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Psychoacoustic analysis of cochlear mechanisms in tinnitus patients with normal auditory thresholds.

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Stefnie Glazer

on 6 December 2013

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Transcript of Psychoacoustic analysis of cochlear mechanisms in tinnitus patients with normal auditory thresholds.

What is tinnitus?
Phantom sensation of sound
No external stimulus
Normal & impaired hearing

Tinnitus in normal hearing individuals
Increase in number of individuals seeking medical attention
Possible inner-ear damage
Difficulty understanding speech, especially in noise, resulting in lower speech-in-noise test results
Psychoacoustic analysis of cochlear mechanisms in tinnitus patients with normal auditory thresholds.
Mean thresholds at high frequencies were significantly higher in the tinnitus group (Fig. 1)
Psychoacoustic measurements revealed the characteristic frequency was the same in both ears but SL was not (Fig. 2)
Mean tinnitus frequency: 6.406 kHz
Mean SL: 12.8 db SL (right) & 14.3 dB SL (left)

Bruzo BC, Carvallo RM (2013)
Presentation by Stefnie Glazer
Only measured up to 8 kHz
Small sample size

Why would these be limitations?
Results: PTCs
There was statistical significance between groups in tail regions
When the center frequency of the noise was the same as the pure tone, the threshold was slightly higher in the tinnitus group
Control group needed more noise to mask the pure tone being tested except at center frequency
• 57 normal hearing individuals
• 16 had bilateral tinnitus
24.5 +/- 4.18 years; 31.3% males, 68.7% females
• 41 individuals had no tinnitus
27.4 +/- 5.95 years; 36.6% males, 63.4% females
• Normal hearing thresholds & tympanograms
• DPOAEs for at least five of the six f2 frequencies
• No middle ear disorders or occupation noise exposure

Auditory Science Lab at The Hospital for Sick Children. http://www.sickkids.ca/Research/Auditory-science-laboratory/Overview-of-ear/Cochlea/index.html
Buzo, B. C., & Carvallo, R. M. (2013) Psychoacoustic analysis of cochlear mechanisms in tinnitus patients with normal auditory thresholds.
International Journal of Audiology, Early online,
1-8. doi:10.3109/14992027.2013.840931
Gelfand, S. (2010). Hearing: An Introduction to Psychological and Physiological Acoustics, 5th Edition.
Informa Healthcare.
ISBN: 978-142008865-6.
Moore, B. C. (2002) Psychoacoustics of normal and impaired hearing.
British Medical Bulletin, 63,
The TEN(HL) Audiometric Test For Diagnosing Dead Regions of the Cochlea. http://www.frye.com/wp/ten_hl/

Previous Research Findings
Tinnitus & normal hearing thresholds:
• OHC dysfunction measured by OAE levels
• Inner hair cell dysfunction and dysfunction of adjacent neurons
• Reduced amplitude of wave I and normal wave V
• Lateral suppression impaired, leading to different PTCs in subjects with tinnitus
Tinnitus & hearing loss:
Neural activity may increase in an attempt to offset for reduced activity, resulting in increased sensitivity and causing tinnitus

Background taken from Auditory Science Lab at The Hospital for Sick Children
“To determine whether there were differences between normal-hearing individuals with tinnitus and those without, in terms of PTCs and TEN test results.”
Statistical Analysis
ANOVA comparison of tinnitus and control groups in terms of PTCs and TEN test results was performed
Significance set to p < .05

Logistic regression analysis was used to determine likelihood that a participant belonged to tinnitus group.
representation of the ear's frequency selectivity (Gelfand, 2010)
TEN test
used clinically to detect dead regions in the cochlea
used in this study to "investigate the frequency selectivity by evaluating the perception of pure tones in the presence of noise"
Psychoacoustic measure of tinnitus
determine pitch & intensity of tinnitus
Test procedures
Measured at 2, 3, 4, 6, & 8 kHz
Pure tones presented at 10 dB SL
Searched for minimum masking level; the noise level required to mask the pure tone was converted to dB SL

TEN test
Measured at .25, .5, 1, 2, 3, 4, 6, & 8 kHz
Noise level set to 50 dB/ERB & 70 dB/ERB
Determined absolute and masked thresholds
What is tinnitus?
What are psychophysical tuning curves (PTCs)?
What does it mean to get a psychoacoustic measurement of tinnitus?
What is a threshold-equalizing noise (TEN) test?
Results: TEN test
Participants did not have dead regions
Significant differences were shown in hearing thresholds (in noise) between tinnitus and control groups except at 0.25 & 0.5 kHz
Mean thresholds (in noise) were higher in the tinnitus group
Logistic Regression Model
Performed: Pearson's test, the deviance test and the Homer-Lemeshow test
Found the logistic regression model was appropriate
98.5% of individuals would have been correctly classified as having tinnitus
Applied statistical model to the data:
y-axis: the probability that a given individual belongs or does not belong to the tinnitus group
Information gained from this study furthers the understanding of the cochlear mechanisms underlying tinnitus.
PTC and TEN test revealed statistical differences between the tinnitus and control group
in the tails of the tuning curves
in the thresholds obtained in the presence of ipsilateral noise
"It is evident that the assessment of hearing via audiometric testing, despite being considered the gold standard for diagnosis hearing loss, is not sufficiently refined to identify minor peripheral changes that can provoke uncomfortable symptoms such as tinnitus."

A low SL does not correspond to the perception of the intensity of the tinnitus.
Hearing thresholds labeled "within normal limits" do not rule out cochlear dysfunction.
No dead regions were found because the participants had normal hearing thresholds (and no loss of 65 dB HL).
TEN test evidence may support deafferentation hypothesis.
PTCs: the lower masking noise needed for tinnitus may be due to lack of attenuation by MOCS, causing decreased signal-to-noise ratio

What does all of this mean?
ERB stands for equivalent rectangular band-width of the auditory filter. i.e. "a noise level of 70 dB/ERB usually leads to a masked threshold of about 70 dB SPL" (Moore, 2002)
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