A temporal model of level-invariant, tone-in-noise detection

Discrimination bandwidths for amplitude modulated and quasi-frequency modulated tones with spectral cues degraded by a roving-level

Theoretically, discriminating an amplitude modulated tone (AM) from a quasi-frequency modulated tone (QFM) is an ideal task for measuring the bandwidth of phase sensitivity because the stimuli have identical amplitude spectra but different phase spectra. The stimuli are perfectly discriminable at narrow bandwidths, but become indistinguishable at wide bandwidths. Measurements, however, are thought to be compromised by auditory distortion products, particularly a cubic distortion tone which interacts with the lower sideband of the stimulus to create an intensity cue. The results and implications of using a roving level procedure to eliminate distortion product effects are discussed.

Nonadditivity of forward and simultaneous masking

The current study measured the additional masking obtained for combinations of forward and simultaneous maskers as a function of forward masker bandwidth, signal delay, and simultaneous masker level. The effects of the two individual maskers were equated in all conditions. Additional masking increased with increasing masker level, increasing signal delay, and decreasing masker bandwidth. The portion of the simultaneous masker that made the greater contribution to additional masking was the part that overlapped with the signal, not with the forward masker. The changes in additional masking observed as a function of forward masker bandwidth and the interaction between the effects of forward and simultaneous maskers call into question the use of additional masking as a measure of basilar membrane compression and present problems for the use of simultaneous noise to simulate hearing loss.

Identification of stimulus cues in narrow-band tone-in-noise detection using sparse observer models

The classical psychophysical paradigm of narrow-band tone-in-noise (TiN) detection has been under investigation for more than 70 years, yet no conclusive answer has been given as to which auditory stimulus features listeners rely on. Here, individual observer models were fit to a large trial-by-trial behavioral data set using a modern statistical analysis procedure. Relative perceptual weights were estimated for a set of auditory features including sound energy, representations of the spectra as well as summary statistics of both fine structure and envelope. The fitted models captured the behavior of all listeners on a single-trial level. The estimated perceptual weights were stable across signal levels. They suggest that responses of observers depended on stimulus energy, though that cue was not always dominant, as well as on band-pass detectors applied to the fine structure spectrum. A subset of the observers exhibited an additional dependence on sound envelope which was best captured by two envelope descriptors: average slope and extrema count. For some listeners, a concurrent analysis of sequential dependencies showed interactions between the current and several preceding decisions. There was no unique answer regarding the strategy individual listeners employ during TiN detection, and implications thereof are discussed.

Estimating critical bandwidths of temporal sensitivity to low-frequency amplitude modulation

Auditory filter bandwidths are measured for a temporal process using an amplitude-modulation detection task. The signal is a 200 Hz wide, sinusoidally amplitude-modulated band of noise centered within an unmodulated notched-noise masker. A modulation rate of 10 Hz is used to avoid possible information loss at more central processing levels for high modulation rates. Threshold functions are obtained for 10-14 notch widths for each of four different center frequencies (0.6, 1, 2, and 4 kHz) to determine the maximum notch width at which the masker has an effect. The ratio of center frequency to maximum notch width is ~2 at all center frequencies. It is proposed that the bandwidths observed in temporal tasks, which are consistently greater than expected from the viewpoint of critical band theory, be characterized as "temporal critical bands." This proposal does not oppose, but provides a complement to the traditional critical band obtained in tasks involving spectral discrimination.

A decision weight analysis of transition bandwidths

A decision weight analysis is used to investigate transition bandwidths [Berg (2007). J. Acoust. Soc. Am. 121, 3639-2645]. The psychophysical task is similar to a standard profile analysis experiment except that the spacing of the tones comprising the stimuli is linear and very narrow (e.g., 20 Hz). An increment in the level of the central tone constitutes the signal. Pitch cues and single channel energy cues are degraded with randomization procedures. Thresholds increase as the number of tones comprising the stimulus (n) increases up to a transition bandwidth and then decrease or stay constant with further increases in n. It is proposed that the transition bandwidth reflects a discrete change in the underlying process, with a temporal process (e.g., envelope processor) dominating for stimulus bandwidths less than the transition bandwidth and a process of spectral profile analysis at wider bandwidths. Estimates of decision weights support the proposal.

An evaluation of models for diotic and dichotic detection in reproducible noises

Several psychophysical models for masked detection were evaluated using reproducible noises. The data were hit and false-alarm rates from three psychophysical studies of detection of 500-Hz tones in reproducible noise under diotic (N0S0) and dichotic (N0Spi) conditions with four stimulus bandwidths (50, 100, 115, and 2900 Hz). Diotic data were best predicted by an energy-based multiple-detector model that linearly combined stimulus energies at the outputs of several critical-band filters. The tone-plus-noise trials in the dichotic data were best predicted by models that linearly combined either the average values or the standard deviations of interaural time and level differences; however, these models offered no predictions for noise-alone responses. The decision variables of more complicated temporal models, including the models of Dau et al. [(1996a). J. Acoust. Soc. Am. 99, 3615-3622] and Breebaart et al. [(2001a). J. Acoust. Soc. Am. 110, 1074-1088], were weakly correlated with subjects' responses. Comparisons of the dependencies of each model on envelope and fine-structure cues to those in the data suggested that dependence upon both envelope and fine structure, as well as an interaction between them, is required to predict the detection results.

Comodulation masking release in bottlenose dolphins (Tursiops truncatus)

The acoustic environment of the bottlenose dolphin often consists of noise where energy across frequency regions is coherently modulated in time (e.g., ambient noise from snapping shrimp). However, most masking studies with dolphins have employed random Gaussian noise for estimating patterns of masked thresholds. The current study demonstrates a pattern of masking where temporally fluctuating comodulated noise produces lower masked thresholds (up to a 17 dB difference) compared to Gaussian noise of the same spectral density level. Noise possessing wide bandwidths, low temporal modulation rates, and across-frequency temporal envelope coherency resulted in lower masked thresholds, a phenomenon known as comodulation masking release. The results are consistent with a model where dolphins compare temporal envelope information across auditory filters to aid in signal detection. Furthermore, results suggest conventional models of masking derived from experiments using random Gaussian noise may not generalize well to environmental noise that dolphins actually encounter.

Estimating the transition bandwidth between two auditory processes: evidence for broadband auditory filters

A spectral discrimination task was used to estimate the frequency range over which information about the temporal envelope is consolidated. The standard consisted of n equal intensity, random phase sinusoids, symmetrically placed around a signal component. The signal was an intensity increment of the central sinusoid, which on average was 1000 Hz. Pitch cues were degraded by randomly selecting the center frequency of the complex and single channel energy cues were degraded with a roving-level procedure. Stimulus bandwidth was controlled by varying the number of tones and the frequency separation between tones. For a fixed frequency separation, thresholds increased as n increased until a certain bandwidth was reached, beyond which thresholds decreased. This discontinuity in threshold functions suggests that different auditory processes predominate at different bandwidths, presumably an envelope analysis at bandwidths less than the breakpoint and across channel level comparisons for wider stimulus bandwidths. Estimates of the "transition bandwidth" for 46 listeners ranged from 100 to 1250 Hz. The results are consistent with a peripheral filtering system having multiple filterbanks.

Effect of variability in level on forward masking and on increment detection

In the first of four experiments, all with the same four subjects, varying the level of a forward masker from interval to interval in a two-interval forced-choice (2IFC) adaptive procedure had little effect on threshold. In the second experiment, the signal level was fixed and performance was measured in units of d'. Varying the level of the forward masker again had little effect. Analyses of trial-by-trial data indicated that subjects did not vote for the interval with the higher-level masker, as would an energy detector. Performance was better on trials where the masker level in the interval with the signal was lower and was relatively independent of masker level in the nonsignal interval. In the third experiment, these results were replicated for a wider range of masker variability and with maskers lower in frequency than the signal. In the fourth experiment, the same range of variability from interval to interval was imposed on the level of the pedestal in an increment-detection task. Results were similar to those observed in forward masking. The results suggest that decision processes involved in both forward masking and increment detection are similar and that neither is based on energy detection. Template matching remains a viable alternative.