In addition to the hearing evaluation and the patient profile obtained regarding the patient's hearing handicap and motivation, other testing may be completed in the sound field, especially speech reception in the presence of noise. These tests can help determine the type of hearing aid to be chosen. They also serve as nonaided pretests that will be compared to aided posttesting.

After reviewing the test results and determining the type and degree of loss to each ear, a decision must be made whether to recommend one hearing aid (monaural amplification) or 2 hearing aids (binaural amplification). For most binaural hearing losses, 2 hearing aids are recommended.

One of the primary reasons for this recommendation is the mounting clinical evidence that indicates that failure to fit hearing aids on both ears of patients with binaural hearing loss can result in temporary and perhaps permanent decrease in the auditory function in the unaided ear.

The deterioration over time of auditory perceptual function in the unaided hearing-impaired ear has been referred to as the %u201Cauditory deprivation%u201D effect.

In addition to avoiding the possible deprivation effects, other advantages exist to binaural amplification, including better sound localization, improvement of speech reception in the presence of noise, improved speech clarity, and more natural and less stressful listening.

Besides determining the size of the hearing aid and whether to fit monaurally or binaurally, the determination of frequency response, gain, and overall output of the hearing aid must be decided. In many settings, Real Ear measurements are made to help select the proper characteristics of the hearing aid.

Specifications of hearing aids from manufacturers are produced using the ANSI S3.22 standards concerning the gain, output, and frequency response of the hearing aid. These measurements are made in a 2-cm3 coupler. This coupler is used to simulate the condition of the aid in an ear, but many differences exist between a metal 2-cm3 coupler and the volume and texture of an ear canal and eardrum, and many individual differences exist between ears. Because of these differences, a Real Ear probe-tube measurement is used to reveal the exact frequency response, gain, and maximum output of the hearing aid in the ear at the site of the eardrum.

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