Processing in the auditory cortex may play a role in the unexplained variability in cochlear implant benefit. P300 and N1/P2 were elicited in post-lingually deaf cochlear implant users wearing a Nucleus multichannel cochlear implant. Four sound contrasts were presented (500-1,000 Hz, /ba/-/da/, /ba/-/pa/ and /i/-/a/). N1 and P2 were present in all subjects for all conditions. Prolonged N1, P2 and P300 latencies were found in the cochlear implant group compared to a control group of subjects with normal hearing. Cochlear implant users show smaller amplitudes of N1 for all the speech signals as well as smaller amplitudes of P2 for the consonants compared to the controls. P300 results of the cochlear implant users were compared to behavioural results of speech recognition testing. A relation was found between P300 amplitude and magnitude for the 500-1,000 Hz and /i/-/a/ contrasts and behavioural speech recognition in cochlear implant users. The results suggest that P300 measurements are useful and have additional value to speech recognition evaluations in cochlear implant users.
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.
Developmental apraxia of speech is a disorder of phonological and articulatory output processes. However, it has been suggested that perceptual deficits may contribute to the disorder. Identification and discrimination tasks offer a fine-grained assessment of central auditory and phonetic functions. Seventeen children with developmental apraxia (mean age 8:9, years:months) and 16 control children (mean age 8:0) were administered tests of identification and discrimination of resynthesized and synthesized monosyllabic words differing in place-of-articulatton of the initiai voiced stop consonants. The resynthetic and synthetic words differed in the intensity of the third formant, a variable potentially enlarging their clinical value. The results of the identification task showed equal slopes for both subject groups, which indicates no phonetic processing deficit in developmental apraxia of speech. The hypothesized effect of the manipulation of the intensity of the third formant of the stimuli was not substantiated. However, the children with apraxia demonstrated poorer discrimination than the control children, which suggests affected auditory processing. Furthermore, analyses of discrimination performance and articulation data per apraxic subject demonstrated a specific relation between the degree to which auditory processing is affected and the frequency of place-of-articulation substitutions in production. This indicates the interdependence of percep tion and production. The resuits also suggest that the use of perceptual tasks has significant clinical value.
Mismatch negativity (MMN) provides an objective measure for evaluating subjects with problems related to speech processing. For a valid neurophysiological profile of speech-processing mechanisms, an efficient procedure to elicit MMNs is needed. In Experiment 1 of this study, MMN recordings were conducted in adults with normal hearing on the effects of decreasing the duration of the interstimulus interval (ISI). Shortening ISI duration does not seem to have a high impact on the individual MMN quality, whereas it does influence group MMN quality. In Experiment 2, MMNs were elicited in a group of cochlear implant users by using a speech sound contrast /bα/-/dα/. A group of good performers produced a signifycant MMN, whereas a group of moderate performers did not. There seems to be a relation between speech perception ability and MMN quality. To fundamentally understand the effects of electrical stimulation of the inner ear and to clinically adjust rehabilitation, diverse data are needed on different aspects of auditory processing. Optimizing the procedure to elicit and MMN is therefore of great clinical value.
Several electrophysiological techniques have been used to supplement behavioural measurements in the evaluation of the benefit of cochlear implantation, namely the electrically evoked auditory brainstem response (EABR), electrically evoked middle latency response (EMLR) and electrically evoked late latency response (EALR). To study the interdependence of these responses, the present paper deals with a combination of EABR, EMLR and EALR measurements obtained from 15 postlingually deaf subjects implanted with the Nucleus multichannel device at the University Hospital Nijmegen. In particular, we investigated whether there were intercorrelations between amplitude and latencies of the evoked potential peaks and/or correlations with long-term speech perception scores. Significant correlations were found between the peak V amplitude of the EABR and the NaPa and NbPb amplitudes of the EMLR. No significant correlation was found between the EABR and EMLR amplitudes on the one hand and EALR peak amplitudes on the other. In addition, no significant correlations were found between any of the EABR or EMLR peak amplitudes and speech perception test results. A moderate but significant relation was found between the EALR peak amplitude and speech perception test results. Unlike latencies of earlier peaks, the latency of the EALR peak P2 was significantly related to the speech perception scores.
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