Journal of Speech and Hearing Research, Volume 27, , June tleseareh Note RELATION BETWEEN REACTION TIME AND LOUDNESS

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1 Journal of Speech and Hearing Research, Volume 27, , June 1984 tleseareh Note RELATION BETWEEN REACTION TIME AND LOUDNESS LARRY E. HUMES JAYNE B. AHLSTROM Vanderbilt University School of Medicine, Nashville, Tennessee The loudness of one-third octave bands of noise eentered at either 1, 2, or 4 khz was measured in 10 normal-hearing young adults for sound levels of db SPL. Reaction times (RT) in response to these same stimuli were also measured in the same subjects. A moderate-to-strong correspondence was observed between the slopes for functions depicting the growth of loudness with sound level and eomparable slopes for the reaction-time data. The correlation between slopes for the RT-intensity function and the loudness-growth function was comparable in magnitude to the test,retest eorrelcttion for the loudness-growth function except at 1 khz. More than 40 years ago. Chocholle (19401 demonstrated that the time it takes to react to a sound varies inversely with its loudness. That is. the louder the sound, the shorter the time needed to react to its presentation. Choeholle further demonstrated that equal-loudness contours derived from the reaction-time (RT) paradigm resembled closely those contours obtained by loudnessbalance methods. Since this pioneering investigation, several other investigators have observed close correspondence between changes in loudness measured with the RT paradigm and loudness-balancing techniques. Loudness changes under partial masking conditions, for example, have been found to be comparable when measured with either technique (Chocholle & Greenbaum, 1966). Recruitment effects have also been equally apparent utilizing either technique (Pfingst, Hienz, Kimm, & Miller, 1975). Because of the close correspondence observed between loudness and RT, several researchers doing behavioral work with animals have utilized the RT paradigm to examine loudness in animals. The use of animals as subjects obviously necessitates the use of an indirect measure of loudness. Stebbins 11966) was apparently the first to suggest this use of the RT paradigm. Since this investigation, the RT paradigm has been utilized to relate reaction times to evoked-potential latencies ~Miller, Moody, & Stebbins. 1969), to study the effects of permanent and temporary hearing loss on loudness perception (Moody, 1973; pfingst et al., 1975). and to examine the effects of partial masking on loudness perception (Moody, 1979). Although all the above animal studies utilized monkeys as experimental subjects, the RT paradigm has proven effective in other species, including cat (Sandlin & Gerken, 1977), chinchilla (Luz & Nugen, 1972), and the house finch (Dooling, Zoloth, & Baylis, 1978). One approach to better establish the relationship between loudness and RT that has not been pursued previously by many investigators is to correlate loudness growth functions and RT-growth functions within the same set of subjects. Individual differences in loudnessgrowth functions obtained with magnitude estimation exist and are reliable, although the factors responsible for these individual differences remain obscure. Statistically significant test-retest correlations of have been established, for example, for the slopes of loudnessgrowth functions at 1000 Hz repeated six times with a 24- hr intersession interval (Wanschura & Dawson, 1974) and two times with an ll-week intersession interval (Logue, 1976). There is not much evidence, however, supporting directly the supposition that those subjects demonstrating the greatest increase in loudness with increase in stimulus level also exhibit the greatest decrease in reaction time for identical stimulus conditions. Reason (1972), for example, obtained only a moderate, although statistically significant, correlation (r =.45) between the slopes of the loudness-growth function and the slopes of the RT-intensity (RT-I) function. Data were obtained only at 1000 Hz by this investigator. It was the purpose of this study, therefore, to obtain RT- I and loudness-growth functions from n0rmal-hearing young adults and to establish correlations between the slopes of these two functions at frequencies of 1, 2 and 4 khz. In this way the strength of the relation between loudness and RT might be evaluated in more detail. The strength of this relation will determine whether RT might be substituted for direct loudness measurements in laboratory animals or with clinical patients. Subjects METHODS Ten normal-hearing young adults aged years (~? = 25.2 yrs.) comprised the subject sample of this study. All subjects had pure-tone air-conduction hearing thresholds ~<10 db HL at octave intervals of Hz in both ears. In addition, middle ear function appeared normal bilaterally in that all subjects had tympanograms of normal shape, amplitude, and peak-pressure point and present acoustic reflexes for a signal level of 100 db HL ( Hz). None of the subjects had participated 1984, American Speech-Language-Hearing Association /84/ /0

2 HUMES & AHLSTROM: RT and Loudness 307 previously in the procedures to be described here. All subjects were paid for their participation. Each subject participated in one 2-hr session. Apparatus All stimuli utilized in this study were one-third octave bands of noise that were created by routing the output of a random-noise generator (GenRad Model 1390B) through low-pass and high-pass sections of a solid-state filter (Krohn-Hite Model 3848). Noise-band rejection rates were 48 db/octave. Attenuation of stimuli was accomplished through a combination of decade attenuators (Hewlett-Packard Model 350D) and programmable attenuators (Coulbourn Instruments Model $85-08). Stimuli were gated by a programmable electronic rise/fall gate (Coulbourn Instruments Model $84-04). All stimuli were amplified (Crown Model D-75) prior to transduction. Sound-field stimuli were delivered via six JBL E-110 loudspeakers wired in parallel. The loudspeakers were positioned to produce a diffuse field around the listener's head. Reverberation times for octave-band signals centered at Hz were all approximately 0.95 s (-+0.1 s). A DEC PDP-11/03 laboratory minicomputer controlled all experimental paradigms including gating of stimuli, attentuation of signals, activation of lights on the subject's response box, and the collection of responses. The computer was also involved in the measurement of reaction times. Procedures The loudness magnitude-estimation procedure utilized in this study was developed from the guidelines for such procedures provided by Stevens (1975). Subjects simply assigned numbers to one-third octave bands of noise presented in the diffuse sound field with the numbers corresponding to the perceived loudness of the noise bursts. When the geometric mean of these estimates is plotted on a log scale against noise level in decibels, the loudness-growth function is defined. Loudness-growth functions were obtained for noise levels spanning a 40-dB range from the lowest to the highest sound level at onethird octave band center frequencies of 1, 2, and 4 khz. The maximum output levels for each of the center frequencies of the one-third octave bands of noise used in the magnitude-estimation procedure were 94, 92, and 88 db SPL, respectively. The loudness-growth functions were obtained over the 40-dB range of noise levels by attenuating these noise levels by 0, 4, 10, 16, 20, 24, 30, 36, and 40 db. Five random sequences of these attenuation values were generated and stored in the computer. The nine attenuation settings described above appeared twice in each sequence for a total of 18 attenuation settings per sequence. A given loudness-growth function was derived by randomly selecting two of the five sequences. Thus, each loudness-growth function was derived using a total of 36 trials with each of the nine attenuation settings being repeated a total of four times. The availability of five random sequences and the use of any two of these for a given loudness-growth function yielded 9.5 possible quasi-random sequences of attenuation settings for the 36 trials. For the magnitude-estimation procedure, the subject was seated in the diffuse sound field with a response box positioned in front of him or her. Each trial began with a 500-ms warning signal followed 500 ms later by a 1-s stimulus presentation (25-ms linear rise/fall time). Activation of a response light followed stimulus termination by 500 ms. The subject then wrote down a number that corresponded to the perceived loudness of the noise burst. When finished, the subject pressed a button which turned off the response light and initiated another trial 500 ms later. This process was repeated until all 36 trials had been completed. As was the case for the magnitude-estimation procedure, RT-I functions were obtained from each subject for one-third octave noise band center frequencies of 1, 2, and 4 khz. RT-I functions were obtained for noise levels spanning a range from the maximum output levels described previously to levels corresponding to the maximum output level minus 40 db. An RT-I function was derived for noise levels representing successive 10-dB decrements in noise level. Fifteen trials were employed for each of the five attenuation settings, yielding a total of 75 trials per RT-I function. The attenuation setting on a given trial was selected randomly by the computer. Each trial in the reaetion-time paradigm began with two lights on the response box flashing alternately. This served as a "ready" signal, informing the subject that the computer was ready for another trial. The subject, when ready, initiated a trial by pressing a button on the response box. A randomly varying delay followed the subject's button press. The delay had a minimum value of 500 ms and a maximum value of 4,500 ms. Following this delay, the noise band was presented at one of the five intensities described above. The stimulus had a 25-ms linear rise time. If the subject responded before 1,000 ms had elapsed since signal onset, the reaction time was measured using the internal clock of the computer and was stored for later retrieval. The signal was then terminated (25-ms fall time). If the subject failed to respond by pressing the button during the 1,000-ms interval following stimulus onset, the trial was terminated and a reaction time of 1,000 ms was retained. Any responses on a given trial prior to stimulus onset or after the 1,000-ms response interval were ignored by the computer. Thus, possible reaction times ranged 0-1,000 ms. The use of a lengthy 1,000-ms response interval enabled this same program to be used for a different experiment using threshold-level signals. For the more intense stimuli used in this experiment, the reaction times never exceeded a value of 567 ms. A new trial was initiated 500 ms following the

3 308 Journal of Speech and Hearing Research June 1984 subject's response. Following completion of 75 trials, the computer determined the mean reaction times for each of the five noise levels. RT-I functions were repeated twice in immediate succession. Finally, the loudness-growth functions were obtained a second time in a manner identical to that described previously. Hence, the 2-hr session was structured as follows: First, three loudness-growth functions were obtained from the listener, one at each center frequency, with each making use of 36 stimulus presentations. The order of center frequency was randomized across subjects. Next, six RT-I functions were obtained, each based on 75 trials, with two functions obtained in immediate succession at each of the three center frequencies. Finally, the loudness-growth function was repeated at each center frequency at the conclusion of the 2-hr session. RESULTS The magnitude estimates for the first loudness-growth function and the reaction times for two replications of the RT-I functions were averaged. Geometric means plotted as a function of stimulus level are displayed in Figures 1 and 2 for 1, 2, and 4 khz. Because the RT-I and loudnessgrowth functions appeared on visual inspection to be linear on log-log coordinates for most subjects, as shown in Figures 1 and 2, the slopes of these functions were calculated for each subject using a least-squares solution to the following equation: log Y = log b + a log P, where Y was either the magnitude estimate or the reaction time at a particular stimulus level expressed in units of sound pressure (P). Pearson r correlation coefficients between Y 1KHz 2KHz 4KHz._c soo 1KHz 2KHz 4KHz 4 SO , 3,0 ~0 0 NOISE LEVEL in db ATTENUATION re: MAXIMUM OUTPUT FIGURE 2. Geometric means of reaction times (RT) for each of the 10 subjects at the three frequencies examined in this study. The abscissa is labeled identically to that of Figure 1. and P were also calculated to evaluate the appropriateness of a straight-line fit to these data. The correlation coefficients and the calculated slopes for each subject are provided in Tables 1, 2 and 3 for the first set of loudnessgrowth functions, the second set of loudness-growth functions (obtained after the RT-I functions), and the RT-I functions, respectively. The high correlations (85% >.9) indicate that it is appropriate to use linear regression techniques to derive the slopes of both the loudnessgrowth and RT-I functions. In general, the average slopes of the RT-I functions are much shallower than those for the loudness-growth functions. The average slope value for the RT-I functions approximates.06, whereas that for the loudness-growth functions approaches.30. Pearson r correlation coefficients were calculated between the slopes for the first loudness-growth function (Table 1) and the second loudness-growth function (Table 2) at each of the three center frequencies. The resulting correlation coefficients were.76,.63, and.69 at 1000, 2000 and 4000 Hz, respectively. All are statistically significant (p <.05). These test-retest correlations enable one to evaluate the correlations between the slopes of the first loudness-growth function and the RT-I function. It ~'o b- i i 4i 40 SO ZO 10 4O SO 20 TO O 4=0 30,,o, I0 ; NOISE LEVEL in d(3 ATTENUATION re: MAXIMUM OUTPUT FIGURE 1. Geometric means of magnitude estimates of loudness for each of the I0 subjects at the three frequencies examined in this study. The abscissa expresses the noise level relative to maximum output at that frequency, and the numbers positioned above the zero point indicate the maximum sound pressure level for that frequency. Thus, the "'0"" point on the abscissa of the left panel coincides with an overall sound pressure level of 94 db SPL for the 1-kHz test signal.? TABLE 1. Correlations and slopes for first loudness-growth function. I khz 2 khz 4 khz ,335 0, , s o.204 ~(SD) (0.086) (0.112) (0.092)

4 HUMES & AHLSTROM: RT and Loudness 309 TABLE 2. Correlations and slopes for second loudness-growth function. 1 khz 2 khz 4 khz ~(SD) (0.091) (0.071) (0.069) would not be reasonable to expect the RT-I function to be correlated more strongly to loudness-growth functions than loudness-growth functions are correlated to themselves. The correlations observed between the slopes of the first loudness-growth function (Table 1) and the RT-I function (Table 3) were.38,.69 and.69 at 1000, 2000, and 4000 Hz, respectively. The correlations observed for the data at 2000 and 4000 Hz are statistically significant (p <.05), whereas that at 1000 Hz is not. DISCUSSION The relationship between reaction time and loudness appears to be somewhat frequency dependent according to the present results. That is, a much stronger and statistically significant correlation between these two measures was observed for test frequencies of 2 and 4 khz, as opposed to 1 khz. All correlations observed, TABLE 3. Correlations and slopes for RT data. All values shown are actually negative. 1 khz 2 khz 4 khz ~(SD) (0.011) (0.013) (0.15) however, were at least of moderate strength and all were positive. This suggests, therefore, that those individuals exhibiting the steepest RT-I functions also tend to exhibit the steepest loudness-growth functions. Again, this is a much less accurate conclusion for the data obtained at 1000 Hz. The only comparable data available for comparison are those obtained by Reason (1972). As noted previously, Reason observed a correlation of.45 between slopes of RT-I and loudness-growth functions obtained at 1000 Hz. Stimuli in his investigation were pure tortes and were apparently delivered to the subject via earphones. Despite these procedural differences, a correlation of.38 was observed in the present study at this same test frequency. Thus, the present data are in excellent agreement with previous results. The strength of the correlations between the slopes of the RT-I functions and the first loudness-growth functions is more impressive, however, when viewed in relation to the test-retest correlations for the loudnessgrowth functions. At 2000 and 4000 Hz, the relation between the reaction time and loudness-growth data is at least as strong as the test-retest correlation of the loudness-growth data. At 1000 Hz, however, the relation between the slopes of the RT-I and loudness-growth functions is considerably weaker than the test-retest reliability of the loudness data. The test-retest correlations observed here for the loudness-growth functions obtained with magnitude estimation procedures are consistent with those reported previously by other investigators (Logue, 1976; Wanschura & Dawson, 1974). The mean slopes for the RT-I and loudness-growth functions, however, are considerably smaller than expected. Loudness-growth functions referenced to sound pressure should have a slope of approximately.6 for the procedures used in this study according to previous results (see Marks, 1974, for review), whereas RT-I functions typically yield slopes of.2 (Scharf, 1980). The slopes observed here were one half to approximately one third their expected value. The procedures and stimuli used were not novel. Perhaps the use of a diffuse sound field as opposed to an anechoic environment or the use of headphones had an influence on the observed slopes. It is not immediately apparent to the authors, however, why a diffuse sound field would yield lower exponents. It is interesting, however, that both the slope for the RT-I and the loudness-growth functions were lower than estimates published previously. This can be taken as further evidence for the covariation of" these two functions. The results from the present investigation suggest that the RT procedure may be used to provide an indirect estimate of loudness, especially for signal frequencies >1 khz. This finding is of considerable importance to animal researchers who use RT data to estimate loudness. Its incorporation as a clinical procedure, however, must be tempered by careful consideration of variables other than loudness that must apparently contribute to the observed RT.

5 310 Journal of Speech and Hearing Research June 1984 ACKNOWLEDGMENTS This research was supported in part by grant 1-R01-OHO0895 from the National Institute of Occupational Safety and Health. The authors express their gratitude to Anne Marie Tharpe for her assistance in this project, and to Barb Coulson and Kathy Lambert for typing the manuscript. REFERENCES CHOCHOLLE, R. (1940). Variation des temps de reaction auditifs en fonction de l'intensite a diverses frequences. Annee Psyehologique, 41, CIaOCHOLLE, R., & GREENBAUM, H. B. (1966). La sonic de sons purs partinetlement masques. Journal de Psychologie, 4, DOOLING, R. J., ZOLOTH, S. R., BAYLIS, J. R. (1978). Auditory sensitivity, equal loudness, temporal resolving power, and vocalizations in the House Finch (Carpodacus Mexicanus). Journal of Comparative and Physiological Psychology, 92, LocuE, A. W. (1976). Individual differences in magnitude estimation of loudness. Perception & Psychophysics, 19, Luz, G. A., & NUGEN, R. D. (1972). Auditory discrimination in the chinchilla: I. Reaction time. U,S. Army Medical Research Laboratory Report No Fort Knox, KY, Department of the Army. MARKS, L. E. (1974). On scales of sensation: Prolegomena to any future psychophysies that will be able to come forth as science. Perception & Psyehophysics, 16, MILLER, J. M., MOODY, D. B., & STEBBINS, W. C. (1969). Evoked potentials and auditory reaction time in monkeys. Sciene~ 163, MOODY, D. B. (1973). Behavioral studies of noise-induced hearing loss in primates: Loudness recruitment. Advances in Otorhinolaryngology, 20, MOODY, D. B. (1979). Partial masking in the monkey: Effect of masker bandwidth and masker band spacing. Journal of the Acoustical Society of America, 66, PFINGST, B. F., HIENZ, R., KIMM, J., & MILLER, J. (1975). Reaction-time procedure for measurement of hearing. I. Suprathreshold functions. Journal of the Acoustical Society of America, 57, REASON', J. T. (1972). Some correlates of the loudness function. Journal of Sound and Vibration, 20, SANDLIN, D., & GERKEN, G. M. (1977). Auditory reaction time and absolute threshold in eat.journal of the Acoustical Society of America, 61, SCHAtlF, B. (1980). Loudness. In E. C. Carterette & M. P. Friedman (Eds.), Handbook of perception (Vol. 4), Hearing. New York: Academic Press. STEBmNS, W. C. (1966). Auditory reaction time and the derivation of equal loudness contours for the monkey.journal of the Experimental Analysis of Behavior, 9, STEVENS, S. S. (1975). Psyehophysics. New York: Wiley. WANSCHURA, R. G., & DAWSON, W. E. (1974). Regression effect and individual power functions over sessions. Journal of Experimental Psychology, 102, Received October 12, 1982 Accepted September 14, 1983 Requests for reprints should be sent to Larry E. Humes, Division of Hearing and Speech Sciences, Vanderbilt University School of Medicine, Nashville, TN