There is noise coming from the audio tape. There is a colorful landscape drawing on the computer screen. A clown appears at the bottom of the screen -- a sign indicating that a word will soon be heard. This is how the Children’s test of word recognition in noise looks like. Docent of logopedics, university lecturer Taina Välimaa is demonstrating the test on her own computer.
In a real setting, the child will do the test in a quiet hearing research room. An audiometer plays a word in the child’s earphones, and the child repeats it upon hearing. The noise in the test is continuous noise filtered from speech. It is close to speech in its frequencies, but no individual words can be discerned due to the filtering.
”As the test progresses, the signal-noise ratio changes when noise gets stronger in relation to speech. As a result, the test will produce a noise speech threshold. The test will tell what kind of a signal-noise ratio results in a 50 % identification of the speech material”, says Välimaa.
Once the noise speech threshold is reached, the test ends.
Graphics and code of the test of word recognition in noise have been designed by the games company Meizi Games from Oulu. The algorithm of the adaptive and automatic test complies to the international ISO 8253-3 standard for testing.
Ordinary background noise may reach 80 decibels in day care centers and schools. Normal speech may reach 60 decibels over one meter’s distance. Therefore, the voice of a teacher instructing the pupils, or a kindergarden teacher’s voice, may easily drown in background noise.
”It is harder for children to detect speech in background noise than for adults. Human neural networks, and phonetic representations and cognitive controls keep developing long into the teens”, Välimaa points out.
Children with hearing impediments find speech processing and language acquisition in background noise even harder than children with normal hearing.
First test for speech detection in background noise
The Children’s test of word recognition in noise project has been running since last autumn with two-year strategic funding from the Academy of Finland. The test is a continuation of the national project directed by professor Sari Kunnari, which studies speech perception in hearing impaired children between one and six years of age, and how their speech and language develops. The aim is to find out what levels of language hearing impaired children find hard to acquire, and where early rehabilitation is required.
”For example, development of vocabulary slows down, which has a connection to reading comprehension and writing. A hearing impediment also makes it harder to perceive the acoustic properties of speech sounds, which makes them harder to acquire for producing language”, Välimaa says.
In connection with the project, development of a test for word recognition in noise has been started as a way to measure how background noise disturbs perception of speech. A standardized method for measuring speech detection in background noise has not existed in Finland. The new test complies with the international ISO 8253-3 standard for designing and applying a test.
The focus in the Children’s test of word recognition in noise is only in identifying individual words. This way only what the child hears is tested, and the working memory is not burdened with having to remember more than one word. The word data consists of a speech corpus of three-year old children, where the words have been collected during previous research projects by the University of Oulu Child Language Research Center.
”The words in the test are not overly complicated adults’ words. We have also had to take into consideration the phonetic structure of the words, and the cognitive control and focusing ability of the children, says Välimaa. She also says that implementing the test of word recognition in noise has required knowledge from people from logopedics, phonetics, audiology, and technology.
The Children’s test of word recognition in noise is currently used for studying, in cooperation with the University Hospital of Oulu unit of ear, nose and throat diseases; normal children between 3 and 12 years of age, to be used as a control group. Study of children with hearing impediments will be started in the autumn in all Finnish university hospitals, Docent of logopedics and university lecturer Taina Välimaa says.
Worrying about the acoustics in spaces with multiple functions
Taina Välimaa tells us that prevalence of early childhood hearing impediments in Finland is 2.1 children in 1000 births, which means a few hundred children per year.
”According to international studies, approximately seven per cent of children show developmental language impediments. Background noise may make it harder for them also to perceive speech. Hearing impediments increase rapidly with age. It has been shown that one in ten 15-year old boys have a hearing defect, and already one in five boys starting their military service.”
In cases between a mild and a serious hearing defect, there remain functioning hair cells in the ear, and sound can be amplified with a hearing aid. In serious and very serious hearing defects, there are not enough hair cells left, but an inner ear implant will aid hearing. The electrical field of the electrodes in the electrode band in the interior part of the implant will activate the hearing nerve, and the sound stimulus is transmitted to the auditory cortex.
Children with a hearing aid can be studied with the test of word recognition in noise to compare perception of speech with and without hearing aids. Children with an ear implant can be studied to find a realistic, functional level with implants, as they cannot hear without it”, says Välimaa.
The test result shows how well the child perceives speech and what areas need rehabilitation. The knowledge is also useful for day care center and school personnel, as well as for families of the children, for taking the acoustics of the environment into consideration. Välimaa is worried about the effect large multi-purpose spaces have on children with hearing defects or impeded language development.
”Noisy spaces are cognitively straining. It is important to think how noise affects learning results.”
Starting point for continuing research and early rehabilitation
The aim of the Children’s test of word recognition in noise is to get it into clinical use in all university hospitals in Finland. The test will also advance scientific basic research.
The test of word recognition in noise is a standard-based indicator with a clear clinical scientific need. According to Välimaa, cooperation in the project will make it possible to start developing new kinds of tests for perceiving speech. Modern technology makes it possible to create realistic sound environments in a sound-proof space, such as canned background noise of a schoolroom or railway station. This will lead to more realistic testing of detection of speech, listening comprehension, internalization of instructions, concentration, and even acquiring of speech and language.
”With these laboratory environments it will be possible to more accurately screen those children who have special difficulties, and support them as early as possible.”
Identifying problems in hearing is the first step in early rehabilitation. When the straining level of background noise is precisely known for each individual child, language learning is secured, as well as learning in school later.
Last updated: 31.7.2017