The masking of silent intervals, or gaps, by surrounding noise bursts was investigated. The durations and the spectrum levels of the two noises were varied and the just detectable gap A T determined. The first experiment demonstrated the conditions in which duration judgments may have provided a cue. The remaining experiments were therefore designed so that this duration cue was not available. The second experiment indicated that changing the second noise duration from 200 to 2 msec did not greatly affect A T, suggesting a close relationship between forward masking and gap detection. Finally, Plomp [J. Acoust. . 36, 277-282 (1964)] has argued that a graph of the level of the second noise in decibels as a function of log iX T traces the time course of decay of the first noise. If so, the data from the third experiment indicate that this decay rate depends on the spectrum level of the noise but not on its duration. Soc. Am

This research investigates the human observer's ability to discriminate between the durations of two silent intervals, each interval preceded and followed by noise bursts called markers.The markers are separated· by T or T +~T' msec and T ranges from 0.3 to 1,000 msec.T is defined as that value of~T' for which the probability of discriminating T from T + AT' is 0.75. We compared the value of AT for conditions in which the markers were fixed in amplitude and duration with conditions in which the marker amplitudes and durations were randomly chosen.~T increased by as much as a factor of 4 when the amplitude and duration of the markers were randomized. The performance decrement was primarily due to randomizing the first marker duration.Models of duration discrimination relate discriminability to the duration of the stimuli presented. Stimuli that differ in duration, however, differ in other ways as well, and the idea that it is only their temporal extent which provides a discrimination cue is open to question. In a recent paper, Abel (1972) investigated the human observer's ability to discriminate between the durations of two silent intervals, each interval preceded and followed by noise bursts called markers. This paradigm is an important one, because the silent intervals differ in temporal extent only. There are no cues related to the total energy or to the energy spectrum of the stimuli. It is therefore of particular interest whether or not discriminability is independent of marker amplitude and duration in this paradigm.In Abel's paradigm, the marker amplitude and duration were fixed from trial to trial and varied between blocks. For these fixed markers, discrimination was affected by marker amplitude indicating that some nontemporal cue might be used (Allan & Kristofferson, 1974). In the present experiment, we investigate an extreme case of marker variability. In our work, the parameters of each of the four markers bounding the two intervals are chosen randomly and independently. For large marker variability, we reopen the question of whether it is only the physical duration of the silent temporal interval which provides the discrimination cue. METHODS SubjectsTwo undergraduates at Arizona State University were paid to participate. The author was also a subject. Two of the three This research was supported in part by a grant from the National Institutes of Health and in part by a faculty research award from the City University of New York. subjects were practiced listeners with at least 3 years of experience in psychoacoustic experiments. ApparatusThe durations of the noises and the gap between them were controlled by a PDP-IS computer. The noise was generated by a random noise generator (General Radio Model 1383), gated, filtered (0 to 20 kHz; Krohnhite Model 3SS0R), and then served as input to TDH-39 headphones. Two observers were run simultaneously in two double-walled lAC chambers. ProeedureThe data were collected using a two-interval forced-choice procedure. A trial began with a flash of a warning light...

For patients with noise-induce sensorineural hearing loss, the results of matching a binaurally presented comparison tone to subjective tinnitus during a 20-days test period are reported. As a control, results of matching an external comparison tom, to a standard tone. are also presented. The variability for tinnitus measurements was extremely large relative to comparable measures for a objective stimuli The relevance of this finding to the nature of tinnitus and to the construction of tinnitus maskers is discussed.