Michael A. Akeroyd

''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.

Are individual differences in speech reception related to individual differences in cognitive ability? A survey of twenty experimental studies with normal and hearing-impaired adults

This paper summarizes twenty studies, published since 1989, that have measured experimentally the relationship between speech recognition in noise and some aspect of cognition, using statistical techniques such as correlation or factor analysis. The results demonstrate that there is a link, but it is secondary to the predictive effects of hearing loss, and it is somewhat mixed across study. No one cognitive test always gave a significant result, but measures of working memory (especially reading span) were mostly effective, whereas measures of general ability, such as IQ, were mostly ineffective. Some of the studies included aided listening, and two reported the benefits from aided listening: again mixed results were found, and in some circumstances cognition was a useful predictor of hearing-aid benefit.

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.

The psychoacoustics of binaural hearing

This paper introduces the major phenomena of binaural hearing. The sounds arriving at the two ears are rarely the same: usually one ear will be partially shadowed from the sound source by the head, and the sound will also have to travel further to get to that ear. The resulting differences in interaural level and time can be detected by the auditory system and can be used to determine the direction of the source of sound. They also facilitate improvements in the detectability of a target sound masked by some other sound from some other direction. In many circumstances there is a special emphasis to the onset of a sound, which helps to perceptually suppress the complex patterns of reflections and reverberations that are present in most listening environments; yet, the auditory system is often insensitive to—and cannot take advantage of—fast dynamic changes within a sound.

Two-eared listening in dynamic situations.

Reports of hearing disabilities, particularly those acoustically and perceptually dynamic circumstances, are associated with compromised binaural capacities. Those disabilities that are compromised largely correspond to the areas where benefits of bilateral fitting over unilateral fitting emerge. The singular exception is for disabilities in “Sound quality and naturalness”. When binaural capacities are measured by traditional static masking level difference paradigms, relationships between compromised binaural capacity and self-reports of disability are largely absent. However, when masking level differences are assessed using dynamic parameters that are more representative of the conditions experienced in everyday living then significant associations between binaural capacities and self-reports of disability do emerge. We contend that, for both the self-report domain and the psychoacoustical domain, procedures should be more properly representative of the dynamic environments that listeners are routinely exposed to.

Critical phase distractions in anaesthesia and the sterile cockpit concept

In aviation, the sterile cockpit rule prohibits non‐essential activities during critical phases of flight, takeoff and landing, phases analogous to induction of, and emergence from, anaesthesia. We studied distraction during 30 anaesthetic inductions, maintenances and emergences. Mean (SD) noise during emergence (58.3 (6.2) dB) was higher than during induction (46.4 (4.3) dB) and maintenance (52 (4.5) dB; p < 0.001). Sudden loud noises, greater than 70 dB, occurred more frequently at emergence (occurring 34 times) than at induction (occurring nine times) or maintenance (occurring 13 times). The median (IQR [range]) of staff entrances or exits were 0 (0–2 [0–7]), 6 (3–10 [1–18]) and 10 (5–12 [1–20]) for induction, maintenance and emergence, respectively (p < 0.001). Conversations unrelated to the procedure occurred in 28/30 (93%) emergences. These data demonstrate increased distraction during emergence compared with other phases of anaesthesia. Recognising and minimising distraction should improve patient safety. Applying aviation’s sterile cockpit rule may be a useful addition to our clinical practice.

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

A short form of the Speech, Spatial and Qualities of Hearing scale suitable for clinical use: the SSQ12.

Abstract Objective: To develop and evaluate a 12-item version of the Speech, Spatial and Qualities of Hearing scale for use in clinical research and rehabilitation settings, and provide a formula for converting scores between the full (SSQ49) and abbreviated (SSQ12) versions. Design: Items were selected independently at the three centres (Eriksholm Research Centre, MRC Institute of Hearing Research, University of New England) to be representative of the complete scale. A consensus was achieved after discussion. Study sample: The data set (n = 1220) used for a factor analysis (2, submitted) was re-analysed to compare original SSQ scores (SSQ49) with scores on the short version (SSQ12). Results: A scatter-plot of SSQ12 scores against SSQ49 scores showed that SSQ12 score was about 0.6 of a scale point lower than the SSQ49 (0–10 scale) in the re-analysis of the Akeroyd et al data. SSQ12 scores lay on a slightly steeper slope than scores on the SSQ49. Conclusions: The SSQ12 provides similar results to SSQ49 in a large clinical research sample. The slightly lower average SSQ12 score and the slightly steeper slope reflect the composition of this short form relative to the SSQ49.

Acoustic, psychophysical, and neuroimaging measurements of the effectiveness of active cancellation during auditory functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) is one of the principal neuroimaging techniques for studying human audition, but it generates an intense background sound which hinders listening performance and confounds measures of the auditory response. This paper reports the perceptual effects of an active noise control (ANC) system that operates in the electromagnetically hostile and physically compact neuroimaging environment to provide significant noise reduction, without interfering with image quality. Cancellation was first evaluated at 600 Hz, corresponding to the dominant peak in the power spectrum of the background sound and at which cancellation is maximally effective. Microphone measurements at the ear demonstrated 35 dB of acoustic attenuation [from 93 to 58 dB sound pressure level (SPL)], while masked detection thresholds improved by 20 dB (from 74 to 54 dB SPL). Considerable perceptual benefits were also obtained across other frequencies, including those corresponding to dips in the spectrum of the background sound. Cancellation also improved the statistical detection of sound-related cortical activation, especially for sounds presented at low intensities. These results confirm that ANC offers substantial benefits for fMRI research.