Cross-modal plasticity and speech perception in pre- and postlingually deaf cochlear implant users.

OBJECTIVE: A great amount of variability is observed in speech perception outcomes with cochlear implants. The mechanisms behind the observed variability need to be elucidated. One possible mechanism contributing to the observed variability is the development of cross-modal plasticity. This study examines the association between visual/auditory cross-modal plasticity and speech perception with a cochlear implant in individuals with pre- and postlingual onset of severe to profound hearing loss. DESIGN: The N1 visual evoked potential (VEP) in response to peripheral visual motion stimuli was recorded in individuals with pre- (N = 10) and postlingual (N = 12) onset of severe to profound hearing loss who use a cochlear implant. The association between the amplitude of the N1 VEP response over the right temporal lobe and sentence and word perception scores obtained with the cochlear implant was examined through linear regression analyses. In addition, the association between the duration of auditory deprivation and the amplitude of the N1 VEP response was examined. RESULTS: As the amplitude of the N1 VEP recorded over the right temporal lobe increased, speech perception scores in individuals with prelingual onset of severe to profound hearing loss decreased. However, a clear association between the amplitude of the N1 VEP over the right temporal lobe and speech perception scores was not observed for individuals with postlingual onset of severe to profound hearing loss. Neither group demonstrated an association between the amplitude of the VEP over the right temporal lobe and the duration of auditory deprivation before cochlear implantation. CONCLUSION: The results suggest that cross-modal plasticity accounts for a significant amount of the variability observed in speech perception performance with a cochlear implant in individuals with prelingual onset of severe to profound hearing loss but not in individuals who acquire severe to profound hearing loss later in life. Furthermore, the results suggest that the influence of cross-modal plasticity on speech perception ability is more greatly influenced by when (pre- or postlingually) a person acquires a severe to profound hearing impairment rather than the duration of auditory deprivation before receipt of a cochlear implant.

Pharmacological enhancement of aural habilitation in adult cochlear implant users.

OBJECTIVE: The purpose of this report was to examine the preliminary data collected under a larger on-going feasibility study conducted with cochlear implant patients exploring the potential benefit of pharmacologically-enhanced aural rehabilitation therapy as a means of increasing speech tracking skills. DESIGN: Eight adult cochlear implant participants participated in a randomized, double-blind study and received either 10 mg d-amphetamine (Treatment group, N = 4) or a placebo (Placebo group, N = 4) 60 minutes prior to a 1.5 hour intensive aural rehabilitation session occurring twice a week for two months. Treatment consisted of a multi-step rehabilitation program individualized for each participant to develop auditory-only speech tracking skills. Prior to and at the conclusion of the therapy sessions, SPECT rCBF imaging and speech tracking assessments were conducted. RESULTS: Speech tracking scores of the placebo and treatment groups were similar before the aural habilitation intervention. In the placebo group, speech tracking performance increased 13.5% for visual plus auditory and auditory only presentations as a function of aural habilitation alone. The 10 mg d-amphetamine-facilitated program resulted in minimal increases in visual plus auditory tracking scores (2%) but led to a 43% increase for auditory-only speech tracking. Regional cerebral blood flow measures indicated no substantial improvement of brain activation in the placebo group while both the extent and magnitude of primary and associative auditory cortex activations increased significantly with the pharmacologically enhanced treatment program. CONCLUSIONS: These data support previous studies indicating an accelerated acquisition of speech and language abilities in stroke patients receiving traditional speech therapy in combination with d-amphetamine. Data, however, are preliminary and further study is warranted.

Mode of communication and classroom placement impact on speech intelligibility.

OBJECTIVE: To examine the impact of classroom placement and mode of communication on speech intelligibility scores in children aged 8 to 9 years using multichannel cochlear implants. DESIGN: Classroom placement (special education, partial mainstream, and full mainstream) and mode of communication (total communication and auditory-oral) reported via parental rating scales before and 4 times after implantation were the independent variables. Speech intelligibility scores obtained at 8 to 9 years of age were the dependent variables. PARTICIPANTS: The study included 131 congenitally deafened children between the ages of 8 and 9 years who received a multichannel cochlear implant before the age of 5 years. RESULTS: Higher speech intelligibility scores at 8 to 9 years of age were significantly associated with enrollment in auditory-oral programs rather than enrollment in total communication programs, regardless of when the mode of communication was used (before or after implantation). Speech intelligibility at 8 to 9 years of age was not significantly influenced by classroom placement before implantation, regardless of mode of communication. After implantation, however, there were significant associations between classroom placement and speech intelligibility scores at 8 to 9 years of age. Higher speech intelligibility scores at 8 to 9 years of age were associated with classroom exposure to normal-hearing peers in full or partial mainstream placements than in self-contained, special education placements. CONCLUSIONS: Higher speech intelligibility scores in 8- to 9-year-old congenitally deafened cochlear implant recipients were associated with educational settings that emphasize oral communication development. Educational environments that incorporate exposure to normal-hearing peers were also associated with higher speech intelligibility scores at 8 to 9 years of age.

Functional brain imaging as an objective measure of speech perception performance in adult cochlear implant users.

In this study we examined the role of functional brain imaging of regional cerebral bloodflow (rCBF) with the use of single photon emission computed tomography (SPECT) for the objective measurement of brain performance in adult cochlear implant (CI) users during speech perception. The subjects consisted of nine normal-hearing and eight CI individuals who watched a 15-min videotape under two conditions: (1) a visual-only presentation; and (2) a left-monaural audio and visual presentation. Cortical activations were observed bilaterally in Brodmann areas 41, 42, 21, 22 and 38 for normal-hearing control subjects. Bilateral activations were also observed in CI individuals who demonstrated high performance on open-set speech recognition tasks; however, activations were smaller in both amplitude and extent than those observed for normal-hearing individuals. CI individuals with minimal open-set recognition demonstrated only unilateral activation of auditory cortex in the hemisphere contralateral to the ear of implantation. These data support SPECT as a tool for objectively documenting cortical activations in adult CI users.

Hearing aid users benefit from induction loop when using digital cellular phones.

OBJECTIVE: Hearing aid users have recently been reported to experience problems with electromagnetic interference when using digital cellular phones. This study was undertaken to investigate the possible benefit of an induction loop system developed for use with some cellular phone models, and also to compare the possible benefit in two languages (Finnish and American English) as well as the benefit with two hearing aid technologies (analog versus digital). DESIGN: The study was performed in controlled laboratory conditions at two tertiary care hearing health care centers, one in Oulu, Finland and the other in Dallas, in the United States. The subjects were experienced users of behind-the-ear hearing aids and served as their own controls in three different listening conditions. Thirty-two eligible subjects (20 in Oulu and 12 in Dallas) participated in three test conditions: 1. call with a landline phone, 2. call with a digital cellular phone alone and 3. call with a digital cellular phone coupled to an induction loop. RESULTS: Sentence recognition scores and subjective judgments using a visual analog scale revealed the poorest results with the digital cellular phone alone. When the induction loop was used with the digital cellular phones, sentence recognition scores and the visual analog scale scores were comparable to the scores obtained with a landline phone. The mean sentence recognition score for analog hearing aids was 62.4% (95% confidence interval 50.2 to 74.6) with the landline phone, 12.6% (-1.6 to 26.9) with the digital cellular phone alone, and 63.3% (44.2 to 82.3) when using the digital cellular phone with the induction loop. For digital hearing aids, the sentence recognition scores were 62.4% (51.9 to 72.9), 37.4% (18.0 to 56.8) and 57.6% (39.0 to 76.2), respectively. There was no significant difference in performance between the two centers. However, when using the digital cellular phone alone, there was no drop in the sentence recognition scores with the few (N = 5) digital hearing aids in Dallas. The subjects ranked the digital cellular phone alone as the poorest test condition and the digital cellular phone with an induction loop as the best. CONCLUSIONS: Induction loops appear to offer one possible solution for the incompatibility problem between hearing aids and digital cellular phones. However, the generalizability of the results must be viewed cautiously, because testing included only one induction loop and two digital cellular phone models.