Comparison of two cochlear implantation techniques and their effects on the preservation of residual hearing. Is the surgical approach of any importance?

The goal of this work was to review the pre-and postsurgical auditory thresholds of two surgical implantation techniques, namely the mastoidectomy with posterior tympanotomy approach (MPTA) and suprameatal approach (SMA), to determine whether there is a difference in the degree of preservation of residual hearing. In a series of 430 consecutive implanted patients 227 patients had measurable pre-operative hearing thresholds at 250, 500, and 1,000 Hz. These patients were divided into two groups according to the surgical technique that was used for implantation. The SMA approach was followed for 84 patients in Amsterdam, whereas the MPTA technique was adhered to 143 patients in Maastricht. The outcome variables of interest were alteration of pre-and postoperative auditory thresholds after cochlear implantation. Complete or partial preservation of residual hearing was obtained in 21.4 and 21.7% in the SMA and MPTA group, respectively. No statistical differences could be found between the SMA and MPTA group (p = 0.96; Chi-square test). The SMA technique is correlated with a similar degree of hearing loss after cochlear implantation compared to the MPTA technique. However, both techniques were not able to conserve a measurable amount of hearing in patients with a substantial degree of residual hearing. Therefore, both surgical techniques need to be refined for patients in which residual acoustical hearing is pursued.

Syllabic compression and speech intelligibility in hearing impaired listeners.

Syllabic compression has not been shown unequivocally to improve speech intelligibility in hearing-impaired listeners. This paper attempts to explain the poor results by introducing the concept of minimum overshoots. The concept was tested with a digital signal processor on hearing-impaired subjects. The results show that moderate syllabic compression may raise speech intelligibility, as long as overshoots are minimized and relatively short time constants are used. Frequency equalization also contributes to speech intelligibility.

The effects of input-output configuration in syllabic compression on speech perception.

Speech perception was tested through a broad-band syllabic compressor with four different static input-output configurations. All other parameters of the compressor were held constant. The compressor was implemented digitally and incorporated a delay to reduce overshoot. We studied four different input-output configurations, including a linear reference condition. Normal-hearing and hearing-impaired subjects participated in the experiments testing perception of meaningful sentences as well as nonsense CVCs in carrier phrases. The speech materials were presented in quiet and in noise. The results from the CVCs were analyzed quantitatively in terms of scores and qualitatively in terms of phoneme confusions. Differences in speech perception due to the different input-output configurations were small. The input-output configuration with the highest amplification of low amplitude sounds yielded the best results. Detailed analysis of the results included a correlational analysis with a number of auditory functions characterizing the ears tested. The pure-tone audiogram provided parameters of auditory sensitivity: average audiometric loss and audiometric slope. Psychophysical tests provided parameters of temporal resolution and frequency selectivity: the temporal resolution factor, temporal gap detection, and auditory filter shape. The correlational analysis showed that the subjects with better temporal acuity obtained better results.