M.C. Pérez-Abalo

Frequency-specific Audiometry Using Steady-state Responses

Objective: To evaluate the audiometric usefulness of steady‐state responses to multiple simultaneous tones, amplitude‐modulated at 75 to 110 Hz. Design: Steady‐state responses to multiple tones amplitude‐modulated at different rates between 75 and 110 Hz and presented simultaneously were recorded at different intensities in normal adults, well babies, normal adults with simulated hearing loss, and adolescents with known hearing losses. Response thresholds were compared with behavioral thresholds. Results: In normal adults the thresholds for steady‐state responses to tones of 0.5, 1, 2, and 4 kHz were 14 ± 11, 12 ± 11, 11 ± 8, and 13 ± 11 dB, respectively, above behavioral thresholds for air‐conducted stimuli, and 11 ± 5, 14 ± 8, 9 ± 8, and 10 ± 10 dB above behavioral thresholds for bone‐conducted stimuli. In well babies tested in a quiet environment, the thresholds were 45 ± 13, 29 ± 10, 26± 8, and 29 ± 10 dB SPL. In adolescents with known hearing losses, the steady‐state responses thresholds predict behavioral thresholds with correlation coefficients (r) of 0.72, 0.70, 0.76, and 0.91 at 0.5, 1, 2, and 4 kHz, respectively. Conclusion: Steady‐state responses to tones amplitude‐modulated at 75 to 110 Hz can be used for frequency‐specific objective audiometry. The multiple‐stimulus technique allows thresholds to be estimated for eight different stimuli at the same time.

Steady state responses to multiple amplitude-modulated tones: an optimized method to test frequency-specific thresholds in hearing-impaired children and normal-hearing subjects.

Objective To evaluate, using statistical methods, the usefulness of the binaural multiple frequency auditory steady state responses (MF SSRs) for objective, frequency-specific audiometry in a large sample of hearing-impaired children and normal-hearing subjects. Design The MF SSRs were recorded in a sample of 43 hearing-impaired children (86 ears) and 40 normal-hearing young adults (80 ears). Simultaneous carrier tones (0.5, 1, 2, and 4 kHz) modulated in amplitude at different rates (77 to 105 Hz) were presented binaurally (TDH 49 earphones) at variable intensities (110 to 20 dB SPL). For each subject the response thresholds (RTHs) at 0.5, 1, 2, and 4 kHz, were determined automatically (F test) and compared with the corresponding behavioral thresholds (BTHs). Results In the normal-hearing subjects, RTHs were detectable, on average, between 11 and 15 dB above the BTH. These differences were significantly smaller in the hearing-impaired (5 to 13 dB). Also a close correspondence was found between the subjective and objective audiogram curves in both groups. The within subject Spearman correlation coefficients calculated between the two curves, were in most cases above the significance cut off point (p < 0.05). Also in 1-way repeated measures analysis of variance, the overall error in the estimation of the audiogram (vector across frequency of absolute distances between the curves) did not differ significantly from zero. Conclusions The binaural MF SSR was proven to be a valid technique for the estimation of an objective audiogram, in a large sample of hearing-impaired children and normal-hearing subjects. With this method, frequency-specific thresholds at 0.5, 1, 2, and 4 kHz could be determined in all subjects (and both ears) with no appreciable loss in accuracy and a considerable reduction in testing time (average recording time = 21 minutes) when compared with other frequency-specific techniques.

Comparison of statistical indicators for the automatic detection of 80 Hz auditory steady state responses

Objective: To evaluate, using receiver operation characteristic (ROC) curves, the performance of several statistical indicators in the objective detection of 80 Hz steady state auditory evoked responses. Design: Steady state auditory evoked responses elicited by amplitude modulated tones of 500 and 1000 Hz, were obtained in 16 normal adults. Recordings were made at intensities ranging from 80 to 30 dB SPL and without stimulation. Four statistics: coherence synchrony measure, circularT2, a new variant of Hotelling T2(labeled HT2) and a test for hidden periodicity (F test) were calculated. The statistics were compared using ROC curves and bootstrapping techniques. Two outcome measures were considered: behavioral threshold prediction and averaging efficiency. Results: All indicators were highly accurate to detect a response (8 to 9 dB above mean behavioral threshold for the 1000 Hz and 14 to 16 dB for the 500 Hz carrier). Responses could be reliable detected after averaging about five individual epochs of long duration. No statistically significant differences were evidenced though in their capability to predict behavioral threshold or their averaging efficiency. Conclusions: Despite the more adequate statistical properties of some of these indicators no significant differences were found in their performance. Thus all of these indicators could be recommended for automatic detection of 80 Hz auditory steady state responses.

Testing topographic differences between event related brain potentials by using non-parametric combinations of permutation tests

MANOVA and repeated measures ANOVA approaches have provided evidence of a number of limitations in several event-related potential (ERP) studies due to violations of their statistical assumptions and the typically moderate size of the available sample. Alternative, computer-intensive methods based on permutation principles have recently been developed. Up to now this methodology has focused mostly on magnitude differences between scalp distributions as measured by t statistics. In this paper the scope of permutation techniques in ERP analysis was widened. A new statistic (D statistic) is introduced to compare the shapes of scalp distributions of ERPs. Additionally a general non-parametric combinatory technique is introduced to evaluate, by means of multivariate permutation tests, several time points and/or recording sites in ERP data. The methodology described here was used to test if two ERP components elicited during word-pair matching tasks to semantic or phonological incongruences had different scalp distributions.

Test accuracy and prognostic validity of multiple auditory steady state responses for targeted hearing screening

The test accuracy and prognostic validity of Multiple Auditory Steady State Responses (MSSR) and click Auditory Brainstem Responses (cABR) was compared within the context of a targeted screening protocol. A sample of 508 high-risk babies was first screened using cABR and MSSR (500 and 2000 Hz). All children (failed/pass) were called back at three to four years of age to determine their hearing status (pure-tone audiometry). Although both methods showed an equally good test performance in the first screen (sensitivity: 100% and specificity: 92–95%), the MSSR may have some potential advantage to identify low-frequency hearing loss. Furthermore, the confirmatory audiometry with MSSR predicted the child hearing status more accurately than the cABR. In conclusion, the MSSR can provide valuable information for the diagnosis and management of infants earlier detected by a screening protocol and further developed might be also useful as a screening test. Sumario Se comparó la eficiencia diagnóstica y el valor pronóstico de los potenciales evocados auditivos de estado estable a múltiples frecuencias (MSSR, siglas en inglés) con los potenciales evocados auditivos de tallo cerebral con clicks (cABR, siglas en inglés) en el contexto de un programa de tamizaje auditivo de niños con factores de riesgo. Inicialmente se realizó un tamizaje con cABR y MSSR (0.5 y 2 kHz) a una muestra de 508 bebés de alto riesgo. Todos los niños (los que pasaron y los que fallaron) se reevaluaron a los 3 o 4 años de edad para determinar su estado auditivo (audiometría tonal). Aunque los dos métodos mostraron igualmente buen desempeño en el primer tamizaje (sensibilidad: 100% y especificidad: 92–95%) los MSSR pueden tener una ventaja potencial para identificar hipoacusias en tonos graves. Además la prueba audiométrica confirmatoria con MSSR predijo el status auditivo del niño con mas precisión que los cABR. En conclusión, los MSSR pueden proporcionar información valiosa para el diagnóstico y tratamiento de niños previamente detectados por un programa de tamizaje y en un futuro pueden ser también útiles como prueba de tamizaje.

Brain potentials and the availability of semantic and phonological codes over time

ERPs were recorded from subjects performing semantic and rhyme matching tasks using either spoken words, printed words or pictures as stimuli. Mismatches enhanced N400 (in the semantic task) and N450 (in the rhyme task). Onset and peak latencies were shorter for N450 than for N400 with spoken words; this relationship was inverted for pictures. Thus these latencies could index availability of semantic and phonological codes. For printed words, the latencies were shorter for N400 than N450, a result that supports direct-access models of reading with late phonological code activation. The longer latencies found for N400 and N450 to pictures could suggest longer initial decoding for pictures with respect to words.

Cross-modal plasticity in deaf child cochlear implant candidates assessed using visual and somatosensory evoked potentials

INTRODUCTION Cross-modal plasticity has been extensively studied in deaf adults with neuroimaging studies, yielding valuable results. A recent study in our laboratory with deaf-blind children found evidence of cross-modal plasticity, revealed in over-representation of median nerve somatosensory evoked potentials (SEP N20) in left hemisphere parietal, temporal and occipital regions. This finding led to asking whether SEP N20 changes are peculiar to deaf-blindness or are also present in sighted deaf children. OBJECTIVE Assess cross-modal plasticity in deaf child cochlear implant candidates using neurophysiological techniques (visual evoked potentials and median nerve somatosensory evoked potentials). METHODS Participants were 14 prelingually deaf children assessed in the Cuban Cochlear Implant Program. Flash visual-evoked potentials and SEP N20 were recorded at 19 scalp recording sites. Topographic maps were obtained and compared to those of control group children with normal hearing. Analysis took into account duration of hearing loss. RESULTS Topographic maps of flash visual-evoked potentials did not show changes in deaf child cochlear implant candidates. However, SEP N20 from right median nerve stimulation did show changes from expansion of cortical activation into the left temporal region in deaf children aged ≥7 years, which was interpreted as neurophysiological evidence of cross-modal plasticity, not previously described for this technique and type of somatosensory stimulus. We interpret this finding as due in part to duration of deafness, particularly related to handedness, since expansion was selective for the left hemisphere in the children, who were all right-handed. CONCLUSIONS Cortical over-representation of SEP N20 in the left temporal region is interpreted as evidence of cross-modal plasticity that occurs if the deaf child does not receive a cochlear implant early in life-before concluding the critical period of neural development-and relies on sign language for communication.

New system for neonatal hearing screening based on auditory steady state responses.

Abstract NEURONIC-A 6.0 is a system for objective detection of hearing loss by means of the recording and analysis of auditory steady state responses. The system generates digitally Amplitude Modulated tones of different frequencies, allowing the mix of these and the simultaneous presentation through different transducers (earphone and bone vibrator) at different intensities. The system also includes a procedure for artefacts rejection based on the trajectory of variation of the residual noise through time and quantitative indicators or statistics, calculated in the frequency domain, to control the acquisition of the response process and detect automatically the presence or absence of the same. The whole working procedure is automated, which means that once the recording has started, a final result can be obtained in binary form (pass or fail) without the intervention of the examiner.

Cross-modal plasticity in cuban visually-impaired child cochlear implant candidates: topography of somatosensory evoked potentials

INTRODUCTION Studies of neuroplasticity have shown that the brains neural networks change in the absence of sensory input such as hearing or vision. However, little is known about what happens when both sensory modalities are lost (deaf-blindness). Hence, this study of cortical reorganization in visually-impaired child cochlear implant (CI) candidates. OBJECTIVE Assess cross-modal plasticity, specifically cortical reorganization for tactile representation in visually-impaired child CI candidates, through study of topography of somatosensory evoked potentials (SEP). METHODS From April through September 2005, SEP from median and tibial nerve electrical stimulation were studied in 12 visually-impaired child CI candidates aged 3-15 years and 23 healthy controls. Following placement of 19 recording electrodes using the International 10-20 System , SEP were recorded and then processed. Topographic maps were obtained for SEP N20 (median nerve) and SEP P40 (tibial nerve), permitting assessment of cortical reorganization by comparing visually-impaired, deaf childrens maps with those of healthy children by means of visual inspection and statistical comparison using a permutation test. RESULTS SEP N20 topography was significantly more extensive in visually-impaired child CI candidates than in healthy children. An asymmetrical pattern occurred from the expansion of hand tactile activation into the temporal and occipital regions in the left hemisphere on right median nerve stimulation. This did not occur for SEP P40 on tibial nerve stimulation (right and left). Magnitude of expanded SEP N20 response was related to severity of visual impairment and longer duration of dual sensory loss. CONCLUSIONS Changes in SEP N20 topography are evidence of cross-modal plasticity in visually-impaired child CI candidates, appearing to result from a complex interaction between severity of visual impairment and duration of multisensory deprivation.

Different functional properties of on and off components in auditory brainstem responses to tone bursts.

Auditory brainstem responses to tone bursts of constant rise and fall time and variable plateau were obtained in 7 normal hearing adults with a vertex to mastoid electrode configuration. In all records, two vertex-positive components (A, B) were present. Peak A is probably an onset response. Peak B latency increased linearly with plateau duration (r = 0.93) and seems to be an off response. White and notched acoustic noise masking had a different effect on the two components. A greater latency shift was observed for peak A than for peak B, thus reducing the interpeak interval in the masked response. When using high-pass noise, as we lowered the cut-off points from 4 to 0.5 kHz, there was also a greater latency increment for peak A than for peak B. These results suggest a more apical cochlear origin for the off response.