402 86th Meeting ß Acoustical Society of America 402

TUESDAY, 30 OCTOBER 1973 ASSEMBLY ROOM, 2:00 P.M.

Session I. Psychological Acoustics II: Masking and Intensity Discrimination

EDWARD C. CARTERETTE, Chairman

Perceptual Systems Laboratory, Department of Psychology, University of California, Los Angeles, California 90024

Contributed Papers (15 minutes)

2:00

I1. Monaural and Binaural Masking Phenomena Utilizing Machine-Generated Waveforms. I. The Phase Angle Alpha. TERRENCE R. DOLAN AND RICHARD HIRSH, Parrely Hearing Institute, Loyola University of Chicago, Chicago, Illinois 60626.•In an effort to further describe the monaural and

binaural processes involved in the detection of a gated tonal signal in a background of gated masking noise, a series of ex- periments has been initiated utilizing computer-generated, reproducible waveforms. The signal used has been a gated 500-Hz tone and the masker is a gated 400-600-Hz bandpass noise. Our initial effort has been concerned with the influence

of the magnitude of the phase angle alpha, the angle at which the tonal signal is added to the noise masker, on the detect- ability of the signal in both homophasic and antiphasic mask- ing conditions. Our results suggest that the magnitude of alpha is extremely important in accounting for performance in the homophasic masking conditions but that the magnitude of alpha does not strongly influence performance in the anti- phasic masking conditions. These results are compared to pre- dictions based on an electrical model described by Jeffress [-J. Acoust. Soc. Am. 41,480-488 (1967)-], which consists of a leaky integrator preceded by a narrow bandpass filter and half-wave rectifier.

2:15

12. Role of the Difference Tone f•.-fl in Masking. F. G. KaZMMER AND D. D. GREENWOOD, University of British Columbia, Vancouver 8, British Columbia, Canada.--When signals are presented on the immediate high-frequency side of a pure-tone masker, it is not the signals, but rather combination tones, that are detected at masked threshold [Greenwood, J. Acoust. Soc. Am. 50, 502-543 (1971)-]. At low to moderate masker intensities, the detected combination tone is where f• is the masker frequency and f•. is the signal frequency. At higher masker levels, the combination tone f•.-fl becomes large enough to play a role. To investigate this role, the com- bination tones f•.-fl and 2fl-f•. were selectively masked in different low-frequency regions, to identify their effects. As has been known, the notch region on the high side of the pure-tone masking pattern creates a secondary peak, which shifts up- ward in frequency and height as masker intensity is raised. At masker levels sufficient to shift this secondary peak upward, beyond 1.5 times fl (masker), both 2fl-f•.(C1)and are detected with about equal likelihood in the higher-fre- quency part of the notch region. Either C1, D1, or both may be detected since their intensities become quite similar at higher masker levels, as supported by more direct estimates [Green- wood, J. Acoust. Soc. Am. 52, 1137-1167 (1972); Hall, J. Acoust. Soc. Am. 51, 1863-1881 (1972)-I.

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2:30

13. Aural Combination Tones and Temporal Masking. B. LESHOWITZ AND E. CUDAHY, Department of Psychology, Arizona State University, Tempe, Arizona 85281.--Greenwood [J. Acoust. Soc. Am. 51, 502-543 (1971)-] has shown that for steady-state masker conditions, in which the signal is a long- duration pure tone and the masker is a continuous pure tone,

a notch appears in the masked audiogram. This notch at the high-frequency side of the masker is caused by the detection of combination tones on the low-frequency side of the masker. The present study investigated the importance of combination tones in temporal masking. A 5-msec tonal signal was presented at various delays relative to onset of a longer-duration sinusoid. Under the forward-masking condition, the previously de- scribed notch in the masked audiogram was not obtained. Signal threshold was found to be a monotonically decreasing function of the difference between signal and masker fre- quency. In a second study, temporal masking was investigated using two pure tones as a complex masking stimulus. The combination tones that were formed by the masker produced masking effects on the low-frequency side of the masker com- parable to those recorded under steady-state conditions. Some implications of these results for the formation of combination tones are discussed. [-This research was supported by an NIH grant.]

2:45

14. Mortaural and Binaural Frequency Selectivity Using Tonal Temporal Masking. W. A. YOST AND B. BERGERT, Communi- cation Sciences Laboratory, Departments of Speech, University of Florida, Gainesville, Florida 32611.•In two experiments, frequency selectivity was investigai:ed using three temporal masking paradigms. In Experiment 1 a 60-msec 70-dB-SPL tone (4-msec rise-decay time) was used to mask a 10-msec (4-msec rise-decay time) 1000-Hz probe tone. The frequency of the masker varied from 250 to 2000 Hz. Masking was mea- sured in the forward masking paradigm in which the time between masker offset and probe-tone onset (/•Tv) was 10 msec, in the backward masking paradigm in which the time between probe-tone offset and masker onset (/•TB) was 0 msec, and in the combined forward-backward masking paradigm in which /•Tv was 10 msec and /•TB was 0 msec. In Experiment 2 the combined forward-backward masking paradigm (masker durations 150 msec, probe-tone duration 10 msec, /•Ta and/•Tv 5 msec each, signal frequency 500 Hz, masker frequencies ranging from 200 to 1000 Hz, and masker intensities 75 dB SPL) was used to study masking in three binaural conditions. In the monotic condition the maskers and

probe tone were presented to the right ear; in the diotic con- dition the maskers and probe tone were presented identically to both ears; and in the dichotic condition the maskers were presented identically to both ears, and the probe tone was pre- sented to the right ear 180 ø out of phase relative to the left ear. In both experiments the function relating the frequency of the masker to the probe-tone threshold (frequency selec- tivity function) was obtained and compared for the threee temporal paradigms in Experiment 1 and for the three binaural conditions in Experiment 2.

3:00

15. The Effect of Masker Duration on Forward and Backward

Masking. M. J. PENNER,* E. CUDAHY, AND G. W. JENKINS, Department of Psychology, Arizona State University, Tempe, Arizona 85281.--Temporal masking of clicks by noise was investigated using forward and backward masking paradigms.

, J. Acoust. Soc. Am., Vol. 55, No. 2, February 1974

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