Biomedical subjects

M F Spiegel

Publications and source records attributed to M F Spiegel.

7 recordsLinked to original sources

PubMed1987

Speech masking. I. Simultaneous and nonsimultaneous masking within stop /d/ and flap closures.

This article reports on investigations of the relative roles of simultaneous and nonsimultaneous masking on detection thresholds using natural speech utterances. Thresholds were obtained for 15-ms probe tones placed in the stop or flap closures of /ada/ and /idi/. Threshold elevations due to simultaneous and nonsimultaneous masking could be explained by the dynamics of neighboring speech spectra. Nonsimultaneous effects were related to spectra at least 30 ms around the probe tone. Although simultaneous masking is usually stronger than nonsimultaneous masking, the relative amplitude of adjacent speech segments in natural speech is sufficiently high near formant regions to cause noticeable effects of nonsimultaneous masking.

Adult↗

PubMed1982

Signal and masker uncertainty with noise maskers of varying duration, bandwidth, and center frequency.

The detectability of sinusoidal signals added to repeatable noise bursts was measured under conditions of signal-frequency uncertainty and masker-waveform uncertainty. Either source of uncertainty raised thresholds by 2-5 dB over those measured in a fixed-signal, fixed-masker condition, while the combination of both types of uncertainty raised thresholds by 8-12 dB. The magnitude of these elevations are similar to those found in a previous study, which employed maskers composed of random sets of equal-amplitude tones (Spiegel et al., J. Acoust. Soc. AM. 70, 1015-1019 (1981)]. When masker level varied by up to 40 dB between the two intervals of a forced-choice trial, and signal thresholds were elevated by only 2.5 dB. The results support a form of profile analysis in which listeners detect signals by noticing a relative change in the masker spectrum.

Auditory Threshold↗

PubMed1981

Factors in the discrimination of tonal patterns. III. Frequency discrimination with components of well-learned patterns.

Estimates of the effectiveness of selective auditory attention were obtained by adjusting the level of a target tone, which was presented as one 40-msec component in a ten-tone sequential pattern. When the levels of target and nontarget tones were the same, frequency-discrimination thresholds (delta f/f) following prolonged training varied from 0.01-0.02 for minimal-uncertainty testing conditions to 0.1-0.2 under high trial-to-trial stimulus uncertainty. The functions relating frequency discrimination to target-tone level are widely separated for the two conditions; comparing them, we conclude that the effects of selective auditory attention can be equated to a 50-dB variation in signal level. Patterns that had been well-learned during the minimal-stimulus (remembered standard) procedure. The results of these latter experiments are consistent with a "top-down" processing interpretation in which well-learned patterns are first identified to locate the portions requiring further resolution.

Acoustics↗

PubMed1981

Thresholds for tones in maskers of various bandwidths and for signals of various bandwidths as a function of signal frequency.

Critical bandwidth (CB), which represents the narrowest filter the auditory system can achieve, may be estimated directly from either of two experiments. A breakpoint emerges from the threshold function of a pure tone presented with maskers of different bandwidth and from the threshold function of noise signals of different widths masked by wideband noise. The bandwidth at which the knee occurs in either function defines the CB. A "conjoint" CB estimate can also be obtained by extrapolating noise-signal thresholds to be threshold level of a tone in wideband noise. Compared to other estimation procedures, the conjoint estimate is less affected by the signal's spectral splatter, the masker's intensity variability in time, and assumptions about the listening band's placement.

Acoustic Stimulation↗

PubMed1981

Two procedures for estimating internal noise.

Internal noise was measured in two paradigms simultaneously. In one method the listener's agreement in choosing the same masker as the one in a pair that sounds most signal-like is used to estimate internal noise [D. M. Green, Psych. Rev. 71, 392--407 (1964)]. In the other the increment in detection performance on those trials having identical as opposed to different maskers is used t estimate internal noise [R. A. Siegel, unpublished Master's thesis, M.I.T. (1979)]. Most results place the estimate of additive internal nose as nearly equal to external noise variability. The estimates from the agreement method can be adversely affected by uncertainty regarding the observation interval and interval biases, whereas the estimates obtained with the detection method are highly sensitive to measurement errors.

Auditory Perception↗

PubMed1981

Signal and masker uncertainty in intensity discrimination.

Intensity discrimination thresholds were assessed in a series of experiments. Signals were in-phase increments in the level of one component of a multitone masker. The main parameters of interest were the effects of signal uncertainty (which frequency is tested on a given trial) and masker uncertainty (which components were selected as the multitone masker on a given trial). Thresholds were measured as a function of signal frequency, number of components, and amount of overall changes in masker level. The results suggest a form of profile processing, in which the signal is detected by comparing levels in adjacent critical bands. Such a mechanism will account for the relatively small effects generally observed with signal uncertainty, for masker uncertainty showing larger effects on thresholds than signal uncertainty, and for the near constancy of signal threshold despite large (60 dB) fluctuations in overall level of the stimulus in the two intervals of the forced-choice trial.

Acoustic Stimulation↗

PubMed1979

The range of spectral integration.

The results of two complementary detection tasks using digitally synthesized noise are reported. In one experiment the bandwidth of the synthetic noise was varied to reveal the region most effective in masking a 1-kHz signal. The bandwidth of the internal filter ("critical band") so measured was about 80 Hz. In another experiment, a wideband noise was used as the masker for a synthetic signal whose bandwidth another experiment, a wideband noise was used as the masker for a synthetic signal whose bandwidth was varied to determine the maximum effective width of the internal filter. Although some earlier experiments suggest maximum effective widths as small as 180-200 Hz (around 1 kHz), the data reported here indicate the range of spectral integration extends from the critical band to a maximum width that may exceed 3 kHz. In addition, the good agreement between the two experiments suggests a new method for estimating critical bandwidths based on the determination of two thresholds: that of a tonal signal in a wideband masker and that of a supracritical-width noise signal in a wider-bandwidth masker.

Adult↗