Distortion-product Emission Levels Research Articles

Method and apparatus for distortion product emission testing of hearing

Apparatus and method are disclosed for the recording of distortion product emission (DPE) levels in human beings. At least one microphone and a sound-delivery system is inserted in the external ear canal in a manner similar to that required to position a small hearing aid. Two primary tones T f1 , T f2 are applied simultaneously to the ear. The cochlea of the inner ear produces a DPE tone which is sensed by the microphone. DPE levels are sensed as a function of input frequencies f 1 and f 2 . Such DPE frequency is equal to 2f 1 -f 2 . Such DPE frequencies are collected in 100 Hz steps by adjusting f 1 and f 2 and maintaining a substantially constant ratio between f 1 and f 2 . Two output forms are created: an DPE audiogram and a DPE input/output function. Noise picked up by the microphone is reduced by averaging the DPE signal many times, yet causing each of the DPE signals that is averaged to be of the same phase as every other DPE signal. Random phase noise is reduced by the averaging process. Body noise may be reduced by using two microphones and applying the output of one such microphones to the plus input of a differential amplifier. The output of the other less sensitive microphone, after amplification and phase adjustment is applied to the negative input of such differential amplifier. The output of such amplifier results with the body noise signal substantially reduced, but with the DPE signal substantially unchanged. This abstract of the disclosure-is not intended to define the scope of the invention.

Distortion product emission features and the prediction of pure tone thresholds

Distortion product emission (DPE) growth functions, demographic data, and pure tone thresholds (PTTs) were recorded in 229 normal-hearing and hearing-impaired ears. Half of the data set (115 ears) was used by a discriminant analysis routine to classify DPE and demographic features into either a normal PTT group or an impaired PTT group (PTT greater than 30 dB SPL [sound pressure level]) at six frequencies in the audiometric range. The six discriminant functions developed from this classification process were then used to predict PTT group membership in the remaining 114-ear data set. Frequency-specific prediction accuracy was approximately 85% overall. Of the 45 DPE and demographic variables evaluated, the DPE amplitude associated with an f2 (a primary tone of frequency) of moderate level (50 dB SPL) and a frequency corresponding to PTT was generally most predictive. DPE features associated with frequencies immediately adjacent to the PTT frequency also appear to be useful. DPE level was found to be weakly correlated with subject age; perhaps for this reason, age was frequently included in discriminant functions. This study describes the DPE measures that can most reliably categorize PTTs as normal or impaired in large populations with varied cochlear hearing status.

Predicting Pure Tone Thresholds in Normal and Hearing-Impaired Ears with Distortion Product Emission and Age

Distortion product emission (DPE) growth functions, demographic data, and pure tone thresholds were recorded in 229 normal-hearing and hearing-impaired ears. Half of the data set (115 ears) was used by a discriminant analysis routine to classify DPE and demographic features into either a normal pure tone threshold (PTT) group or an impaired PTT group (PTT greater than 30 dB SPL) at six frequencies in the audiometric range. The six discriminant functions developed from this classification process were then used to predict pure tone threshold group membership in the remaining 114-ear data set. Frequency-specific prediction accuracy varied from 71% (correct classification of hearing impairment at 1025 Hz) to 92% (correct classification of normal hearing at 2050 Hz). Of the 45 DPE and demographic variables evaluated, the DPE amplitude associated with an f2 of moderate level (50 dB SPL) and a frequency corresponding to pure tone threshold was generally most predictive. DPE level was found to be weakly correlated with subject age and perhaps for this reason age was frequently included in discriminant functions. For our data, discriminant functions with one variable, two variables, or 5-10 variables showed no differences in predictive performance. This research suggests that DPE measures can reliably categorize pure tone thresholds as normal or impaired in large populations with varied cochlear hearing status.