Listening in noisy situations by normal-hearing listeners and cochlear implant users
When you are trying to listen to someone in a crowded room, your brain has to perform the following quite demanding tasks.
- The outputs of the early frequency analyses performed in the two inner ears must be sorted, so that the frequency components arising from the target voice are grouped together.
- The target voice must be tracked over time.
- Decisions must be made on how to interpret missing data, such as when part of the speech is masked by an extraneous noise.
- Attentional mechanisms must select the target voice for further processing.
- Linguistic analyses must be performed on the selected voice.
Our CBU research programme studies all of these processes, with the focus on identifying their neural basis and determining how they interact with each other. To do so, we combine traditional behavioural methods such as those derived from psychophysics, with electrophysiological, computational, and neuroimaging techniques.
We are particularly interested in patients whose hearing has been restored surgically by either a cochlear implant (CI) or Auditory Brainstem Implant (ABI). By directly stimulating the auditory system with electrical pulses, we aim to provide new insights into how the auditory system works, and to develop new methods for improving hearing in users of these devices.
- Used a behavioural study to show that the pitch of complex sounds must be extracted by a neural mechanism that receives input from the Superior Olivary Complex (Gockel et al., 2011a)
- Employed scalp-based electrophysiological recordings to investigate whether pitch has been extracted at or before the Inferior Colliculus (Gockel et al., 2011b).
- Performed a computational analysis on single-cell auditory-nerve recordings to study whether the brain is likely to exploit differences in the timing of neural responses, between auditory nerve fibres, to extract the frequencies of pure tones and of low-numbered harmonics.
Gockel, H., Carlyon, R. P. and Plack, C. J. (2011a). “Combination of spectral and binaurally created harmonics in a common central pitch processor,” J. Assoc. Res. Otolaryngol. 12, 253-260
Gockel, H. E., Carlyon, R. P., Mehta, A. and Plack, C. J. (2011b). “The Frequency Following Response (FFR) May Reflect Pitch-Bearing Information But is Not a Direct Representation of Pitch,” Journal of the Association for Research in Otolaryngology 12, 767-782
In contrast to auditory streaming, another phenomenon important for hearing in noisy environments does not depend on attention. When a sound is briefly interrupted, and the interruption is filled with a noise that “would have” masked the sound, it is heard to continue uninterrupted. We generated some stimuli that could be heard as vowel-like only due to this “continuity illusion”. We then showed, using fMRI, that although the activation of a vowel-sensitive region (the Middle Temporal Gyrus) was reduced by a competing task, this reduction was the same for illusory and for veridical vowels (Heinrich et al., 2011).
Carlyon, R. P., Cusack, R., Foxton, J. M. and Robertson, I. H. (2001). “Effects of attention and unilateral neglect on auditory stream segregation,” Journal of Experimental Psychology: Human Perception and Performance 27, 115-127
Carlyon, R. P., Billig, A. J., Deeks, J. M., Monstrey, J. and Davis, M. H. (2013). “Auditory streaming of syllables: words fuse more readily than non-words,” Association for Research in Otolaryngology, 36th Midwinter Research Meeting Baltimore, Maryland, USA.
Heinrich, A., Carlyon, R. P., Davis, M. H. and Johnsrude, I. S. (2011). “The continuity illusion does not depend on attentional state: fMRI evidence from illusory vowels,” J. Cog. Neurosci. 23, 2675-89
Thompson, S. K., Carlyon, R. P. and Cusack, R. (2011). “An Objective Measurement of the Build-Up of Auditory Streaming and of Its Modulation by Attention,” Journal of Experimental Psychology-Human Perception and Performance 37, 1253-1262
For some patients, damage to the auditory nerve, for example as a result of tumour removal, precludes the use of a CI, and an electrode array is placed on the surface of the cochlear nucleus. Speech perception with the Auditory Brainstem Implants (ABIs) is very variable across patients, with the majority unable to understand speech in the absence of lipreading cues.
Our research with both groups of patients involves bypassing the clinical speech processor and stimulating the auditory system with custom-designed electrical stimuli. We aim to:
- Understand the basis for poor pitch perception by CI users, using a combination of behavioural experiments and auditory nerve recordings (Carlyon et al., 2010; Carlyon and Deeks, in press)
- Develop new methods for extending the range of pitch percepts that CI patients can hear (Macherey et al., 2011; Macherey and Carlyon, 2012)
- Understand the relationship between the neural excitation produced by acoustic and electric stimulation – for example with patients who have normal acoustic hearing in the unimplanted ear (Carlyon et al., 2011).
- Identify electrodes in both CI and ABI listeners that do not effectively excite nearby neurons, determine whether this degrades speech perception, and devise ways of re-programming an implant to overcome this deterioration.
- Study the fundamental differences in the auditory processing of electric pulse trains presented to a CI vs an ABI, with the ultimate aim of devising new methods for improving speech perception by ABI users.
Carlyon, R. P., Deeks, J. M. and McKay, C. M. (2010). “The upper limit of temporal pitch: Stimulus duration, conditioner pulses, and the number of electrodes stimulated,” J. Acoust. Soc. Am. 127, 1469-1478
Carlyon, R. P., Macherey, O., Frijns, J. H. M., Axon, P. R., Kalkman, R. K., Boyle, P., Baguley, D. M., Briggs, J., Deeks, J. M., Briaire, J. J., Barreau, X. and Dauman, R. (2011). “Pitch Comparisons between Electrical Stimulation of a Cochlear Implant and Acoustic Stimuli Presented to a Normal-hearing Contralateral Ear,” Jaro-Journal of the Association for Research in Otolaryngology 11, 625-640
Carlyon, R. P. and Deeks, J. M. (in press). “Relationships between auditory nerve activity and temporal pitch perception in cochlear implant users,” in Basic Aspects of Hearing: Physiology and Perception edited by B. C. J. Moore, R. D. Patterson, I. M. Winter, R. P. Carlyon and H. E. Gockel, pp. (Springer,, New York)
Macherey, O., Deeks, J. M. and Carlyon, R. P. (2011). “Extending the limits of place and temporal pitch perception in cochlear implant users,” Journal of the Association for Research in Otolaryngology 12, 233-251
Macherey, O. and Carlyon, R. P. (2012). “Place-pitch manipulations with cochlear implants,” J. Acoust. Soc. Am. 131, 2225-2236