Listening in noisy situations by normal-hearing listeners and cochlear implant users

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.

 

Projects

Pitch perception

Pitch is important for the enjoyment of music and for the perception of prosody in speech. Furthermore, a difference between the pitches of two sounds provides the listener with one of the most powerful cues for sound segregation. Our research focuses on identifying the computations that the brain performs to calculate pitch, and in constraining the possible neural bases of pitch perception. To achieve these goals we use a wide range of techniques including psychophysical, computational, and electrophysiological approaches. For example, we have

  • 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.

Relevant publications

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

Cognition and Sound Segregation

A straightforward scenario would be for the brain to use physical cues to separate sounds automatically into “auditory streams”, and for higher-level processes such as attention and language processing to select and interpret the desired stream. Our research shows that, in fact, these higher-level processes can affect the segregation process itself. For example, briefly diverting a listener’s attention away from a sequence of tones can strongly affect how those tones are perceptually organised when the listener starts attending to them again (Carlyon et al., 2001; Thompson et al., 2011). Furthermore, the lexical status of a syllable can affect whether it is fused into a single percept or streamed apart, with words fusing more readily than non-words (Carlyon et al., 2013).

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).

Relevant publications

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

Hearing by Cochlear Implant and Auditory Brainstem Implant Users

More than 200,000 patients worldwide have had their hearing restored by a cochlear implant (CI). However, although speech perception in quiet is often good, even the most successful users have difficulty in noisy situations and in perceiving pitch. These two problems are related, in that pitch differences between sounds are one of the most powerful cues to perceptual segregation for normal-hearing listeners.

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.

Relevant publications

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

 

Research team

Dr John Deeks, Senior Investigator Scientist

Dr Hedwig Gockel
, Senior Investigator Scientist

Mr Alex Billig
, Ph.D. student

Mr Phil Gomersall, Ph.D. student