Monaural and binaural loudness of 5- and 200-ms tones in normal and impaired hearing

The difference in level required to match monaural and binaural loudness of 5- and 200-ms tones was measured for listeners with normal and impaired hearing. Stimuli were 1-kHz tones presented at levels ranging from 10 to 90 dB sensation level. Sixteen listeners (eight normal and eight with losses of primarily cochlear origin) made loudness matches between equal-duration monaural and binaural tones using an adaptive 2AFC procedure. The present results corroborate existing data for 200-ms tones in normal listeners and provide new data for 5-ms tones. On average, the binaural level difference required for equal loudness of monaural and binaural tones is about the same for 5- and 200-ms tones of equal level and changes as a function of level. The group data for normal and impaired listeners are in reasonable agreement with data in the literature. However, the data from some of the impaired listeners deviate markedly from the average, indicating that group data do not accurately represent the behavior of all impaired listeners. Derived loudness functions from the loudness-matching data are reasonably consistent with individual data in the literature.     

Interactions between test- and inducer-tone durations in induced loudness reduction

A tone usually declines in loudness when preceded by a more intense inducer tone. This phenomenon is called "loudness recalibration" or "induced loudness reduction" (ILR). The present study investigates how ILR depends on level, loudness, and duration. A 2AFC procedure was used to obtain loudness matches between 2500-Hz comparison tones and 500-Hz test tones at 60 and 70 dB SPL, presented with and without preceding 500-Hz inducer tones. For 200-ms test and comparison tones, the amount of ILR did not depend on inducer level (set at 80 dB SPL and above), but ILR was greater with 200- than with 5-ms inducers, even when both were equally loud. For 5-ms tones, ILR was as great with 5- as with 200-ms inducers and about as great as when test and inducer tones both lasted 200 ms. These results suggest that (1) neither the loudness nor the SPL of the inducer alone governs ILR, and (2) inducer duration must equal or exceed test-tone duration to yield maximal amounts of ILR. Further analysis indicates that the efferent system may be partly responsible for ILR of 200-ms test tones, but is unlikely to account for ILR of 5-ms tones.     

Binaural versus monaural loudness: supersummation of tone partially masked by noise

A series of three experiments used the method of magnitude estimation to examine binaural summation of the loudness of a 1000-Hz tone heard in the quiet and against various backgrounds of masking noise. In the quiet, binaural loudness as measured in sones, is twice monaural loudness. Two conditions of noise masking acted to increase the ratio of binaural/monaural loudness in sones above 2:1--that is, to produce supersummation. (1) When tone was presented to both ears, but masking noise to just one ear (dichotic stimulation), the loudness of the binaural tone was 30%-35% greater than the sum of the loudness of the monaural components. This increase in summation provides a suprathreshold analog to increases in threshold sensitivity observed with dichotic stimulation (masking-level differences). (2) Supersummation was also evident when tone and noise alike were presented to both ears (diotic stimulation); here, the binaural tone's loudness was 10%-25% greater than the sum of the monaural components. The increase in summation with diotic stimulation may be related to the characteristics of binaural summation of the noise masker itself.     

On the relation between the growth of loudness and the discrimination of intensity for pure tones

The intensity jnd is often assumed to depend on the slope of the loudness function. One way to test this assumption is to measure the jnd for a sound that falls on distinctly different loudness functions. Two such functions were generated by presenting a 1000-Hz tone in narrow-band noise (925-1080 Hz) set at 70 dB SPL and in wideband noise (75-9600 Hz) set at 80 dB SPL. Over a range from near threshold to about 75 dB SPL, the loudness function for the tone is much steeper in the narrow-band noise than in the wideband noise. At 72 dB SPL, where the two loudness curves cross, the tone's jnd was measured in each noise by a block up-down two-interval forced-choice procedure. Despite the differences in slope (and in sensation level), the jnd (delta I/I) is nearly the same in the two noises, 0.22 in narrow-band noise and 0.20 in wideband noise. The mean value of 0.21 is close to the value of 0.25 interpolated from Jesteadt et al. [J. Acoust. Soc. Am. 61, 169-176 (1977)] for a 1000-Hz tone that had the same loudness in quiet as did our 72-dB tone in noise, but lay on a loudness function with a much lower slope. These and other data demonstrate that intensity discrimination for pure tones is unrelated to the slope of the loudness function.     

Dependence of binaural loudness summation on interaural level differences, spectral distribution, and temporal distribution

Loudness of interaurally correlated narrow- and broadband noises was investigated using a loudness estimation paradigm (with two anchors) presented via headphones. Throughout the experiments (most performed by 12 subjects), the results from both anchors agreed very well. In the first experiment, third-octave-band noises centered around 250, 710, or 2000 Hz, as well as broadband red (-10 dB/oct), pink (-3 dB/oct), and blue (+10 dB/oct) noises, with interaural level differences of delta L = 0, 4, 10, 20, and infinity dB, were presented as test signals while the same sound presented monaurally or diotically served as anchor. The binaurally summed loudness at delta L = 0 dB was found to be larger than the loudness of a monaural signal of the same SPL by a factor of about 1.5 and decreased with increasing delta L. No dependence of this behavior on frequency, level, or spectral shape was found. In a second experiment, abutting frequency bands of varying width were alternately presented to the subject's left and right ears with the overall spectrum encompassing the whole audio range. The binaural loudness was larger for fewer but broader frequency bands. In a third experiment, uniform exciting noise was switched between the two ears at various speeds. Increasing the switching frequency gave rise to an increase in loudness of about 20%. All results are discussed from the viewpoint of the use of the standardized loudness meter. At this point, there is no evidence that any significant systematic errors due to single-channel evaluation (in contrast to the human two-channel processing) are made by measuring loudness using these meters.     

Louder sounds can produce less forward masking: effects of component phase in complex tones

The influence of the degree of envelope modulation and periodicity on the loudness and effectiveness of sounds as forward maskers was investigated. In the first experiment, listeners matched the loudness of complex tones and noise. The tones had a fundamental frequency (F0) of 62.5 or 250 Hz and were filtered into a frequency range from the 10th harmonic to 5000 Hz. The Gaussian noise was filtered in the same way. The components of the complex tones were added either in cosine phase (CPH), giving a large crest factor, or in random phase (RPH), giving a smaller crest factor. For each F0, subjects matched the loudness between all possible stimulus pairs. Six different levels of the fixed stimulus were used, ranging from about 30 dB SPL to about 80 dB SPL in 10-dB steps. Results showed that, at a given overall level, the CPH and the RPH tones were louder than the noise, and that the CPH tone was louder than the RPH tone. The difference in loudness was larger at medium than at low levels and was only slightly reduced by the addition of a noise intended to mask combination tones. The differences in loudness were slightly smaller for the higher than for the lower F0. In the second experiment, the stimuli with the lower F0s were used as forward maskers of a 20-ms sinusoid, presented at various frequencies within the spectral range of the maskers. Results showed that the CPH tone was the least effective forward masker, even though it was the loudest. The differences in effectiveness as forward maskers depended on masker level and signal frequency; in order to produce equal masking, the level of the CPH tone had to be up to 35 dB above that of the RPH tone and the noise. The implications of these results for models of loudness are discussed and a model is presented based on neural activity patterns in the auditory nerve; this predicts the general pattern of loudness matches. It is suggested that the effects observed in the experiments may have been influenced by two factors: cochlear compression and suppression.     

The influence of middle-ear muscle contraction on auditory threshold for selected pure tones

The influence of middle-ear muscle (MEM) contraction on auditory threshold has been measured for pure tones of 0.25, 0.5, and 1.5 kHz. The reflex-activating signal was a 3-kHz pure tone. Signal paradigms were chosen to reduce or eliminate the effects of binaural loudness summation, contralateral direct masking, and contralateral remote and backward masking effects, and to maximize the influence of MEM contraction. Results indicate that under no condition was behavioral threshold affected by the MEM contraction induced using a pure-tone stimulus of 3 kHz, 105 dB SPL.     

Monaural and interaural intensity discrimination: level effects and the "binaural advantage"

This study examined whether the level effects seen in monaural intensity discrimination (Weber's law and the "near miss") in a two-interval task are also observed in discrimination of interaural intensity differences (IIDs) in a single-interval task. Both tasks were performed for various standard levels of 4-kHz pure tones and broadband noise. The Weber functions (10 log deltaI/I versus I in dB) in the monaural and binaural conditions were parallel. For noise, the Weber functions had slopes close to zero (Weber's law) while the Weber functions for the tones had a mean slope of -0.089 (near miss). The near miss for the monaural and binaural tasks with tones was eliminated when a high-pass masker was gated with the listening intervals. The near-miss was also observed for 250- and 1000-Hz tones in the binaural task despite overall decreased sensitivity to changes in IID at 1000 Hz. The binaural thresholds showed a small (about 2-dB) advantage over monaural thresholds only in the broadband noise conditions. More important, however, is the fact that the level effects seen monaurally are also seen binaurally. This suggests that the basic mechanisms responsible for Weber's law and the near miss are common to monaural and binaural processing.     

Loudness recalibration as a function of level

Recent research on loudness has focused on contextual effects on loudness, both assimilation and recalibration. The current experiments examined loudness recalibration [Marks, J. Exp. Psychol. 20, 382-396 (1994)]. In the first experiment, an adaptive tracking procedure was used to measure loudness recalibration as a function of standard- and recalibration-tone level. The standard-tone frequencies were 500 and 2500 Hz and the levels were 80-, 70-, 60-, and 40-dB SPL, and threshold. Seventeen dB of loudness recalibration was obtained (combined over both frequencies) in the 60-dB SPL condition. This amount of loudness recalibration, while substantial, is still less than that obtained by Marks (22 dB), using the method of paired comparisons. The second experiment sought to duplicate Marks' earlier experiment [Marks, J. Exp. Psychol. 20, 382-396 (1994), experiment 2]. The results of this experiment (21 dB) were almost identical to those obtained by Marks. The results of experiment 1 indicate that loudness recalibration is maximum when the recalibration tone is moderately louder than the subsequent standard tones. Relatively little loudness recalibration is exhibited when the standard-tone level equals the recalibration-tone level. In addition, there is no loudness recalibration at threshold. The tracking procedure also identified that the onset of loudness recalibration is very rapid. The difference between the maximum loudness recalibration obtained at each frequency (11 dB at 500 Hz, 6 dB at 2500 Hz) suggests that loudness recalibration is dependent upon the frequency of the standard tone.     

Binaural loudness summation for speech presented via earphones and loudspeaker with and without visual cues

Preliminary data [M. Epstein and M. Florentine, Ear. Hear. 30, 234-237 (2009)] obtained using speech stimuli from a visually present talker heard via loudspeakers in a sound-attenuating chamber indicate little difference in loudness when listening with one or two ears (i.e., significantly reduced binaural loudness summation, BLS), which is known as "binaural loudness constancy." These data challenge current understanding drawn from laboratory measurements that indicate a tone presented binaurally is louder than the same tone presented monaurally. Twelve normal listeners were presented recorded spondees, monaurally and binaurally across a wide range of levels via earphones and a loudspeaker with and without visual cues. Statistical analyses of binaural-to-monaural ratios of magnitude estimates indicate that the amount of BLS is significantly less for speech presented via a loudspeaker with visual cues than for stimuli with any other combination of test parameters (i.e., speech presented via earphones or a loudspeaker without visual cues, and speech presented via earphones with visual cues). These results indicate that the loudness of a visually present talker in daily environments is little affected by switching between binaural and monaural listening. This supports the phenomenon of binaural loudness constancy and underscores the importance of ecological validity in loudness research.     

Frequency selectivity in loudness adaptation and auditory fatigue

An intermittent monaural tone may induce a decline in the loudness of a continuous tone presented to the same ear [Canévet et al., Br. J. Audiol. 17, 49-57 (1983)]. Two experiments studied the frequency selectivity of loudness adaptation induced in this manner. The method of successive magnitude estimations was used to measure the loudness of a monaural 84-s test tone before and after a single presentation of a 24-s inducer tone in the same ear. The first experiment shows that, for an inducing tone (500, 1000, or 3000 Hz) approximately 15 dB more intense than a test tone set to one of 21 different frequencies, adaptation is greatest when the two tones have the same frequency; with increasing difference between the test-tone and inducer frequencies, adaptation progressively declines. The second experiment measured frequency selectivity in the loudness reduction caused by a 1000-Hz inducer as a function of its level. As inducer level went from 75 to 95 dB (with test tone constant at 60 phons), selectivity passes progressively from the type seen in short-term or low-level fatigue (maximal for the 1000-Hz test tone) to a type seen in long-term or high-level fatigue (maximal for the 1000-Hz test tone) to a type seen in long-term or high-level fatigue (maximal at frequencies higher than that of the inducer or fatiguing tone). A common cochlear origin and a continuity between the mechanisms of ipsilaterally induced adaptation and high-level fatigue are suggested by the data.     

Asymmetry of masking between complex tones and noise: partial loudness

This experiment examined the partial masking of periodic complex tones by a background of noise, and vice versa. The tones had a fundamental frequency (F0) of 62.5 or 250 Hz, and components were added in either cosine phase (CPH) or random phase (RPH). The tones and the noise were bandpass filtered into the same frequency region, from the tenth harmonic up to 5 kHz. The target alone was alternated with the target and the background; for the mixture, the background and target were either gated together, or the background was turned on 400 ms before, and off 200 ms after, the target. Subjects had to adjust the level of either the target alone or the target in the background so as to match the loudness of the target in the two intervals. The overall level of the background was 50 dB SPL, and loudness matches were obtained for several fixed levels of the target alone or in the background. The resulting loudness-matching functions showed clear asymmetry of partial masking. For a given target-to-background ratio, the partial loudness of a complex tone in a noise background was lower than the partial loudness of a noise in a complex tone background. Expressed as the target-to-background ratio required to achieve a given loudness, the asymmetry typically amounted to 12-16 dB. When the F0 of the complex tone was 62.5 Hz, the asymmetry of partial masking was greater for CPH than for RPH. When the F0 was 250 Hz, the asymmetry was greater for RPH than for CPH. Masked thresholds showed the same pattern as for partial masking for both F0's. Onset asynchrony had some effect on the loudness matching data when the target was just above its masked threshold, but did not significantly affect the level at which the target in the background reached its unmasked loudness. The results are interpreted in terms of the temporal structure of the stimuli.     

Functional magnetic resonance imaging measurements of sound-level encoding in the absence of background scanner noise

Effects of sound level on auditory cortical activation are seen in neuroimaging data. However, factors such as the cortical response to the intense ambient scanner noise and to the bandwidth of the acoustic stimuli will both confound precise quantification and interpretation of such sound-level effects. The present study used temporally "sparse" imaging to reduce effects of scanner noise. To achieve control for stimulus bandwidth, three schemes were compared for sound-level matching across bandwidth: component level, root-mean-square power and loudness. The calculation of the loudness match was based on the model reported by Moore and Glasberg [Acta Acust. 82, 335-345 (1996)]. Ten normally hearing volunteers were scanned using functional magnetic resonance imaging (tMRI) while listening to a 300-Hz tone presented at six different sound levels between 66 and 91 dB SPL and a harmonic-complex tone (F0= 186 Hz) presented at 65 and 85 dB SPL. This range of sound levels encompassed all three bases of sound-level matching. Activation in the superior temporal gyrus, induced by each of the eight tone conditions relative to a quiet baseline condition, was quantified as to extent and magnitude. Sound level had a small, but significant, effect on the extent of activation for the pure tone, but not for the harmonic-complex tone, while it had a significant effect on the response magnitude for both types of stimulus. Response magnitude increased linearly as a function of sound level for the full range of levels for the pure tone. The harmonic-complex tone produced greater activation than the pure tone, irrespective of the matching scheme for sound level, indicating that bandwidth had a greater effect on the pattern of auditory activation than sound level. Nevertheless, when the data were collapsed across stimulus class, extent and magnitude were significantly correlated with the loudness scale (measured in phons), but not with the intensity scale (measured in SPL). We therefore recommend the loudness formula as the most appropriate basis of matching sound level to control for loudness effects when cortical responses to other stimulus attributes, such as stimulus class, are the principal concern.     

Decision rules in detection of simple and complex tones

Detection of simple and complex tones in the presence of a 64-dB SPL uniformly masking noise was examined in two experiments. In both experiments, the signals were either pure tones (220, 1100, or 3850 Hz) or an 18-tone complex consisting of equally intense components between 110 and 7260 Hz. In experiment 1, psychometric functions were obtained for detection in a 2I, 2AFC task. Results for eight normal listeners show that the psychometric functions are parallel for simple and complex tones. As expected, the masked thresholds for the pure tones are 43-44 dB SPL independent of frequency; the masked threshold for the complex tone is about 37 dB SPL per tone. These results indicate that the simultaneous presence of signal energy in many auditory channels aids detection. In experiment 2, psychometric functions were obtained with all four signals presented in random order within a block of trials. Results for four normal listeners show that the psychometric functions are parallel to one another and to those obtained in experiment 1. The thresholds are elevated to about 46 dB for the pure tones and to 40.5 dB for the complex tone. These results are nearly, but not quite, consistent with a multiband energy-detector model using an optimum decision rule; it appears that listeners may only make an unweighted sum of decision variables across an optimum selection of channels.     

Masked detection and discrimination of tone sequences under conditions of monaural and binaural masking release

Experiment 1 examined detection and discrimination of monaural four-tone sequences composed of 400-, 500-, and 625-Hz sinusoids. In the baseline conditions, the masker was monaural composed of 25-Hz-wide bands of random noise centered on 320, 400, 500, 625, and 781 Hz. In the binaural masking release conditions, the noise was presented diotically. In the monaural masking release conditions, the noise was presented to the same ear as the signal, but it was comodulated. Tones had half-amplitude durations of 30, 60, or 150 ms. There was no delay between successive tones, so the rate of frequency change depended on tone duration. Listeners discriminated between sequences composed of 500-400-625-500 Hz and 500-625-400-500 Hz. Discrimination results were poor for rapid sequences in both monaural and binaural masking release conditions relative to baseline conditions. Results from experiment 2 indicated that poor discrimination for rapid sequences could also occur in the baseline conditions, provided that the frequency separation among tonal components was small. Sluggish processing in the present paradigm was not restricted to conditions relying on binaural cues. It is argued that sluggishness may reflect a long temporal window in monaural and binaural masking release conditions or an interaction between poor cue quality and task difficulty.     

Subjective loudness level measurements and equal loudness contours in a bottlenose dolphin (Tursiops truncatus)

Loudness level measurements in human listeners are straightforward; however, it is difficult to convey the concepts of loudness matching or loudness comparison to (non-human) animals. For this reason, prior studies have relied upon objective measurements, such as response latency, to estimate equal loudness contours in animals. In this study, a bottlenose dolphin was trained to perform a loudness comparison test, where the listener indicates which of two sequential tones is louder. To enable reward of the dolphin, most trials featured tones with identical or similar frequencies, but relatively large sound pressure level differences, so that the loudness relationship was known. A relatively small percentage of trials were "probe" trials, with tone pairs whose loudness relationship was not known. Responses to the probe trials were used to construct psychometric functions describing the loudness relationship between a tone at a particular frequency and sound pressure level and that of a reference tone at 10 kHz with a sound pressure level of 90, 105, or 115 dB re 1 μPa. The loudness relationships were then used to construct equal loudness contours and auditory weighting functions that can be used to predict the frequency-dependent effects of noise on odontocetes.     

Cortical responses to the 2f1-f2 combination tone measured indirectly using magnetoencephalography

The simultaneous presentation of two tones with frequencies f(1) and f(2) causes the perception of several combination tones in addition to the original tones. The most prominent of these are at frequencies f(2)-f(1) and 2f(1)-f(2). This study measured human physiological responses to the 2f(1)-f(2) combination tone at 500 Hz caused by tones of 750 and 1000 Hz with intensities of 65 and 55 dB SPL, respectively. Responses were measured from the cochlea using the distortion product otoacoustic emission (DPOAE), and from the auditory cortex using the 40-Hz steady-state magnetoencephalographic (MEG) response. The perceptual response was assessed by having the participant adjust a probe tone to cause maximal beating ("best-beats") with the perceived combination tone. The cortical response to the combination tone was evaluated in two ways: first by presenting a probe tone with a frequency of 460 Hz at the perceptual best-beats level, resulting in a 40-Hz response because of interaction with the combination tone at 500 Hz, and second by simultaneously presenting two f(1) and f(2) pairs that caused combination tones that would themselves beat at 40 Hz. The 2f(1)-f(2) DPOAE in the external auditory canal had a level of 2.6 (s.d. 12.1) dB SPL. The 40-Hz MEG response in the contralateral cortex had a magnitude of 0.39 (s.d. 0.1) nA m. The perceived level of the combination tone was 44.8 (s.d. 11.3) dB SPL. There were no significant correlations between these measurements. These results indicate that physiological responses to the 2f(1)-f(2) combination tone occur in the human auditory system all the way from the cochlea to the primary auditory cortex. The perceived magnitude of the combination tone is not determined by the measured physiological response at either the cochlea or the cortex.     

Monaural level discrimination under dichotic conditions

The ability to make judgments about the stimulus at one ear when a stimulus is simultaneously presented to the other ear was tested. Specifically, subjects discriminated the level of a 600 Hz target tone presented at the left ear while an identical-frequency distractor was simultaneously presented at the other ear. When there was no distractor, threshold was 0.7 dB. Threshold increased to 1.1 dB when a distractor with a fixed phase and level was introduced contra-aurally to the target. Further increases in threshold were observed when an across-presentation variability was introduced into the distractor phase (threshold of 1.6 dB) or level (threshold of 5.8 dB). When both the distractor level and phase varied, the largest threshold of 7.3 dB was obtained. These increases in threshold cannot be predicted by common binaural models, which assume that a target stimulus at one ear can be processed without interference from the stimulus at the nontarget ear. The measured thresholds are consistent with a model that utilizes two binaural dimensions that roughly correspond to the loudness and the position of a fused binaural image. The results show that, with binaurally fused tonal stimuli, subjects are unable to listen to one ear.     

Asymmetry of masking between complex tones and noise: the role of temporal structure and peripheral compression

Thresholds for the detection of harmonic complex tones in noise were measured as a function of masker level. The rms level of the masker ranged from 40 to 70 dB SPL in 10-dB steps. The tones had a fundamental frequency (F0) of 62.5 or 250 Hz, and components were added in either cosine or random phase. The complex tones and the noise were bandpass filtered into the same frequency region, from the tenth harmonic up to 5 kHz. In a different condition, the roles of masker and signal were reversed, keeping all other parameters the same; subjects had to detect the noise in the presence of a harmonic tone masker. In both conditions, the masker was either gated synchronously with the 700-ms signal, or it started 400 ms before and stopped 200 ms after the signal. The results showed a large asymmetry in the effectiveness of masking between the tones and noise. Even though signal and masker had the same bandwidth, the noise was a more effective masker than the complex tone. The degree of asymmetry depended on F0, component phase, and the level of the masker. The maximum difference between masked thresholds for tone and noise was about 28 dB; this occurred when the F0 was 62.5 Hz, the components were in cosine phase, and the masker level was 70 dB SPL. In most conditions, the growth-of-masking functions had slopes close to 1 (on a dB versus dB scale). However, for the cosine-phase tone masker with an F0 of 62.5 Hz, a 10-dB increase in masker level led to an increase in masked threshold of the noise of only 3.7 dB, on average. We suggest that the results for this condition are strongly affected by the active mechanism in the cochlea.     

Steps in loudness summation

The dependence of binaural loudness summation on interaural phase of tones ranging between 250 and 1400 Hz was investigated in a series of experiments using a loudness-matching procedure. Observers matched loudness of monaural-binaural and binaural-binaural pairs of alternating tones by adjusting the amplitude of one of the two. Adjustable and reference components of each tone pair were equal in frequency and were varied independently in interaural phase angle through the range +/- 177 degrees. For each tone frequency, steps in loudness summation of approximately 3 dB were obtained in the vicinity of a constant value of phase angle, theta t, which depends on the Hornbostel-Wertheimer constant (tau H) according to the relations theta t = 2 pi f tau H for tones of low frequency (f less than or equal to 1/2 tau H), and theta t = 2 pi(1 - f tau H) for tones of higher frequency (1/2 tau H less than or equal to f less than or equal to 1/tau H). Spatial relationships among alternating tones observed in the above conditions covaried with relative loudness in a complex manner, but exhibited qualitative changes in the vicinity of theta t.