Donald E. Robinson

Effect of Varying the Interaural Noise Correlation on the Detectability of Tonal Signals

Data are presented on the effects of varying the interaural correlation for noise on the detectability of a 500‐cps tonal signal. The noise correlation was reduced by adding uncorrelated noise in the noise channels to the ears. Comparisons are made between data obtained with this method of reducing the noise correlation and with previous data obtained by introducing a displacement in time in the noise to one ear. Masking‐level differences are presented, based on fifty‐percent thresholds, obtained with the constant method and on the detectability index d′ obtained in a two‐interval, forced‐choice situation.

Effects of masker waveform and signal‐to‐masker phase relation on diotic and dichotic masking by reproducible noise

The proportions of hits and false alarms were estimated for the detection of a 500-Hz sinusoidal signal in each of 25, reproducible samples of wideband, white, Gaussian noise. The effects of signal phase were investigated under diotic (MoSo) and dichotic (MoS pi) conditions and compared to the predictions of two major models of binaural hearing. Averaging the data over samples obscured important across-sample and across-subject differences in performance. The proportions of hits and false alarms for individual noise samples presented under the MoSo condition were highly correlated with those for the same noise samples under the dichotic MoS pi condition, suggesting that the cues determining performance under these conditions are related. Signal-to-masker phase had a large effect on the proportion of hits under the MoSo condition, but only a small effect under the MoS pi condition. The Vector model predicts a large effect of signal phase under the MoS pi condition, and is, therefore, imcompatible with this aspect of the data. The expected value of the decision variable of the EC model is independent of signal phase. However, when the variance of the decision variable is also considered, the EC model does predict changes in the proportion of hits with the phase of the signal, comparable to those observed here. Further, it was shown that, if minor changes in the form of the EC models decision variable or in the distribution of the internal noise parameters are assumed, the expected value of the decision variable also changes with the phase of the signal.

Models of auditory masking: a molecular psychophysical approach.

Gilkey et al. [J. Acoust. Soc. Am. 78, 1207-1219 (1985)] measured hit proportions and false alarm proportions for detecting a 500-Hz tone at each of four starting phase angles in each of 25 reproducible noise samples. In the present paper, their results are modeled by fitting the general form of the electrical analog model of Jeffress [J. Acoust. Soc. Am. 48, 480-488 (1967)] to the diotic data. The best-fitting configurations of this model do not correspond to energy detectors or to envelope detectors. A detector composed of a 50-Hz-wide single-tuned filter, followed by a half-wave rectifier and an integrator with an integration time of 100 to 200 ms fits the data of all four subjects relatively well. Linear combinations of the outputs of several detectors that differ in center frequency or integration window provide even better fits to the data. These linear combinations assign negative weights to some frequencies or to some time intervals, suggesting that a subjects decision is based on a comparison of information in different spectral or temporal portions of the stimulus.

Formulas for the Coefficient of Interaural Correlation for Noise

Formulas for the coefficients of interaural correlation for noise are derived for the case where there are three similar sources, one ear, one for the other, and one for both; and for the case where there are two sources, one for one ear and one for both. Some confusion in the literature heaven these two formulas is pointed to.

Explanation of Masking‐Level Differences That Result from Interaural Intensive Disparities of Noise

The detectability of a monaurally presented 500‐cps signal was measured at each of several values of interaural correlation for a wide‐band noise masker. The results, when expressed in terms of masking‐level differences (MLDs), are in agreement with data reported by Whitmore and Wilbanks and show a function of similar form to that described by Robinson and Jeffress. Additionally, the detectability of a monaural signal was investigated as a function of the interaural intensive relations of a wide‐band noise masker. The data are in agreement with results originally shown by Hirsh, and since, replicated several times. That is, detectability is greatest when the level of the noise masker at the two ears is equal, and decreases as the level of the masker at the nonsignal ear is attenuated. The data are used to estimate parameters for a simple model that attempts to account for changes in detectability that occur when a monaural signal is presented with binaural, correlated noise having an interaural level difference. The model proposes that at low external noise levels, internal noise leads to a decrease in interaural‐noise correlation. Predictions from the model are in reasonable agreement with data reported previously.

Comparison of frequency selectivity for the monaural and binaural hearing systems: Evidence from a probe‐frequency procedure

Frequency selectivity was measured for one monaural system condition (NOSO) and two binaural system conditions (NOSπ and NOSM) using the probe‐frequency method originated by Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)]. Subjects were first trained to detect a 500‐Hz tone in noise for each condition of the experiment. Following training, the usual detection paradigm was altered such that on 25% of the trials a second signal of a different frequency was substituted for the 500‐Hz signal. Performance at each of these secondary or probe‐frequencies was transformed into equivalent decibels of attenuation by means of psychometric functions obtained at 500 Hz. A correction was then applied to these data which compensated for the relationship between frequency and the size of the MLD. The transformed and corrected data were interpreted as describing attenuation characteristics of an internal auditory filter. No systematic difference was found between attenuation characteristics for the two binaural system conditions. However, the attenuation characteristics for the binaural system conditions were approximately twice as wide as those for the NOSO condition.

Detection of binaurally masked tones by the cat

Detection of diotic and dichotic tones partially masked by noise was studied in the cat. The continuous noise masker was always diotic (N0). The single gated tone burst had a frequency of 0.5, 1.0, or 1.5 kHz, and was presented in phase (S0), 180° out of phase (Sπ), and monaurally (SM). The transducers were held in a fixed spatial relation to the auditory canal by means of “pinna inserts” and leather helmets. An avoidance response in a shuttle box was used to measure detectability. The cats displayed as large a release from masking in the Sπ condition at 1.0 and 1.5 kHz as at 0.5 kHz. At 1.5 kHz, the cats showed a greater release from masking than did the human observers studied under comparable conditions.

Discriminability of bursts of reproducible noise

The ability of human listeners to discriminate pairs of bursts of reproducible noise was examined. A same-different psychophysical method was used. Bursts in a pair were identical on same trials. On different trials, bursts were identical except for tau ms of independent noise located at either the beginning, middle, or end of the pairs of bursts. As the temporal position of the tau ms of independent noise was moved from the beginning to the end of the bursts of noise, discriminability increased. For each temporal position of the independent noise, discriminability was a function of the ratio of the duration of the independent noise (tau) to the total burst duration.

Phase effects for a sine wave masked by reproducible noise

A tone‐in‐noise detection task was used to assess the filtering properties of the auditory system. In the first experiment, ten 150‐ms samples of reproducible noise were used as maskers. The signal was a 500‐Hz tone either 20 or 100 ms in duration. The 100‐ms signal was centered temporally in the noise; the 20‐ms signal occurred either at the beginning, center, or end of the noise. The starting phase of the signal was varied from 0°–315° in steps of 45°. Signal thresholds, collected by the method of adjustment, were a cyclical function of starting phase and could be described by an energy model [Green and Swets, Signal Detection Theory and Psychophysics (Krieger, Huntington, NY, 1966/1974)]. A vector description of these data revealed an invariant property of each sample of noise, which we call the ‘‘noise vector.’’ The relationship among the parameters of the noise vectors over the various signal conditions suggest the presence of temporal interactions due to narrow‐band filtering. These relationships ar...

Forward masking of diotic and dichotic clicks by noise

The first part of the present study measured click thresholds during forward masking as a function of masker level and the temporal relation of the 6‐kHz low‐pass filtered noise masker to the click (300‐ms duration with a 20‐ms temporal gap or 10‐ms duration with a 5‐ms gap). Also varied were the spectral content of the click (low‐pass filtered at 1 kHz or 5 kHz) and the interaural phase of the click (0° or 180°). The difference in frequency content had no effect on the amount of masking for the 300‐ms masker while greater masking was found for the 1‐kHz click with the 10‐ms masker. This combination (1 kHz, 10 ms) was also the only one to produce masking level differences (MLDs) when the click was presented dichoticly. The second part of the experiment investigated the effects of combining the maskers used in the first part. Additional masking (above that predicted by an energy sum) was found, as has been reported elsewhere [M. J. Penner and R. M. Shiffrin, J. Acoust. Soc. Am. 67, 617–627 (1980)]; however...