More than 800,000 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. Most of our research with CI patients involves bypassing the clinical speech processor, stimulating the auditory system with custom-designed electrical stimuli, and either requiring listeners to make simple judgements (such as saying which of two sounds has the higher pitch) and/or recording the neural response using electrodes on the scalp or that are part of the implant itself. This has allowed us to:

 

• Develop a new speech-processing strategy that improves speech perception in noise (Lamping et al, 2020).
• Apply a computational method (biologically inspired nonlinear gradient optimisation) to auditory-nerve recordings to measure neural excitation patterns and to identify regions of poor neural health (Garcia et al, 2021).
• Show how different psychophysical and electrophysiological measures reveal different biophysical aspects of neural health (Brochier et al, 2021).
• Invent an EEG method that measures the size and selectivity of the thalamo-cortical response to electrical stimulation (Carlyon et al, 2021).

 

Relevant publications

 T. Brochier, F. Guérit, J.M. Deeks, C. Garcia, M. Bance, and R.P. Carlyon (2021). “Evaluating and comparing behavioural and electrophysiological estimates of neural health in cochlear implant users”. J. Assoc. Res. Otolaryngol. 22, 67–80.

R.P. Carlyon, F. Guérit, J.M. Deeks, A. Harland, R. Gransier, J. Wouters, S. de Rijk, and M. Bance (2021). “Using interleaved stimulation to measure the size and selectivity of the sustained phase-locked neural response to cochlear-implant stimulation”. J. Assoc. Res. Otolaryngol. 22, 141-159.

C. Garcia, T. Goehring, S. Cosentino, R. E. Turner, J.M. Deeks, T. Brochier, T. Rughooputh, M. Bance, and R.P. Carlyon (2021). “The Panoramic ECAP method: estimating patient-specific patterns of current spread and neural health in cochlear implant users“. J. Assoc. Res. Otolaryngol. https://doi.org/10.1007/s10162-021-00795-2

W. Lamping, J.M. Deeks, J. Marozeau, and R.P. Carlyon (2020). “The effect of phantom stimulation and pseudomonophasic pulse shapes on pitch perception by cochlear implant listeners”. J. Assoc. Res. Otolaryngol. 21, 511-526.

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. These issues are not only of scientific importance but also inform attempts to encode pitch in auditory prostheses such as cochlear implant (see above). To achieve these goals we use a wide range of techniques including psychophysical, computational, and electrophysiological approaches. For example, we have

• Shown that listeners can hear a true musical pitch that arises from an auditory after image, and where it is unlikely that neurons phase-lock to the pitch at the time that it is heard (Gockel and Carlyon, 2016).
• Demonstrated that listeners can make musical interval judgements between complex tones whose components are higher than 8 kHz, and whose frequencies are unlikely to be encoded by phase locking. However these judgements were less accurate than at low frequencies, consistent with pitch being most accurately encoded when phase locking cues are present. (Gockel et al, 2021)
• Employed scalp-based electrophysiological recordings to investigate whether pitch has been extracted at or before the Inferior Colliculus (Gockel et al., 2011).
• 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 (Carlyon et al, 2012).

Relevant publications

R.P. Carlyon, C.J. Long, and C. Micheyl (2012). “Across-channel timing differences as a potential code for the frequency of pure tones”. J. Assoc. Res. Otorhinolaryngol. 13, 159-171.

H.E. Gockel and R.P. Carlyon (2016). “On Zwicker tones and musical pitch in the likely absence of phase locking corresponding to the pitch”. J. Acoust. Soc. Am. 140, 2257-2273.

H.E. Gockel, and R.P. Carlyon (2021). “On musical interval perception for complex tones at very high frequencies,” J. Acoust. Soc. Am. 149, 2644–2658.

H.E. Gockel, R. P. Carlyon, A. Mehta, and C.J. Plack, (2011). “The Frequency Following Response (FFR) May Reflect Pitch-Bearing Information But is Not a Direct Representation of Pitch,” J. Assoc. Res. Otolaryngol. 12, 767-782.

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, we have shown that:

• Briefly diverting a listener’s attention away from a sequence of tones can strongly affect how those tones are perceptually organized when the listener starts attending to them again (Carlyon et al., 2001; Thompson et al., 2011).
• 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 (Billig et al., 2013).
• Listeners can choose whether to hear an ambiguous sound sequence as coming from one or two sources, with the neural correlates of this choice being observable using MEG in the auditory cortex (Billig et al, 2016).

Relevant publications

A.J. Billig and R.P. Carlyon (2016). “Automaticity and Primacy of Auditory Streaming: Concurrent Subjective and Objective Measures”. Journal of Experimental Psychology: Human Perception and Performance. 42, 339-353. Also featured in the “In other journals” section of Science, 359, 6383 p. 1482 (2018), as “We choose what we want to hear”.

R.P. Carlyon, R. Cusack, J.M. Foxton, and I.H. Robertson (2001). “Effects of attention and unilateral neglect on auditory stream segregation,” Journal of Experimental Psychology: Human Perception and Performance 27, 115-127

A.J. Billig, M.H. Davis, J.M. Deeks, J. Monstrey and R. P. Carlyon (2013). “Lexical influences on auditory streaming”, Current Biology  23, 1585–1589

S.K. Thompson, R.P. Carlyon, and R. Cusack (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

 

Dr Bob Carlyon, Programme Leader and Deputy Director

 

Dr Alan Archer-Boyd, Investigator Scientist

Dr John Deeks, Senior Investigator Scientist

Ms. Charlotte Garcia, Ph.D. student

Dr Hedwig Gockel, Senior Investigator Scientist

Dr. Tobias Goehring, MRC Fellow

Dr. Francois Guerit, Postdoctoral Research Associate

Mr. Andrew Harland,  Research Associate