Mary Florentine

Temporal integration in normal hearing, cochlear impairment, and impairment simulated by masking

To assess temporal integration in normal hearing, cochlear impairment, and impairment simulated by masking, absolute thresholds for tones were measured as a function of duration. Durations ranged from 500 ms down to 15 ms at 0.25 kHz, 8 ms at 1 kHz, and 2 ms at 4 and 14 kHz. An adaptive 2I, 2AFC procedure with feedback was used. On each trial, two 500‐ms observation intervals, marked by lights, were presented with an interstimulus interval of 250 ms. The monaural signal was presented in the temporal center of one observation interval. The results for five normal and six impaired listeners show: (1) normal listeners’ thresholds decrease by about 8 to 10 dB per decade of duration, as expected; (2) listeners with cochlear impairments generally show less temporal integration than normal listeners; and (3) listeners with impairments simulated using masking noise generally show the same amount of temporal integration as normal listeners tested in the quiet. The difference between real and simulated impairments ...

Level discrimination as a function of level for tones from 0.25 to 16 kHz

Difference limens for level (delta L in dB = 20 log [(p + delta p)/p], where p is pressure) were measured as a function of level for tones at 0.25, 0.5, 1, 2, 4, 8, 10, 12, 14, and 16 kHz. At each frequency, test levels encompassed the range from near threshold to 95 dB SPL in steps of 10 dB or smaller. The stimulus duration was 500 ms and the interstimulus interval was 250 ms. An adaptive two-alternative forced-choice procedure with feedback was used. Results for six normal listeners show individual differences among listeners, but the general trends seen in the average data clearly are present in the individual data and show the following. First, the delta Ls at all but the highest frequencies are generally smaller at high levels than at low levels. Second, the delta Ls at equal SPLs are largely independent of frequency up to about 4 kHz, but increase with frequency above 4 kHz. Third, at 8 and 10 kHz, the delta Ls are clearly nonmonotonic functions of level, showing consistent deterioration in the mid-level delta Ls relative to the low- and high-level delta Ls. The present data are discussed qualitatively in terms of current models of level discrimination.

An excitation‐pattern model for intensity discrimination

This paper evaluates two different versions of Zwicker [Acustica 6, 365–381 (1956)] and Maiwald’s [Acustica 18, 193–207 (1967)] excitation‐pattern model for intensity discrimination. The single‐band version is that originally used by Zwicker and Maiwald. They assumed that performance was determined by the critical band in which the excitation grows most rapidly with increasing level of the stimulus. The multiband version forms an optimum decision based on information in all critical bands. Predictions from the two versions of the model are compared to data for intensity discrimination of tones as a function of level and frequency, for partially masked tones and for white noise. In general, the single‐band version yields predictions in qualitative agreement, but not in quantitative agreement with the intensity‐resolution data for pulsed tones. The multiband version yields predictions in good qualitative as well as quantitative agreement with the data, except at high frequencies.

Gap Detection in Normal and Impaired Listeners: The Effect of Level and Frequency

Temporal summation and temporal resolution are often thought to be different aspects of the same integration process. However, a long integration time is required to optimize performance in a temporal summation task, whereas a short integration time is required to optimize performance in a temporal resolution task. Indeed, the integration times found in temporal summation experiments are typically one-to-two orders of magnitude larger than those found in temporal resolution experiments (for review, see Green, this volume, see also de Boer, this volume). It is possible to reconcile this large difference either by assuming that a compressive nonlinear transformation (Divenyi and Shannon 1983) or neural adaptation (Irwin and Kemp 1976; Irwin and Purdy 1982) takes place prior to integration, but in this paper we implicitly treat the two integration processes as separate by considering only temporal resolution and the corresponding short integration time.

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)].

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.

Growth of Loudness in Listeners with Cochlear Hearing Losses: Recruitment Reconsidered

This article examines how loudness grows with increasing intensity near threshold in five listeners with hearing losses of predominantly cochlear origin. It provides evidence against the pervasive and long-held notion that such listeners show abnormally rapid loudness growth near their elevated thresholds. As in a previous study for listeners with normal hearing, loudness functions near threshold were derived from loudness matches between a pure tone and four- or ten-tone complexes using a simple model of loudness summation. This study assumed that the loudness function had the same form for any component of a complex, but a scale factor that depended on the amount of hearing loss allowed the loudness at threshold to vary with frequency. The best-fitting loudness functions had low-level local exponents [i.e., slopes of the low-level loudness function plotted as log(loudness) versus log(intensity)] that were within the normal range. At 0 dB SL, the average local exponents were 1.26 for the listeners with hearing losses compared with 1.31 for normal listeners, which indicates that loudness near threshold grows at similar rates in normal listeners and listeners with hearing losses. The model also indicated that, on average, the loudness at threshold doubled for every 16 dB of hearing loss. The increased loudness at threshold, together with somewhat enlarged local exponents around 20 dB SL, accounts for the near-normal loudness often obtained for high-SPL tones in listeners with hearing losses. Such loudness functions are consistent with the steep functions shown by classical data on loudness matches between tones for which thresholds are normal and tones for which thresholds are elevated. Thus, the present data indicate that an abnormally large loudness at an elevated threshold is likely to be a better definition of recruitment than the classical definition of it as an abnormally rapid growth of loudness above an elevated threshold.

Tuning curves and pitch matches in a listener with a unilateral, low-frequency hearing loss

Psychoacoustical tuning curves and interaural pitch matches were measured in a listener with a unilateral, moderately severe hearing loss of primarily cochlear origin below 2 kHz. The psychoacoustical tuning curves, measured in a simultaneous-masking paradigm, were obtained at 1 kHz for probe levels of 4.5-, 7-, and 13-dB SL in the impaired ear, and 7-dB SL in the impaired ear, and 7-dB SL in the normal ear. Results show that as the level of the probe increased from 4.5- to 13-dB SL in the impaired ear, (1) the frequency location of the tip of the tuning curve decreased from approximately 2.85 to 2.20 kHz and (2) the lowest level of the masker required to just mask the probe increased from 49- to 83-dB SPL. The tuning curve in the normal ear was comparable to data from other normal listeners. The interaural pitch matches were measured from 0.5 to 6 kHz at 10-dB SL in the impaired ear and approximately 15- to 20-dB SL in the normal ear. Results show reasonable identity matches (e.g., a 500-Hz tone in the impaired ear was matched close to a 500-Hz tone in the normal ear), although variability was significantly greater for pitch matches below 2 kHz. The results are discussed in terms of their implications for models of pitch perception.

Intensity perception. XIV. Intensity discrimination in listeners with sensorineural hearing lossa)

Intensity discrimination of pulsed tones (also called level discrimination) was measured as a function of level in 13 listeners with sensorineural hearing impairment of primarily cochlear origin, one listener with a vestibular schwannoma, and six listeners with normal hearing. Measurements were also made in normal ears presented with masking noise spectrally shaped to produce audiograms similar to those of the cochlearly impaired listeners. For unilateral impairments, tests were made at the same frequency in the normal and impaired ears. For bilateral-sloping impairments, tests were made at different frequencies in the same ear. The normal listeners showed results similar to other data in the literature. The listener with a vestibular schwannoma showed greatly reduced intensity resolution, except at a few levels. For listeners with recruiting sensorineural impairments, the results are discussed according to the configuration of the impairment and are compared across configurations at equal SPL, equal SL, and equal loudness level. Listeners with increasing hearing losses at frequencies above the test frequency generally showed impaired resolution, especially at high levels, and less deviation from Webers law than normal listeners. Listeners with decreasing hearing loss at frequencies above the test frequency showed nearly normal intensity-resolution functions. Whereas these trends are generally present, there are also large differences among individuals. Results obtained from normal listeners who were tested in the presence of masking noise indicate that elevated thresholds and reduced dynamic range account for some, but not all, of the effects of recruiting sensorineural impairment on intensity resolution.

Level discrimination of tones as a function of duration

Difference limens for level [delta Ls (dB) = 20 log[p + delta p)/p), where p is the pressure] were measured as a function of duration for tones at 250, 500, and 8000 Hz. Stimulus durations ranged from 2 ms to 2 s, and the stimulus power was held constant. Rise and fall times were 1 ms. The interstimulus interval was 250 ms. At each frequency, three levels were tested: 85, 65, and approximately 40 dB SPL. An adaptive two-alternative forced-choice procedure with feedback was used. For three normal listeners, delta Ls decreased as duration increased, up to at least 2 s, except at 250 Hz. At 250 Hz, delta L stopped decreasing at durations between 0.5 and 1 s. In a double logarithmic plot of delta L versus duration, the rate of decrease is generally well fitted by a sloping line. The average slope is -0.28; it is steeper at high levels than at low levels. Because the average slope is shallower than the -0.5 slope predicted for an optimum detector, it may be that fast adaptation of auditory-nerve activity and/or memory effects interfere with level discrimination of long-duration tones. Finally, the delta Ls at 8 kHz decreased nonmonotonically with increasing level.