Intensity Discrimination Data Research Articles

Effects of stimulus variability in auditory development.

Stimulus variability can affect the performance of child and adult listeners differently. For informational masking, stimulus variability appears to have a greater effect on children than adults in some conditions and a comparable effect in others. For intensity discrimination, children are less prone than adults to threshold elevation with the introduction of interval-by-interval stimulus level jitter. These results have been interpreted as reflecting different aspects of auditory processing. Informational masking in children is thought to reflect greater difficulty focusing on the signal cue. The intensity discrimination data have been interpreted as reflecting higher levels of internal noise and reduced sensitivity for intensity in children relative to adults. In the case of informational masking, supra-threshold masker variability may have a greater disruptive effect on signal processing, and in the case of intensity discrimination, variability near threshold has a smaller effect due to reduced sensitivity. Susceptibility to the disruptive effects of stimulus variability will be discussed as a means of gaining insight into the factors limiting auditory processing in children.

Development and the role of internal noise in detection and discrimination thresholds with narrow band stimuli

The experiments reported here examine the role of internal noise in the detection of a tone in narrow band noise and intensity discrimination for narrow band stimuli in school-aged children as compared to adults. Experiment 1 used 20-Hz wide bands of Gaussian and low-fluctuation noise centered at 500 Hz to assess the role of stimulus fluctuation in detection of a 500-Hz pure tone. Additional conditions tested whether performance was based on level and/or level-independent cues. Children's thresholds were elevated with respect to adults, and whereas adults benefited from the reduced fluctuation of low-fluctuation noise, children did not. Results from both groups were consistent with the use of a level cue. Experiment 2 estimated intensity increment thresholds for a narrow band Gaussian noise or a pure tone, either with or without a presentation-by-presentation level rove, an additional source of level variability. Stimulus variability was found to have a larger effect on performance of adults as compared to children, a rather counterintuitive finding if one thinks of children as more prone to informational masking introduced by stimulus variability. Both tone-in-noise and intensity discrimination data were consistent with the hypothesis that children's performance is limited by greater levels of internal noise.

Systematic covariation of the parameters in the near-miss to Weber's law, pointing to a new law

The exponent in the power function modeling of the near-miss to Weber's law is known to depend on several experimental factors, such as tone frequency and the presence or absence of noise. This paper presents data that confirm a theoretical argument that the near-miss exponent also depends on the definition of ‘just-noticeably different’ used empirically. Intensity discrimination data were collected for pure, 1000-Hz tones presented in quiet. Referent sound pressure levels ranged from 40 to 80 dB SPL in 10-dB steps. For each referent, the tone judged louder than the referent with probability equal to ν was determined, with ν ranging from 0.16 to 0.84 . It was found that the power function exponent decreases monotonically with ν . Moreover, it was found that the two power law parameters co-vary systematically with ν , implying a submodel that has an interesting fixed-point property.

Recasting (the near-miss to) Weber's law.

The authors argue mathematically that a common, power-function model of the just-noticeable difference in stimulus intensities is logically inconsistent with an exponent other than 1 in those frequent situations in which a particular averaging over experimental conditions has taken place. The authors show that an alternative power-law model, one which does not share this logical inconsistency, provides a good fit to many well-known, psychoacoustic intensity discrimination data. They also show that the exponent in this alternative model must be nonconstant with the discrimination criterion in experiments implementing this averaging of data.

A method for relating loudness-matching and intensity-discrimination data.

A method that allows direct comparisons between pure-tone loudness-matching and intensity-discrimination data in normal and hearing-impaired listeners is described. This method makes a minimal number of assumptions about the relations between loudness perception and intensity-discrimination performance. Loudness is considered to be related to overall, perceived stimulus magnitude and intensity-discrimination performance is considered to reflect the accuracy with which a loudness judgment can be made. Because pure-tone intensity-discrimination performance varies as a function of stimulus level in normal ears, the standard level required to produce a particular difference limen in an impaired ear can be inferred from normal-ear intensity-discrimination data. Thus, plotting standard levels yielding normal difference limens as a function of standard levels yielding the equivalent sized difference limens from a threshold-shifted ear produces a function directly comparable to loudness recruitment functions. If loudness-growth and intensity-difference limens were tightly coupled in threshold-shifted ears, then stimuli that yield equal size difference limens would be equally loud. This relation was tested by obtaining loudness-matching and intensity-discrimination data from normal-hearing listeners with thresholds shifted by a wideband noise and hearing-impaired listeners with cochlear-type hearing losses. The results from these listeners show similarities between the traditional loudness-recruitment functions and "intensity-recruitment" functions derived from the assumed relation between the two measures. The primary difference between the functions is at low and moderate sensation levels where loudness grows at a more rapid rate than the difference limen.

Sound intensity processing by the goldfish.

Capacities of the goldfish for intensity discrimination were studied using classical respiratory conditioning and a staircase psychophysical procedure. Physiological studies on single saccular (auditory) nerve fibers under similar stimulus conditions helped characterize the dimensions of neural activity used in intensity discrimination. Incremental intensity difference limens (IDLs in dB) for 160-ms increments in continuous noise, 500-ms noise bursts, and 500-ms, 800-Hz tone bursts are 2 to 3 dB, are independent of overall level, and vary with signal duration according to a power function with a slope averaging - 0.33. Noise decrements are relatively poorly detected and the silent gap detection threshold is about 35 ms. The IDLs for increments and decrements in an 800-Hz continuous tone are about 0.13 dB, are independent of duration, and are level dependent. Unlike mammalian auditory nerve fibers, some goldfish saccular fibers show variation in recovery time to tonal increments and decrements, and adaptation to a zero rate. Unit responses to tone increments and decrements show rate effects generally in accord with previous observations on intracellular epsp's in goldfish saccular fibers. Neurophysiological correlates of psychophysical intensity discrimination data suggest the following: (1) noise gap detection may be based on spike rate increments which follow gap offset; (2) detection of increments and decrements in continuous tones may be determined by steep low-pass filtering in peripheral neural channels which enhance the effects of spectral "splatter" toward the lower frequencies; (3) IDLs for pulsed signals of different duration can be predicted from the slopes of rate-intensity functions and spike rate variability in individual auditory nerve fibers; and (4) at different sound pressure levels, different populations of peripheral fibers provide the information used in intensity discrimination.

The relations among critical ratios, critical bands, and intensity difference limens in man.

Band-narrowing estimates of the critical bandwidth (CB) are consistently larger than critical-ratio (CR) estimates for the same signal frequency. Bilger [in Hearing and Davis: Essays Honoring Hallowell Davis, edited by S.K. Hirsh et al. (Washington U.P., St. Louis, 1976), p. 191] proposed that this difference could be accounted for by reference to intensity-discrimination performance [CR(Hz)/CB(Hz) = delta I/I]. To test this hypothesis, band-narrowing, critical-ratio, and intensity-discrimination data were collected for four normally hearing, well-trained listeners. Signal frequency was 2000 Hz and two noise levels were used: 20 and 50 dB N0. The relations proposed by Bilger among critical-bandwidth estimates from band-narrowing experiments, critical-ratio estimates from pure-tone detection in wideband noise, and intensity discrimination for a critical-band-wide noise in wideband noise are not supported by the results of individual listeners, or results averaged across listeners.

Binaural intensity discrimination data compared with left‐right‐averaged and with superior‐ear data

Binaural intensity difference thresholds were compared with monaural thresholds based upon left‐ and right‐ear means, and with the thresholds of the ear showing superior intensity difference sensitivity for the test frequency. Consistent with other recent finding [W. Jesteadt and C. C. Wier, J. Acoust. Soc. Am. 61, 1599–1603 (1977)] the ΔI/I ratios for binaural listening were lower than the averaged monaural ratios for frequencies 250, 1000, and 3000 Hz. The superior‐ear data, however, matched the binaural data well, and appeared to separate from left‐right‐averaged ΔI/I ratios. The suggestion is offered that the contribution of the less sensitive ear, in amplitude discrimination, may be negligible, at least for some varieties of stimuli.

Experimental test of a predicted relation between intensity discrimination and loudness matching

According to previous theoretical work on intensity perception, two stimuli are matched in loudness if and only if their intensities divide the respective dynamic ranges of the stimuli proportionately in terms of number of JNDs [R. R. Riesz, J. Acoust. Soc. Am. 5, 211–216 (1932); J. S. Lim, W. M. Rabinowitz, L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Am. 62, 1256–1267 (1977)]. This paper reports the results of new experiments designed to test this prediction using a common set of subjects and comparable experimental conditions. Intensity discrimination data and loudness‐matching data were obtained on four subjects over essentially the whole dynamic range for three types of stimuli: a 1000‐Hz tone, a 1000‐Hz tone partially masked by noise, and a flat wide‐band noise. Generally speaking, the empirical loudness matches were found to agree with the loudness matches predicted by the theory on the basis of the discrimination data. [Work supported by NIH and NSF.]

Thresholds for linear amplitude change of a continuous pure tone.

The human auditory sensitivity in detecting linear amplitude change of a continuous pure tone has been studied in normal-hearing subjects. It is shown that for short glide durations (less than 100 ms) the duration of the following plateau exerts a significant influence on the DLI. The average DLI at 1 kHz and 60 dB HL was found to be of the order of 0.8 dB when the intensity glide had a duration of 10 ms and was followed by a much longer plateau. For longer glide durations (greater than or equal to 200 ms) the DLI increased significantly as compared with shorter durations. There was no significant difference between increasing and decreasing intensity change. Significantly larger DLIs were found at 250 and 500 Hz than at 1, 2 and 4 kHz. The sound level was found to have a significant influence on the DLI. At low levels of 40 dB HL, and lower, the increase in DLI for detecting sound levels is highly significant. A falling exponential function offers a mathematical description of the relationship with good fit. It is concluded that an integrating mechanism with an integration time of approx. 200 ms could explain the auditory ability to detect linear amplitude glides of a continuous tone. The results are discussed in relation to previous intensity discrimination data, where pulse pairs, continuous intensity modulation or intensity glides were used as stimuli.

Intensity and Frequency Discrimination in One- and Two-Interval Paradigms

In an attempt to extend detection theory beyond the intensive domain, both frequency and intensity discrimination data were collected for four subjects using several psychophysical procedures. These included Yes-No, 2IFC, Same-Different with a positive increment, and Same-Different with a negative increment. The two-interval conditions were run with both fixed and random bases. Two increment sizes were used for each condition. The results for intensity discrimination showed the dependencies on method so that the desired intermethod evaluation of frequency discrimination could be effected. Intersubject variability was significantly greater for frequency than for intensity discrimination, but the frequency data for each individual were quite orderly.

A THEORY OF VISUAL INTENSITY DISCRIMINATION

1. A theory of visual intensity discrimination is proposed in terms of the photochemical events which take place at the moment when a photosensory system already adapted to the intensity I is exposed to the just perceptibly higher intensity I+DeltaI. Unlike previous formulations this theory predicts that the fraction DeltaI/I, after rapidly decreasing as I increases, does not increase again at high intensities, but reaches a constant value which is maintained even at the highest intensities. 2. The theory describes quantitatively the intensity discrimination data of Drosophila, of the bee, and of Mya. 3. With some carefully considered exceptions the intensity discrimination data of the human eye fall into two classes: those with small test areas or with red light, which form a single continuous curve describing the function of the retinal cones alone, and those with larger areas, and with white, orange, and yellow light, which form a double curve showing a clear inflection point, and represent the separate function of the rods at intensities below the inflection point and of the cones at intensities above it. 4. The theory describes all these data quantitatively by treating the rods and cones as two independently functioning photosensory systems in accordance with the well established duplicity idea. 5. In terms of the theory the data of intensity discrimination give critical information about the order of both the photochemical and dark reactions in each photosensory system. The reactions turn out to be variously monomolecular and bimolecular for the different animals.