Temporal Integration Of Loudness Research Articles

Modeling Temporal Integration of Loudness

Modeling Temporal Integration of Loudness

Spectral loudness summation for sequences of short noise bursts

Recent loudness data of single noise bursts indicate that spectral loudness summation depends on signal duration. To gain insight into the mechanisms underlying this duration effect, loudness was measured as a function of signal bandwidth centered around 2 kHz for sequences of 10-ms noise bursts at various repetition rates and, for comparison, for single noise bursts of either 10- or 1000-ms duration. The test-signal bandwidth was varied from 200 to 6400 Hz. For the repeated noise bursts, the reference signal had a bandwidth of 400 Hz. For the single noise bursts, data were obtained for two reference bandwidths: 400 and 3200 Hz. In agreement with previous results, the magnitude of spectral loudness summation was larger for the 10-ms than for the 1000-ms noise bursts. The reference bandwidth had no significant effect on the results for the single noise bursts. Up to repetition rates of 50 Hz, the magnitude of spectral loudness summation for the sequences of noise bursts was the same as for the single short noise burst. The data indicate that the mechanism underlying the duration effect in spectral loudness is considerably faster than the time constant of about 100 ms commonly associated with the temporal integration of loudness.

So/ren Buus. Thirty years of psychoacoustic inspiration

So/ren Buus did his MSc at the Acoustics Laboratory, Technical University of Denmark (DTU), in 1975 on the topic headphone calibration. He showed the importance of reliable reference values for psychoacoustic research and So/ren was a great inspiration for my work [Scand. Audiol. 20, 205–207 (1991); 27, 105–112 (1998)]. Already from the seventies, temporal integration of loudness has been a major topic in the collaboration with So/ren [Buus et al., J. Acoust. Soc. Am. 105, 3464–3480 (1999)] and the measurements of temporal integration over a wide range of presentation levels led to the important finding about the shape of the loudness function [Buus et al., J. Acoust. Soc. Am. 100, 669–680 (1997)]. So/ren talked about the importance of the psychophysical procedure and the influence from the procedure on the results [Buus, Proceedings 19th Danavox Symposium (2001), pp. 183–226]. The goal was to obtain reliable, unbiased, and precise results. An overview of some of the above investigations will be presented together with recent results from a MSc project on headphone calibration of short duration sounds for ABR measurements.

Effect of signal duration on categorical loudness scaling in normal and in hearing-impaired listeners.

The present study sought to determine whether the duration of white-noise bursts affects their loudness category rating in the same way for hearing-impaired as for normally-hearing subjects. Twelve normally-hearing and 12 hearing-impaired subjects took part. Categorical loudness growth functions were obtained for 16.25 ms, 32.5 ms, 75 ms, 150 ms and 300 ms white noise bursts. Temporal integration of loudness was defined as the intensity difference needed for stimuli of different durations to result in identical category ratings. In normally-hearing subjects, temporal integration of loudness occurred mainly with the short-duration (16.25 ms and 32.5 ms) stimuli, whereas it was found with almost every stimulus duration in hearing-impaired subjects. In other words, temporal integration of loudness between 16.25 ms and 300 ms stimulus duration was greater in hearing-impaired listeners and there was a difference between normal and hearing-impaired subjects regarding change in loudness perception with stimulus duration. Consequently, the use of fixed-duration stimuli hinders loudness normalization.

On loudness at threshold.

Absolute thresholds for and loudness matches between pure tones and four- and ten-tone complexes were used to assess the form of the function relating loudness to sensation level, SL, at low and moderate levels. The components of the tone complexes had equal SLs and were separated by one, two, four, or six critical bands. Six listeners with normal hearing were tested. The thresholds for the multitone complexes indicate that they generally can be detected even when the level of a single component is a few dB below the threshold. The average detection advantage is consistent with predictions for multiple observations in independent, frequency-selective auditory channels, but differences among listeners are apparent. The loudness matches also vary somewhat among listeners. Five of the six listeners matched tone complexes composed of subthreshold components to a pure tone a few dB above threshold. This indicates that the loudness of tones at or even below threshold is greater than zero for these five listeners. A simple model of loudness summation was used to obtain loudness functions from the individual listeners' loudness matches. The slopes of the loudness functions [log(loudness) plotted as a function of log(intensity)] generally exceed unity at low levels and are near 0.2 at 40 dB SL. This shallow slope at moderate levels agrees with loudness functions derived from data on temporal integration of loudness. The average loudness function derived from the present data also is in good agreement with a variety of previous data obtained by magnitude estimation, magnitude production, ratio production, and measurements of binaural loudness summation.

Temporal integration of loudness, loudness discrimination, and the form of the loudness function.

Temporal integration for loudness of 5-kHz tones was measured as a function of level between 2 and 60 dB SL. Absolute thresholds and levels required to produce equal loudness were measured for 2-, 10-, 50-, and 250-ms tones using adaptive, two-interval, two-alternative forced-choice procedures. The procedure for loudness balances was new and employed ten interleaved tracks to obtain concurrent measurements for ten tone pairs. Each track converged at the level required to make the variable stimulus just louder than the fixed stimulus. Thus, the data yield estimates of the just-noticeable difference (jnd) for loudness level and temporal integration for loudness. Results for four listeners show that the amount of temporal integration, defined as the level difference between equally loud short and long tones, varies markedly with level and is largest at moderate levels. The effect of level increases as the duration of the short stimulus decreases and is largest for comparisons between the 2- and 250-ms tones. The loudness-level jnds are also largest at moderate levels and, contrary to traditional jnds for the level of two equal-duration tones, they do not appear to depend on duration. The latter finding indicates that loudness discrimination between stimuli that differ along multiple dimensions is not the same as level discrimination between stimuli that differ only in level. An equal-loudness-ratio model, which assumes that the ratio of loudnesses for a long and short tone at equal SPL is the same at all SPLs, can explain the level dependence of temporal integration and the loudness jnds. It indicates that the loudness function [log(loudness) versus SPL] is flatter at moderate levels than at low and high levels in agreement with earlier findings for 1-kHz tones [M. Florentine et al., J. Acoust. Soc. Am. 99, 1633-1644 (1996)].

Temporal integration of loudness as a function of level

This study compared temporal integration of loudness for 1-kHz tones and broadband noises. Absolute thresholds and levels required to produce equal loudness were measured for 5-, 30-, and 200-ms stimuli using adaptive, two-interval, two-alternative forced-choice procedures. Levels ranged from 5 to 80 dB SL for noises and from 5 to 90 dB SL for tones. Results for 6 listeners with normal hearing show that the amount of temporal integration, defined as the level difference between equally loud 5- and 200-ms stimuli, varies nonmonotonically with level. The average amount of temporal integration varies from about 10–12 dB near threshold, to a peak of 18–19 dB when the 5-ms tone is about 56 dB and the 5-ms noise is about 76 dB SPL; at higher levels, the amount of temporal integration decreases to 10 dB for tones and 13 dB for noises with levels around 100 dB SPL. These results indicate that modified power functions cannot account for the growth of loudness for tones at all durations. They also indicate that the growth of loudness may, at least in part, be consistent with the nonlinear input/output function of the basilar membrane. [Work supported by NIH-NIDCD R01DC02241.]

The growth of loudness of brief sounds

The purpose of this paper is to review the literature on temporal integration of loudness and to derive the form of the loudness function for brief stimuli from existing data. The review of 19 studies reveals that the level difference between equally loud sounds of different durations varies with overall level. The variation is orderly across durations. For 1-kHz tones, the level differences between equally loud 5- and 200-ms stimuli appears to vary nonmonotonically with level. The available data indicate that it ranges from about 17 dB at low sensation levels to about 10 dB around 95 dB SL. For complex sounds, the level difference between equally loud 5- and 200-ms stimuli appears to decrease linearly from about 17 dB at low sensation levels to about 10 dB around 80 dB SL. The loudness functions derived for 5-ms stimuli are steeper than those for 200-ms stimuli. For the 1-kHz tones, the exponent of the best-fitting power function increases from 0.30 for 200-ms tones to 0.33 for 5-ms tones. [Work supported by NIH-NIDCD and The Technical University of Denmark.]

Temporal integration of loudness under various conditions of contralateral stimulation

A study was conducted to investigate the effect an ongoing auditory stimulus presented to one ear might have on loudness summation in the opposite ear. This knowledge would be relevant in interpreting the results of experiments employing simultaneous dichotic loudness balances to measure, for example, perstimulatory adaptation. Three experienced listeners matched the loudness of variable‐duration (0.01–3.0 sec), 1‐kHz sinusoids to the loudness of a 1‐sec, 1‐kHz sinusoid presented at 60 dB SPL, using a transformed up/down procedure. These loudness‐summation functions were obtained under each of five contralateral‐stimulation conditions: silence (control condition), continuous 60‐dB SPL white noise, and continuous 1‐kHz pure‐tone stimulation at 75, 60, and 45 dB SPL. The presence of a contralateral stimulus had no real effect on the shape of the loudness‐summation function. [Work supported by the Veterans Administration.]

Auditory temporal integration as a function of intensity

In a series of experiments on the detection of tone-bursts and noise-bursts of different durations at different intensity levels while the signal/noise ratio is maintained constant, two effects of the intensity level have been found in different parts of the range of stimulus durations. Firstly, very short duration stimuli (less than 20 ms) appear to be relatively less detectable at intermediate (60 dB SPL) levels than at higher and lower levels. Similar results were found for the relative loudness of these stimuli. Secondly, in support of certain studies on the temporal integration of loudness, the critical duration (or endpoint of energy integration) appears to become shorter with increasing overall level.