Model Of Loudness Perception Research Articles

Representation of Instantaneous and Short-Term Loudness in the Human Cortex.

Acoustic signals pass through numerous transforms in the auditory system before perceptual attributes such as loudness and pitch are derived. However, relatively little is known as to exactly when these transformations happen, and where, cortically or sub-cortically, they occur. In an effort to examine this, we investigated the latencies and locations of cortical entrainment to two transforms predicted by a model of loudness perception for time-varying sounds: the transforms were instantaneous loudness and short-term loudness, where the latter is hypothesized to be derived from the former and therefore should occur later in time. Entrainment of cortical activity was estimated from electro- and magneto-encephalographic (EMEG) activity, recorded while healthy subjects listened to continuous speech. There was entrainment to instantaneous loudness bilaterally at 45, 100, and 165 ms, in Heschl's gyrus, dorsal lateral sulcus, and Heschl's gyrus, respectively. Entrainment to short-term loudness was found in both the dorsal lateral sulcus and superior temporal sulcus at 275 ms. These results suggest that short-term loudness is derived from instantaneous loudness, and that this derivation occurs after processing in sub-cortical structures.

Perceptual weights for loudness judgments of six-tone complexes.

Subjects with normal hearing (NH) and with sensorineural hearing loss (SNHL) judged the overall loudness of six-tone complexes comprised of octave frequencies from 0.25 to 8 kHz. The level of each tone was selected from a normal distribution with a standard deviation of 5 dB, and subjects judged which of two complexes was louder. Overall level varied across conditions. In the "loudness" task, there was no difference in mean level across the two stimuli. In the "sample discrimination" task, the two complexes differed by an average of 5 dB. For both tasks, perceptual weights were derived by correlating the differences in level between matched-frequency tones in the complexes and the loudness decision on each trial. Weights obtained in the two tasks showed similar shifts from low to high frequency components with increasing overall level. Simulation of these experiments using a model of loudness perception [Moore and Glasberg (2004), Hear Res. 188, 70-88] yielded predicted weights for these stimuli that were highly correlated with predicted specific loudness, but not with the observed weights.

Development of a new method for deriving initial fittings for hearing aids with multi-channel compression: CAMEQ2-HF

described a procedure, CAMEQ, for the initial fitting of multi-channel compression hearing aids. The procedure was derived using a model of loudness perception for impaired hearing. We describe here the development of a new fitting method, CAMEQ2-HF, which differs from CAMEQ in the following ways: (1) CAMEQ2-HF gives recommended gains for centre frequencies up to 10 kHz, whereas the upper limit for CAMEQ is 6 kHz; (2) CAMEQ is based on the assumption that the hearing aid user faces the person they wish to hear and uses a free-field-to-eardrum transfer function for frontal incidence. CAMEQ2-HF is based on the assumption that the user may wish to hear sounds from many directions, and uses a diffuse-field-to-eardrum transfer function; (3) CAMEQ2-HF is based on an improved loudness model for impaired hearing; (4) CAMEQ2-HF is based on recent wideband measurements of the average spectrum of speech.Sumario describieron un procedimiento, CAMEQ, para la adaptación inicial de auxiliares auditivos con compresión de múltiples canales. El procedimiento se basó en el uso de un modelo de percepción de la intensidad subjetiva para casos de audición disminuida. Describimos aquí el desarrollo de un nuevo método de adaptación, CAMEQ2-HF, que difiere del CAMEQ en las siguientes formas: (1) CAMEQ2-HF proporciona ganancias recomendadas para las frecuencias centrales hasta 10 kHz mientras que el límite superior para el CAMEQ es 6 kHz; (2) CAMEQ se basa en la suposición de que el usuario de un auxiliar auditivo (se ubica de frente)hace frente a la persona que quiere oír y usa la función de transferencia campo libre-membrana timpánica para una incidencia frontal. CAMEQ2-HF se basa en la suposición de que el usuario quiere oír los sonidos desde muchas direcciones y usa una función de transferencia campodifuso-a-membrana timpánica; (3) CAMEQ2-HF se basa en un modelo de intensidad subjetiva mejorada para la audición disminuida; (4) CAMEQ2-HF se basa en las recientes mediciones de banda ancha del espectro promedio del habla.

Perceptual Reinforcement of Speech Signal Based on Partial Specific Loudness

In the presence of background noise, the perceptual loudness of speech signal significantly decreases, resulting in the deterioration of intelligibility and clarity. In this letter, we propose a novel approach to enhance the perceived quality of the speech signal when the additive noise cannot be directly controlled. Instead of controlling the background noise, we propose to reinforce the speech signal so that it can be heard more clearly in noisy environments. To find a suitable reinforcement rule, the loudness perception model proposed by Moore et al. is adopted. Experimental results show that the loudness of the reinforced signal can be maintained at the level almost the same as that of the original noise-free speech, and the proposed algorithm can enhance the perceived speech quality under various noise environments.

A revised model of loudness perception applied to cochlear hearing loss

We previously described a model for loudness perception for people with cochlear hearing loss. However, that model is incompatible with our most recent and most satisfactory model of loudness for normal hearing. Here, we describe a loudness model that is applicable to both normal and impaired hearing. In contrast to our earlier model for impaired hearing, the new model correctly predicts: (1) that a sound at absolute threshold has a small but finite loudness; (2) that, for levels very close to the absolute threshold, the rate of growth of loudness is similar for normal ears and ears with cochlear hearing loss; (3) the relation between monaural and binaural threshold and loudness; (4) recent measures of equal-loudness contours. Like the earlier model, the new model can account for the loudness recruitment and reduced loudness summation that are typically associated with cochlear hearing loss.

Least-mean-square estimation of new equal-loudness level contours from recent data based on a loudness perception model

Since probable large errors were suggested in 1985 in the equal-loudness level contours by Robinson and Dadson [Br. J. Appl. Phys. 7, 166–181 (1956)], which were standardized as ISO 226, a considerable amount of data on the equal-loudness relation has been accumulated. Most of the data consistently show a large discrepancy up to more than 20 phons from the contours, especially below 1 kHz. To obtain reliable contours from these new data sporadically given for some specific frequencies and phons, a model function representing the equal-loudness relation was derived from a loudness function modified by the two-stage loudness perception model. Values of the parameters of the model function were obtained by fitting the function to the experimental data. Equal-loudness level contours could be drawn by use of the model function with the parameter values interpolated along the frequency axis. The resultant equal-loudness level contours showed clear differences from those by Robinson and Dadson for all loudness levels over the whole frequency range, particularly in the frequency range lower than 1 kHz. In contrast, the contours rather resemble those given by Fletcher and Munson in 1933 and by Churcher and King in 1937 in the midfrequency range at relatively low loudness levels. [Work supported by NEDO.]

Interaural coherence and the lateralization of noise by interaural level differences

Coherent noise, with an interaural cross correlation of unity, and incoherent noise, where signals to left and right ears are independent, sound very different. The former produces a compact lateralized image. The latter produces a diffuse image that fills the head. Nevertheless, listening experiments show that coherent and incoherent noise images seem to be equally affected by small interaural level differences (ILD). The ILD threshold for lateralizing incoherent noise is less than half a dB greater than the threshold for lateralizing coherent noise. In this sense, the human binaural system appears to behave like an ideal level meter, insensitive to the wave form and envelope fine structures that determine coherence. The small discrepancy (less than 0.5 dB) can be understood from a standard model of loudness perception—incorporating critical band filtering, half-wave rectification, amplitude compression (0.6 power law), and temporal integration (300 ms). The same model can also account for the small observed difference in lateralization ILD thresholds for coherent noise (N0) and antiphasic noise (Nπ). It can further account for the observed noise bandwidth dependence of lateralization ILD thresholds. [Work supported by the NIDCD.]

Psychophysical and cognitive limitations to speech perception by cochlear implant users

Deaf listeners with cochlear implants (CIs) achieve significant levels of speech recognition, but their performance range remains wide. Unfortunately, our understanding of the speech perception mechanisms employed by CI users is still incomplete. In particular, we do not know the exact combination of acoustic cues that are employed by CI users to understand speech, nor do we understand how sensory information is represented and combined, and how that information is used to perform speech identification. We have attempted to address this issue by developing mathematical models (Multidimensional Phoneme Identification or MPI models) that aim to predict phoneme identification for individual cochlear implant users based on their discrimination along specified acoustic dimensions. Mathematically, the MPI model is a multidimensional extension of the Durlach–Braida model of loudness perception. The MPI model can explain most of the vowel pairs or consonant pairs that should be more frequently confused by groups of CI users. In this presentation we will discuss individual data suggesting that speech perception by CI users may be limited by two kinds of factors: psychophysical (i.e., limited jnd’s along relevant acoustic dimensions) and cognitive (related to imperfect integration of different acoustic cues). [Work supported by NIDCD (R01-DC03937), NOHR and DRF.]

Further evaluation of a model of loudness perception applied to cochlear hearing loss.

This paper describes further tests of a model for loudness perception in people with cochlear hearing loss. It is assumed that the hearing loss (the elevation in absolute threshold) at each audiometric frequency can be partitioned into a loss due to damage to outer hair cells (OHCs) and a loss due to damage to inner hair cells (IHCs) and/or neurons. The former affects primarily the active mechanism that amplifies the basilar membrane (BM) response to weak sounds. It is modeled by increasing the excitation level required for threshold, which results in a steeper growth of specific loudness with increasing excitation level. Loss of frequency selectivity, which results in broader excitation patterns, is also assumed to be directly related to the OHC loss. IHC damage is modeled by an attenuation of the calculated excitation level at each frequency. The model also allows for the possibility of complete loss of IHCs or functional neurons at certain places within the cochlea ("dead" regions). The parameters of the model (OHC loss at each audiometric frequency, plus frequency limits of the dead regions) were determined for three subjects with unilateral cochlear hearing loss, using data on loudness matches between sinusoids presented alternately to their two ears. Further experiments used bands of noise that were either 1-equivalent rectangular bandwidth (ERB) wide or 6-ERBs wide, centered at 1 kHz. Subjects made loudness matches for these bands of noise both within ears and across ears. The model was reasonably accurate in predicting the results of these matches without any further adjustment of the parameters.

Loudness perception with pulsatile electrical stimulation: the effect of interpulse intervals.

The effect of interpulse intervals on the perception of loudness of biphasic current pulse trains was investigated in eight adult cochlear implantees at three different stimulus levels encompassing the psychophysical dynamic range. Equal-loudness contours and thresholds were obtained for stimuli in which two biphasic pulses were presented in a fixed repetition period (4 and 20 ms), and also for single-pulse/period stimuli with rates varying between 20 and 750 Hz. All stimuli were of 500-ms duration, and the phase durations of each pulse were 100 microseconds or less. The results of these experiments were consistent with predictions of a three-stage model of loudness perception, consisting of a peripheral refractory effect function, a sliding central integration time window, and a central equal-loudness decision device. Application of the model to the data allowed the estimation of neural refractory characteristics of the subjects' remaining peripheral neural population. The average neural spike probability for a 50-Hz stimulus was predicted to be about 0.77, with an associated neural refractory time of 7.3 ms. These predictions did not vary systematically with level, implying that the effect of increasing current level on loudness results more from recruitment of neurons than from any increase in average spike probability.

Range as a factor determining the information of loudness judgments: Overcoming small sample bias.

Abstract Experiments on the absolute identification of pure tones were conducted at a single frequency in order to explore several effects. We measured the change in transmitted information as the stimulus range was varied, and we also measured the change in transmitted information as the number of categories within a fixed range was increased. In the former case, we found that information increased with increasing range. In the latter case, we found that information increased with increasing number of categories, but the increase was due to a purely mathematical effect. Transmitted information was estimated by means of computer simulation designed to overcome, in part, small sample bias. This simulator is of potential use to others by helping them calculate transmitted or mutual information accurately using a minimum number of experimental trials. The graph of calculated information against number of trials was found to assume a characteristic shape. Garner and Hake (1951) and Garner (1953) demonstrated how one could quantify the information transmitted to a participant who was required to judge the loudness of tones of a fixed frequency. The experimental paradigm is well known. The continuum of sound intensities between two fixed intervals (dB HL) could be divided into an arbitrary number of loudness categories (Garner used 4, 5, 6, 7, 10 and 20). The participant was trained to identify a tone as belonging to a specific category. He or she was then presented with a large number of tones of unknown intensity, and was required to sort them as well as he or she was able into the correct categories. The data were entered into a matrix, which is known as a confusion matrix, and, using the methods of Shannon and Weaver (1949), the mean information transmitted per stimulus was calculated (Attneave 1959, Norwich, 1993). A problem encountered in the measurement of channel capacities is the large number of trials that must be conducted in order to obtain accurate values. A trial is a single presentation to a participant of a tone whose intensity is unknown to him or her. Houtsma (1983) introduced the idea of obtaining plausible values by extending data through computer simulation. Studies of this type are referred to as one-dimensional because, for example, the tone was permitted to vary only in loudness and not in pitch (Garner, 1962). It was discovered by Miller (1956) that such one-dimensional stimuli could transmit to the participant no more than about 2.5 bits, or 1.75 natural units of information per stimulus. A natural unit of information is just information calculated using natural logarithms. It can be obtained from the information in bits by multiplying by 0.693... Earlier investigators have begun the exploration of the effects of stimulus range and number of stimulas categories on transmitted information. Braida and Durlach (1972), working within the framework of a theoretical model of loudness perception, have derived a relationship between information and sensitivity which, in turn, can be related to range. Luce, Weber and Green (1976) explored the effect of varying stimulus categories over a range fixed about a central intensity. Essentially, transmitted information was found to increase with both range and number of categories, saturating at a value not greater than approximately 2.5 bits. It has not been clear how these two variables independently cause the transmitted information to increase. OBJECT OF STUDY Our experiments were designed to study three effects. (a) By means of computer simulation, we explored the change in the calculated information (including the small sample bias) as the number of trials increases from zero to, say, 20,000. (b) We examined the change in transmitted information associated with differences in the total range of stimuli. For example, does the transmitted information differ when stimuli are selected over the range 1-90 dB HL as compared with 1-70 dB HiL? …

A temporal integration model for loudness perception of repeated impulsive sounds.

A loudness perception model for repeated impulsive sounds that have exponentially rising and decaying envelopes was studied. The loudness of repeated impulsive sound is the same as that of a single burst of impulsive sound up to a certain repetition rate. A critical repetition rate R0 beyond which the loudness increases with increase in rep-etition rate was found to lie between 0.2 and 0.7 Hz. In other words, the critical time period, 1/R0, was 2∼5 s. If it is assumed, therefore, that our auditory system has a capacity to hold loudness sensation for 2∼5 s, the result of our experiment can be ex-plained. An integrator of loudness which has a rise time constant of 100 ms and a decay time constant of 5 s yields a good descriptor of the experimental results.