Binaural masking level difference in skilled reading children and children with dyslexia.

BACKGROUND: Combining stimuli arriving at both ears makes it possible to locate sounds in the environment and to better detect signals or understand speech in noise when the sound sources are separated spatially. The sensitivity of the binaural system to interaural differences in time and amplitude can be investigated by means of the binaural masking level difference (BMLD). The age at which the BMLD reaches adult levels appears to depend partly upon masker bandwidth. Less is known about the effect of masker's level on the development of BMLD in children. In the present study we assessed the effect of masker level on the BMLD of 3rd and 5th grade skilled reading children. In view of possible binaural hearing effects in dyslexia, the BMLD of a group of 5th grade children with reading difficulties was measured. METHODS: Detection thresholds of 500 Hz pure tone were measured at noise levels of 40 dBHL, 50 dBHL and 60 dBHL. RESULTS: All subjects presented increased MLD values with the rise of noise intensity between 40 dBHL and 60 dBHL. Among the skilled readers the results showed that younger children had smaller BMLDs than older children at all masker levels. However, a significant group-by-intensity interaction indicated that although the reading disabled group had reduced BMLD values than older skilled readers at noise levels of 50 dBHL and 60 dBHL, no difference was found between their BMLD values and those of the young skilled readers at noise levels of 50 dBHL and 60 dBHL. Moreover, their BMLD values at noise level of 40 dBHL were higher than those of the 3rd grade typically reading students while no difference was found between them and 5th grade efficient readers. CONCLUSIONS: These results support the existence of both quantitative and qualitative differences in binaural hearing of children with developmental dyslexia.

Cortical neural activity underlying speech perception in postlingual adult cochlear implant recipients.

Auditory event-related potentials (AERPs) and the simultaneously obtained behavioral measures (performance accuracy and reaction time) were used to study speech perception in postlingual adult cochlear implant (CI) recipients and in normal-hearing (NH) controls. AERPs were recorded while subjects were performing oddball discrimination tasks with increasing acoustic-phonetic demand. The tasks consisted of pairs of natural syllables that differed by one of the following phonetic contrasts: vowel place, voicing, vowel height, and place of articulation. Results indicated that the P3 potential was comparable in CI recipients and NH controls when the acoustic cues to the perception of the phonetic contrast were accessible. With the reduction in accessibility to the essential temporal and/or spectral cues, CI recipients exhibited delayed (prolonged P3 latency) and less synchronous (reduced amplitude) central speech-sound processing compared to NH controls. Among the phonetic contrasts used in the present study the place of articulation contrast yielded (1) the most prominent differences between CI recipients and NH controls across all measures, and (2) significant correlations between the neurophysiologic manifestation of speech discrimination (i.e. P3 latency), and conscious integration of perceptual information (i.e. performance accuracy and reaction time). Thus, P3 exposed the difficulties imposed on the impaired auditory system of CI recipients especially when elicited by speech contrasts that required processing of brief temporal-spectral cues. These findings support the P3 potential as a sensitive neural index of cortical processing that may provide information regarding accessibility and neural encoding of distinct acoustic-phonetic cues in CI recipients.

Electrical stimulation levels and electrode impedance values in children using the Med-El Combi 40+ cochlear implant: a one year follow-up.

The present study was designed to follow changes in electrical stimulation levels and electrode impedance values (EIV) in children using the Med-El Combi 40+ cochlear implant (CI) during the first 12 months of implant use. The maps of 24 prelingually deaf children implanted at a mean age of 5.9 years (range 1-15.9 years) using the TEMPO+ speech processor programmed with CIS+ strategy were examined at five time points: initial stimulation, and 1, 3, 6, and 12 months post-initial stimulation. Most comfortable levels (M) and electrode impedance values (EIV) were analyzed according to three cochlear segments: apical, medial, and basal. Results indicated a significant increase in M levels until the 3-month time point, thereafter stabilization was evident. Furthermore, M levels in the apical segment were lower than those in the medial and basal segments. EIV decreased from initial stimulation to the 3-month time point and was then stable through the study follow up. Interestingly, the finding of higher EIV in the apical segment may be attributed to the physical characteristics of the Med-El electrode. In conclusion, the pattern of stabilization of M levels found in the present study is similar to that reported for children using other devices. The data presented here may be useful as a guideline for programming M levels and monitoring EIV in infants and young children. They may further help clinicians to identify those children that fall outside the 'typical' range.

NRT-based versus behavioral-based MAP: a comparison of parameters and speech perception in young children.

The present study was designed to evaluate the effect of neural response telemetry (NRT)-based cochlear implant (CI) programming versus behavioral-based programming on electrical stimulation parameters (MAP) threshold (T) and comfortable (C) levels and speech perception abilities in young children, during the first year of implant use. Ten congenitally deaf children at the age of 12-39 months (mean age: 25.2 months) implanted with the Nucleus 24R(CS) CI participated in the study. The group was randomly divided into two: (1) NRT-based MAP group (n = 5) consisted of children who were programmed using intra-operative NRT measurements; (2) behavioral-based MAP group (n = 5) consisted of children who were programmed using the behavioral responses of the patients. MAP parameters as well as sound-field aided thresholds and speech perception abilities were compared between the two groups at consecutive programming sessions: 1, 3, 6, and 12 months post initial stimulation. Results indicated no significant differences among NRT-based MAPs and behavioral-based MAPs. Although MAP profiles at initial stimulation differed in the apical region, these differences decreased with time. In addition, a gradual increase of T and C levels of NRT-based MAPs as well as those of behavioral-based MAPs was evident until the 1-month time point, thereafter stabilization occurred. Sound-field aided thresholds improved with time for both groups; however, they were found to be significantly better for the NRT-based MAP group. Despite these differences, speech perception abilities were comparable among groups at 12 months post initial stimulation. NRT-based programming was found to be significantly shorter than behavioral-based programming. In conclusion, for this small group of children, our findings support the use of NRT for programming of young children during the initial period after implantation.

Reduced auditory efferent activity in childhood selective mutism.

BACKGROUND: Selective mutism is a psychiatric disorder of childhood characterized by consistent inability to speak in specific situations despite the ability to speak normally in others. The objective of this study was to test whether reduced auditory efferent activity, which may have direct bearings on speaking behavior, is compromised in selectively mute children. METHODS: Participants were 16 children with selective mutism and 16 normally developing control children matched for age and gender. All children were tested for pure-tone audiometry, speech reception thresholds, speech discrimination, middle-ear acoustic reflex thresholds and decay function, transient evoked otoacoustic emission, suppression of transient evoked otoacoustic emission, and auditory brainstem response. RESULTS: Compared with control children, selectively mute children displayed specific deficiencies in auditory efferent activity. These aberrations in efferent activity appear along with normal pure-tone and speech audiometry and normal brainstem transmission as indicated by auditory brainstem response latencies. CONCLUSIONS: The diminished auditory efferent activity detected in some children with SM may result in desensitization of their auditory pathways by self-vocalization and in reduced control of masking and distortion of incoming speech sounds. These children may gradually learn to restrict vocalization to the minimal amount possible in contexts that require complex auditory processing.

Low-resolution electromagnetic tomography (LORETA) in children with cochlear implants: a preliminary report.

The current preliminary report describes the utilization of low-resolution electromagnetic tomography (LORETA) in a small group of highly performing children using the Nucleus 22 cochlear implant (CI) and in normal-hearing (NH) adults. LORETA current density estimations were performed on an averaged target P3 component that was elicited by non-speech and speech oddball discrimination tasks. The results indicated that, when stimulated with tones, patients with right implants and NH adults (regardless of stimulated ear) showed enhanced activation in the right temporal lobe, whereas patients with left implants showed enhanced activation in the left temporal lobe. When stimulated with speech, patients with right implants showed bilateral activation of the temporal and frontal lobes, whereas patients with left implants showed only left temporal lobe activation. NH adults (regardless of stimulated ear) showed enhanced bilateral activation of the temporal and parietal lobes. The differences in activation patterns between patients with CI and NH subjects may be attributed to the long-term exposure to degraded input conditions which may have resulted in reorganization in terms of functional specialization. The difference between patients with right versus left implants, however, is intriguing and requires further investigation.

Effect of voice onset time (VOT), stop burst and vowel on the perception of voicing in Hebrew stops: preliminary results.

Very few studies investigated systematically the acoustic cues for the perception of voicing stops in Hebrew. Voicing is characterized by several parameters of which the voice onset time (VOT) was found to be the primary cue for its perception. There are, however, other known acoustic cues to voicing such as transition to the first formant (F1) and the initial burst. The purpose of the present study was to measure the relative weighting of these various acoustic cues in the perception of Hebrew voicing, using the conflicting cues paradigm. Thirteen adults with normal hearing participated in this study. Stimuli consisted of one pair of meaningful words that differ in the voicing of the initial stop. Four different continua were constructed from the pair of natural stimuli. The first two consisted of the voiced burst combined with the vowel that was truncated from the consonant-vowel combination (where the consonant was voiced or voiceless). The remaining two continua consisted of the voiceless burst combined with the same truncated vowels. For each stimulus, a VOT continuum was created varying from -40 to +40 ms in 10 ms segments. Subjects were tested using a two alternative forced choice labeling procedure. The percent of responses to each stimulus of each VOT continuum (/b-p/) was calculated for each individual and combination. The results show that each acoustic cue contributed to the perception of initial voicing in Hebrew: (1) When the stimulus was constructed from the voiced cues, positive VOT values were needed for the voice/voiceless distinction; (2) when the stimulus was constructed from the voiceless cues, negative VOT values were needed for the voicing distinction; and (3) when the stimulus was constructed from voiced and voiceless cues, intermediate VOT values were needed for the voicing distinction. These results provide initial information regarding the relative effect of the acoustic cues in the perception of Hebrew stop voicing.

Changes over time in electrical stimulation levels and electrode impedance values in children using the Nucleus 24M cochlear implant.

OBJECTIVE: The present study was designed to evaluate changes in psycho-electric parameters, i.e. threshold levels, comfortable levels, dynamic range, and electrode impedance values during the 1st year post-implantation, in children using the Nucleus 24M cochlear implant system. METHODS: The maps of 25 pre-lingual children programmed with ACE strategy in Monopolar 1 + 2 mode were examined at five time points: connection, 1, 3, 6, and 12 months post-initial stimulation. Maps and electrode impedance values were analyzed according to three cochlear segments: basal, medial, and apical. RESULTS: Significant elevations of thresholds, comfortable levels, and dynamic range were found during the first few months of implant use. Specifically, threshold increased and dynamic range widened until the 3 months visit, whereas comfortable levels continued to increase until the 6 months visit, thereafter levels stabilized. Electrode impedance values decreased significantly from connection to the 1-month visit thereafter a stabilization of values was evident. In addition, thresholds and comfortable levels were found to be significantly lower in the apical segment, whereas dynamic range and electrode impedance values did not differ among the cochlear segments. CONCLUSIONS: Significant changes in psycho-electric parameters and electrode impedance values were evident during the first 6 months of implant use. Given the important role of an optimal map for speech perception, frequent programming sessions during the first few months of implant use are essential.

Auditory backward masking in normal hearing children.

Backward masking (BM) is an auditory phenomenon in which the threshold of an auditory signal is elevated due to the presence of another signal (masker) that follows it. Models related to central auditory temporal processes, such as the 'temporal window' model, have been suggested to explain this phenomenon. If this assumption is correct then BM thresholds are expected to improve as a function of age. Electrophysiological data suggest that the central auditory system undergoes maturation in the first two decades of life. Empirical data on the development of BM with age are limited. Therefore, the goals of the present study were to study the effect of age on the performance of backward masking in normal developing children and to determine the age at which children reach adult-like performance. Subjects were 30 normal developing children divided into three groups according to age: 7, 9 and 11 years old. Stimuli consisted of a 1000 Hz pure tone and a bandpass masker (600-1400 Hz). Three BM threshold estimates were obtained for each subject using a three-alternative forced-choice adaptive procedure. The data show a trend for improvement in backward-masking thresholds with increasing age. Specifically, 7 and 9 year-old children performed significantly poorer than those reported for adults, whereas 11 year-old children reached adult-like performance. These data contribute to the small body of literature on backward masking in normal developing children. They are in keeping with what is known regarding the age of physiological maturation of the auditory system and have important clinical implications in the assessment of children with suspected temporal processing deficits.