It's All in the Timing!

Hearing test results are often explained by showing the amount of decibel loss at each tone frequency and comparing it to a normal range. In addition, the residual ability to understand words in quiet conditions at various sound levels is measured. Although this tried and true approach has been quite useful over the years, research in the areas of psychological and physiological acoustics has shown that hearing is much more involved than a simple tone test or single word repetition would suggest. The importance of timing cues should not be underestimated. Time of arrivals and their differences at each ear during everyday listening enhance our ability to segregate sources and thus understand conversation in the presence of unwanted sounds such as multiple talkers, vacuum cleaner, radios, refrigerator, microwave oven, water running from a faucet,... just to name a few. Understanding speech in such conditions is intimately related to the ear's neural clock! A normal hearing mechanism uses timing of sounds with such precision (on the order of microseconds) that scientists marvel at the complexity. An ear with cochlear damage such as missing 'inner hair cells' and/or distorted excitation patterns will compromise the accuracy of information regarding voice locations and characteristics, potentially reducing one's ability to separate voices of family members and/or strangers. As we age, the ability of the brainstem to process small differences in phase between the ear diminishes, leading to potential problems in grouping multiple sounds. Though a properly adjusted hearing aid can provide a higher volume which enhances selected speech patterns , it may not enable normal pick up of rapid timing cues (fine structure). There is great variability among the hearing impaired as to the use of time information. Training can be an important factor in the final result. An audiologist with background in such matters will be able to counsel an individual regarding the potential benefits as well as limitations of amplification.

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