Spatial Hearing Is Impaired in Children with Bilateral Cochlear Implants.
Robel Alemu (University of Toronto), Abstract #142.
Robel Alemu, MSc, PhD Candidate, University of Toronto
The present study aimed to explore spatial hearing abilities of children with bilateral cochlear implants (BCI) in response to stationary and moving sounds.
Benefits of BCI in children are clear but binaural/spatial hearing remains impaired. It is not known whether these deficits extend to perception of moving versus stationary sound.
Localization was measured in a 2-m x 2-m x 2-m soundbooth with a speaker and LED light fixed to the end of a 1-m moving arm and concealed by a black curtain. Stimuli were either auditory (band-pass filtered white-noise or 40-Hz amplitude modulated 1-kHz pure tone) or visual (blue light). Stationary stimuli were presented at any location along a pseudorandom range within a 120° arc in the azimuthal plane and moving stimuli were presented with different degree change (0, 20, 40, where “+” indicates rightward and “–“ indicates leftward). Root-mean-square error (RMSE) between stationary stimulus location over the 120 arc were calculated and response and logistic regression quantified perception of moving sound direction. Participants were 22 children with BCI [MAge(SE) = 13.3(0.71) years] and 6 typically developing (TD) peers [MAge(SE) = 12.8(0.54) years].
Data were collected from 14 children who received implants simultaneously at 4.74 years and 8 who received their first CI at age 2.63 years and the second after an inter-implant delay of 3.10 years ± 0.87 SE. Results revealed high errors for localization of both auditory and visual stationary stimuli in the BCI group [RMSEauditory=24.2(12.1); RMSEvisual=9.47(11.6)] compared to TD peers [RMSEauditory=3.95(1.19); RMSEvisual=3.62(4.06)]. Perception of moving stimuli was also impaired as measured by low slopes to sound (Slope=0.08) and light (Slope=0.7) in the BCI group compared to peers (Slopeauditory=0.91; Slopevisual=1.13).
Findings reveal significant spatial perception impairments in children with BCI which are not restricted to hearing.
Neural Correlates of Auditory Working Memory in Cochlear Implant Users Are Related to Speech Perception in Noise Ability.
Priyanka Prince, Joseph Chen, Trung Le, Andrew Dimitrijevic, and Vincent Lin (Sunnybrook Research Institute), Abstract #143.
Priyanka Prince, MSc, Sunnybrook Research Institute
To explain the variability found in speech perception in noise in cochlear implant users using neurological measures.
A common concern for individuals with severe-to-profound hearing loss fitted with cochlear implants (CIs) is difficulty following conversations in noisy environments. Previous work has shown that clinically measured speech perception in noise (SIN) scores yield high degrees of variability in CI users where 10-22% of variance can be explained by age and duration of hearing and even less can be explained by surgical factors leaving a majority of the variance unaccounted for. A possible factor contributing to the wide range of speech perception scores is individual differences in the recruitment of cognitive resources including working memory and attention.
In this study, we investigated behavioural and neural correlates of auditory working memory in 14 CI users using high-density electroencephalogram (EEG) while participants completed an N- back task consisting of two conditions, 0-back and 2-back. The behavioural outcomes and neural activations from this task were then correlated with SIN scores. The auditory stimuli presented in each trial was ten double-digit numbers (DDN).
Behavioural results yielded significant correlations between the 2- back task performance and speech in noise perception in noise. CI users with higher SIN scores perform more accurately on the 2- back condition compared to CI users with lower speech perception scores suggesting higher degrees of working memory ability in this group. Electrophysiology showed that auditory encoding (N1) was significantly related to speech in noise perception and significant correlations between neural oscillations (alpha/beta, beta, and theta) and SIN ability were observed.
These results suggest that differences in working memory, during the encoding of speech stimuli, contributes to the observed variability in speech in noise perception in cochlear implant users.
Developmental Balance Effects of Vestibular and Auditory Impairments in Childhood.
Melissa Hazen, Sharon Cushing, and Karen Gordon (The Hospital for Sick Children), Abstract #138.
Melissa Hazen, MSc., Aud(C), Audiologist, PhD Candidate, The Hospital for Sick Children
This study aims to: 1) define the prevalence of vestibular impairments in children presenting with risks; and 2) determine the relationship between vestibular impairment and poor balance in these children.
Risk factors for pediatric vestibular impairments (VI) which could impair balance are hearing loss, migraine, and dizziness. For example, VIs often occur in children with hearing loss (HL) (20- 70%). The problem is that present clinical test batteries to identify VI require behavioral cooperation and comprehension of the task which makes testing vestibular function in young children challenging. Potential candidate tests for pediatric vestibular testing are measures of the vestibular ocular reflex (VOR) and vestibular myogenic potentials (VEMPs) which assess the otoliths. Early identification of children with VI could direct habilitation and avoid developmental delays.
A retrospective review of previously validated measures of vestibular end-organ function (VOR tests, VEMPs) and measures of balance function (BOT2) were available in a clinical cohort of 603 children who presented with risks for VI. They were divided into two cohorts (HL:202; No HL:401). The average age in the HL group (F:102, M:100) was 10.05 years (SD=5.45), and in the No HL group (F:225, M:176) was 10.72 years (SD=5.49). Comparisons between available vestibular tests and balance were conducted using mixed model linear regressions, accounting for covariates of age, sex, etiology, and degree of HL.
Rates of VI in the HL group ranged from 30-50% and occurred in 10- 30% of the No HL group. Balance function on the BOT2 fell below the normative range in more of the HL group (37%) than the No HL group (18%) (t(247.23)=4.94, p<0.05).
The findings suggest that risks of pediatric VI are particularly high in children with hearing loss.
Objective Measures of Quality of Life in Cochlear Implant Users.
Andrew Dimitrijevic (Sunnybrook Research Institute), Abstract #145.
Andrew Dimitrijevic, PHD, Scientist, Sunnybrook Health Sciences
To determine if objective measures such as psychoacoustics and electrophysiology (i.e., EEG) can be used to predict subjective impressions of hearing quality of life (QoL) in cochlear implant (CI) uses.
Recent work has shown that hearing QoL in CI users cannot be predicted by standard clinical outcome measures such as speech perception in noise. One reason for this apparent discrepancy is that QoL reflects listening ability/difficulties in the “real world” with complex visual and auditory distractors whereas standard clinical measures occur in tightly controlled sound booths with minimal distractions. We hypothesized that measures using stimuli and conditions that mimic realistic listening environments would yield strong relationships to QoL.
A behavioural and EEG paradigm based on selective spatial attention in the presence of talker distractors were developed. Behaviourally, target triple digits were presented at a single centre loudspeaker while distractor triple digits were presented at speakers situated at ±45° or ±90°. The distractor voice was either the same or different as the target sound. The target to distractor ratio was adaptively varied to yield 50% performance. The EEG portion of the experiment used an audiobook “The Diary of a Wimpy Kid” played from the centre speaker as a stimulus while distractors (different story segments) were played at ±45° or ±90° and same/difference voices. “Neural speech tracking” determined by computing the coherence between the audiobook speech envelope and brain response. QoL was assessed using the SSQ (Speech, Spatial Qualities) and the CIQOL35 questionnaires.
Fifteen adult CI users participated. Significant correlations were observed between SSQ and target-distractor ratio. Similarly, significant correlations were observed between SSQ and neural speech tracking originating from the auditory cortex.
Despite the subjective nature of QoL assessments, objective estimates of QoL based on psychoacoustics and EEG is feasible.