Validation of the adaptive scan method in the quest for time-efficient methods of testing auditory processes

A major barrier to the clinical application of psychophysical testing of central auditory processes is the time required to obtain precise estimates of different listening abilities. In this study, we validate a novel adaptive scan (AS) method of threshold estimation that is designed to adapt on a range of values around threshold rather than on a single threshold value. This method has the advantage of providing the listener with greater familiarity with the stimulus characteristics near threshold while maintaining precise measurement and increasing time-efficiency. Additionally, we explore the time-efficiency of AS through comparison with two more conventional adaptive algorithms and the method of constant stimuli in two common psychophysical tasks: the detection of a gap in noise and the detection of a tone in noise. Seventy undergraduates without hearing complaints were tested using all four methods. The AS method provided similar threshold estimates with similar precision to those from the other adaptive methods and, thus, it is a valid adaptive method of psychophysical testing. We also provide an analysis of the AS method based on precision metrics to propose a shortened version of the algorithm that maximizes the time/precision tradeoff and can achieve similar thresholds to the adaptive methods tested in the validation. This work lays the foundation for using AS across a wide variety of psychophysical assessments and experimental situations where different levels of precision and/or time-efficiency may be required.

Monaural masking release in random-phase and low-noise noise

Two masking-release paradigms thought to involve across-channel processing are comodulation masking release (CMR) and profile analysis. Similarities between these two paradigms were explored by comparing signal detection in maskers that varied only in degree of envelope fluctuation. The narrow-band-noise maskers were 10 Hz wide and their envelope fluctuations were manipulated using the low-noise noise algorithm of Pumplin [J. Acoust. Soc. Am. 78, 100-104 (1985)]. Masking conditions included the classic CMR conditions of an on-frequency band, multiple (five) incoherent bands, or multiple coherent bands. Detection was compared using both random-phase noise (RPN) and low-noise noise (LNN) maskers. In one set of conditions, the signal was identical to the on-frequency masker, yielding an intensity discrimination task. Conditions that included RPN maskers and tonal signals resembled the classic CMR paradigm, whereas conditions including LNN and noise signals more closely resembled the classic profile analysis paradigm. Other conditions may be considered hybrids. This combination of conditions provided a wide variety of within- and across-channel cues for detection. The results suggest that CMR and profile analysis could be based upon the same set of stimulus cues and perhaps the same perceptual processes.

Measurement of auditory temporal processing using modified masking period patterns

A common metric of auditory temporal processing is the difference in the threshold for a pure-tone signal masked by either unmodulated or amplitude-modulated noise. This technique may be viewed as a modification of the masking period pattern technique. Such measurements have been proposed as an efficient means of estimating auditory temporal resolution in a clinical setting, although in many cases threshold differences may reflect additional spectro-temporal processes. The primary purpose of the present experiment was to examine interactions among signal frequency and masker bandwidth and the effects of modulation frequency on modified masking period patterns. The results revealed unmodulated-modulated threshold differences that increased with increasing masker bandwidth and decreased with increasing modulation frequency. There was little effect of signal frequency for narrow-band noise maskers that were equal in absolute bandwidth across frequency. However, unmodulated-modulated threshold differences increased substantially with increasing signal frequency for bandwidths proportional to the signal frequency and for wideband maskers. Although the results are interpreted in terms of a combination of both within-channel and across-channel cues, the specific contributions of these cues in particular conditions are difficult to ascertain. Because modified masking period patterns depend strongly upon a number of specific stimulus parameters, and because it is difficult to determine with any precision the underlying perceptual processes, this technique is not recommended for use as a clinical measure of auditory temporal processing.

Amplitude-modulation detection at low- and high-audio frequencies

Estimates of temporal acuity under comparable conditions at low- and high-audio frequencies are rare. The present study used the amplitude-modulation detection paradigm to estimate temporal acuity over a range of audio frequencies from 800 to 12,800 Hz. Amplitude-modulation detection was measured as a function of modulation frequency for bandlimited noise carriers, and the resulting temporal modulation-transfer functions were used to characterize temporal acuity. The most important result from the two experiments reported is that systematic manipulations of carrier upper-cutoff frequency produced estimates of temporal acuity that did not vary from 800 to 12,800 Hz. When the modulated noise bands were filtered after modulation to control for potential spectral cues, the low-pass cutoff of the modulation-transfer function varied with the carrier bandwidth. However, when the standard stimulus was a quasifrequency-modulated (QFM) noise and the signal was an unfiltered, amplitude-modulated noise, the low-pass cutoff of the modulation-transfer function was independent of carrier bandwidth. These results are consistent with a growing body of evidence demonstrating that auditory temporal acuity is constant throughout most of the audible frequency range.

The influence of stimulus envelope and fine structure on the binaural masking level difference

A masking level difference (MLD) paradigm was used to investigate the influence of stimulus envelope and stimulus fine-structure characteristics on monaural and binaural hearing. The degree of masker envelope fluctuation was manipulated by selecting narrow-band noises (50 Hz) on a continuum of values of the normalized fourth moment of the envelope. The noises were specified as low-noise noise (LNN), medium-noise noise (MNN), and high-noise noise (HNN). Fine-structure cues were studied by measuring thresholds at 500 and 4000 Hz, regions in which the availability of such cues to the auditory system differ substantially. In addition, thresholds were measured for Gaussian noise maskers (GN) and for maskers having a flat magnitude spectrum, termed equal-magnitude noise (EMN) maskers. The results indicated lower NoSo thresholds for LNN than for the other four masker types. Furthermore, there were no differences in threshold for maskers having moderate and high degrees of envelope fluctuation (MNN and HNN). The NoS pi thresholds were not significantly different across masker type and were characterized by large individual differences among the seven listeners. The results are considered in relation to models of monaural and binaural processing. Consistent with previous reports, the results indicate that binaural detection depends on interaural differences in the stimulus envelope and fine structure at low frequencies and changes in the envelope at high frequencies.

Comodulation masking release for single and multiple rates of envelope fluctuation

Two experiments are presented that investigate the influence of envelope fluctuation rate upon the magnitude of comodulation masking release (CMR). In Experiment 1, thresholds were measured for a tonal signal centered in either one or five masker bands. The maskers were either narrow-band noises or 100% sinusoidally amplitude-modulated (SAM) tones. The five masker bands had either the same (coherent) or different (incoherent) envelopes. Envelope rate was varied by manipulating either the noise bandwidth (10-200 Hz) or the SAM rate (10-128 Hz). The CMR values were largest for slow envelope rates. In Experiment 2, envelope coherence was simultaneously manipulated at two rates by amplitude modulating (10 Hz) narrow-band noises (100 Hz). The modulation depth was 100%, 83%, or 50%. The CMR based on the coherence of the noise carriers was about 5 dB, regardless of the SAM coherence or the modulation depth. The CMR based on the SAM coherence decreased from about 19 to 2 dB as modulation depth decreased, regardless of the noise-carrier coherence. Thresholds were highest when the envelope fluctuations were incoherent at both rates and were lowest when the envelope fluctuations were coherent at both rates. These data suggest that the auditory system is able to make across-frequency envelope comparisons at both envelope rates simultaneously.