Wandering through the Exhibit Hall at the American Academy of Audiology (AAA) convention in Chicago was akin to a child browsing through a large and available candy store. What to sample first? I spent two full days in the exhibits and still couldn't get to see it all.
The "Claro" is Phonak's hearing aid entry into the digital era. It includes a number of features of proven value and user convenience, plus a few others based on a creative fitting rationale, albeit one that has yet to be confirmed with published clinical research.
One feature of proven value is directional microphones. According to the research, it doesn't really matter if the directional microphones are used with analog or digital instruments. They still operate in a way that suppresses sounds arriving at the sides or the rear compared to sounds (presumably speech sounds) that come from the front. The type of directional microphone function in the Claro, however, can only be accomplished with digital hearing aids because of the nature of the signal processing required.
With other directional hearing aids, the characteristics are fixed. That is, the area of maximum suppression of sounds arriving from the rear or the sides is predetermined in the design of the system. With the Claro, on the other hand, the directional characteristics change as the position of the maximum interfering noises in the rear or to the side change.
For example, if the noise position moves from right rear to left rear, the hearing aid will automatically and rapidly adjust its maximum directional orientation from right to left. The wearer doesn't have to do a thing; the hearing aid does the sensing and the adaptation. It seems like a nice feature to have if one is often immersed in a changing noisy background.
The Claro's design rationale was to try to replicate the cochlear dynamics of a normal ear. To this end, they separated the audible frequency range into 20 bands of amplification, modeled on the psychoacoustic concept of the "critical band." This psychoacoustic factor is thought to underlay the analysis and identification of complex sounds (wider critical bands, common among people with hearing loss, are associated with poorer speech perception). In the normal ear, the selectivity of these critical bands change as the sound signal increases and decreases in intensity, with the number of bands being stimulated affecting the perceived loudness. Also, in the normal cochlea, some weaker signals may actually be suppressed as the signal intensity of adjacent sounds increase. Unlike the usual hearing aid, which more or less amplifies all the sounds within its operating range, the design intention of the Claro is to suppress sounds in the same way a normal ear does. The intent is to increase wearer comfort and improve speech perception (yet to be confirmed by independent research).
The 20 bands also permit the inclusion of a circuit that senses the presence of noise in each of the bands. It does this by exploiting the fact that noise tends to vary (fluctuate) in intensity less than a speech signal. What happens is that noise tends to "flatten" out a speech spectrum, by filling the gaps (either caused by pauses or the weaker consonants) between the speech peaks (produced by the more powerful vowels). If the system judges that a great deal of noise is co-existing with speech in any of the bands, the amount of amplification in that band is automatically reduced. Other hearing aids have similar types of circuits, but with a fewer number of bands. To my knowledge, this is the only one that includes 20 different bands, thus ensuring that the resulting gain reduction affects only that narrow portion of the spectrum where the noise is located. Moreover, the actual amount of gain reduction depends upon the contribution of that particular frequency band for the comprehension of speech. Middle and high frequencies, for example, are more important for speech understanding than the lower frequencies and thus would receive less gain reduction in the presence of noise than the lower frequencies.
The hearing aid includes other interesting features. For example, it continually scans the acoustic environment and automatically changes its amplification pattern to one designed either for quiet or for a noisy environment. It is not necessary for the user to make this decision or to activate a remote control; the decision process is built into the hearing aid's circuitry. During the fitting process, loudness measurements are made while narrow bands of signals are delivered right through the hearing aid. The fitting software then automatically programs the response of the instrument based on the results of these loudness measurements. In this concept, the actual threshold pattern of hearing loss is less important than the way the ear perceives the loudness of sounds at various supra-threshold levels (where we do most of our actual listening). The aid includes a programmable telecoil and a plastic cover over the microphones that is supposed to reduce wind noise.
Acknowledgement:
Dr. Ross' work is supported, in part, by GRANT #133E980010 from the U.S. Department of Education, NIDRR, to the Lexington Center. Mention of products or companies by the author does not Indicate SHHH endorsement, nor should exclusion suggest disapproval. Since everyone's communication problems and needs vary, SHHH suggests consulting with your hearing health professional.