Adults and school aged children are able to follow instructions and respond to stimuli for a basic pure tone audiometry evaluation. Hearing testing for very young children mainly involves observing their behavioral responses to different auditory stimuli. A Behavioral Observation Audiometry (BOA) test is accomplished without any active reinforcement, and depends on the audiologist's subjective observation of responses. BOA is usually restricted for babies aged 18 to 24 months or younger, but can also be used as an informal way of assessing older children, children with physical or intellectual disabilities who have difficulties performing a conventional hearing test.
What type of auditory stimuli is used for BOA?
For a behavioral testing, pure tone signals cannot be used in isolation. Babies tend to lose interest in pure tone stimuli and may stop responding to them despite being able to hear the tones. During BOA, the stimuli used include warble tones or FM tones, narrow band and white noises, and speech stimuli. The test is most often performed in the sound-field setting using speakers, but in slightly older children headphones may be used to obtain ear-specific responses.
Auditory Behavior Index
The Auditory Behavior Index (Northern & Downs, 1991) summarizes the different behavioral responses babies show to auditory stimuli in the first 2 years of life. Although all the behaviors cannot be summarized in a single list, these are the most common responses seen. The Auditory Behavior Index is required to understand what responses to look out for at which age range during the testing as well as to monitor the child's auditory development. Responses at the earlier stage of life are mostly gross motor movements or reflexive behaviors that become more specific and finer as the child ages.
Reflexive behaviors include startle responses (usually to loud sounds), arms or leg jerks, changes in sucking behavior, eye-blinks, and facial twitches. These are mainly involuntary responses to auditory stimuli and are usually brief. Attentive behaviors are changes in ongoing activity as a direct result of shifts in attention in the presence of sound. These include quieting responses, changes in breathing patterns, vocalizations, starting or stopping of crying, changes in facial expressions, and trying to locate the sound source. In addition to understanding the hearing level of a child, the audiologist is also required to remain alert to the responses that are below the level of a child's chronological age that may indicate a possible developmental or intellectual disability and the need for appropriate referral and management.
Advantages and Disadvantages of BOA
BOA is widely debated test of an infant's hearing levels. Although an objective test may be a more accurate test tool, behavioral assessments provide an understanding of a child's auditory behavior. It is difficult to eliminate tester bias during BOA testing which increases variability during test and between tests. Infants responses are also quick to reach extinction and therefore the test needs to be completed as quickly and efficiently as possible. Behavioral responses are more useful for monitoring a child's auditory development rather than a singular test for diagnosis.
Ref: Hearing in Children - Northern & Downs