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May 1981

Volume 69, Issue S1, pp. 31-S125

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back to top Session I. Psychological Acoustics II: Masking
Contributed Papers
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Signal versus masker uncertainty with noise maskers (A)

Murray F. Spiegel and David M. Green

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S21-S21 (1981); (1 page)

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Older studies found very little change in threshold when signal frequency was fixed or randomized across trials. However, the maskers were different in each observation interval and listeners had to detect signals based on a departure from an estimation of the maskers' long‐term spectra. Signal uncertainty may elevate thresholds up to 6 dB when the procedure allows listeners to compare directly the waveforms in each interval. Furthermore, masker uncertainty, caused by choosing different maskers for each trial, has at least as great an effect as signal uncertainty. The results support the conclusion that a signal is detected not only on the basis of energy in a critical band, but also by comparing it to the levels in adjacent bands. [Work supported by NIH.]
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Effect of signal phase on the detectability of a tone masked by two closely‐spaced tones (A)

W. M. Hartmann

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S21-S21 (1981); (1 page)

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We reopen the question of an appropriate representation to describe the masking of a sine tone midway in frequency between two maskers [A. R. Phipps and G. B. Henning, J. Acoust. Soc. Am. 59, 442–447 0976)]. We argue that when the maskers are closely spaced in frequency, signal detection is mediated by recognizable differences in the stimulus envelope. For unit maskers, separated in angular frequency by δ, and for signal amplitude a, the square of the envelope is given by ‖E‖2  =  2 + 2 cos (δt) + a2 + 4a cos ϕ cos (δt/2), where ϕ is the signal phase relative to the mean of the masker phase angles. Rhythmic envelope variations caused by the signal occur at a rate of δ/(4π) Hz. Our 2IFC detection experiments find that for sufficiently long signal durations the large dependence on signal phase reported by Phipps and Henning is greatly reduced. [Work supported by NSF grant BNS 79‐14155.]
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Tuning curves and suppression (A)

Daniel L. Weber

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S21-S21 (1981); (1 page)

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Psychophysical tuning curves measured in forward masking appear more sharply tuned than those measured in simultaneous masking. This difference is often attributed to the operation of the suppression process during simultaneous stimulus presentation and the absence of suppression for nonsimultaneous presentations. An alternative interpretation is that the difference in the tuning curves simply reflects the difference in the effective excitation patterns which results from a filtering process: Simultaneous masking occurs as an interaction of the stimuli prior to filtering, forward masking occurs as an interaction after filtering. If the difference between simultaneous‐ and forward‐masking tuning curves were due to suppression, then the simultaneous, off‐frequency “maskers” would actually be suppressing the signal. Thus, suppression effects (e.g., a reduction in forward masking produced by the signal) should result from adding these off‐frequency “maskers” to the signal. In fact, the suppression effects predicted from this account are not observed, consistent with the “filter” explanation. [Research supported by NSF.]
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Psychophysical tuning curves: Stimulus ensemble and level effects (A)

Craig C. Wier and Susan J. Norton

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S21-S21 (1981); (1 page)

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Monaural masked thresholds were obtained for tone bursts in forward‐masking, simultaneous masking, and pulsation‐threshold paradigms as a function of masker frequency and probe level. Thresholds were obtained in both the presence and absence of a continuous, broadband background noise adjusted to a constant E/N0 = 15. Probe frequencies were 300, 1000, an 3000 Hz and probe levels were 10, 30 and 50 dB SL (re threshold in the absence of the background noise). Data were collected primarily with a method‐of‐adjustment psychophysical procedure. Some data were also collected for the limiting conditions with a two‐interval forced‐choice procedure for comparison. The data were plotted as psychophysical tuning curves. The extent to which physical parameters of the stimulus ensembles are sufficient to account for differences in tuning‐curve parameters and the necessity to consider alternative explanations will be discussed. [Research supported by PHS Grant No. RR‐07096, and grants from NINCDS and the Deafness Research Foundation.]
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The effects of probe duration on simultaneous‐masking tuning curves (A)

Susan J. Norton and Craig C. Wier

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S21-S21 (1981); (1 page)

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Monaural masked thresholds were obtained for tone bursts in a simultaneous‐masking paradigm as a function of masker frequency and probe duration. Probe frequency was 1000 Hz and probe durations ranged from 20 to 250 ms. Temporal‐integration functions were determined for the probe and it was presented at both fixed SLs SPLs. Masker duration was fixed at 250 ms. Data were collected primarily with a method‐of‐adjustment procedure. The extreme probe durations were also measured using a two‐interval forced‐choice procedure. The effects of probe duration in simultaneous‐masking paradigms on estimates of frequency selectivity based on tuning‐curve parameters will be discussed. [Research supported by PHS Grant No. RR‐07096, and grants from NINCDS and the Deafness Research Foundation.]
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Masking curves of tinnitus (A)

Curt Mitchell, Jack Vernon, and Robert Johnson

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S21-S22 (1981); (2 pages)

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Tones were used to determine masking curves of tinnitus in 32 subjects, These masking curves were classified into four types on the basis of their relation to the subjects audiogram. Also similar audiograms were examined to determine whether they had similar masking curves. Some similarities were noted but in many cases there was no correlation between the audiogram and the masking curves, that is subjects with similar audiograms, and tinnitus sensations, might have quite different masking curves. The findings also supported previous studies where tinnitus masking curves were found to differ significantly from conventional tone‐on‐tone masking curves. It was also found that in some cases tinnitus sensations could not be masked with tones or noise bands.
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Binaural analysis and unmasking effects (A)

D. R. Soderquist

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S22-S22 (1981); (1 page)

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A series of investigations was done examining the homophasic (NOSO) and antiphasic (NOSII) effects in pulsation threshold (PT) and masked threshold (MT) conditions. The initial investigation examined the BMLD by manipulating two variables: (a) Lowpass noise spectrum level and (b) interaural phase of the signal. The results showed increasing phase effects (8–10 dB) for PT as a function of increasing noise level. The BMLD at MT was small and constant (3–4 dB) as a function of noise level. Further investigations showed that homophasic conditions yielded smaller unmasking (lateral suppression) than did the antiphasic condition. The unmasking effects appeared when the signal duration was 125 ms and not when the signal duration was 50 ms. The BMLD occurred in the PT condition regardless of the signal duration. Data in a forward masking paradigm will also be presented.
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Dichotic listening reconsidered as a type of masking paradigm (A)

Judith L. Lauter

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S22-S22 (1981); (1 page)

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In most dichotic experiments, sounds played to each ear are drawn from the same set, i.e., masking signals are drawn from the same catalog as the target signals. We wish to consider the possibility of using maskers that are not identical to the target sound set. We have tested the influence of a series of maskers on identification of tonal patterns, with masker presented simultaneously and contralaterally to the target signal. Maskers were designed to sample the range from performance with monaural presentation (i.e., no masker) to performance in the situation where masker catalog is the same as target catalog (the traditional “dichotic listening” arrangement). Maskers studied included: Noise or tone gated on and off with the target, sounds mimicking the temporal fine structure of the target, etc. We have found that: (1) Such maskers can be used to reveal ear differences of the magnitudes found in more traditional dichotic designs, and (2) manipulation of the physical characteristics of the masker may prove a means of studying the psychoacoustical dimensions of some types of complex sounds. [Work supported by NINCDS NS 03856.]
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“Temporal masking” in discrimination of tone glides (A)

M. J. Collins

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S22-S22 (1981); (1 page)

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Difference limens for tone‐glide stimuli are reported to be greater when the glide precedes a contiguous 200‐ms fixed‐frequency segment than when the glide follows a contiguous fixed‐frequency segment [M. J. Collins and H. Stromberg, J. Acoust. Soc. Am. 66, Suppl. 1, S9 (1979)]. The present study was carried out to test the hypothesis that the effect was due, in part, to “temporal masking” of the tone glide by the fixed‐frequency segment. Six normal hearing subjects served as listeners. Reference stimuli consisted of 30‐ms glide segments, preceded or followed by fixed‐frequency (2200 Hz) segments of varied duration. Endpoint frequencies of the reference glide segments were 1680, 2200, and 2710 Hz for both glide‐preceding and glide‐following conditions. Results indicated that, in general, a greater amount of “masking” was imposed by fixed‐frequency segments which preceded glides than by fixed‐frequency segments which followed glides. This was particularly evident for the conditions which involved discrimination between no glide and some glide (2200‐Hz endpoint frequency): essentially no “forward” masking was observed with significant “backward” masking for the comparable glide‐preceding condition. [Work supported by NIH.]
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Forward masking of diotic and dichotic clicks by noise (A)

Thomas E. Hanna, Donald E. Robinson, and Richard M. Shiffrin

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S22-S22 (1981); (1 page)

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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 the magnitude was decreased for certain conditions. This result, as well as certain effects on the MLD and results of a final study, can be explained by assuming an interaction between the two maskers [G. P. Widin and N. F. Viemeister, J. Acoust. Soc. Am. 68, 475–479 (1980)]. These data conflict in part with the predictions of additivity of masking obtained from the Penner and Shiffrin model, and suggest modifications to that model may be needed. [Work supported by NSF.]
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Forward and simultaneous masking for maskers and signals that differ in frequency (A)

Walt Jesteadt and James R. Lehman

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S22-S22 (1981); (1 page)

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The amount of masking of a 1000‐Hz signal was determined for maskers of 694, 833, 1000, 1095, or 1200 Hz, presented at 30, 50, 70, or 90 dB SPL. Forward‐masking data were obtained for 10‐ms signals with onsets 4, 8, 16, or 32 ms after the offset of the 320‐ms masker. Simultaneous‐masking data were obtained for 10‐ms and 200‐ms signals with offsets that occurred 10 ms before the masker offset. The time course of recovery from forward masking was the same for all masker frequencies. As expected, simultaneous masking was greater than forward masking. This difference was particularly large for masker frequencies above the signal frequency. More masking occurred for short‐duration signals than for long‐duration signals when the signal and masker differed in frequency, in spite of the greater opportunities for off‐frequency listening provided by the short signals. This result suggests that the use of longer duration signals will result in narrower simultaneous‐masking tuning curves. [Work supported by NIH and NSF.]
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Estimates of the ratio of external to internal noise obtained using repeatable samples of noise (A)

R. H. Gilkey, T. E. Hanna, and D. E. Robinson

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S23-S23 (1981); (1 page)

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Several experiments conducted in our laboratory have used repeatable noise as a masking stimulus. The proportion of trials on which a subject made identical decisions when presented with identical signal‐plus‐noise or noise‐alone stimuli was used to estimate the ratio of external to internal noise standard deviations (R). R was estimated using 2AFC; single interval, Yes‐No; and single interval, four‐category rating paradigms. The effect of both signal level and noise level on the obtained value of R were systematically investigated. Diotic and dichotic conditions were compared. In discussing these results, the assumptions necessary to estimate R are evaluated. Particular emphasis is placed on considerations of whether the internal noise is independent of the external noise. The forms of the internal and the external noise distributions are also examined. [Work supported by NSF.]
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Perspectives on additive internal noise (A)

Ronald A. Siegel

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S23-S23 (1981); (1 page)

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In a previous talk [R. A. Siegel and H. S. Colburn, J. Acoust. Soc. Am. Suppl I 63, S66 (1979)] we presented results of experiments in which additive internal/external noise variability ratios (σI/σE) were derived by measuring improvement of 2 IFC detectability of tonal signals in Gaussian maskers when the maskers in the two intervals were identical. σI/σE was measured for both NOSO and NOSII. Our estimate of σI/σE differed from estimates obtained by different procedures [e.g., D. M. Green, Psychol. Rev. 71, 1392–1407]. We present here a possible explanation for the discrepancy: By listening to different subintervals of identical maskers. subjects create independent effective maskers, thus precluding any improvement in threshold over that measured when truly independent maskers are presented in the two intervals. Our procedure thus appears inferior to procedures used by others. We warn other investigators about this pitfall which may be encountered in internal noise studies. We will also discuss implications on modeling of binaural interaction of our result that external noise is a significant factor in NOSII detection. We will concentrate on the widely held belief that binaural interaction serves to cancel out external noise, leaving only internal noise. [Work supported by NIH.]
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Masking of vibrotactile sensation from a remote site (A)

Ronald T. Verrillo, Bruce G. Calman, and George A. Gescheider

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S23-S23 (1981); (1 page)

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The masking of vibrotactile signals delivered to the index fingertip was measured as a function of the intensity of the masker, which was administered to the thenar eminence of the same hand. Combinations of test and masker frequencies were used so that the two signals would occur within the response ranges of the Pacinian and non‐Pacinian mechanoreceptor systems. When the frequencies of both masker and test signal were within the range of either system (within channel), masking was effective. A 300‐Hz masker (Pacinian) was unable to affect the detection of a 23‐Hz signal (non‐Pacinian). A 23‐Hz masker (non‐Pacinian) did effectively mask a 300‐Hz signal (Pacinian). It was shown that the cross‐channel masking is due to the spread of the mechanical disturbance from the thenar to the fingertip and that the amplitude of the masker was sufficient to excite both systems. Results will be discussed within the context of a duplex mechanism for mechano‐reception. [Work supported by NIH.]
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