Shelly Godar

Benefits of bilateral cochlear implants and/or hearing aids in children

This study evaluated functional benefits from bilateral stimulation in 20 children ages 4–14, 10 use two CIs and 10 use one CI and one HA. Localization acuity was measured with the minimum audible angle (MAA). Speech intelligibility was measured in quiet, and in the presence of 2-talker competing speech using the CRISP forced-choice test. Results show that both groups perform similarly when speech reception thresholds are evaluated. However, there appears to be benefit (improved MAA and speech thresholds) from wearing two devices compared with a single device that is significantly greater in the group with two CI than in the bimodal group. Individual variability also suggests that some children perform similarly to normal-hearing children, while others clearly do not. Future advances in binaural fitting strategies and improved speech processing schemes that maximize binaural sensitivity will no doubt contribute to increasing the binaurally-driven advantages in persons with bilateral CIs.

Bilateral cochlear implants in children: Localization acuity measured with minimum audible angle

Objective: To evaluate sound localization acuity in a group of children who received bilateral (BI) cochlear implants in sequential procedures and to determine the extent to which BI auditory experience affects sound localization acuity. In addition, to investigate the extent to which a hearing aid in the nonimplanted ear can also provide benefits on this task. Design: Two groups of children participated, 13 with BI cochlear implants (cochlear implant + cochlear implant), ranging in age from 3 to 16 yrs, and six with a hearing aid in the nonimplanted ear (cochlear implant + hearing aid), ages 4 to 14 yrs. Testing was conducted in large sound-treated booths with loudspeakers positioned on a horizontal arc with a radius of 1.5 m. Stimuli were spondaic words recorded with a male voice. Stimulus levels typically averaged 60 dB SPL and were randomly roved between 56 and 64 dB SPL (±4 dB rove); in a few instances, levels were held fixed (60 dB SPL). Testing was conducted by using a “listening game” platform via computerized interactive software, and the ability of each child to discriminate sounds presented to the right or left was measured for loudspeakers subtending various angular separations. Minimum audible angle thresholds were measured in the BI (cochlear implant + cochlear implant or cochlear implant + hearing aid) listening mode and under monaural conditions. Results: Approximately 70% (9/13) of children in the cochlear implant + cochlear implant group discriminated left/right for source separations of ≤20°, and, of those, 77% (7/9) performed better when listening bilaterally than with either cochlear implant alone. Several children were also able to perform the task when using a single cochlear implant, under some conditions. Minimum audible angle thresholds were better in the first cochlear implant than the second cochlear implant listening mode for nearly all (8/9) subjects. Repeated testing of a few individual subjects over a 2-yr period suggests that robust improvements in performance occurred with increased auditory experience. Children who wore hearing aids in the nonimplanted ear were at times also able to perform the task. Average group performance was worse than that of the children with BI cochlear implants when both ears were activated (cochlear implant + hearing aid versus cochlear implant + cochlear implant) but not significantly different when listening with a single cochlear implant. Conclusions: Children with sequential BI cochlear implants represent a unique population of individuals who have undergone variable amounts of auditory deprivation in each ear. Our findings suggest that many but not all of these children perform better on measures of localization acuity with two cochlear implants compared with one and are better at the task than children using the cochlear implant + hearing aid. These results must be interpreted with caution, because benefits on other tasks as well as the long-term benefits of BI cochlear implants are yet to be fully understood. The factors that might contribute to such benefits must be carefully evaluated in large populations of children using a variety of measures.

Studies on bilateral cochlear implants at the University of Wisconsin's Binaural Hearing and Speech Laboratory.

This report highlights research projects relevant to binaural and spatial hearing in adults and children. In the past decade we have made progress in understanding the impact of bilateral cochlear implants (BiCIs) on performance in adults and children. However, BiCI users typically do not perform as well as normal hearing (NH) listeners. In this article we describe the benefits from BiCIs compared with a single cochlear implant (CI), focusing on measures of spatial hearing and speech understanding in noise. We highlight the fact that in BiCI listening the devices in the two ears are not coordinated; thus binaural spatial cues that are available to NH listeners are not available to BiCI users. Through the use of research processors that carefully control the stimulus delivered to each electrode in each ear, we are able to preserve binaural cues and deliver them with fidelity to BiCI users. Results from those studies are discussed as well, with a focus on the effect of age at onset of deafness and plasticity of binaural sensitivity. Our work with children has expanded both in number of subjects tested and age range included. We have now tested dozens of children ranging in age from 2 to 14 yr. Our findings suggest that spatial hearing abilities emerge with bilateral experience. While we originally focused on studying performance in free field, where real world listening experiments are conducted, more recently we have begun to conduct studies under carefully controlled binaural stimulation conditions with children as well. We have also studied language acquisition and speech perception and production in young CI users. Finally, a running theme of this research program is the systematic investigation of the numerous factors that contribute to spatial and binaural hearing in BiCI users. By using CI simulations (with vocoders) and studying NH listeners under degraded listening conditions, we are able to tease apart limitations due to the hardware/software of the CI systems from limitations due to neural pathology.

Difference in precedence effect between children and adults signifies development of sound localization abilities in complex listening tasks

The precedence effect refers to the fact that humans are able to localize sound in reverberant environments, because the auditory system assigns greater weight to the direct sound (lead) than the later-arriving sound (lag). In this study, absolute sound localization was studied for single source stimuli and for dual source lead-lag stimuli in 4-5 year old children and adults. Lead-lag delays ranged from 5-100 ms. Testing was conducted in free field, with pink noise bursts emitted from loudspeakers positioned on a horizontal arc in the frontal field. Listeners indicated how many sounds were heard and the perceived location of the first- and second-heard sounds. Results suggest that at short delays (up to 10 ms), the lead dominates sound localization strongly at both ages, and localization errors are similar to those with single-source stimuli. At longer delays errors can be large, stemming from over-integration of the lead and lag, interchanging of perceived locations of the first-heard and second-heard sounds due to temporal order confusion, and dominance of the lead over the lag. The errors are greater for children than adults. Results are discussed in the context of maturation of auditory and non-auditory factors.

Development of Sound Localization Strategies in Children with Bilateral Cochlear Implants.

Localizing sounds in our environment is one of the fundamental perceptual abilities that enable humans to communicate, and to remain safe. Because the acoustic cues necessary for computing source locations consist of differences between the two ears in signal intensity and arrival time, sound localization is fairly poor when a single ear is available. In adults who become deaf and are fitted with cochlear implants (CIs) sound localization is known to improve when bilateral CIs (BiCIs) are used compared to when a single CI is used. The aim of the present study was to investigate the emergence of spatial hearing sensitivity in children who use BiCIs, with a particular focus on the development of behavioral localization patterns when stimuli are presented in free-field horizontal acoustic space. A new analysis was implemented to quantify patterns observed in children for mapping acoustic space to a spatially relevant perceptual representation. Children with normal hearing were found to distribute their responses in a manner that demonstrated high spatial sensitivity. In contrast, children with BiCIs tended to classify sound source locations to the left and right; with increased bilateral hearing experience, they developed a perceptual map of space that was better aligned with the acoustic space. The results indicate experience-dependent refinement of spatial hearing skills in children with CIs. Localization strategies appear to undergo transitions from sound source categorization strategies to more fine-grained location identification strategies. This may provide evidence for neural plasticity, with implications for training of spatial hearing ability in CI users.

The Effect of Differential Listening Experience on the Development of Expressive and Receptive Language in Children With Bilateral Cochlear Implants

Objectives: Growing evidence suggests that children who are deaf and use cochlear implants (CIs) can communicate effectively using spoken language. Research has reported that age of implantation and length of experience with the CI play an important role in a predicting a child’s linguistic development. In recent years, the increase in the number of children receiving bilateral CIs (BiCIs) has led to interest in new variables that may also influence the development of hearing, speech, and language abilities, such as length of bilateral listening experience and the length of time between the implantation of the two CIs. One goal of the present study was to determine how a cohort of children with BiCIs performed on standardized measures of language and nonverbal cognition. This study examined the relationship between performance on language and nonverbal intelligence quotient (IQ) tests and the ages at implantation of the first CI and second CI. This study also examined whether early bilateral activation is related to better language scores. Design: Children with BiCIs (n = 39; ages 4 to 9 years) were tested on two standardized measures, the Test of Language Development and the Leiter International Performance Scale-Revised, to evaluate their expressive/receptive language skills and nonverbal IQ/memory. Hierarchical regression analyses were used to evaluate whether BiCI hearing experience predicts language performance. Results: While large intersubject variability existed, on average, almost all the children with BiCIs scored within or above normal limits on measures of nonverbal cognition. Expressive and receptive language scores were highly variable, less likely to be above the normative mean, and did not correlate with Length of first CI Use, defined as length of auditory experience with one cochlear implant, or Length of second CI Use, defined as length of auditory experience with two cochlear implants. Conclusions: All children in the present study had BiCIs. Most IQ scores were either at or above that found in the general population of typically hearing children. However, there was greater variability in their performance on a standardized test of expressive and receptive language. This cohort of children, who are mainstreamed in schools at age-appropriate grades, whose mothers’ education is high, and whose families’ socioecononomic status is high, had, as a group, on average, language scores within the same range as the normative sample of hearing children. Further research identifying the predictors that contribute to the high variability in both expressive and receptive language scores in children with BiCIs will provide useful information that can aid in clinical management and decision making.

Binaural sensitivity in children who use bilateral cochlear implants

Children who are deaf and receive bilateral cochlear implants (BiCIs) perform better on spatial hearing tasks using bilateral rather than unilateral inputs; however, they underperform relative to normal-hearing (NH) peers. This gap in performance is multi-factorial, including the inability of speech processors to reliably deliver binaural cues. Although much is known regarding binaural sensitivity of adults with BiCIs, less is known about how the development of binaural sensitivity in children with BiCIs compared to NH children. Sixteen children (ages 9-17 years) were tested using synchronized research processors. Interaural time differences and interaural level differences (ITDs and ILDs, respectively) were presented to pairs of pitch-matched electrodes. Stimuli were 300-ms, 100-pulses-per-second, constant-amplitude pulse trains. In the first and second experiments, discrimination of interaural cues (either ITDs or ILDs) was measured using a two-interval left/right task. In the third experiment, subjects reported the perceived intracranial position of ITDs and ILDs in a lateralization task. All children demonstrated sensitivity to ILDs, possibly due to monaural level cues. Children who were born deaf had weak or absent sensitivity to ITDs; in contrast, ITD sensitivity was noted in children with previous exposure to acoustic hearing. Therefore, factors such as auditory deprivation, in particular, lack of early exposure to consistent timing differences between the ears, may delay the maturation of binaural circuits and cause insensitivity to binaural differences.

Source segregation in noisy environments by children with normal hearing and bilateral cochlear implants.

Spatial release from making (SRM) refers to the improvement in speech intelligibility measured when target and maskers are spatially separated, as opposed to when they are co‐located. SRM is affected by numerous factors that are of interest in this study. Asymmetrical placement of maskers to one side of the head leads to SRM as large as 12 dB in normal‐hearing (NH) adults, due to a combination of monaural head‐shadow and binaural interaction effects. In addition, SRM is affected by the content of the masker and its similarity to the talker. To better study these effects in children, we recently measured SRM when maskers were either symmetrically or asymmetrically distributed in the horizontal plane to the right and left. In addition, the sex of the talker and thus its similarity to the masker were varied. In the NH groups, children between the ages of 4–6 and 7–9 years and adults were tested. In addition, children who are deaf and use bilateral cochlear implants, also 4–6 and 7–9 years of age, participate...

Emergence of sound localization acuity in children who are fitted with bilateral cochlear implants

Sound localization was investigated in children who are born deaf and hear with either monaural or bilateral cochlear implants (CIs). Using a 2AFC discrimination task with stimuli to the right/left, in a sound proof booth, loudspeaker locations varied along the horizontal plane between +/‐70 deg. Minimum audible angle (MAA) thresholds were estimated adaptively. In study 1, 4‐14 year‐old children who received two CIs in sequential procedures participated. They were first tested while functioning monaurally, then at 3‐ and 12‐months following activation of bilateral hearing. Following bilateral activation, MAA thresholds were significantly lower, especially after 12 months. In study 2 children were 2.5 years old, with 6‐20 months of bilateral experience. MAAs were typically better when children had ⩾12 months of exposure to bilateral stimulation. Overall, these findings suggest that binaural hearing abilities can be established in an auditory system that is strictly stimulated with electrically pulsed signa...

Localization suppression and fusion measure of the precedence effect in young children

This study investigated aspects of the precedence effect (PE) known as fusion and localization dominance in children 4–5 years of age. Stimuli were three, 25‐ms noise bursts (2‐ms rise/fall times) with 250‐ms ISI. On PE conditions the lead stimulus was presented from one of six locations in azimuth, and the lag was at 0 deg. Lead‐lag delays varied from 5 to 100 ms. Localization was measured using an identification paradigm. Fusion was measured separately whereby subjects reported whether a single auditory event or two auditory events were perceived. Children reported two sounds on 75% of trials (fusion threshold) at delays ranging from 15 to 35 ms. Below fusion thresholds, the localization of the lead was similar to that of single‐source stimuli. Above fusion thresholds lead localization was significantly degraded, persisting out to 100 ms. Localization of the lag was poor at all delays on which it was reported as being heard. According to these results localization dominance (difficulty localizing the la...