A. Quentin Summerfield

''Sparse'' Temporal Sampling in Auditory fMRI

The use of functional magnetic resonance imaging (fMRI) to explore central auditory function may be compromised by the intense bursts of stray acoustic noise produced by the scanner whenever the magnetic resonance signal is read out. We present results evaluating the use of one method to reduce the effect of the scanner noise: “sparse” temporal sampling. Using this technique, single volumes of brain images are acquired at the end of stimulus and baseline conditions. To optimize detection of the activation, images are taken near to the maxima and minima of the hemodynamic response during the experimental cycle. Thus, the effective auditory stimulus for the activation is not masked by the scanner noise.

Hearing-impaired children in the United Kingdom, I : auditory performance, communication skills, educational achievements, quality of life, and cochlear implantation

Objectives: The objectives of this study were to identify variables that are associated with differences in outcome among hearing-impaired children and to control those variables while assessing the impact of cochlear implantation. Study Design: In a cross-sectional study, the parents and teachers of a representative sample of hearing-impaired children were invited to complete questionnaires about children’s auditory performance, spoken communication skills, educational achievements, and quality of life. Multiple regression was used to measure the strength of association between these outcomes and variables related to the child (average hearing level, age at onset of hearing impairment, age, gender, number of additional disabilities), the family (parental occupational skill level, ethnicity, and parental hearing status), and cochlear implantation. Results: Questionnaires were returned by the parents of 2858 children, 468 of whom had received a cochlear implant, and by the teachers of 2241 children, 383 of whom had received an implant. Across all domains, reported outcomes were better for children with fewer disabilities in addition to impaired hearing. Across most domains, reported outcomes were better for children who were older, female, with a more favorable average hearing level, with a higher parental occupational skill level, and with an onset of hearing-impairment after 3 years. When these variables were controlled, cochlear implantation was consistently associated with advantages in auditory performance and spoken communication skills, but less consistently associated with advantages in educational achievements and quality of life. Significant associations were found most commonly for children who were younger than 5 years when implanted, and had used implants for more than 4 years. These children, whose mean (preoperative, unaided) average hearing level was 118 dB, were reported to perform at the same level as nonimplanted children with average hearing levels in the range from 80 dB to 104 dB, depending on the outcome measure. Conclusions: When rigorous statistical control is exercised in comparing implanted and nonimplanted children, pediatric cochlear implantation is associated with reported improvements both in spoken communication skills and in some aspects of educational achievements and quality of life, provided that children receive implants before 5 years of age.

Modulation and task effects in auditory processing measured using fMRI

Active listening has been reported to elicit a different sensory response from passive listening and is generally observed as an increase in the magnitude of activation. Sensory activation differences may therefore be masked by the effect of attention. The present study measured activation induced by static and modulated tones, while controlling attention by using target‐discrimination and passive listening tasks. The factorial design enabled us to determine whether the stimulus‐induced activation in auditory cortex was independent of the information‐processing demands of the task. Contrasted against a silent baseline, listening to the tones induced widespread activation in the temporal cortex, including Heschls gyrus (HG), planum temporale, superior temporal gyrus (STG), and superior temporal sulcus. No additional auditory areas were recruited in the response to modulated tones compared to static tones, but there was an increase in the response in the STG, anterior to HG. Relative to passive listening, the active task increased the response in the STG, posterior to HG. The active task also recruited regions in the frontal and parietal cortex and subcortical areas. These findings indicate that preferential responses to the changing spectro‐temporal properties of the stimuli and to the target‐discrimination task involve distinct, non‐overlapping areas of the secondary auditory cortex. Thus, in the present study, differences in sensory activation were not masked by the effects of attention. Hum. Brain Mapping 10:107–119, 2000.

Time-course of the auditory BOLD response to scanner noise

It is a concern for auditory fMRI studies that acoustic noise generated by the scanner produces an auditory response that can confound stimulus‐induced activation. To establish how to minimize this problem, the present study mapped the time‐course of the auditory response to a burst of acoustic scanner noise by employing a single‐event method. Recorded bursts of scanner noise were interspersed with clustered‐volume acquisitions at a range of stimulus‐to‐imaging delays to map the response with a temporal resolution of 1 sec. There were strong responses (1.5% signal change) to scanner noise in primary and secondary auditory cortex. In both cortical areas, the mean response rose to a peak by 4–5 sec after stimulus onset and decayed after a further 5–8 sec. The time course indicates that noise contamination in auditory fMRI can be substantially reduced by using a 9–12‐sec repetition time, thus maximizing the dynamic range available for displaying the response to acoustical stimuli of interest. Magn Reson Med 43:601–606, 2000.

Sound-Level Measurements and Calculations of Safe Noise Dosage During EPI at 3 T

This paper describes systematic methods for measuring and controlling sound levels within a magnetic resonance scanner. The methods are illustrated by application to the acoustic noise generated by a 3 T scanner during echoplanar imaging (EPI). Across five measurement sessions, sound pressure levels at the center of the head gradient coil ranged from 122 to 131 dB SPL [123 to 132 dB(A)]. For protection against damaging noise exposure, UK and US industrial guidelines stipulate that the maximum permitted daily noise dosage is equivalent to 90 dB(A) for 8 hours, where noise dosage is a function of the level of an acoustic signal and the length of exposure to it. Without hearing protection, this equivalent level would be exceeded by less than 5 seconds of exposure to the measured levels of scanner acoustic noise. These findings highlight the importance of noise reduction and hearing protection for those exposed to the acoustic noise generated during EPI. J. Magn. Reson. Imaging 2000;12:157–163.

Self-reported benefits from successive bilateral cochlear implantation in post-lingually deafened adults: randomised controlled trial.

Adult users of unilateral Nucleus CI24 cochlear implants with the SPEAK processing strategy were randomised either to receive a second identical implant in the contralateral ear immediately, or to wait 12 months while they acted as controls for late-emerging benefits of the first implant. Twenty four subjects, twelve from each group, completed the study. Receipt of a second implant led to improvements in self-reported abilities in spatial hearing, quality of hearing, and hearing for speech, but to generally non-significant changes in measures of quality of life. Multivariate analyses showed that positive changes in quality of life were associated with improvements in hearing, but were offset by negative changes associated with worsening tinnitus. Even in a best-case scenario, in which no worsening of tinnitus was assumed to occur, the gain in quality of life was too small to achieve an acceptable cost-effectiveness ratio. The most promising strategies for improving the cost-effectiveness of bilateral implantation are to increase effectiveness through enhanced signal processing in binaural processors, and to reduce the cost of implant hardware.

Reading Fluent Speech from Talking Faces: Typical Brain Networks and Individual Differences

Listeners are able to extract important linguistic information by viewing the talkers facea process known as speechreading. Previous studies of speechreading present small closed sets of simple words and their results indicate that visual speech processing engages a wide network of brain regions in the temporal, frontal, and parietal lobes that are likely to underlie multiple stages of the receptive language system. The present study further explored this network in a large group of subjects by presenting naturally spoken sentences which tap the richer complexities of visual speech processing. Four different baselines (blank screen, static face, nonlinguistic facial gurning, and auditory speech) enabled us to determine the hierarchy of neural processing involved in speechreading and to test the claim that visual input reliably accesses sound-based representations in the auditory cortex. In contrast to passively viewing a blank screen, the static-face condition evoked activation bilaterally across the border of the fusiform gyrus and cerebellum, and in the medial superior frontal gyrus and left precentral gyrus (p < .05, whole brain corrected). With the static face as baseline, the gurning face evoked bilateral activation in the motion-sensitive region of the occipital cortex, whereas visual speech additionally engaged the middle temporal gyrus, inferior and middle frontal gyri, and the inferior parietal lobe, particularly in the left hemisphere. These latter regions are implicated in lexical stages of spoken language processing. Although auditory speech generated extensive bilateral activation across both superior and middle temporal gyri, the group-averaged pattern of speechreading activation failed to include any auditory regions along the superior temporal gyrus, suggesting that fluent visual speech does not always involve sound-based coding of the visual input. An important finding from the individual subject analyses was that activation in the superior temporal gyrus did reach significance (p < .001, small-volume corrected) for a subset of the group. Moreover, the extent of the left-sided superior temporal gyrus activity was strongly correlated with speech-reading performance. Skilled speechreading was also associated with activations and deactivations in other brain regions, suggesting that individual differences reflect the efficiency of a circuit linking sensory, perceptual, memory, cognitive, and linguistic processes rather than the operation of a single component process.

Hearing-impaired children in the United Kingdom, IV: cost-effectiveness of pediatric cochlear implantation

Objective: To estimate the cost-effectiveness of pediatric cochlear implantation by conducting a cost-utility analysis from a societal perspective. Design: In a cross-sectional survey, the parents of a representative sample of hearing-impaired children assessed the health utility of their child using a revised version of the Health Utilities Index Mark III questionnaire. Linear regression was used to estimate the gain in health utility associated with implantation while controlling for eight potentially confounding variables: average (4-frequency, unaided, preoperative) hearing level (AHL), age at onset of hearing-impairment, age, gender, number of additional disabilities, parental occupational skill level, ethnicity, and parental hearing status. The gain in health utility was accumulated to estimate the number of quality-adjusted life years (QALYs) that would be gained from implantation over 15 yr and over a child’s lifetime. The incremental societal cost of implantation, calculated in euros (&U20AC;) at 2001/2 levels, was estimated by summing the incremental costs of implantation that are incurred in the health sector, in the education sector, and by the child’s family. The cost-effectiveness of cochlear implantation was estimated by calculating the incremental societal cost per QALY gained and was compared with an upper limit of acceptability of &U20AC;50,000 per QALY. Results: The parents of 403 implanted children, and 1863 nonimplanted children, completed the health utility questionnaire. Higher health utility was associated with a more favorable AHL, an older age at onset of hearing impairment, female gender, having fewer additional disabilities, having parents with a greater occupational skill level, white ethnicity, and implantation. The gain in health utility associated with implantation was estimated to be higher for children with a worse preoperative AHL and who were implanted when younger. Over 15 yr, for a child implanted at age 6 with a preoperative loss of 115 dB, 2.23 QALYs were estimated to be gained, compared with a mean incremental societal cost of &U20AC;57,359, yielding a mean cost per QALY of &U20AC;25,629. Cost-effectiveness was more favorable: (1) when estimated over a child’s lifetime rather than 15 yr, (2) for children with a worse preoperative AHL, and (3) for children who were implanted when younger. Conclusions: The mean cost of gaining a QALY for the children in the present sample falls within acceptable limits. The strategy of giving highest priority for implantation to children with the greatest loss of hearing, and who are younger, maximizes benefit for a given cost.

Active control of the volume acquisition noise in functional magnetic resonance imaging: Method and psychoacoustical evaluation

Functional magnetic resonance imaging (fMRI) provides a noninvasive tool for observing correlates of neural activity in the brain while a subject listens to sound. However, intense acoustic noise is generated in the process of capturing MR images. This noise stimulates the auditory nervous system, limiting the dynamic range available for displaying stimulus-driven activity. The noise is potentially damaging to hearing and is distracting for the subject. In an active noise control (ANC) system, a reference sample of a noise is processed to form a sound which adds destructively with the noise at the listeners ear. We describe an implementation of ANC in the electromagnetically hostile and physically compact MRI scanning environment. First, a prototype system was evaluated psychoacoustically in the laboratory, using the electrical drive to a noise-generating loudspeaker as the reference. This system produced 10-20 dB of subjective noise-reduction between 250 Hz and 1 kHz, and smaller amounts at higher frequencies. The system was modified to operate in a real MR scanner where the reference was obtained by recording the acoustic scanner noise. Objective reduction by 30-40 dB of the most intense component in scanner noises was realized between 500 Hz and 3500 Hz, and subjective reduction of 12 dB and 5 dB in tests at frequencies of 600 Hz and at 1.9 kHz, respectively. Although the benefit of ANC is limited by transmission paths to the cochlea other than air-conduction routes from the auditory meatus, ANC achieves worthwhile attenuation even in the frequency range of maximum bone conduction (1.5-2 kHz). ANC should, therefore, be generally useful during auditory fMRI.

Binaural specialisation in human auditory cortex: an fMRI investigation of interaural correlation sensitivity

A listeners sensitivity to the interaural correlation (IAC) of sound plays an important role in several phenomena in binaural hearing. Although IAC has been examined humans, little is known about the neural basis of sensitivity to IAC in humans. The present study employed functional magnetic resonance imaging to measure blood oxygen level-dependent (BOLD) activity in auditory brainstem and cortical structures in human listeners during presentation of band-pass noise stimuli between which IAC was varied systematically. The stimuli evoked significant bilateral activation in the inferior colliculus, medial geniculate body, and auditory cortex. There was a significant positive relationship between BOLD activity and IAC which was confined to a distinct subregion of primary auditory cortex located bilaterally at the lateral extent of Heschls gyrus. Comparison with published anatomical data indicated that this area may also be cytoarchitecturally distinct. Larger differences in activation were found between levels of IAC near unity than between levels near zero. This response pattern is qualitatively compatible with previous measures of psychophysical and neurophysiological sensitivity to IAC. extensively in neurophysiological studies in animals and in psychophysical studies in