child to "feel"
accent. They are important, let the infant know the cues to pick up the
perception of accents in rhythm (possible for infants? how do they "pick up" the
accents? body feelings? visual cues?
Perception of accents in rhythm
ARE POSSIBLE FOR INFANTS. Infants bounced every 2 beats preferred rhythm
with auditory accent every two beats. Infants bounced every 3 beats
preferred rhythm with auditory accent every three beats.Infants who were
blindfolded when bounced, still sensed accents, but did not bounce when
viewing someone else doing it. VISUAL CUES ARE NOT ENOUGH TO ALLOW
INFANTS TO ENCODE RHYTHMIC ACCENTS.
music memory in infants, can they remember pieces they haven't heard in a while?
Saffran et al (2000)
Experimental group spent significantly more time listening to the novel
(unfamiliar) pieces (10/11 infants chose unfamiliar music)
Control group (who hadn't listened to ANY of the pieces previously)
showed no preference for either the familiar or novel pieces (7/14
listened to "familiar" pieces more, 7/14 listened to novel pieces more)
Practical benefits of ID singing:
Increases attention (just like ID speech)
Reduces body movement (making feeding and diaper changes easier)
Calms infant, reduces crying, and brings about sleep more easily
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