Groenen PÀP, Makhdouni M, van den Brink JL, Stoll man MHP, Snik AFM, vtin den Broek P, The relation between electric auditory brain stem and cognitive responses and speech perception in cochlear implant users. Acta Otolaryngol (Stockh) 1996; 116: 785-790. Electrically evoked brainstem responses (EABR) and event-related cortical potentials were recorded in seven postlingually deaf adults who were experienced users of a Nuclcus multichannel cochlear implant. The patients were divided into two subgroups: good performers and moderate performers, Poor EABR were found in two of the moderate performers. The latencies and amplitudes of the cortical N1-P2 complex in the good performers were within the same range as those of subjects with normal hearing, but were deviant in the group of moderate performers. This may indicate disturbed cochleotopical organization of the auditory cortex in the latter group. P300 measurements in the good performers showed normal latencies, whereas in the moderate performers they were prolonged. The results suggest that the outcomes of electrophysiological measurements to assess the integrity of a patient's auditory neural system on a brainstem and. a cortical level, are related to the patient's performance with the cochlear implant.

The development of auditory processing in children was investigated in a longitudinal study. A group of 20 children with normal cognitive and language development underwent several auditory tests at the ages of 6, 7, 8, 10 and 12 years. At the age of 10 years, three subjects were lost to follow-up, as was one more subject at the age of 12 years. The auditory performance of the children was compared to the performance of a group of 20 adults. The auditory test battery consisted of a speech-in-noise test, a filtered speech test, a binaural fusion test and two auditory sequencing tests. At the ages of 6, 7 and 8 years, data on the performance on an auditory word discrimination test, an auditory synthesis test, an auditory closure test and a number recall test were also obtained. All auditory tests except the speech-in-noise test showed a clear effect of age on the performance of children. Our data suggest that maturational effects play an important role in auditory processing (at least) up to an age of 12-13 years. Correlations between the tests are in general not indicative of large amounts of overlap between the different tests. Factor analysis shows that three factors account for 68-70% of explained variance, with the three factors contributing equally. A composite score obtained by averaging all (sub)test scores can be used next to the individual test scores to describe the development of auditory processing abilities in children.

In humans, the binaural interaction at the brainstem level has been studied for over 15 years. The binaural interaction component (BIC) is obtained by subtracting the summed auditory brainstem response (ABR) in the monaural stimulus mode from the ABR obtained in the binaural stimulus mode. By nature of this subtraction process, the signal-to-noise ratio of the difference waveform is poor, requiring an objective detection criterion to decide whether a significant BIC is present. In this study, the effectiveness of two analysis methods was compared. The first method is the "3 SD' method, which is based on a signal-to-noise evaluation. The second method is a template matching method, in which templates are derived from normal hearing subjects' responses and individual responses are cross-correlated with these templates. The templates were allowed to shift over a range of -0.8 to 0.8 ms in search of the maximum correlation coefficient. Thirty-nine subjects with normal hearing and five patients with a unilateral profound hearing loss participated in the study. ABRs were obtained with rarefaction and condensation clicks at a rate of 15/s and a level of 70 dB nHL. Latencies of the ABR waves I, III and V for all normal hearing subjects and for the normal ear of the patients were within the normal range. The efficiencies of both methods, defined as the number of normal hearing adults with a significant BIC plus the number of patients without a significant BIC divided by the total number of subjects, were determined. The results show that the "3 SD' method is superior to the template matching method: the efficiencies were 95% and 70% respectively, when responses to rarefaction and condensation clicks were taken together. With the "3 SD' method, a significant BIC is demonstrated in almost all normal hearing subjects (97%). However, the "3 SD' method also falsely indicated a significant BIC in one patient. These results suggest that the BIC may have clinical value in studying binaural interaction in humans.

The insertion gain measured in 34 children of up to 6 years of age with symmetrical sensorineural hearing loss, who were fitted successfully with binaural hearing aids, was compared in retrospect to the calculated insertion gain using two different prescriptive methods: the half-gain rule (HGR) and the desired sensation level method (DSL). The measured and calculated values were in fair agreement with the results of both of the prescription methods. The desired saturated sound pressure levels calculated using the DSL method and those measured on a 2-cc coupler were in fair agreement.

In this study, the effect of time-compression and expansion of speech on speech perception in noise was measured for a group of hearing-impaired and a group of language-impaired children relative to control groups of normal children and normal adults. The children's ages ranged from 9 to 12 years. For all time-scale modified conditions, both hearing-impaired and language-impaired children had significantly higher speech recognition thresholds in noise (SRTN) than their normal peers, who performed almost equally well as the adult control group. Time-expansion was shown to have a negligible effect on SRTN for all groups when compared to the control condition, i.e. 0% time-compression. The difference in SRTN between the control and the impaired groups was, in general, not significantly altered by the degree of time-compression or expansion of speech, although a clear trend towards greater differences for increasing time-compression was observed. Five tests of auditory discrimination and auditory memory were also administered to both groups of impaired children. In a step-wise multiple regression procedure, 94% of variation in SRTN in the control condition could be explained by the score on the ADIT C (type Wepman; discrimination task) and the maximum speech recognition score for monosyllables in quiet.