investigating human auditory cortex responses to voice pitch ...ucjts38/files/steinmetzger 2019...1...

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Investigating human auditory cortex responses to voice pitch information with near-infrared light

Kurt Steinmetzger1, Martin Andermann1, Esther Megbel1, Zhengzheng Shen2, Bastian Meinhardt1, Mark Praetorius2 und André Rupp1

3 April 2019 IZN Heidelberg

1 Section of Biomagnetism, Department of Neurology, Heidelberg University Hospital 2 CI Rehabilitation Centre, Section of Otology and Neurootology, ENT Clinic, HeidelbergUniversity Hospital

Steinmetzger 2019 IZN Heidelberg | Investigating human auditory cortex responses to voice pitch information with near-infrared light | 3 April 2019

Introduction

In a three-year project, we are currently investigating the cortical representation of speech melody.

We are particularly interested in the comparison of normal-hearing listeners and users of cochlear implants (CIs).

The main goal of the project is to identify objective measures that quantify the listening success with CIs.

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Introduction

The project has a two-part structure:

First, normal-hearing listeners are tested to validate the method and the experimental paradigm.

Secondly, these results are used as a functional model to compare the CI users with.

Today, I will be talking about the results of part one and will conclude with data obtained from the first CI user.

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Introduction

CIs are surgically implanted devices that replace the damaged inner ear. The auditory nerve receives direct electrical stimulation via an electrode array inserted into the cochlea.

CIs are still the only successful sensory prosthesis used in humans and enable even deaf children to acquire language.

However, a fundamental limitation when listening through a CI is that the access to pitch information is severely limited.

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Introduction

Especially for pre-lingually implanted children, objective measures are urgently needed to better monitor the develop-ment of their hearing.

However, CIs are incompatible with some common neuroscientific methods (fMRI, MEG) and cause large signal artefacts in electrophysiological measurements (EEG).

Near-infrared spectroscopy (NIRS), in contrast, is a noise-free method that is fully compatible with CIs.

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Near-infrared spectroscopy (NIRS)

For this project, a combined NIRS/EEG system was acquired.

When both methods are combined, brain activity can be measured with a high spatial and temporal resolution.

For NIRS-only measurements, the preparation time can be reduced to a few minutes, which is crucial when testing young children.

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There are two types of NIRS sensors: Sources emit light towards the cortex and detectors at nearby sites record how much of that light has passed the tissue.

The more active the cortical area in between source and detector (i.e. the measurement channel), the more light is absorbed.

The greater the distance between source and detector, the deeper the light travels.

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Pinti 2018 AnnNYAcadSci



In active cortical areas, the concentration of oxygenated haemoglobin strongly increases, while that of deoxygenated haemoglobin decreases slightly.

The physiological basis as well as the experimental designs of NIRS and fMRI studies closely resemble each other.

Most NIRS studies use block designs to elicit strong experimental effects, as the haemoglobin changes in the blood evolve over the course of several seconds.

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Pinti 2018 AnnNYAcadSci


Experiment 1 – Speech sounds with and without pitch

Is the spatial resolution of NIRS high enough to distinguish between speech sounds with and without a pitch contour?

Stimuli: I. Harmonic complex tonesII. Inharmonic complex tonesIII. Speech-shaped noise

Methods: Normal-hearing subjects (n=10)Passive listening task~35-minute block stimulation16 secs of sound, 16–20 secs pause

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I. Strong pitch

II. Weak pitch

III. No pitch



I. The 3D-digitised positions of the NIRS sensors vary little across subjects.

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II. Comparison strong > weak pitch contour: Stronger activity in bilateral auditory cortex for strong pitch.

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p<0.05





III. Comparison strong > no pitch contour: Stronger activity in the anterior part of right auditory cortex for strong pitch.

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p<0.05





III. Comparison strong > no pitch contour: Stronger activity in the anterior part of right auditory cortex for strong pitch.

IV. Comparison weak > no pitch contour: Stronger activity in the posterior part of right auditory cortex for weak pitch.

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p<0.05



However, all three classes of stimuli evoke a marked decrease of cortical activity in fronto-temporal areas!

Concurrently, activity in posterior cortical regions increased.

The most likely explanation for this effect is that the passive stimulation made the subjects divert their attention away from the sound.

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Experiment 2 – Speech sounds with different pitch contours

Is NIRS sensitive enough to distinguish between the cortical activity evoked by speech sounds with different pitch contours?

Stimuli: I. Vowels with same pitch contoursII. Vowels with different pitch contours

Methods: Normal-hearing subjects (n=10)Passive listening task, same as before~55-minute block stimulation

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I. Same pitch

II. Different pitch



I. The 3D-digitised positions of the NIRS sensors again vary little across subjects.

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II. Vowels with same pitch contours: Strong activity in right auditory cortex.

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p<0.001





III. Vowels with different pitch contours: Strong bilateral activity in auditory cortex.

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p<0.001





III. Vowels with different pitch contours: Strong bilateral activity in auditory cortex.

IV. Comparison different > same pitch: Stronger activation in right auditory cortex, and left anterior temporal region.

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p<0.001



Preliminary results of the first adult CI user: CI in left ear, but normal hearing in right ear.

1. With CI and blocked right ear.

Comparison different > same pitch: Stronger bilateral activation, but just below significance threshold.

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p<0.05



Preliminary results of the first adult CI user: CI in left ear, but normal hearing in right ear.

1. With CI and blocked right ear.

Comparison different > same pitch: Stronger bilateral activation, but just below significance threshold.

2. With normal right ear and CI switched off.

Comparison different > same pitch: Stronger activity in right auditory region, just above significance threshold.

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p<0.05


Summary & Outlook

The results so far:

I. The spatial resolution of NIRS appears to be high enough to distinguish between the different stimulus classes.

II. The prosodic differences of the stimuli evoke stronger differences in the right auditory cortex.

The next steps:

I. The NIRS data will be compared with M/EEG-Data obtained from the same normal-hearing listeners.

II. More NIRS data from adult CI users will be obtained.

III. Repeated NIRS measurements of young CI users and age-matched controls.

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Thank you for your attention!

We would like to thank the Dietmar HoppStiftung and MED-EL for generously supporting our project for a period of three years!

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investigating human auditory cortex responses to voice pitch ...ucjts38/files/steinmetzger 2019...1...

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