Acoust. Sci. & Tech. 30, 6 (2009) #2009 The Acoustical Society of Japan Equal-loudness-level contours of older adults measured by magnitude estimation method: A preliminary study Kenji Kurakataà National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 6, 1–1–1 Higashi, Tsukuba, 305–8566 Japan ( Received 7 May 2009, Accepted for publication 21 May 2009 ) Keywords: Equal-loudness-level contour, Aging effect, Magnitude estimation method PACS number: 43.66.Cb, 43.66.Sr [doi:10.1250/ast.30.446] 1. Introduction The pure tones were presented to listeners in an anechoic Equal-loudness-level contours (ELLCs) show combina- room via a loudspeaker (DS-205; Mitsubishi Electric Corp.). tions of sound pressure levels and frequencies of pure tones The listener sat on a chair facing the loudspeaker at a distance that are perceived as being equally loud. An ISO standard [1] of 2.5 m. specifies normal ELLCs in a free field that were determined The ME method without a modulus was used to measure for otologically normal persons aged 18–25 years inclusive. the loudness of pure-tone stimuli, which were presented to As humans age, their auditory system’s characteristics listeners one by one in random order. After each presentation, change progressively. For that reason, older adults are expected the listeners assigned the stimulus a positive number that they to show different ELLCs. However, few attempts (e.g., thought corresponded to the magnitude of loudness and Ref. [2]) at measuring age-related changes of loudness per- responded orally. Each listener performed three trials for each ception have been reported so far. A possible hindrance of such stimulus. The first trials were for practice and were excluded measurements is that individual differences in hearing ability from analyses. The measurement time per listener was about changes among older adults are greater than those among 30 min. young adults. Consequently, more subjects must be examined Study participants were 12 young adults and 35 older to present a good overall picture of their loudness perception. adults. After screening for abnormalities in their audiometric The magnitude estimation (ME) method can measure the profiles, data taken from 10 young adults (age range, 22–27 sensory magnitude efficiently, including the tone loudness. In years; median, 25 years) and 28 older adults (age range, 61– most cases, few responses are necessary for each subject to 86 years; median, 69.5 years) were adopted. The male and estimate one value on a psychophysical magnitude function. female listeners were equinumerous. They had no previous Although ME has been criticized as being subject to various experience in magnitude estimation tasks or other psycho- biases [3], this method might be useful for obtaining ELLCs acoustic experiments. for numerous listeners in a short time. Schneider et al. [4] examined the applicability of ME 3. Derivation of ELLCs to deriving ELLCs. They were able to obtain contours. The geometrical mean of the two numbers assigned to However, the contours were not directly comparable to the each stimulus was first calculated to obtain a magnitude well-established ones in the ISO standard because of their estimate of individual listeners. Then, group medians of measurement condition (monaural listening using an ear- young and older listeners were calculated for each stimulus. 2n 2n phone). Listeners were all students under 30 years of age. A loudness function, expressed as É ¼ kðP À P0 Þ [5], In this Letter, I report the results of a preliminary study in was fitted to estimates of listener groups for each frequency which ELLCs were derived from magnitude estimates of pure tone. In the equation, É is the magnitude estimate of tones; the listeners were young and older adults. The loudness, P is the sound pressure of the stimulus tone, and applicability of the ME method to ELLC measurement for k and n respectively signify parameters that determine the older adults is examined. form of the function. In addition, P0 is the sound pressure of the stimulus tone at the threshold, as measured for each 2. ME for pure tones frequency before the experiment, employing the same Pure tones with a duration of 1 s were used as stimuli. The listeners. frequency was 125, 250, 500, 1,000, 2,000, 4,000, or 8,000 Hz. An assumption was made to derive ELLCs: tones to The sound pressure level was varied in 10 dB steps from 25 dB which the same number had been assigned by listeners were at to 85 dB for the 125, 250, and 8,000 Hz tones and from 15 dB to the same loudness, irrespective of their tone frequency. Once 75 dB for tones of other frequencies. Consequently, the number the loudness functions at 1,000 Hz and other frequencies are of stimuli were 49 (7 frequencies  7 levels) in total. obtained, ELLCs can be drawn by connecting sound pressure levels of tones with different frequencies but the same Ãe-mail: [email protected] loudness É. 446 K. KURAKATA: EQUAL-LOUDNESS-LEVEL CONTOURS OF OLDER ADULTS Fig. 1 ELLCs of ISO standard [1] (dotted lines) and Fig. 2 ELLCs of young listeners (dotted lines) and older those of young listeners measured by the ME method listeners (solid lines with filled circles) measured by (solid lines with filled circles). The hearing thresholds the ME method. The hearing thresholds are also shown are also shown for comparison (ISO standard, dashed for comparison (young listeners, dashed line; older line; present study, solid line with open circles). listeners, solid line with open circles). Figure 1 presents the ELLCs in the ISO standard and 4. Conclusion those of young listeners measured using ME. These two sets The results of this study indicate that the ME method was of ELLCs show good agreement, except at the highest able to yield ELLCs comparable to those in the ISO standard frequencies at high loudness levels. The discrepancy between obtained with other measurement methods. Using the ME the two sets of ELLCs was very small, considering that the method, ELLCs for numerous older adults are obtainable in a contours of this study were obtained from only 10 listeners short time. Those ELLCs will clarify the age-related change and that the variation among studies used for ISO ELLC in loudness perception. construction was 10 dB or more in some cases [1]. Therefore, ME can produce ELLCs efficiently with precision comparable References to those of other psychophysical methods, such as the method [1] ISO 226, Acoustics — Normal equal-loudness-level contours of constant stimuli and the bracketing method. (International Organization for Standardization, Geneva, 2003). Figure 2 portrays ELLCs of young and older listener [2] D. W. Robinson and M. A. Dadson, ‘‘A re-determination of the groups measured using ME. Some aging effects are observ- equal-loudness relations for pure tones,’’ Br. J. Appl. Phys., 7, able in the figure. First, the older listener group was less 166–181 (1956). sensitive to high-frequency tones of 4,000 Hz and higher than [3] G. A. Gescheider, Psychophysics: the Fundamentals, 3rd ed. was the young listener group. The contours of older listeners (Lawrence Erlbaum Associates, Mahwah, N.J., 1997), pp. 332– show steady growth as the frequency increases above 334. [4] B. Schneider, A. A. Wright, W. Edelheit, P. Hock and C. 1,000 Hz, whereas those of young listeners distinctly show Humphrey, ‘‘Equal loudness contours derived from sensory a dip at 4,000 Hz. Second, the older listener group was magnitude judgments,’’ J. Acoust. Soc. Am., 51, 1951–1959 apparently more sensitive to low-frequency tones of 250 Hz (1972). and below than was the young listener group. This lowering [5] J. P. A. Lochner and J. F. Burger, ‘‘Form of the loudness does not mean that older adults can hear tones of those function in the presence of masking noise,’’ J. Acoust. Soc. Am., frequencies better than do young adults. Rather, it suggests 33, 1705–1707 (1961). that the relative sensitivity to low-, middle-, and high- frequency tones differs between the two age groups. 447.