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Retrospective Theses and Dissertations

Masters Thesis (Open Access)

The Relationship Between Recruitment and Masking 1975

Charles Solomon University of Central Florida

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THE RELATIONSHIP BETI~EEN RECRUITMENT AND MASKING

BY CHARLES SOLOMON B.A., Florida Technological University, 1974

THESIS Submitted in partial fulfillment of the requirements for the d~gree of ~1as ter of Arts in the Graduate Studies Program of Florida Technological University

Orlando, Florida

1975

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ACKNOWLEDGEMENT

For their encouragement, guidance, support, and assistance in the preparation of this thesis, I wish to thank Thomas Bunn, Dr. Raymond W. Buchanan, Dr. Albert A. Pryor and Dr. David B. Ingram. My particular thanks go to Dr. Thomas A. Mullin who is both my thesis director and friend.

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TABLE OF CONTENTS Page LIST OF TABLES

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INTRODUCTION

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Recruitment Defined • • • ••••••••• Recruitment Tests •••. . Clinical Significance • . • • • • . • • • Difference Limen of Intensity .••.•• Masking Tests for RecruitmeRt •.••••••• Masking and the Concept of ·the Critical Band Clinical Masking •••.•••. Adaptation and Tone Decay ••• . Stapedius Reflex and Recruitment .

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STATEMENT OF THE PROBLEM METHODOLOGY

Test Site • • • • . • . • • Subjects . . • . • • • • • • • • Instrumentation . . • . • • • Rooms Audiometer . . • . Testing Procedure Data Analysis RESULTS

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DISCUSSION SUMMARY AND CONCLUSIONS

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Implications for Further Study APPENDIX A BIBLIOGRAPHY

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Difference Between the Intensity of the Test Tone and the Masking Level (DTM) •

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LIST OF TABLES

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TABLE 1

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Analysis of Variance of the Difference Between. the Intensity of the Test Tone and the Masking Level (DTM) as a Function of Normal H~aring, Sensorineural Recruiting, and Sensorineural Non-Recruiting Persons Summary of Statist1cal Data of DTM

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Introduction

Recruitment Defined Loudness recruitment is an abnormally rapid growth of the sensation of loudness as the jotensity of a sound is increased (Fowler, 1928). Recruitment Tests The Alternate Binaural Loudness Balance Test (ABLB) described by Fowler is used to detect abnormal loudness growth in a pathological ear.

The task of the patient is to compare the loudness of a tone

heard in his impaired ear to the loudness perceived when the same signal is alternately heard in his normal ear.

The examiner makes

adjustments to the stimulus intensity presented to the impaired ear until equal loudness is reported by the patient in both ears (Fowler, 1928, 1937 and Jerger, 1952}.

The sensation of equal loudness

normally occurs at 30 dB above the threshold of the impaired ear (Davis, 1970). Because the ABLB cannot be administered to a person with a bilateral hearing loss, Reger (1936) proposed a Monaural Bi-Frequency Loudness Balance (MBFLB) test during which the patient makes an equal loudness judgement between two different test frequencies presented to the same ear.

Davis and Goldstein (1970) state that

the MBFLB can show recruitment clearly only if there is a 25 dB

2

difference in the threshold between the two frequencies. Clinical Significance Loudness recruitment, as determined by the ABLB, is a clinically significant phenomenon.

It is used to help differentiate between

cochlear (i.e. inner ear) pathology and retro-cochlear (i.e. tumor --

-

of cranial nerve VIII) pathology.

The existence of recruitment

is an indication of cochlear pathology whereas the absence of recruitment is common in persons with normal hearing, conductive loss and retro-cochlear pathology (Dix, Hallpike and Hood, 1948, and Jerger, 1952). Difference Limen of Intensity (DL Intensity) Hirsh (1952) defined DL intensity as the smallest increment intensity of a stimulus which is just noticeable.

Matkin and Olsen

(1971) stated that since the ABLB and MBFLB tests could not, because of their nature, be administered to persons with sensorineural hearing loss across all frequencies in both ears, research was initiated to develop other means for detecting the absence or presence of loudness recruitment. Bekesy {1947) designed an audiometer in which the test stimulus intensity is controlled by the patient keying a motor driven attenuator.

The attenuator is mechanically linked to an ink pen

which records attenuator movement on an audiogram.

The patient

controls the attenuator in a manner to cause the test signal to move repeatedly between minimum audibility and inaudibility.

In early

3

studies with the Bekesy audiometer, threshold tracings were analyzed for excursion amplitude, a reduction of which was interpreted as a reduced DL Intensity and an indirect measure of recruitment. Denes and Naunton (1950) and Luscher and Zwislocki {1951) proposed tests for recruitment- based upon abnormal sensitivity to small intensity changes above the threshold of hearing.

Hirsh,

Palva and Goodman (1954) questioned these findings and cast doubt upon their validity.

It remained for Jerger, Shedd, and Harford

(1959) to perform the research which indicated that a reduced difference limen of intensity and -loudness recruitment are probably separate indications of cochlear pathology.

The Short Increment

Sensitivity Index (SIS!) test is the product of this research. Masking Tests for Recruitment European researchers experimented with masking to indicate the absence or presence of loudness recruitment.

Huizing (1942)

measured the masking of one tone (i.e. 1000Hz) by another {i.e. 4000 Hz) as a function of the intensity of the masking tone.

Langenbeck

(1950) measured the masked threshold of pure tones at various frequencies in the levels.

pre~ence

of broad band noise at several intensity

Hirsh (1952) stated that these results were inconclusive

and that interpretations were difficult because the concept of critical band was not considered. Masking and the Concept of Critical Band The concept of critical band holds that only the energy of the

4

noise in the frequency band immediately surrounding the test frequency contributes to the masking of that frequency (Fletcher, 1940).

Masking is the amount by which the threshold of audibil i ty

of a sound is raised by the presence of another (masking) sound (Ward, 1953) .

Two general types of masking noise are normally

available on commercial audiometers:

broad band noise, corresponding

to the hearing frequencies and narrow band noise, corresponding to one half the critical band on either side of the pure tone frequency being tested (Price, 1971). Clinical Masking Audiologists routinely use masking in the non-test ear in order to remove the non-test ear from participation in the evaluation of the test ear.

In pure tone testing, narrow band noise is preferred

because the sound pressure level of the noise is lower than broad band noise and there is no attendant reduction of effectiveness of the masking signal.

Effective masking is the amount of signal

required to alter the threshold of a tone.

The procedure for

determining the level of effective masking is to introduce a tone into a normal ear at an intensity of 30 dB above threshold and then to add masking noise to the same ear at an intensity which no longer permits the tone to be heard.

A number of normal subjects must be

used before the clinician may consider the audiometer as calibrated for effective masking (Martin, 1972).

5

Adaptation and Tone Decay Persons with normal hearing or conductive hearing losses are able to hear a continous tone presented above their threshold without adapting to the tone (Hochberg, 1973).

Persons with

cochlear or retro-cochlear disorders will manifest some adaptation or tone decay.

. .

-

In cochlear disorders, the decay is usually

minimal and confined to the higher frequencies.

In cases of retro-

cochlear lesions, severe or complete tone decay is characteristic (Carhart, 1957). (1957).

The tone decay test was described by Carhart

The procedure consists of requiring the patient to hear

a tone for 60 seconds.

Each time the patient signals that the

tone is no longer audible before 60 seconds have elapsed, the intensity of the tone is increased 5 dB until the patient is capable of identifying the presence of the signal for 60 seconds.

The

difference between this level and this threshold is the amount of tone decay. Stapedial Reflex and Recruitment The measurement of the auditory mechanism using clinical impedance technique was first proposed by Metz (1946).

Subsequently,

Metz (1952) reported that a bilateral stapedius muscle reflex can be elicited by stimulating a normal hearing subject's ear with broad band noise 65 dB above threshold or with pure tone signals from 70 to 100 dB above threshold.

The reflex threshold level

in patients

with cochlear pathology frequently occurs at levels less than 60 dB

6

above the threshold for pure tones; this measu.rement as an

o~jecttve,

of loudness recruitment.

thus, Metz (1952} suggested

simple technique for the detection

Alberti (1974) questioned the assumption

that stapedius reflex sensation levels are useful in predicting presence/absence of

r~cruitment

-

and demonstrated that there was

essentially no difference in stapedius reflex levels of patients with and wi-thout recruitment.

Statement of the Problem

The presence or absence of recruitment is a critical factor in the audiological appraisal of a hearing impaired person.

The

ABLB and MBFLB tests are limited to testing only specific types of losses.

Additionally, both tests require a substantial degree

of sophistication in administration. Although the SISI test serves a similar function in the diagnostic procedure, it does not measure recruitment and is therefore not an appropriate substitute.

There appears to be a

need for a direct test of recruitment which eliminates interference from intervening variables (i.e. tone decay), requires no modification to most clinical audiometers, and simplifies testing for both clinician and patient. The purposes of this study are:

(1) to quantify the relationship

between recruitment and the level of effective narrow band masking; and (2) to quantify the relationship between recruiting and nonrecruiting ears in persons with sensorineural pathology measured by the difference in their levels of effective narrow band masking. Hypothesis:

Suprathreshold levels of effective narrow band

masking are significantly different for recruiting and non-recruiting ears in persons with sensorineural pathology.

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Methodology

Test Site All testing was conducted in the auditory research laboratory at Florida Technological University in Orlando, Florida. Subjects Seven normal-hearing persons with pure tone thresholds of less than 20 dB (ANSI 1969) at all frequencies of 250 to 8000 Hz inclusive, seven persons with non-recruiting sensorineural hearing loss, and seven persons with recruiting sensorineural hearing loss were used in this study.

The existence of recruitment was determined by

use of ABLB and MBFLB tests as appropriate. students from 19 to· 42 years of age.

Subjects were college

A total of 60 hearing tests

were performed in order to obtain sufficient subjects to satisfy the criteria for assignment to the groups. A total of 21 persons were divided into three groups: Control Group (seven normal-hearing students); Group;

and the Recruiting Group.

the

the Non-Recruiting

The Control Group provided

masking calibration and normative data. Instrumentation Rooms:

A testing room (Industrial Acoustics Company Series

1200) was used during all testing performed in this study. Audiometer All tests were performed on a calibrated clinical/research

9

audiometer {Grayson Stadler Model 1702A}.

Subjects received stimuli

through a matched set of earphones (Telephonics TDH-39) with cushions (MX 41 AR) while seated in the test room. Testing Procedure Presentation of stimuli

~nd

measurement of subject responses

were in accordance with accepted audiometric technique as described by Hochberg (1973} and Martin (1972). were utilized:

The following tests

Air and Bone Pure Tone Thresholds, ABLB/MBFLB and

Effective Masking Level.

A pulsed tone was used for all pure

tone stimuli in order to obviate the possible introduction of tone decay as an intervening variable.

Effective masking level testing

was performed at 4000 Hz since that frequency is typically an affected one in persons with sensorineural hearing impairment.

Additionally,

the degree of loss is normally not severe enough to preclude testing below the maximum 4000 Hz output of the audiometer.

Narrow band

noise was used as the masker. Upon satisfying the prerequisites for assignment to one of the three groups, each subject was tested to determine, (1) his thr€shold at 4000 Hz and (2) the effective masking level required to mask a 4000 Hz tone 30 dB above threshold.

The difference between the

intensity of the test tone and the effective masking level was determined (DTM) and recorded for each subject.

Additionally, the

mean DTM was determined and recorded for each group.

10 Data Analysis An analysis of variance based on the DTM's of each group \'las perfonned to pennit rejection of the null hypothesis (i .e . there is no difference between DTM's of the groups).

Subsequently, three

t tests were perfonned to quantify specific differences between all --groups.

A confidence level based upon the value of t was extrapol -

ated from a t Distribution Table.

Because the computer used to

compute -F and -t tests would not accept a negative number, each DTM value was increased by 10 prior to computation and the r~sults were reduced by 10 after computation.

Results

The analysis of variance of the difference between the intensities of the test tone and the masking signal (DTM) as a function of nonnal hearing, s-ensorineural recruiting, and sensorineural non-recruiting subjects yielded a significant [at the .01 ~ ~ ..

.. .

level of confidence (Table 1).

This indicated that there was a

difference between groups in the amount of noise required to mask the tone.

Table 2 shows the DTM mean for each group as well as the

variance, standard deviation, range, and computed values of t. Significant differences between groups were shown by the ! tests. The control and recruiting groups had 7 dB and 10 dB ranges respectively_while the non-recruiting group had a range of 5 dB. There was a greater difference between

orr~

means of the control

group and the non-recruiting group than there was between the control group and the recruiting group. negative DTM mean.

The non-recruiting group had a

The greatest variance of DTM within a group was

in the recruiting group while the least variance was in the nonrecruiting group.

Raw data of the DTM for each subject is shown in

Appendix A.

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TABLE 1 Analysis of Variance of the Difference Between the Intensity of the Test Tone and the Masking Level (DTM) as a Function of Normal Hearing, Sensorineural Recruiting, and Sensorineural Non-Recruiting Persons.

Source of Variation

DF

ss

MS

F

2

682.67

341.33

54.30

Within Subjects

18

113.14

6.29

Total

20

795.81

Between Subjects

** F.99 (2,18)

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=

**

6.01

TABLE 2 Summary of Statistical Data of DTM

DTM

Control Group

Recruiting Group

Mean

11.00 dB

6.43 dB

Non-Recruiting Group

(-2.71 dB)

Variance

6.67

9.62

2.57

Standard Deviation

2.56

3.10

1.60

Range

8 to 15 dB

2 to 12 dB

Oto (-5) dB

Groups

Computed Value of t

E.

Control, Recruiting

2.80

.02

11.94

. 01

6.93

. 01

Control, Non-Recruiting Non-Recruiting, Recruiting

13

14 Discussion

The noise level required to mask the test tone was greater than the threshold of the test tone in the control group and the recruiting group, but less than the test tone threshold in the non-recruiting group.

Viewed from the perspective of test tone

threshold, the control group and the recruiting group heard the test tone at an intensity less than the masking noise.

Conversely,

the non-recruiting group heard the test tone at an intensity greater than the masking signal. The control group mean DTM conformed to expectations based on the literature concerning effective masking (Martin, 1972).

The

recruiting group mean DTM was 4.57 dB less than that of the control group;

however, the non-recruiting group mean DTM was 13.71 dB

less than that of the control group and had a negative value.

The

difference between the mean DTM's of the recruiting group and nonrecruiting group was 9.14 dB. The theoretical significance of these findings is that sensorineural impaired ears respond to masking signals in a manner sufficiently unique to consider the response a characteristic of recruitment. Additionally, a sensorineurally impaired ear which does not recruit responds to a masking stimulus in a manner sufficiently unique to consider the response a characteristic of the absence of recruitment.

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The clinical significance of the?e findings does not appear to be as readily usable as does the theoretical.

Although the

difference between DTM's of the recruiting and non-recruiting groups was 9.14 dB, the range of the recruiting group was from 2 to 12 dB with a variance of 9.62 and a standard deviation of 3.10. The discriminating ability of an instrument with such a broad lattitude could result in imprecise clinical judgements were it to be used.

The non-recruiting group parameters appear to offer more

potential for producing precise clinical judgements regarding the absence of recruitment.

The range of the non-recruiting group was

from 0 to (-5) dB with a variance 2.5 and a standard deviation of 1.6. In the presence of a sensorineural loss, a DTM with a negative value could be used to indicate the absence of recruitment thereby saving valuable clinic time.

Should the DTM be of positive value, the

ABLB could then be performed on the patient to confirm the presence of recruitment. This study was designed to control the potential intervening variable of tone decay;

however, there are other potential intervening

variables which could have influenced the results and produced extranoeus variance.

These are the severity of the sensorineural

hearing loss, the slope of the loss, and the frequency selected for testing.

Less susceptible to control are the screening functions,

performed by the sub-cortical ascending audiological pathways, which also could have intervened.

Summary and Conclusions

Suprathreshold levels of effective narrow band masking are significantly different for recruiting and non-recruiting ears in persons with sensori neura 1 pa-tho 1ogy. The response behavior to the masking stimulus elicited from the non-recruiting group appears to have the potential for a rapid screening test to establish the absence of recruitment. Further research in this area would appear to have a high probability of contributing to the existing body of knowledge by quantifying the effects of potential intervening variables on the relationship between masking and recruitment. Implications for Further Study This study should be replicated in its original form as well as with the addition of potential intervening variables such as test frequency, severity of hearing loss, slope of hearing loss, and inversion of the sequence of stimulus presentation (i.e. determine the DTM with the masking at a fixed intensity).

The relationship

between the DTM and the SIS! test should be explored and, finally, the DTM of patients with confirmed tumors of cranial nerve VIII should be measured to determine the value of this procedure as a site of 1esion test.

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APPENDIX A Di ffer·ence Between the Intensity of the

Test Tone and the Masking Level (DTM)

Subject No.

1) Control

- · - 2) Recruiting

3) Non-Recruiting

1.

+10

+7

-3

2.

+14

+2

0

3.

+8

+12

-5

4.

+10

+5

-2

5.

+15

+8

-2

6.

+9

+ 5

-4

7.

+11

+6

-3

17

BIBLIOGRAPHY

Alberti, P. W. R. M. Stapedius Reflex Sensation Level in J. Jerger (reporter). Second International Symposium of Impedance Measurement held at Houston. ASHA, 1974, 16, 73-75. Bekesy, George V. A New Audiometer. 1947, 35, 411-422.

Acta Oto-Laryngologica,

Clinical Determination of Abnormal Adaptation. Carhart, R. Archives of Otolaryngology, 1957, 65, 32-39. Abnormal Hearing and Deafness. In H. Davis and Davis, H. S. R. Silverman (Ed.), Hearing and Deafness. New York: Holt, Rinehart, and Winston Inc., 1970. Davis, H. Acoustics and Psychoacoustics. In H. Davis and S. R. Silverman (Ed.), Hearing and Deafness. New York: Holt, Rinehart, and Winston Inc., 1970. Davis, H. and Goldstein, R. Audiometry: Other Auditory Tests. In H. Davis and S. R. Silverman (Ed.), Hearing and Deafness. New York: Holt, Rinehart, and Winston Inc., 1970. Denes, P. and Naunton, R. F. The Clinical Detection of Auditory Recruitment. Journal of Laryngology, 1950, 64, 375-398. Observations upon the Dix, M. R., Hallpike, C. S. and Hood, J. D. Loudness Recruitment Phenomenon with Especial Reference to the Differential Diagnosis of Disorders of the Internal Ear and Eighth Nerve. Proceedings of the Royal Society of Medicine, 1948, 41, 516-526. Fletcher, H. 12, 47.

Auditory Patterns.

Review of Modern Physics, 1940,

Fowler, E. P. Marked Deafened Areas in Normal Ears. Otolaryngology, 1928, 8, 151-156. Hirsh, I. J. 1952.

The Measurement of Hearing.

New York:

Archives of McGraw-Hill,

Difference Limen and Hirsh, I. J., Palva, T. and Goodman, A. Recruitment. Archives of Otolaryngology, 1954, 60, 525-540.

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19

Hochberg, H. Interpretation of Audiometric Results. Bobbs-Merrill, 1973.

New York:

Huizing, H. C. Die Bestimung der Regression bie der Gehorprfung und der Physikalische, Physiologische und Psychologische Zusammenhang bie der Gehorprothese. Acta Oto-Laryngologica, Stockholm: 1942, 30, 487-499. Jerger, J. A Diff'erence Limen Recruitment Test and its Diagnostic Significance. Laryngoscope, 1952, 62, 1316-1332. Jerger, J. , Shedd, J •. L. and Harford, E. On the Detection of Extremely Small Changes- ~n Sound Intensity. Archives of Otolaryngology, 1959, 69, 200-211. Langenbeck, B. Die Geraushaudiometrie als Diagnostiche Methode. Z. Laryngol, Rhinal, Otol, 1950, 29, 103-121. Metz, 0. The Acoustic Impedance Measured on Normal and Pathological Ears. Acta Oto-Laryngologica (Suppl.). Stockholm, 1946, 63 Metz, 0. Threshold of Reflex Contractions of Muscle of Middle Ear and Recruitment of Loudness. Archives of Otolaryngology, 1952, 55, 536-543. Luscher, E. and Zwislocki. Comparison of the Various Methods Employed in the Determination of the Recruitment Phenomenon. Journal of Laryngology, 1951, 65, 187-195. Martin, F. N. Clinical Audiometry and Masking. Bobbs-Merrill, 1972.

Indianapolis:

Matkin, N. D. and Olsen, W. 0. Differential Audiology. In D. E. Rose (Ed.), Audiological Assessment. Englewood Cliffs, New Jersey: Prentice-Hall, 1971. Price, L. L. Pure Tone Audiometry. In D. E. Rose (Ed.), Englewood Cliffs, New Jersey: Audiological Assessment. Prentice-Hall, 1971. Reger, S. N. Differences in Loudness Response of the Normal and Hard of Hearing Ear at Intensity Levels Slightly above the Threshold. Annals of ' Otology, Rhinology and Laryngology, 1936, 45, 1029-1039. Ward, W. D. Auditory Fatigue and Masking. In J. Jerger (Ed.), Modern Developments in Audiology. New York: Academic Press, 1963. Winer, B. J. Statistic~l Principles 1n Experimental Design. York: McGraw-Hill, 1971.

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