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.

Children who use bilateral cochlear implants (BiCIs) show significantly poorer sound localization skills than their normal hearing (NH) peers. This difference has been attributed, in part, to the fact that cochlear implants (CIs) do not faithfully transmit interaural time differences (ITDs) and interaural level differences (ILDs), which are known to be important cues for sound localization. Interestingly, little is known about binaural sensitivity in NH children, in particular, with stimuli that constrain acoustic cues in a manner representative of CI processing. In order to better understand and evaluate binaural hearing in children with BiCIs, the authors first undertook a study on binaural sensitivity in NH children ages 8-10, and in adults. Experiments evaluated sound discrimination and lateralization using ITD and ILD cues, for stimuli with robust envelope cues, but poor representation of temporal fine structure. Stimuli were spondaic words, Gaussian-enveloped tone pulse trains (100 pulse-per-second), and transposed tones. Results showed that discrimination thresholds in children were adult-like (15-389 ls for ITDs and 0.5-6.0 dB for ILDs). However, lateralization based on the same binaural cues showed higher variability than seen in adults. Results are discussed in the context of factors that may be responsible for poor representation of binaural cues in bilaterally implanted children.

Hypothesis A novel reaching for sound (RFS) methodology can yield a high level of spatial hearing ability in 2-3 year old children with normal hearing and with bilateral cochlear implants (BiCIs). Background A growing number of children who are deaf are receiving BiCIs at a young age. Their spatial hearing abilities are emerging, but highly variable within the population. Our novel reaching for sound method utilizes an ecologically valid approach that engages children and maintains their motivation. The present work was aimed at using the novel RFS method to evaluate spatial hearing in 2-3 year olds with normal hearing and with BiCIs. Methods Six children with BiCIs and fifteen children with NH, ages 2-3 years participated. In the BiCI group testing was done in bilateral or single CI (unilateral) conditions. Loudspeakers were separated by either ±60°, ±45°, ±30° or ±15° degrees. On each trial a small toy was hidden behind one of the loudspeakers, and the child’s task was to reach through a hole in the curtain above the loudspeaker, to indicate source location. Children were reinforced for correct responses. At each angle, the ability of the child to reach criterion of ≥80% correct was assessed. Results All BiCI users reached criterion at all angles tested in the bilateral condition, however, performance was poorer when using a single CI. Of the 15 NH children, 13 were able to perform the task accurately and reached criterion at all angles. Conclusions Spatial hearing skills studied with the RFS method revealed novel findings regarding the emergence of sound localization in very young BiCI users.