David S. Emmerich

A reexamination of the frequency discrimination of random‐amplitude tones, and a test of Henning’s modified energy‐detector model

A surprising result is reported by Henning [G. B. Henning, J. Acoust. Soc. Am. 39, 336–339 (1966)]: For frequencies lower than 4000 Hz, frequency discrimination was not impaired by the introduction of random differences in level between the two tones to be discriminated in a two‐interval forced‐choice (2IFC) task. This result is inconsistent with a model of detection and discrimination proposed by Henning [G. B. Henning, J. Acoust. Soc. Am. 42, 1325–1334 (1967)], one of a class of models in which the observer monitors the output of a single auditory filter, as well as with excitation‐pattern models of frequency discrimination. In the first experiment reported here, however, an impairment of frequency discrimination with random differences in level is found when a within‐subjects experimental design is used. In a second experiment, the role of pitch‐intensity relationships in an experimental situation similar to that of Henning (1966) is explored. Finally, in a third experiment, an independent test of this...

Monaural envelope correlation perception, revisited: Effects of bandwidth, frequency separation, duration, and relative level of the noise bands

This article presents the results of two experiments investigating performance on a monaural envelope correlation discrimination task. Subjects were asked to discriminate pairs of noise bands that had identical envelopes (referred to as correlated stimuli) from pairs of noise bands that had envelopes which were independent (uncorrelated stimuli). In the first experiment, a number of stimulus parameters were varied: the center frequency of the lower frequency noise band in a pair, f1; the frequency separation between component noise bands; the duration of the stimuli; and the bandwidth of the component noise bands. For a long stimulus duration (500 ms) and a relatively wide bandwidth (100 Hz), subjects could easily discriminate correlated from uncorrelated stimuli for a wide range of frequency separations between the component noise bands. This was true both when f1 was 350 Hz, and when f1 was 2500 Hz. In each case, narrowing the bandwidth to 25 Hz, or shortening the duration to 100 ms, or both, made the task more difficult, but not impossible. In the second experiment, the level of the higher frequency noise band in a pair was varied. Performance did not decrease monotonically as the level of this band was decreased below the level of the other band, and only showed marked impairment when the level of the higher frequency band was at least 60 dB below that of the lower frequency band. The pattern of results in these two experiments is different from that which is obtained when the same stimulus parameters are varied in experiments investigating comodulation masking release (CMR). This suggests that the mechanisms underlying CMR and those underlying the discrimination of envelope correlation are not identical.

Receiver‐Operating Characteristics Determined under Several Interaural Conditions of Listening

The ability of subjects to detect sinusoidal signals in a continuous background of white Gaussian noise was investigated for several different interaural relations of the signal and of the noise stimuli. The functions, referred to as receiver operating characteristics (ROCs), relating the proportion of correct detections of the signal to the proportion of false alarms were determined in each case. A rating procedure was employed to determine the ROCs. The area under the ROC was found to be a good estimate of the percent correct obtained with a two‐interval forced‐choice (2IFC) technique—a relation to be expected on theoretical grounds. The ROCs were not significantly affected by the presence of trial‐by‐trial feedback.

Frequency discrimination of tones presented in filtered noise.

Previous research (Emmerich et al., 1983) in which tones were presented in the center of the notches in band-reject noise backgrounds suggests that information from frequency regions remote from the nominal signal frequency is useful in frequency discrimination. The present work extends the earlier findings by presenting tones on either side of a notch so that only one (or the other) tail of the excitation patterns of the tones would fall into the notch. In addition, tones were presented in high-pass noise, low-pass noise, and various combinations of the two. The results again indicate that remote information affects frequency discrimination, and they are also consistent with the hypothesis that the low-frequency tail of the excitation pattern is more useful for frequency discrimination than is the high-frequency tail.

Frequency discrimination and signal detection in band‐reject noise

An experiment was conducted in order to compare the importance of information from frequency regions remote from the nominal signal frequencies for frequency discrimination and signal detection. In both tasks, signals were presented within the ‘‘notch’’ of band‐reject noise, and different notch widths were employed. The results indicate that information is integrated over a wider range in frequency discrimination than in signal detection. Further, experiments in which a noise floor was present as well as band‐reject noise, indicate that disrupting the information from regions remote from the nominal signal frequencies impairs frequency discrimination even in the absence of any significant impairment of signal detection performance.

Synthetic stimuli attenuate the effect of attention on the dichotic right-ear advantage

This study assessed attentional effects on the right-ear advantage (REA) for a dichoticlistening task that used synthetic-speech syllables. Presenting subjects with monaural tone cues at various intervals prior to dichotic pairs of natural-speech syllables, T. A. Mondor and M. P. Bryden 1991 (The influence of attention on the dichotic REA. Neuropsychologia, 29, 1179-1190) found a reduced REA with longer intervals. This suggested that tone cues at longer intervals helped overcome a right-ear attentional bias. Despite sufficient statistical power, in the present study no reduction in the REA was found with longer intervals between tones and synthetic-speech syllables. As synthetic-speech stimuli tend to fuse better into the percept of a single stimulus than do natural-speech stimuli, attentional effects on the REA may be reduced with dichotic stimuli that fuse.

Edge effects on frequency discrimination of tones presented in low‐ and high‐pass noise backgrounds

Previous research has indicated that frequency discrimination performance is poorer for tones presented near the sharp spectral edge of a low-pass noise than for tones presented near the edge of a high-pass noise, or for tones in the same low-pass noise with high-pass noise added [Emmerich et al., J. Acoust. Soc. Am. 80, 1668-1672 (1986)]. The present study extends these findings in order to investigate how the steepness of the spectral edges of low- and high-pass maskers influences the discriminability of tones presented near these edges. Frequency discrimination was measured in each of three high- and low-pass noise backgrounds (which differed in the steepness of their filter skirts). The following results were obtained: (1) In the low-pass noise background, frequency discrimination performance improved as the filter skirt became more gradual; (2) in the high-pass noise background, performance first improved and then became poorer as the filter skirt became shallower; and (3) performance in low-pass noise was poorer than that in high-pass noise for the two steepest slopes employed (96 and 72 dB/oct) but not for the shallower slope (36 dB/oct). Results are discussed in the context of lateral suppression and edge pitch effects, and of a trade-off between possible edge effects and masking.

An investigation of the facilitation of simple auditory reaction time by predictable background stimuli

Two experiments explored a surprising result reported by Emmerich, Pitchford, and Becker (1976): Simple reaction time (RT) to an auditory stimulus can be facilitated by the presence of a tonal background (or masker). In the first experiment, simple RT to a tonal signal was investigated for a variety of background frequencies and loudness levels, and significant facilitation of RT was found for low levels of the background. In the second experiment, no evidence of facilitation was found when the background stimulus was a randomly varying narrow-band noise, although evidence for facilitation was again found with a constant tonal background.

Response Latencies in the YES‐NO Signal Detection Situation

Response latencies were recorded from observers given the task of detecting sinusoidal signals presented in a white noise background. On each trial, the probability that a signal would be presented was 0.5. The observers indicated their decisions as to whether or not a signal had been presented by pressing buttons. They were instructed to adopt different decision criteria (strict, medium, or lax) for making a YES response during different sessions of the experiment. For most criteria adopted, the mean latency of YES responses was less than the mean latency of NO responses. In addition, the mean latency of YES responses made after a signal had been presented was less than the mean latency of YES responses made after noise alone had been presented. Similarly, the mean latency of NO responses to noise alone was less than the mean latency of NO responses to signals. Latencies varied widely as a function of the criterion adopted. Receiver operating characteristics were constructed from the latency distribution...

Response latency, latency‐based receiver‐operating characteristics, and uncertainty about interaural phase in the detection of in‐phase and out‐of‐phase tones presented in noisea)

Subjects were given the task of detecting tonal signals presented in a continuous background of white noise which was always in phase at the ears (No). The signals were either in phase (So), or phase-reversed (S pi) at the ears. The analysis of response latencies (for similar levels of performance) indicated that there were consistent differences in the processing of the two types of signals. Latencies were longer, and somewhat more variable, for S pi than for So signals. It was also found that the theory of signal detectability can contribute to an understanding of what and how decisions are made. Latencies were treated as confidence ratings in order to determine latency-based receiver operating characteristics (LROCs) for the detection task. It was observed that the LROCs for the interaural condition No-So tend to leave the origin at a steeper angle than do those for the interaural condition No-S pi, presumably reflecting the different sensory and decision processes employed in the two conditions. When the two interaural conditions were intermixed within blocks of trials, performance was slightly impaired in comparison to the situation in which the interaural condition remained constant throughout blocks of trials.