Auditory function and speech understanding in listeners who qualify for EAS surgery

For patients with relatively good low-frequency hearing and relatively poor high-frequency hearing, who met the pre-implant criteria for combined electric and acoustic stimulation (EAS), our aims were to i) assess deficits in low-frequency auditory function, ii) to identify measures which might be sensitive to changes resulting from the insertion of an intracochlear electrode array, and iii) to quantify the relationship between measures of auditory function and performance on tasks of speech and melody recognition.

Measures of frequency selectivity, temporal resolution, and nonlinear cochlear function, along with measures of word, sentence, consonant, vowel, and melody recognition, were obtained from 5 normal-hearing and 17 hearing-impaired listeners. The hearing-impaired listeners had auditory thresholds at 500 Hz, ranging from 20 to 60 dB HL, and thresholds at 1 kHz, ranging from 60 to 100 dB HL.

Nonlinear cochlear function was either reduced or absent. Frequency selectivity at 500 Hz was significantly reduced but still present in most patients. Temporal resolution, when measured at low modulation frequencies, was normal. Speech recognition in a modulated background revealed significantly poorer performance than normal. Speech and melody recognition varied over a large range. No measure of auditory function was correlated significantly with speech recognition. However, frequency selectivity was related to melody recognition.

(1) Patients who qualify for EAS surgery have a wide range of speech and melody recognition abilities. (2) A number of the psychophysical measures tested may prove more sensitive than the audiogram in determining the degree of damage inflicted by the intracochlear electrode array. (3) Speech recognition was not correlated with any of the measures of auditory function.