Basic comprehensive audiograms performed in accordance with age-appropriate behavioral methodologies are conducted in a soundproof test booth.
BOA – Behavioral Observation Audiometry:
Birth to 8 Months of Age
BOA assesses the infant’s responsiveness to sound, but does not obtain actual hearing thresholds. The audiologist observes the infant’s bodily reactions to sound, such as body movement, eye widening, eye blink, changes in sucking and breathing, and startle. This may be accomplished through loudspeakers, called the “sound field,” or through headphones. When used in conjunction with Otoacoustic Emissions, significant hearing loss can be ruled in or out.
Note: Sound field Audiometry does not provide ear specific information, but measures hearing from the better ear, if the ears are different. Headphone testing assesses hearing from each ear separately.
VRA – Visual Reinforcement Audiometry:
8 Months to 2 ½ Years of Age
Although exact thresholds for hearing cannot be obtained, a close estimate may be obtained in many cases with good reliability. The baby is seated on the parent’s lap between right and left loudspeakers, or using earphones. When a sound such as a tone, speech or music is presented at a level deemed loud enough for the baby to hear, he will turn his head or shift his eyes to the right or left in a localized response to the sound. This response is reinforced by the activation of a lighted mechanical toy mounted on the loudspeaker.
2 ½ Years to 5 Years of Age
Exact hearing thresholds may be obtained. This method replaces the more adult “raise the hand” or “press the button” technique, and is used because a child under the age of 5 often cannot cooperate for the standard method. The child is conditioned to play audiometry by asking her to place a puzzle piece in a puzzle, put a ring on a stick, or drop a block in a box. The child is taught to hold the toy up to her right or left ear in a “listening” attitude. When the sound is presented through the earphone, she is encouraged to immediately respond. Two testers are usually present, one sitting with the child in the booth (this can be the parent) and the other behind the audiometer.
- Speech reception threshold (SRT): The softest level at which speech is heard. The child is asked to point to his body parts or asked to repeat words as the volume is decreased.
- Word recognition (speech discrimination, SDS): How clearly the child can understand phonetically balanced words (PBK) designed specifically for the pediatric population. He is asked to repeat words if he is able to cooperate. If unable to repeat words, a picture-vocabulary book is used, and word intelligibility by picture index is obtained by asking the child to point to one of 4 or 6 pictures on a page.
Otoacoustic Emissions (OAE):
This test is conducted in all newborn hearing screenings in U.S. hospitals at time of birth. An OAE is a sound which is generated from the outer hair cells of the inner ear. This sound can be evoked and recorded in the office. A tiny probe is placed inside the baby’s or child’s ear canal. It measures the response, or echo, produced when tones of varying pitch are played into the ears. The presence of OAEs indicates good outer hair cell function, which is in agreement with normal or near normal hearing. The absence of OAEs reveals outer hair cell dysfunction, indicating a probable hearing loss.
Impedance Testing for pediatrics includes two tests:
- Tympanometry (acoustic immittance): An objective test of middle ear function used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane). A probe is placed in the ear canal, generating a tone, and variations of air pressure in the ear canal are produced. This test further distinguishes between conductive and sensorineural hearing loss.
- Acoustic reflex testing (stapedius muscle): This is accomplished during the tympanometric test. The acoustic reflex is a muscle contraction occurring in the middle ear in response to loud sound; the presence or absence of this reflex yields more information about the severity, location and cause of the hearing loss.