Este binecunoscut faptul ca bebelusii nenascuti pot recunoaste vocile mamelor si pot distinge muzica de zgomot. Dar ceea ce aud ei de fapt, ramane inca neclar.

Oamenii cercetatorii de la Universitatea din Florida au mai adaugat o piesa la acest puzzle. Intr-o serie de experiente unice executate pe o oaie cu scopul de a inregistra cu exactitate ce fel de sunete ajung la urechea fetala, cercetatorii s-au sprijinit pe descoperirile anterioare, conform carora fetusii umani aud probabil mai bine frecventele joase decat cele inalte. Aceasta inseamna ca ei aud mai bine vocalele decat consoanele si sunt mult mai senzitivi la partea melodica a vorbirii decat la cea inalta, a afirmat Ken Gerhard, profesor de stiintele comunicatiei al universitatii.

In ceea ce priveste muzica, "ei vor auzi mai degraba sunetul tobei decat cel al vioarei" afirma Gerhardt care a condus cercetarea prezentata in numarul Noiembrie-Decembrie al jurnalului de Audiologie si Neuro-Ontologie.

Profesorul Anthony DeCasper de la departamentul de psihologie al Universitatii Greensboro, din Carolina de Nord, afirma ca rezultatele Universitatii din Florida nu sunt relevante pentru ca sunt obtinute din urechea interna, care se presupune ca ar inregistra sunetele exact cum feotusul ovin le-ar auzi. Descoperirile - rezultate din implantarea unui dispozitiv subtire in urechea interioara a unui fetus ovin care inregistreaza semnalul pe care urechea il transmite creierului - se potrivesc cu concluziile altor cercetatori, bazate pe studii mai putin invazive cu privire la feotusul uman, afirma el.

"Modul in care vocea mamei suna in uter ar fi ca si cum o persoana ar vorbi din spatele unei draperii grele" afirma DeCasper.

Cercetarea are de asemenea implicatii in ceea ce priveste grija fata de bebelusii prematuri. Maternitatile sunt in mod traditional locuri relativ zgomotoase, aprovizionate cu o serie de aparate sonore, cu conversatii umane si cercetatori precum Gerhardt, DeCasper si ceilalti sunt ingrijorati si ridica semne de intrebare despre modul in care sunetele la care sunt expusi bebelusii nascuti prematur le pot influenta cresterea in greutate.

Gerhardt afirma ca a inceput cercetarile despre auzul fetal ca raspuns la anchetele agentiilor legislative in vigoare si a Marinei americane. Amandoua institutiile sunt ingrijorate despre modul in care zgomote puternice, precum un foc de arma sau motorul unui vapor, pot afecta auzul bebelusilor ce sunt purtati de femeile insarcinate. Gerarhardt si Robert Abrams, un profesor emerit de obstretica si ginecologie de la aceeasi universitate, s-au decis sa cerceteze problema cu ajutorul unei oi deoarece experimentele altor cercetatori au demonstrat ca proprietatile de transmitere a sunetului la femeia insarcinata si oaie sunt asemanatoare. Experientele au relevat ca sarcina a temperat sunetele cele mai inalte. Chiar concertele rock nu sunt probabil destul de zgomotoase pentru a reprezenta o amenintare pentru auzul fatului, a spus Gerhardt. Cercetarea, care a primit mai mult de un milion de dolari de la Marina Americana, a contribuit la liniile directoare de siguranta a locului de munca ce limiteaza astazi durata de expunere la zgomot ridicat a femeilor gravide.

In cercetarea respectiva, Gerhardt si Abrahams s-au focalizat specific pe felul de sunete auzite de fatul ovin. Metoda lor a fost unica: au implantat un dispozitiv de inregistrare in interiorul urechii unui fat ovin, apoi au derulat 64 de propozitii inregistrate intr-o boxa in aer liber langa mama-oaie. Sunetele pe care dispozitivul amplasat in interior le-a detectat au fost inregistrate si derulate inapoi in fata a 30 de ascultatori umani in scopul de a stabili cat de mult si care portiuni ale frazelor au fost auzite de fat. Pentru a efectua comparatia, cercetatorii au plasat de asemenea un microfon in interiorul uterului oii si, in aer liber, au efectuat teste similare cu ascultatorii umani.

Rezultatele au fost surprinzatoare, cu cu o inteligibilitate a frazelor "de fapt mult mai mare decat noi anticipasem" afirma Gerhardt.

Partial, aceasta a fost neasteptat, pentru ca o mare parte din zgomotul care ajunge la fat vine de la vocea mamei sale, precum ar fi cel provenit din miscare, respiratie si procese digestive. Chiar si intr-o camera linistita, mama purtatoare poate fi un biotop zgomotos. De asemenea, feotusii nu "aud" pe atat de mult precum copiii sau adultii, pentru ca urechile lor sunt umplute cu fluid, afirma el. Mai mult, o mare parte din zgomot este transmis in urechile lor interioare prin intermediul vibratiilor din craniul lor. Ca atare, vocea mamei tinde sa fie cel mai dominant si totodata cel mai recurent sunet in interiorul sarcinii.

Ascultatorii umani au inteles toate frazele inregistrate in aer liber, circa 70% din frazele inregistrate in interiorul sarcinii si circa 30% din frazele inregistrate in urechea interioara a fatului ovin.

Cercetarile au relevat motivul pentru care frazele inregistrate in urechea fatului au dovedit o atat de scazuta inteligibilitate a fost acela ca cuvintele care au o consonantica de frecventa mai inalta tind sa nu fie intelese sau sunt confundate. Cu alte cuvinte, cuvantul englez "ship (oaie)", poate fi cu usurinta auzit ca "slit (deschizatura)" sau ca "sit (a sedea)". Vocalele de o frecventa mai joasa, prin contrast, tind sa penetreze urechea interioara intr-o masura mult mai mare.

Charlene Krueger, profesoara-asistent la catedra de pediatrie a Universitatii din Florida, care lucreaza cu bebelusi prematuri, a opinat ca in timp ce un feotus aude vocea mamei sale oricand ea vorbeste si este izolata de frecventele inalte, copiii nascuti prematur nu aud tot timpul vocile mamei lor pentru ca in mod obisnuit mamele lor nu pot fi la marginea patului 24 de ore pe zi. De asemenea, in timp ce un copil nenascut este izolat de multe frecvente, prematurii sunt expusi la toate frecventele sunetului din camera copiilor. Ea este de asemenea interesata sa afle cum aceasta expunere marita, combinata cu pierderea vocii materne, poate influenta dezvoltarea copiilor nascuti prematur.

Sursa: EurekAlert! http://www.eurekalert.org/pub_releases/2004-01/uof-ura012204.php

Sursa: http://www.provita-craiova.com/articol-sunet.php

UF research adds to evidence that unborn children hear 'melody' of speech
GAINESVILLE, Fla. --- It is well known that unborn babies can recognize their mothers' voices and distinguish music from noise. But exactly what they hear remains unclear.

Now, scientists at the University of Florida have added a piece to the puzzle. In a series of unique experiments on a pregnant ewe designed to record exactly what sounds reach the fetal ear, UF research has bolstered previous findings suggesting that human fetuses likely hear mostly low-frequency rather than high-frequency sounds. That means they hear vowels rather than consonants and are more sensitive to the melodic parts of speech than to pitch, said Ken Gerhardt, a UF professor of communication sciences and disorders and an associate dean of the Graduate School.

As for music, "they're not going to hear the violins, but they will hear the drums," said Gerhardt, who led the research reported in the November-December issue of the journal Audiology and Neuro Otology.

Anthony DeCasper, a professor of developmental psychology at the University of North Carolina-Greensboro, said the UF results are noteworthy because they were obtained from the inner ear, which presumably would register sounds exactly as a sheep fetus would hear them. The findings – which resulted from implanting a tiny electronic device in the inner ear of a fetal sheep that tapped into the signal the ear sends to the brain – dovetail with what other researchers have concluded based on less invasive studies involving human fetuses, he said.

"The way I put it is, the way the mother's voice would sound in utero would be like Lauren Bacall speaking from behind a heavy curtain," DeCasper said.

The research also may have implications for the care of premature babies. Neonatal care units are traditionally relatively noisy places, replete with beeping machines and the hum of conversation, and research by Gerhardt, DeCasper and others is raising awareness and questions about how the sounds "premies" are exposed to may influence normal growth and development, researchers said.

Gerhardt said he began researching fetal hearing in response to inquiries from law enforcement agencies and the U.S. Navy. Both were concerned about how loud noises, such as gunfire or the rumble of a ship's engine, could affect the hearing of babies being carried by pregnant servicewomen.

Gerhardt and Robert Abrams, a UF professor emeritus of obstetrics and gynecology, decided to study the issue using sheep because experiments by other researchers had shown that properties of sound transmission in pregnant women and sheep are similar. Their experiments revealed the womb dampened all but the loudest sounds. Even loud rock concerts are probably not noisy enough to pose a threat to fetal hearing development, Gerhardt said. The research, which has received more than $1 million from the Navy, the National Institutes of Health and the March of Dimes, contributed to federal workplace safety guidelines that today limit the duration of extremely loud noise exposure for pregnant women.

In their recently reported research, Gerhardt and Abrams focused specifically on the kinds of sounds fetal sheep hear. Their method was unique: They implanted an electronic "pickup" inside the inner ear of a fetal sheep, then played 64 recorded sentences on a loudspeaker in the open air near the mother sheep. The sounds the pickups detected were recorded and played back to 30 human adult listeners in order to determine how much or what portions of the sentences the fetus actually heard. For comparison, the researchers also placed a microphone inside the uterus of the ewe and in the open air, then performed identical tests with human listeners.

The results were surprising, with the intelligibility of sentences "actually much higher than we anticipated," Gerhardt said.

In part, that was unexpected because much of the noise that reaches a fetus comes from its mother's own voice, movement, breathing and digestive processes. Even in a quiet room, the womb can be noisy place, he said. Also, fetuses don't "hear" as much with their ears as children or adults do because their ears are filled with fluid, he said. Rather, much noise is transmitted to their inner ears through vibrations in their skulls. As a result, the mother's voice tends to be the most dominant and recurring sound in the womb.

The listeners understood all of the sentences recorded in the open air, about 70 percent of the sentences recorded in the womb and about 30 percent of the sentences recorded in the fetal sheep's inner ear.

The recordings revealed the reason the inner ear-recorded sentences proved so much less intelligible was that the higher-frequency consonants in words tended to be absent or confused. In other words, "ship" could easily be heard as "slit" or "sit." Lower-frequency vowels, by contrast, tended to penetrate the inner ear to a much greater extent.

Charlene Krueger, a UF assistant professor of nursing who works with premature babies, said that while a fetus hears its mother's voice whenever she speaks and is insulated from higher frequencies, infants born prematurely don't hear their mother's voices all the time because their mothers usually can't be at the bedside 24 hours a day. Also, while unborn children are insulated from many frequencies, premies are exposed to all the frequencies of the sounds in the nursery. She is interested in finding out how this added exposure, combined with the loss of the mother's voice, might influence the premies' development.

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Writer: Aaron Hoover, 352-392-0186, Această adresă de e-mail este protejată de spamboţi; aveţi nevoie de activarea JavaScript-ului pentru a o vizualiza
Sources: Ken Gerhardt, 352-392-6622, Această adresă de e-mail este protejată de spamboţi; aveţi nevoie de activarea JavaScript-ului pentru a o vizualiza
Charlene Krueger, 352-273-6332, Această adresă de e-mail este protejată de spamboţi; aveţi nevoie de activarea JavaScript-ului pentru a o vizualiza

http://www.eurekalert.org/pub_releases/2004-01/uof-ura012204.php