Eli Osman

A Correlation Model of Binaural Masking Level Differences

This paper presents a quantitative functional model, called the correlation model, to be used for interpreting empirical results on binaural masking level differences (BMLDs), which are obtained experiments on the detection of sinusoidal signals embedded in binaural noise. The receiver is presumed to behave as if it computes a statistical decision variable equivalent to a linear combination of three quantities, the energy levels at the channels deriving from the two ears and the interchannel cross correlation, where the coefficients are dependent on the interaural noise cross correlation and the interaural amplitude ratio for noise but are completely independent of signal parameters. Additive internal noise is assumed. Equations for BMLDs are derived with the restriction of equal noise levels at the two ears. Predictions derived from the model are compared with empirical results from several studies. These show BMLDs for antiphasic, homophasic, and monoaural input configurations at different frequencies o...

Effects of Waveform Correlation and Signal Duration on Detection of Noise Bursts in Continuous Noise

Studies of the masking of noise bursts by continuous noise revealed the pedestal effect previously reported by others for 100‐cps tones. The correlation ρ between mask and probe waveforms was found to affect detection: the pedestal effect—evidenced with ρ = 1 or with ρ = −1—was absent with ρ = 0. In a second experiment, the pedestal effect was found to diminish as probe bursts were shortened in duration from 100 to 5 msec. The results of these and related experiments provide support for the energy‐detection model of Pfafflin and Mathews. Tone and noise probes are considered to be detected by virtue of the energy changes they produce. Some features of the energy‐detection model are discussed.

Attentional strategies in dichotic listening

A person can attend to a message in one ear while seemingly ignoring a simultaneously presented verbal message in the other ear. There is considerable controversy over the extent to which the unattended message is actually processed. This issue was investigated by presenting dichotic messages to which the listeners responded by buttonpressing (not shadowing) to color words occurring in the primary ear message while attempting to detect a target word in either the primary ear or secondary ear message. Less than 40% of the target words were detected in the secondary ear message, whereas for the primary ear message (and also for either ear in a control experiment), target detection was approximately 80%. Furthermore, there was a significant negative correlation between buttonpressing performance and secondary ear target-detection performance. The results were interpreted as being inconsistent with automatic processing theories of attention.

Weber's law, the "near miss," and binaural detection.

Weber functions (ΔI/I in dB) for gated 250-Hz tones were studied for monaural and several binaural stimulus configurations (homophasic, and antiphasic with varying phase angle for addition of signal to masker). The various cues for discrimination of signal plus masker from masker alone are functions of intensity increments at one or both ears, an intensity increment at one ear coupled with a decrement at the other, or the introduction of a phase difference between the ears. The decline of the Weber fraction with increasing masker level (the “near miss” to Weber’s law) was confirmed for monaural discrimination over the entire 40-dB range, and a similar rate of decline was found for various binaural stimuli over the lower half of that range. The data also confirm the individual differences found in other studies for sensitivity favoring either interaural amplitude or interaural phase shifts.

Effect of temporal overlap on brightness matching of adjacent flashes.

Flashes having durations of 10, 20, 50, and 100 msec were matched in brightness to an adjacent 200-msec standard. When the standard and test stimuli terminated together, the results confirmed earlier demonstrations of the Broca–Sulzer phenomenon. Different functions relating the growth of brightness to duration were generated, however, when the flashes matched to each other had coincident onsets or coincident mid-durations. The matches made with stimuli terminating together were shown to exhibit transitivity: Targets which are as bright as a standard are approximately as bright as each other. Finally, an effect of relative luminance on apparent temporal position is described.

Correlation model of binaural detection: interaural amplitude ratio and phase variation for signal

Predictions of the correlation model of binaural masking‐level differences (BMLDs) are presented for the class of experiments in which the noise waveforms at the two ears are identical, while the tonal‐signal parameters for interaural amplitude ratio and interaural phase shift are varied. These predictions are compared to empirical data, and their relations to predictions of the equalization‐cancellation model and a lateralization model are discussed.

Temporal Masking of Clicks by Noise Bursts

Masking of clicks by noise bursts (60, 75, 85, and 95 dB SPL) was studied as a function of the temporal position of the click relative to the burst—from 50 msec before mask onset to 10 msec after mask cessation. Backward masking increases slowly at first and then rapidly as the probe approaches mask onset. Simultaneous masking is independent of the temporal position of the probe and of mask duration (10, 100, and 500 msec) and is given solely by mask intensity. No overshooting of the temporal‐masking functions was found near onset or termination of the masking bursts—a finding that contrasts markedly with the results of “analogous” studies in vision.

Intensity Discrimination, the “Pedestal” Effect, and “Negative Masking” with White‐Noise Stimuli

Millers data on masking and intensity discrimination with white‐noise stimuli are reanalyzed. Since the masking and increment stimuli in Millers study were, in fact. correlated, their sound pressures (rather than sound powers) were added. Recalculation of the extents of masking from the relative DLs shows that there was less masking than had originally been computed. The masked increment is 25 dB (not 12 dB) less than the masker when the latter is at 25 dB SL or above. Below 25 dB. there is “negative masking,”

Effect of Masking Noise on Lateralization and Loudness of Clicks

The effects of monaural masking noise on loudness and on lateralization of clicks were compared for noise levels ranging between 35 and 65 dB SPL. For different fixed levels of unmasked clicks, sound‐pressure levels of the masked clicks were adjusted by the subjects to produce centered sound images. In a second experiment, similar procedures were used to generate equal‐loudness functions. For both loudness and lateralization, the effect of masking noise was greatest with high levels of noise and low intensities of click. In every case, the masking effect was greater for loudness than for lateralization.

Magnitude Estimation of the Loudness of Clicks

Numerical estimations of the loudness of click stimuli were found to be a power function of sound pressure. The exponent (0.49) of the function is smaller than those previously reported in studies utilizing sustained tones or noises.