Dr. Lynne Werner's Research Interests

Faculty Biography - Lynne A. Werner Ph.D.

If you click on the following pictures you will jump to a description of the respective interest area.

Infants' Hearing Capacity	Methods for Testing Infants' Hearing
What do infants hear?	How do you get a baby to tell you "I hear that"?
Mechanisms of Hearing Development	Hearing Development in Special Populations
Why does hearing change as infants grow?	Does hearing develop differently in some infants?

Infants' Hearing Capacity

Dr. Werner's research has shown that 3-month-olds cannot hear very quiet sounds and that they need bigger differences between sounds to tell that the sounds are different. It is probably not a coincidence that people talk to babies in a special way. But by the time infants are about 6 months old many aspects of their hearing are mature. They still are little less sensitive to sound than adults are, but they can distinguish between many sounds as well as adults can. Our hearing is not completely mature, however, until we are about 10 years old.

Methods for Testing Infants' Hearing

The method that we use to measure infant's sensitivity to sound is called an observer-based method. The difference between this method and other methods is that rather than asking an observer to decide whether an infant responded to a sound, we ask the observer to decide whether a target sound has been presented to the infant. The trick is that the infant's behavioral response is the only information upon which the observer can base that decision. If the observer can consistently tell when a target sound was presented, based only on the infant's behavior, then the infant must have heard and responded to the sound. This method can be very sensitive because even subtle infant responses can be used by the observer, and we always know whether the observer was right or wrong.

The infant sits on a parent's lap in the test booth and listens to sounds presented through an earphone. An assistant directs the infant's gaze ahead using quiet toys. The infant learns to respond to the target sound, but not to other sounds or when no sound occurs. A mechanical toy is used to encourage the infant to respond to the target sound.

The observer watches the infant from the adjacent control room. When the infant is quiet and looking ahead, the observer signals the computer to present a trial. The observer does not know whether a target sound will be presented. Sometimes a target sound is presented. Sometimes no sound is presented or a nontarget sound is presented. The observer decides on the basis of the infant's response whether or not a target sound has been presented. The observer receives feedback after each trial. It is whether the observer is correct or incorrect that tells us that the infant is making a consistent response. Every time the observer correctly identifies the presentation of a target sound, the infant's response is reinforced by the activation of the mechanical toy. So if the infant keeps on making that response every time the target sound occurs, then she or he will get to see the mechanical toy.

Hearing Development in Special Populations

If an infant does not receive the usual sound stimulation, will their hearing development be affected? For example, when an infant has an ear infection, less sound reaches the inner ear. Fortunately, while most infants have ear infections, the infection does not last long. Some infants, though, have many ear infections, and in these cases hearing development may be affected. Infants with Down Syndrome also appear to be less sensitive to sound than other infants. Currently we do not know how that difference in sensitivity affects the development of infants with Down Syndrome. Research in Dr. Werner's laboratory is aimed at learning specifically how the hearing of these two groups of infants develops.

Mechanisms of Hearing Development

To hear a sound, the sound has to be able to reach the inner ear, we have to have a working ear to change the sound into a message the brain can understand and the parts of the brain that are connected to the ear have to be able to decode that message. We also have to pay attention to a sound that we want to hear. As it turns out, hearing changes during infancy because each of these capacities is maturing. The inner ear functions before birth, and it is probably mature in infants who are born at term. Research at the University of Washington has shown that infants' middle ear is not as efficient at passing sound on to the inner ear though. Research conducted by Dr. Werner in collaboration with Dr. Richard Folsom has also shown that important maturation of the parts of the brain that are used in hearing also takes place in the first 6 months of postnatal life. Dr. Werner has also found that after 6 months of age, an important limitation on infants' hearing is their inability to pay attention to one sound to the exclusion of others.