Mechanisms of auditory attention in normal and hearing impaired listeners

194 Pages·2016·2.59 MB·English

Mechanisms of auditory attention in normal and
hearing impaired listeners
Christofer W. Bester, BSc (Hons)

Supervised by:
1
Emeritus Professor Don Robertson
2
Emeritus Professor Geoff Hammond

This thesis is presented for the degree of Doctor of Philosophy of the
University of Western Australia

1
School of Anatomy, Physiology and Human Biology
2
School of Psychology

2015
Abstract.
Near-threshold tones presented in background noise are detected at a
relatively higher rate if presented more frequently than other tones,
and/or if preceded by a clearly audible cue tone of the same or similar
frequency. A potential candidate that has been suggested to underlie the
formation of this so-called attentional filter is the medial olivocochlear
system (MOCS). This thesis addresses the extent and nature of the
potential MOCS role in forming the attentional filter.
Three sets of experiments are included in the present work. The first set
of experiments correlated the depth of the attentional filter with the
strength of a single MOCS process, the MOCS acoustic reflex, using the
suppression of otoacoustic emissions in normal -hearing participants. The
second set of experiments explored the depth of the attentional filter
using the difference in detection rate of the more frequently presented
tones and the infrequently presented tones, in participants with a loss of
the MOCS efferent t argets due to sensorineural hearing loss (SNHL).
Sensorineural hearing loss participants were recruited with a range of
severities of hearing loss, from mild to moderately -severe, so that fi lter
depth could be correlated with the level of hearing loss. The final set of
experiments measured the attentional filter in cochlear implant
recipients, as a group presumed to have no remaining MOCS action on
the cochlea, but who had undergone a period of auditory relearning. The
findings of the thesis are:
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1. In normal-hearing participants there was no evidence for increasing
depth of the attentional fil ter with increasing strength of the MOCS
acoustic reflex, as assessed by the contralateral suppression of
otoacoustic emissions.
2. The depth of the attentional filter was found to decrease slightly
with increasing MOCS acoustic reflex strength, although this was a
weak effect which was observed primarily on the low -frequency
side of the attentional filter.
3. In these clinically normal hearing participants, there was a range of
auditory thresholds from -5 to 10 dB HL. A negative correlation
was found between the depth of the low-frequency side of the
attentional filter and hearing level. The depth of the low -frequency
side of the attentional filter decreased to zero over this small range
of subclinical hearing levels.
4. Individuals with SNHL and a loss of otoacoustic emissions had
decreased depth of the attentional fil ter. At the lowest level of
SNHL, the low-frequency side of the attentional filter was no
longer suppressed in comparison with the more-frequently
presented centre frequency. The depth of the high -frequency side of
the fil ter decreased progressively with increasing SNHL, and was
near zero at 60 dB HL.
5. Two participants with conductive hearing loss, who were assumed
to have a hearing loss without an associated loss of MOCS targets
in the cochlea, showed a similar decrease in filter depth as the
SNHL group.
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6. Five of the six cochlear implant recipients, who were presumed to
have no remaining MOCS targets in the cochlea, showed no
evidence of an attentional filter when the stimuli were presented
with free-field acoustics. However, one implant recipient showed a
normal attentional fi lter.
7. Four implant recipients were re -tested with a programmed, direct
stimulation that had no acoustic stimulus, to eliminate the
potentially unwanted effects of the commercial speech processor
used previously. Two of the cochlear implant recipients tested with
programmed, direct stimulation showed an attentional filter.
The decreased depth of the attentional filter with increasing MOCS
acoustic reflex strength in normal -hearing participants is not consistent
with a role for the MOCS in forming the attentional filter. In participants
with SNHL, the decreased depth of the high -frequency side of the f ilter
occurred at levels of hearing loss physiologically relevant to the
impairment of the MOCS efferent targets. In contrast, the loss of the
low-frequency side of the attentional fil ter occurred before clinical
SNHL is classified, and at a hearing level that is not typically associated
with appreciable impairment to the MOCS efferent targets, the outer hair
cells. The subclinical changes in hearing level may be associated with
recent research into so-called “hidden” hearing losses, which have been
identif ied in individuals with normal auditory thresholds. These hidden
hearing losses have been associated with auditory neuropathy, and this
neuropathy may be selective for the fibres that form the afferent input to
the MOCS. The loss of the low-frequency side of the filter may then be
due to reduced input to the MOCS with auditory neuropathy, or it may be
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due an alternative, non-MOCS mechanism whose impairment is
associated with the low-level elevation in auditory thresholds. These
results are consistent with a t least a partial role for the MOCS in
forming the filter. However, the loss of the attentional fil ter in two
participants with conductive hearing loss may suggest that the hearing
loss alone can result in the loss of the attentional filter. Finally, the
finding that at least one cochlear implant recipient who had profound
SNHL prior to implantation was able to form the attentional filter
suggests that there must be an alternative mechanism that is able to form
the fil ter in some cochlear implant recipients .
The attentional filter is thought to improve the detectability of signals of
interest in noisy environments. The impaired formation of the filter with
SNHL may then contribute to the poor speech -in-noise perception
associated with this hearing impairment . In addition, the filter decreased
in depth at subclinical hearing levels, which may indicate an important
“hidden” detriment to auditory ability before clinical hearing loss is
classified. Finally, most of the cochlear implant recipients did not show
a typical attentional filter, which may contribute to the difficulties with
speech in noise perception associated with the implants. However, the
apparent presence of the attentional filter in at least one cochlear
implant recipient indicates that the filter can be formed in some
individuals with no remaining MOCS action on the cochlea. Variations
in the ability to form an attentional filter may be a contributing factor to
the wide range in cochlear implant outcomes, in particular when
discriminating signals in competing background noise.
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Table of contents
Abstract. ............................................................................................................................. i
Table of contents .............................................................................................................. vi
List of figures ................................................................................................................. viii
Abbreviations .................................................................................................................... x
Acknowledgements .......................................................................................................... xi
Candidate Contributions ................................................................................................. xii
Chapter 1. General Introduction ................................................................................... 1
1.1 The attentional filter: History ............................................................................. 3
1.2 The attentional filter: Cues ................................................................................. 5
1.3 The medial olivocochlear system: Proposed role ............................................... 7
1.4 The medial olivocochlear system: Anatomy ...................................................... 8
1.5 The medial olivocochlear system: Physiology ................................................. 10
1.6 The medial olivocochlear system: Effects on hearing...................................... 11
1.7 The medial olivocochlear system: In humans .................................................. 15
1.8 The medial olivocochlear system: Forming the attentional filter..................... 19
1.9 The medial olivocochlear system: Related structures ...................................... 25
1.10 Central mechanisms ......................................................................................... 27
1.11 Structure and aims of the thesis ........................................................................ 28
Chapter 2. General Methods ....................................................................................... 31
2.1 Acoustic Stimuli ............................................................................................... 32
2.2 Psychophysical procedures............................................................................... 33
2.3 Auditory thresholds .......................................................................................... 34
2.4 Cued probe-target procedure to measure the attentional filter ......................... 34
Chapter 3. Formation of the attentional filter in normal-hearing participants ............ 37
3.1 Introduction ...................................................................................................... 38
3.2 Methods ............................................................................................................ 40
3.2.1 Participants ................................................................................................ 40
3.2.2 MOCS acoustic reflex strength measurement ........................................... 40
3.2.3 Preliminary study ...................................................................................... 44
3.2.4 Primary experiment: Attentional filters and the suppression of OAEs ..... 45
3.3 Results .............................................................................................................. 46
3.3.1 Activation of the middle-ear muscle reflex............................................... 46
3.3.2 Preliminary study: TEOAEs ..................................................................... 46
3.3.3 Preliminary study: DPOAEs ..................................................................... 48
3.3.4 Preliminary study: OAE relationships and the selective attention task .... 49
3.3.5 Primary experiment: Attentional filters and the suppression of OAEs ..... 52
3.3.6 Primary experiment: Detection rates measurement .................................. 55
3.3.7 Primary experiment: TEOAE suppression ................................................ 55
3.3.8 Primary experiment: DPOAE suppression ............................................... 60
3.4 Discussion ........................................................................................................ 66
Chapter 4. Formation of the attentional filter in hearing-impaired participants ......... 74
4.1 Introduction ...................................................................................................... 75
4.2 Methods ............................................................................................................ 77
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4.2.1 Participants ................................................................................................ 77
4.2.2 Measuring the attentional filter. ................................................................ 78
4.3 Results .............................................................................................................. 79
4.3.1 Normal-hearing & SNHL groups: Audiometric results ............................ 79
4.3.2 Normal hearing & SNHL groups: Attentional filters ................................ 82
4.3.3 Conductive hearing loss participants: Audiometric results ....................... 87
4.3.4 Conductive hearing loss participants: Attentional filters .......................... 89
4.4 Discussion ........................................................................................................ 90
Chapter 5. Formation of the attentional filter in cochlear implant recipients using
acoustic presentation ..................................................................................................... 101
5.1 Introduction .................................................................................................... 102
5.2 Methods .......................................................................................................... 104
5.2.1 Participants .............................................................................................. 104
5.2.2 Stimulus Presentation .............................................................................. 105
5.2.3 Preliminary study: Simulation ................................................................ 106
5.2.4 Preliminary study: Threshold & attentional filter procedures................. 108
5.2.5 Primary Experiment: Measuring the attentional filter ............................ 108
5.2.6 Statistics .................................................................................................. 109
5.3 Results ............................................................................................................ 111
5.3.1 Preliminary study: Simulation results ..................................................... 111
5.3.2 Preliminary study: Threshold & attentional filter procedures................. 113
5.3.3 Primary experiment: Measuring the attentional filter ............................. 115
5.4 Discussion ...................................................................................................... 120
Chapter 6. Formation of the attentional filter in cochlear implant recipients using
programmed, direct stimulation .................................................................................... 127
6.1 Introduction .................................................................................................... 128
6.2 Methods .......................................................................................................... 130
6.2.1 Participants .............................................................................................. 130
6.2.2 Constructing the stimuli .......................................................................... 130
6.2.3 Measuring the attentional filter ............................................................... 132
6.2.4 Shifted target experiments....................................................................... 134
6.2.5 Statistics .................................................................................................. 134
6.3 Results ............................................................................................................ 135
6.3.1 Stimulation details ................................................................................... 135
6.3.2 Attentional Filter measurements ............................................................. 136
6.4 Discussion ...................................................................................................... 141
Chapter 7. General Discussion.................................................................................. 148
7.1 Implications & Future Directions ................................................................... 159
7.1.1 Formation of the filter in normal hearing individuals ............................. 160
7.1.2 Formation of the attentional filter with conductive hearing loss ............ 163
7.1.3 An alternative mechanism able to form the attentional filter .................. 164
7.2 Conclusions .................................................................................................... 165
References ..................................................................................................................... 166
Chapter 8. Appendix ................................................................................................. 175
8.1 Depth of the attentional filter as a function of OAE suppression................... 175
8.1.1 TEOAE suppression ................................................................................ 175
8.1.2 DPOAE suppression ............................................................................... 177
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List of figures
Chapter 1
Figure 1.1: The attentional filter measured by Greenberg and Larkin (1968) .................. 4
Figure 1.2: Schematic diagram of the MOCS anatomy .................................................... 9
Figure 1.3: Auditory nerve fibre firing rate with MOCS activation in quiet .................. 12
Figure 1.4: Auditory nerve fibre firing rate with MOCS activation in noise .................. 14
Figure 1.5: Schematic of proposed MOCS role in filter formation ................................ 21
Figure 1.6: Change in filter depth after a vestibular neurectomy ................................... 22
Chapter 2
Figure 2.1: Sound spectrum of broadband background noise ......................................... 32
Figure 2.2: Structure of the two interval forced choice procedure ................................. 33
Chapter 3
Figure 3.1: Examples of OAE data, including DPOAE spectrum, DPOAE fine structure
and a DPOAE I/O function, as well as the TEOAE waveform ................................. 42-43
Figure 3.2: TEOAE response with and without noise for 3 participants ........................ 47
Figure 3.3: DPOAE response with and without noise for 3 participants ........................ 49
Figure 3.4: Attentional filters for 15 normal hearing participants .................................. 52
Figure 3.5: Attentional filters for 15 normal hearing participants, for the three sessions
used to measure the filter ................................................................................................ 54
Figure 3.6: Attentional filters across three sessions for two participants ....................... 55
Figure 3.7: Correlation between TEOAE suppression and depth of the attentional filter ..
......................................................................................................................................... 56
Figure 3.8: Correlation between DPOAE suppression and depth of the attentional filter ..
......................................................................................................................................... 61
Chapter 4
Figure 4.1: Audiograms for normal hearing and SNHL participants ........................ 80-81
Figure 4.2: Attentional filters for the normal hearing and SNHL groups ....................... 83
Figure 4.3: Depth of the attentional filter as a function of hearing loss for the normal
hearing and SNHL groups .............................................................................................. 85
Figure 4.4: Schematics for attentional filters with normal hearing and SNHL .............. 86
Figure 4.5: OAE suppression as a function of hearing loss for the normal hearing group
......................................................................................................................................... 87
Figure 4.6: Audiograms for two conductive hearing loss participants ........................... 88
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