Psychometric functions for loudness discomfort and most comfortable loudness levels.

PSYCHOMETRIC FUNCTIONS FOR LOUDNESS DISCOMFORT AND MOST COMFORTABLE LOUDNESS LEVELS DONALD D. DIRKS and CANDACE KAMM

UCLA School of Medicine, Los Angeles, California Adaptive procedures were used to determine psychometric functions for loudness discomfort level (LDL) and most comfortable loudness (MCL) for pure tones and speech using normal and hearing-impaired listeners. For the LDL, both groups demonstrated steeply rising functions with the 50g point at ,~ 100 dB SPL. The MCL data resulted in two functions, one (Function A) differentiating MCL from less intense stimulus levels and the second (Function B) differentiating between MCL and more intense levels. Function A may be considered a lower bound and Function B an upper bound for MCL. For the normal listeners, the difference between the functions at 50% response ranged from 9.9 to 19.9 dB depending upon the experimental condition. For the hearing-impaired subjects, this range was restricted to 4.5 dB, primarily as a result of a shift in Function A toward higher sound pressure levels. The measurements of most comfortable loudness level ( M C L ) and loudness discomfort level ( L D L ) are often incorporated in procedures designed for the selection of hearing aids. The MCL has been used to determine sound pressure levels where stimuli are most comfortable under conditions of amplification (Watson, 1944). Most clinicians use some variation of the procedure in which the volume control of a hearing aid is adjusted until a comfort level is obtained for constant input signal (Carhart, 1946). The measurement of uncomfortable loudness level or L D L has been considered an index of tolerance to loud sounds. In hearing aid evaluation procedures, the L D L has been considered an estimate of the optimal saturation sound pressure level for amplification by defining an upper limit beyond which amplified sounds become uncomfortable for a listener (McCandless and Miller, 1972; Shapiro, 1975, 1976). Originally, Watson (1944) suggested the measurement of uncomfortable loudness level as a diagnostic test for loudness recruitment. Subsequently, the L D L has gained some popularity in differential diagnosis of auditory disorders (Hood and Poole, 1966; Hood, 1968; Dix, 1968). Despite general interest in these procedures, poor reliability, especially for M C L measurement, has been reported (Davis et al., 1946; Pollack, 1952; Berger and Lowry, 1971; Woods, Ventry, and Gatling, 1973). The poor reliability has been associated in part with procedural differences among investigators and also with the apparently unstable criterion required in making M C L and L D L judgments. 613

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The first comprehensive study of comfort listening levels for pure tones was described by Pollack (1952). He observed a similarity between the shape of monaural MCLs and equal loudness contours for pure tones at moderate intensity levels. Larger intersubject differences in the MCL were also reported. Of interest are the results demonstrating a "range of comfortable listening levels" (Pollack, Figure 2, p. 160), based upon upper and lower limits that an individual will accept as comfortable. The observed ranges of comfortable listening levels against a quiet background for an individual varied from ,~ 20 dB at low test frequencies to ,~ 35 dB in the middle frequency region. Other investigators also reported large intrasubiect differences in MCL and attributed them primarily to differences in procedure or stimulus, or both. Using a Bekesy tracking procedure, Woods et al. (1973) noted an average difference in MCL of approximately 18 dB between ascending and descending methods. Berger and Lowry (1971) suggested that MCL should be considered a range rather than a specific level. Their conclusion was primarily based on results in which the average MCL varied over a range of ,~ 20 dB for five different stimuli as compared to an 11-dB variation at threshold for the same stimuli. However, Pollack's results (1952), demonstrating a wide intensity range over which an individual considers a stimulus to be comfortably loud, may present an even stronger argument that MCL encompasses a range rather than a specific level. This individual range of comfortable listening levels may in itself contribute to reported variations in MCL between investigations. One of the goals of the current study was to describe the range of comfortable listening level by determining the psychometric function for most comfortable loudness using adaptive procedures. Pollack's (1952) results also indicated that the introduction of a background noise raised the lower limit of the comfort range, but did not significantly shift the upper limit, thus restricting the comfort range. A similarly restricted range of comfort listening might be anticipated in patients with cochlear hearing loss. Thus, following our initial experiment, we decided to determine psychometric functions for MCL over a wider range than in the initial investigation and on selected impaired ears with sensorineural hearing loss as well as normal listeners. Results of investigations on loudness discomfort level for tones and speech also demonstrate some diversity. For normal listeners, discomfort levels have been reported at sound pressure levels (SPL) as high as 120 dB (re: 0.0002 dyne/cm 2) for speech (Davis, 1946), but more typically have been found at SPLs of ~ 100 dB (Hood and Poole, 1966; Stephens and Anderson, 1971; Morgan, Wilson, and Dirks, 1974). Since the results of these latter studies are in reasonable agreement, it is possible that Davis et al. (1946) focused on levels where sounds became painful or unbearably loud, rather than merely uncomfortable. Hood and Poole (1966) also demonstrated that persons with Meniere's disease achieved LDLs at levels similar to those observed in normal listeners, whereas patients with VIIIth nerve disorders had raised LDLs. These authors suggested that the LDL measurement may be sufficiently re614 Journal of Speech and Hearing Research

19 613-627 1976


liable for use in the differential diagnosis of sensorineural hearing loss. Adaptive procedures (Levitt, 1971) were used in the current experiments to obtain psychometric functions for L D L and M C L in normal and selected hearingimpaired listeners so that comparative features of these functions could be examined. METHOD

Subjects Ten young adults with air conduction hearing threshold levels no poorer than 15 dB re: ANSI-1969 at octave frequencies between 250 and 8000 Hz served as subjects. The subjects had normal tympanometry and an acoustic reflex (Madsen ZO-70). Each subject was tested during four experimental sessions (one hour each) while seated in a sound-treated room (IAC, Model

1200). Instructions and Procedures For the L D L condition, each subject judged whether or not experimental stimuli were uncomfortably or unpleasantly loud, using the following instructions suggested by Morgan et al. (1974): This is a test in which you will be hearing sounds or words. We want you to decide when the sound or word is at a level that you think is uncomfortably loud or unpleasantly loud. By "uncomfortably or unpleasantly loud" we mean when the sound or word is so loud that you would choose not to listen to it for any period of time. Push the "yes" button when the sound or word is at a loudness to which you would not choose to listen. Push the "no" button when the sound or word is below that level. Following each sound or word you must respond "yes" or "no." Three adaptive strategies (Levitt, 1971) were employed during each test session to estimate the 29.3, 50.0, and 70.7% points on the L D L psychometric function. The stimulus level on any one trial was determined by the level of the preceding stimulus and the subject's response to that stimulus. A simple up-down procedure in which stimulus intensity was increased following each negative response from the subject and decreased after any positive response was used to obtain the 50g point on the L D L function. Two transformed up-down strategies described by Levitt (1971, p. 471) were used to estimate points on the L D L function above and below 50g. The strategies chosen were described as Entries 2 and 3 in Table 1 of Levitt (1971). For the first transform, which estimated the 70.7g level, two consecutive positive responses were required for a stimulus level decrease and only one negative response for a level increase. The second transform converged on the 29.3g point of the L D L function. The stimulus level was increased only after two consecutive negative responses and decreased following any positive response. DIRKS, K&MM: Psychometric Functions 615


For the MCL condition, the following instructions similar to those suggested by Ventry et al. (1971) were employed: The purpose of this test is to find and maintain a loudness at which sounds and words are most comfortable to listen. We want you to decide when the sound or word is at a level which you feel is your most comfortable listening level. Push the "yes" button when the sound or word is at your most comfortable listening level. Push the "no" button when the sound or word is louder or softer than the most comfortable level. Following each sound or word, you must respond either "yes" or "no." Remember, the purpose of this test is to find and maintain a loudness level at which sounds and words are most comfortable to listen. MCL adaptive procedures were identical to those used for LDL measurements, with one important modification. Preliminary testing for MCL demonstrated two distinct functions, one (Function A) with a positive and the other (Function B) with a negative slope. For Function A, the probability of an MCL judgment increased with stimulus intensity as the subject discriminated levels which were softer than MCL from those in the MCL range. For Function B, the probability for most comfortable loudness judgments decreased as stimulus intensity increased until loudness discomfort levels were approached. For these judgments, the subject chose between levels in the MCL range and louder stimuli. The appearance of the two functions is most likely due to a change in the internal reference criteria of subjects produced by the direction (increasing or decreasing) of the intensity increment following the subject's initial most comfortable loudness judgment. Function A, then, may be considered a lower bound while Function B may constitute an upper bound for MCL. It became evident that the two MCL functions encompassed a substantial range for normal listeners, and, in order to restrict the experiment to a reasonable time period, only the 29.3 and 50.0~ points on each portion of the MCL psychometric function were estimated. The 29.3 and 50.0~ points on MCL Function A were obtained by the same methods as for the LDL conditions. In contrast to the procedures used for estimating points on the LDL function and on MCL Function A, stimulus intensity was increased following positive MCL judgments in order to obtain points on MCL Function B. Specifically, the 50~ point on MCL Function B was estimated by decreasing stimulus intensity after a negative response and increasing intensity following a positive response. The 29.3~ level on MCL Function B was obtained by increasing stimulus level after any positive response and decreasing stimulus level following two consecutive negative responses. For both MCL and LDL procedures, an initial stimulus level was attained by the simple up-down procedure using 10 dB steps, ascending from a SPL of ,~ 20 dB until a reliable positive response was established. Then each test strategy was executed in 2 dB steps until eight reversals (from increasing stimulus intensity to decreasing stimulus intensity and vice versa) were obtained. The initial two reversals were eliminated in order to reduce bias due to the initial stimulus level (Levitt, 1971). The midpoints of the last six runs 616 Journal of Speech and Hearing Research

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were averaged to provide appropriate estimates of the three levels on the LDL psychometric functions and the two levels on each MCL function. The order of presentation of the test strategies was randomized and the order of the presentation of LDL and MCL conditions was counterbalanced for each test session. Instrumentation and Stimuli Test stimuli consisted of pure tones of 500 and 2000 Hz (300-msec duration) and spondaic words. Stimuli were separated by an interstimulus interval of four seconds. The pure-tone signals were generated by an audio oscillator (Hewlett-Packard 200 AB) and gated by an electronic switch (Grason-Stadler 829D) and interval timer (Grason-Stadler 471-1). The output of the electronic switch was fed into an amplifier/attenuator complex (Grason-Stadler 162). The output was then fed through an amplifier (Grason-Stadler M-224) with a built-in high-pass filter (,~ 250 Hz cutoff) with 6 dB/ octave slope). The output of the amplifier was routed to a fixed attenuator, and then to a TDH-49 earphone mounted in a supraaural cushion (MX-41/AR). The fixed attenuator was required to reduce the amplifier signal which had been maximized for optimum signal-to-noise ratio. The speech stimuli consisted of two lists of spondaic words recorded by a male speaker with a general American dialect. The intensity of the speech signal was specified by measuring the level of a 1000-Hz calibration tone which was originally recorded at the average level of frequent peaks of the spondaic words as measured on a VU meter conforming to ANSI C16.5-1954. During the test procedure, the output of a tape recorder (Ampex A6-350) was routed through the same equipment as the tonal stimuli except for the electronic switch-timer combination. The intensity level of the test stimulus was monitored on a graphic level recorder (Bruel and Kjaer 2305) at the output of the fixed attenuator immediately preceding the earphone. A permanent record of signal levels presented during the test session was thus obtained and used later to calculate the midpoints of the judgments during the experimental runs. The SPL generated by the earphone was measured in an NBS 9A 6 cm 3 coupler and read on an audio spectrometer (Bruel and Kjaer 2112) prior to data acquisition and periodically during the experiment. Daily calibrations of the electrical signals were performed by measuring the voltage developed by the signals across the terminals of the earphone. RESULTS Loudness Discomfort Level Mean and standard deviation results for the 29.3, 50.0, and 70.7~ points on the LDL function are summarized in Table 1 and the means are illustrated in DIRKS, KAMM: Psychometric Functions 617


F i g u r e 1. A positive response was defined as a comfortable loudness j u d g m e n t d u r i n g the M C L condition a n d as an u n c o m f o r t a b l e loudness j u d g m e n t d u r i n g the L D L condition. T h e slopes of the L D L functions are extremely steep: the total range for the three stimuli b e t w e e n 29.3 a n d 70.770 points was encomp a s s e d w i t h i n ~-- 2.4 dB.

TABLE 1. Means and standard deviations for most comfortable loudness levels (MCL) and loudness discomfort levels (LDL) for 10 normal-hearing listeners. Tabled values are sound pressure levels in decibels (re: 0.0002 dyne/cm2).

Stimulus Speech 500 Hz 2000 Hz

Mean SD Mean SD Mean SD

MCL Function A Function B (f6 Positive Response) 29.3 50.0 50.0 29.3

LDL (~ Positive Response) 29.3 50.0 70.7

69.6 10.2 79.1 9.0 78.4 9.4

96.9 9.6 99.6 8.1 99.3 '5.3

74.5 8.9 83.2 7.6 83.0 7.7

88.9 6.7 93.1 6.7 94.0 5.7

MOST COMFORTABLE LOUDNESS LEVEL

91.2 8.3 94.4 7.0 95.3 7.2

97.0 9.3 100.8 7.9 100.8 5.2

99.3 9.9 101.6 8.6 101.3 5.5

L O U D N E S SDISCOMFORT LEVEL

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FIGURE 1. Mean sound pressure levels (re: 0.0002 dyne/cm 2) for several points on psychometric functions for most comfortable level (MCL) and loudness discomfort level (LDL) for 10 normal listeners. Results are illustrated for 500- and 2000-Hz tones and for spondaic words. 618

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1976


The standard deviations for the stimuli ranged from 5.2 to 9.9 dB. These results are in general agreement with the variability for LDL observed in two earlier studies from this laboratory (Morgan et al., 1974; Morgan and Dirks, 1974) using psychophysical methods different from the current investigation. Smaller standard deviations were observed for the 2000-Hz tone than for the speech and 500-Hz signals. The larger variability for the speech stimuli may reflect larger variations in loudness level among the various spondaic words than among repetitions of tonal stimuli. The differences in standard deviations for the 2000- and 500-Hz tones cannot be readily explained. Analysis of variance revealed statistically significant differences among the three points on the LDL functions (F [2, 18] = 25.7, p < 0.01) and between subiects (F [9, 54] = 98.01, p < 0.01). Replications over four trials were not significant (F [3, 27] = 1.00, p < 0.01). In addition, no significant differences were demonstrated for LDL across stimuli (F [2, 18] = 2.77, p < 0.01). The SPLs of the LDLs at 50% ranged from 97.0 to 100.8 dB for the experimental stimuli. These results are in good agreement with the findings of several previous LDL investigations (Hood and Poole, 1966; Stephens and Anderson, 1971; Morgan et al., 1974) for pure-tone stimuli within the 500- to 2000-Hz range. Most Comfortable Loudness Level Mean and standard deviations for the 29.3 and 50.0% points on MCL Function A and B are shown in Table 1. The mean MCL results are also presented graphically in Figure 1. Although the slope of each function is relatively steep, the range between the 50% points on the MCL functions is large. The differences in SPL between the 50% points on Function A and B were 14.4 dB for spondaic words (74.5 to 88.9 dB), 9.9 dB for 500 Hz (83.2 to 93.1 dB), and 11.0 dB for 2000 Hz ( 83.0 to 94.0 dB ). Analysis of variance for MCL measurements demonstrated statistically significant differences among test stimuli ( F [2, 18] = 15.51, p < 0.01), among the points on the Function A and B (F [2, 18] = 21.05, p < 0.01), and between subjects (F [9, 54] = 13.01, p < 0.01). No significant differences were observed for replications over four test sessions (F [3, 27] = 2.59, p < 0.01). The standard deviations for the test stimuli ranged from 5.7 to 10.2 dB. The standard deviations for the 29.3% point on Function A were always slightly larger than standard deviations for other points on both MCL functions and were smaller than those observed by Ventry et al. (1971) and Berger and Lowry ( 1971 ) for selected pure tones and speech. The MCL results demonstrate two functions with wide disparity in sound pressure levels at which MCL judgments were obtained. Because of the wide range over which individuals demonstrate MCL judgments, it is difficult to directly compare the current results to previous studies in which only averaged MCL levels were reported and the location of the individually measured levels within the total MCL range is uncertain. However, several comparisons beDm~:s, KA_MM:Psychometric Functions 619


tween the present data and ear/ier results can be considered. The upper and lower limits in a range of comfortable listening levels described by Pollack (1952) encompassed a 25-dB range at 500 Hz and a 30-dB range at 2000 Hz. These ranges are somewhat larger than those estimated from the 5070points on Function A and B in the current study but are more comparable to the ranges (from 15.3 to 21.6 dB) between the 29.3% points on Function A and B. The latter ranges correspond closely to differences approximating 18 dB between MCLs obtained via an ascending and descending Bekesy tracking technique reported by Woods et al. (1973). SUPPLEMENTAL EXPERIMENTS To delineate the MCL functions more thoroughly than in the first experiment, transformed adaptive strategies (Levitt, 1971) were employed to estimate the 15.9, 29.3, 50.0, 70.7, and 84.1% points on Function A and B (for spondaic words and pure tones of 500 and 2000 Hz) for three subjects who had participated in the first experiment. The 50.0 and 29.3% points on the functions were obtained with the same adaptive procedures used in the main experiment. Several additional strategies were employed to estimate the 15.9, 70.7, and 84.1% points. The transforms were those described as Entries 2, 5, and 6 in Table 1 of Levitt (1971, p. 471). To obtain the 15.9% point on Function A, the stimulus intensity was decreased following any positive response and increased only after four consecutive negative responses. The 15.9% of Function B was estimated by decreasing the stimulus intensity after four consecutive negative responses and increasing stimulus intensity following any positive response. The 70.7% on Function A was obtained by decreasing stimulus level following two consecutive positive responses and increasing stimulus intensity after any negative response. Conversely, the 70.7% point on Function B was estimated by increasing stimulus level following two consecutive positive responses and decreasing intensity following a negative response. The strategy converging on the 84.1% point on Function A involved increasing stimulus intensity after any negative response and decreasing intensity following four consecutive positive responses. The 84.1% point on Function B required any negative response to decrease stimulus level, but four consecutive positive responses to increase the intensity of the stimulus. Possible changes in the MCL functions for individuals with hearing impairment were also investigated. Adaptive transforms were employed to define the 15.9, 50.0, and 84.1% points on both portions of the MCL functions and the 50.0% point on the LDL function. Two individuals with bilateral sensorineural hearing threshold levels (re: ANSI-1969) of 40 and 50 dB at the experimental test frequency of 2000 Hz were used as subjects. The hearing loss was presumably of cochlear origin. Results of auditory tests showed the presence of an acoustic reflex, no adaptation at a suprathreshold level of 20 dB (Olsen and Noffsinger, 1974), a rollover index of < 0.45 on the performance 620 Journal o[ Speech and Hearing Research

19 613-627 1976


intensity-PB function (Jerger and Jerger, 1971) and high SISI scores. Otoscopic and radiological examinations were normal. RESULTS Mean results of the expanded MCL functions for the three normal listeners are shown in Figure 2 and reported in the upper portion of Table 2 toMOST COMFORTABLE LOUDNESS LEVEL

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Fzcurm 2. Mean sound pressure levels (re: 0.0002 dyne/cm 2) for several points on psychometric functions for most comfortable loudness (MCL) and loudness discomfort levels (LDL) for three normal listeners. Results are illustrated for 500- and 2000-Hz tones and for spondaic words. gether with the L D L functions obtained in the first experiment for the three subjects. The SPL intervals between the 50% points on Function A and B averaged 19.9 dB for spondees (68.4 to 88.3 dB), 17.4 dB for 500 Hz (75.5 to 92.9 dB), and 17.4 dB for 2000 Hz (73.1 to 90.5 dB), slightly larger than those observed for the total group in the first experiment. The L D L function for these three subjects is also shown in Figure 2 and approximates the average results from the entire group in the first experiment. The mean results for the hearing-impaired subjects are reported in the lower portion of Table 2 and illustrated in Figure 3. Also shown in Figure 3 are DmI(S, KnMM: Psychometric Functions 621


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FIGURE3. Mean sound pressure levels (re: 0.0002 dyne/cm 2) for several points on psychometric functions for most comfortable loudness (MCL) and loudness discomfort levels (LDL) at 2000 Hz for three normal listeners and for two hearing-impaired subjects. comparable data points for the three normal-hearing subjects. The SPL of the LDL at the 50.0~ point was 102.2 dB in general agreement with the levels required for LDL in the normal group in the initial experiment but slightly higher than the LDL at 50.0% for the smaller group of normal listeners. The slope of the MCL Function A is more gradual for the cochlear loss subjects than for the normal listeners, although the slopes of MCL Function B are similar. The SPLs required for 50.0g MCL response in the ears with cochlear loss are 13.8 dB higher than normal for Function A, but only 0.9 dB higher for Function B. For the normal subjects, an MCL judgment is highly probable (p > 0.5) over a 17.4-dB range, but for the hearing-impaired group, the range is markedly reduced to 4.5 dB. This restriction is due almost completely to a shift upward in Function A of the MCL to higher intensity levels. DISCUSSION

The present results demonstrate the existence of a wide intensity range over which a normal listener judges a stimulus to be most comfortably loud. The probability of obtaining a most comfortable loudness judgment was dependent in this experiment upon two separate subject decisions: first, differentiating MCL levels from stimulus intensities lower than MCL and second, discriminating between MCL levels and stimuli at levels more intense than Dmxs, KAMM: Psychometric Functions 623


MCL. These two factors generated the two probability functions for MCL shown in Figures 1 and 2. For the normal listeners, the intensity intervals in which there was a 0.5 or higher probability of obtaining an MCL judgment encompassed ranges as high as 19.9 dB. These results indicate that the SPL at which MCL judgments are obtained is highly dependent on procedure, even though the instructions remain constant. The large deviations in average MCLs between ascending and descending measurement techniques reported by Woods et al. (1973) may also reflect different reference criteria for MCL judgments imposed by the two procedures. As in our experiments, Woods' subjects may have differentiated between MCL and less intense levels using the ascending technique, and between MCL and louder stimulus levels when the descending procedure was used. Considering that the MCL is most appropriately viewed as a range of levels over which an individual judges a stimulus as most comfortable, procedures in which a single MCL is estimated may be necessarily restrictive. Unfortunately, it is often difficult or impossible to determine precisely which point on the wide MCL range has been measured by previous investigators. The extremely large MCL range, coupled with uncertainties regarding the point on the function under test, may have contributed as much to the high variability among subjects and among results of previous MCL studies as have the reported instructional and stimulus variables. Differences in MCL levels for speech and pure tones have been observed here and in earlier studies (Ventry eta|., 1971; Berger and Lowry, 1971). Our data demonstrate a trend toward smaller differences in MCL and LDL results between speech and pure tones with increasing stimulus intensity. For example, in Figure 1, for MCL Function A, the differences between speech and pure tones range from 8.5 to 9.5 dB, whereas the differences for MCL Function B and the LDL function vary from 3.2 to 5.8 dB and from 2.4 to 3.8 dB, respectively. Several parameters differentiate speech from pure-tone stimuli, including peak factors, temporal characteristics, and bandwidth. The trend in our data toward smaller differences between speech and tones as stimulus intensity increased may suggest that the difference in bandwidth between these stimuli is an important variable to consider. Zwicker, Flottorp, and Stevens (1957) demonstrated that loudness increases as stimulus bandwidth increases, provided the critical bandwidth has been exceeded, and the amount of loudness summation is dependent on intensity. In the present investigation, a wide-band stimulus, such as speech, would be expected to be judged louder than a pure tone of the same intensity. Thus, judgments of comfortable or uncomfortable loudness would be made at lower SPLs for speech than for pure-tone stimuli, which is the result observed in our data. The fact that the differences between results for speech and tonal stimuli diminished with increases in intensity is supported by the Zwicker, Flottorp, and Stevens (1957) data which demonstrated more loudness summation for stimuli at SPLs between -~ 40 dB and 80 dB than for stimuli above or below this range. Berger and Lowry (1971) recently suggested that MCL should be consid624 Journal of Speech and Hearing Research

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ered a range rather than a level on the basis of the increased variability across stimuli at MCL levels as compared to measurements at threshold. Although this conclusion may have validity, it may be premature since there are alternative explanations that should be examined. The decreased variability between complex signals ( speech and music) and tonal signal at threshold as compared to MCL levels reported in that study may reflect the increased effect of loudness summation for stimuli presented at moderate levels, rather than an inherent difference between MCL and threshold judgments. A basic problem in comparing results between speech and pure-tone stimuli is the difficulty in specifying the intensity levels of two such different physical stimuli. First, there is a large difference in the peak factor (ratio of peak to rms power) for speech (estimated at ,-- 14 dB by Wathen-Dunn and Lipke, 1958) as compared to tones (3 fiB). Second, the fluctuating nature of the speech produces problems in specifying precise sound pressure levels. Most investigators have equated speech intensity to the sound pressure level of a calibration tone whose level corresponds to the peaks of the speech signal as observed on a VU meter. Because of these factors, conclusions regarding the behavioral results for speech and pure-tone stimuli are usually restricted to relative (intrastudy) comparisons. These problems complicate inferences regarding the comparative physical level of stimuli which are judged equivalent for a particular loudness characteristic, such as MCL. For the two ears with sensorineural hearing loss, LDLs approximated those observed among the normal listeners (Figure 3), a finding consistent with the results of Hood and Poole (1966) for patients with Meniere's disease. The MCL Function B for the subjects with cochlear impairment was observed at approximately the same sound pressure level as in the normal group. However, because of the increase in sound pressure level required for MCL judgment on Function A, the range over which MCL judgments have high probability of occurrence (p ~ 0.5) is restricted. This result supports the hypothesis proposed by Pollack (1952) that, for patients with mild to moderate cochlear hearing loss, the minimum SPLs required for MCL judgments would be elevated over the levels required in normal listeners, while the upper limit of the comfort range would remain essentially the same for both groups. The current LDL data, together with earlier results (Hood and Poole, 1966; Morgan and Dirks, 1974; Morgan et al., 1974) suggest that these measurements provide a reliable estimate of the SPL at which signals become uncomfortable for an individual. With further validation, this subjective estimate may be of value in determining individual tolerance levels and, during amplification, for setting saturation sound pressure level output limits. Supposedly, limiting the saturation sound pressure level according to an LDL of > 0.50 on the psychometric function would prevent exposure to amplified signals which are uncomfortably loud for the hearing aid user. This possibility requires further verification on a large sample of persons with sensorineural hearing loss. Clinical use of MCL measurements in hearing aid evaluation has generally involved setting the gain of a hearing aid so that normal conversational speech DIR~S, KAMM: Psychometric Functions 625


can be h e a r d at a most comfortable loudness level. Because the present d a ta indicate a wide range for M C L iudgments, procedures which produce unspecified single M C L levels m a y be highly restrictive and contribute to unreliable results. The use of adaptive procedures to define points on b o th M C L functions (A and B) m a y more completely describe the comfortable range of h e a r i n g which is most useful to the listener and m a y allow the clinician to c o m p a r e prob a b l e shifts in this range of comfortable listening i m p o s e d b y amplification. Although defining the range of comfortable loudness m a y be s o m e w h a t more time consuming than currently used procedures, the information that would accrue, and the precision of that information, m a y m o r e realistically and reliably estimate comfort ranges u n d e r conditions of amplification.

REFERENCES AMERICAN NATIONALSTANDARDSINSTITUTE,Specification for Audiometers. ANSI $3.6-1969. New York: American National Standards Institute (1969). BERGER, K. W., LowRY, J. F., Relationships between various stimuli for MCL. Sound, 5, 1114 ( 1971 ). CARHART, J., Volume control adjustment in hearing aid selection. Laryngoscope, 56, 510526 (1946). DAVIS, H., HUDGINS,C. W., MARQUIS,R. J., NICHOLS,R. H., PETERSON,G. E., Ross, D. A., and STEVENS, S. S., The selection of hearing aids. Laryngoscope, 56, 85, 135 (1946). DIx, M. R., Loudness recruitment and its measurement with especial reference to the loudness discomfort level test and its value in diagnosis. Ann. Otol. Rhinol. Laryng., 77, 1131-1151 (1968). ttooD, J. D., Observations upon the relationship of loudness discomfort level and auditory fatigue to sound pressure level and sensation level. J. acoust. Soc. Am., 44, 959-964 (1968). HOOD, J. D., and POOLE, J. P., Tolerable limit of loudness: its clinical and physiological significance. 1. acoust. Soc. Am., 40, 47-53 (1966). JERGER, J., and JERGER, S., Diagnostic significance of PB word functions. Arch. Otolaryngol., 93. 573-580 ( 1971 ). LEVITT, H., Transformed up-down methods in psychoacoustics. 1. acoust. Soc. Am., 49, 467477 ( 1971 ). MCCANDLESS, G. A., and MILLER, D. L., Loudness discomfort and hearing aids. National Hearing Aid J, 25, 7 ( 1972 ). MORGAN, D., and DIRKS, D., Loudness discomfort level under earphone and in the free field: The effects of calibration methods. J. acoust. Soc. Am., 56, 172-178 (1974). MORGAN, D., WILSON, R., and DIRKS, D., Loudness discomfort level: Selected methods and stimuli. 1. acoust. Soc. Am., 56, 577-581 (1974). OLSEN, W., and NOFFSINGER, D., Comparison of one new and three old tests of auditory adaptation. Arch. Otolaryng., 99, 94-99 ( 1974 ). POLLACK, I., Comfortable listening levels for pure tones in quiet and in noise. J. acoust. Soc. Am., 24, 158-162 (1952). SHAPmO, I., Prediction of most comfortable loudness levels in hearing aid evaluation. 1. Speech Hearing Dis., 40, 434-438 ( 1975 ). SHAPmO, I., Hearing aid fitting by prescription. Audiology, 15, 163-173 (1976). STEPHENS, S. D. G., and ANDERSON, C. M. B., Experimental studies in the uncomfortable loudness level. 1. Speech Hearing Res., 14, 262-270 (1971). VENTRY, I. M., WOODS, R. W., RUBIN, M., and HILL, W., Most comfortable loudness for pure tones, noise, and speech. J. acoust. Soc. Am., 49, 1805-1813 (1971). WATHEN-DUNN, W., and LIPKE, D., On the power gained by clipping speech in the audio band. J. acoust. Soc. Am., 30, 36-40 (1958). 626 ]ournal of Speech and Hearing Research

19 613-627

1976


WATSON, L. A., Certain fundamental principles in prescribing and getting hearing aids. Laryngoscope, 54, 531-558 (1944). WooDs, R. W., VENTaY, I. M., and GATLXNC,L. W., Effect of ascending and descending measurement methods on comfortable loudness levels for pure tones. J. acoust. Soc. Am., 54, 205-206 (1973). ZWICKER, A., FLOTTORP, G., and STEVENS, S. S., Critical band width in loudness summation. I. acoust. Soc. Am., 29, 548-557 (1957). Received January 12, 1976. Accepted April 26, 1976.

DmKS, KAMM: Psychometric Functions 627


Optimized loudness-function estimation for categorical loudness scaling data.

Predictors of tinnitus discomfort, adaptation and subjective loudness.

Loudness as a cue for acceptable noise levels.

Autophonic loudness perception in Parkinson's disease.

Development of a multi-category psychometric function to model categorical loudness measurements.

Electrocochleography and experimentally induced loudness recruitment.

Perceptual weights for loudness judgments of six-tone complexes.

An improved model for loudness coding during auditory adaptation.

Spectral loudness summation for electrical stimulation in cochlear implant users.

A Loudness Model for Time-Varying Sounds Incorporating Binaural Inhibition.

Four triggering factors in loudness adaptation.

Elevated Acoustic Startle Responses in Humans: Relationship to Reduced Loudness Discomfort Level, but not Self-Report of Hyperacusis.

Contour identification with pitch and loudness cues using cochlear implants.

Temporary threshold shift, loudness, and auditory evoked potentials.

Noncombination of pitch and loudness in multidimensional scaling.

Loudness perception and speech intensity control in Parkinson's disease.

Growth of loudness at 1000 and 3000 Hz.

On the effect of interaural phase differences on loudness.

Induced Loudness Reduction and Enhancement in Acoustic and Electric Hearing.

Intensity perception. VIII. Loudness comparisons between different types of stimuli.

Development and current status of the "Cambridge" loudness models.

Loudness summation using focused and unfocused electrical stimulation.

Attributes of loudness, pitch and rate among male children.

Intuitive visualizations of pitch and loudness in speech.