Detection of simultaneous modulation of interaural time and level differences: Effects of modulation rate and relative phase (L)
ABSTRACT The binaural system is known to be sluggish, i.e., unable to track modulations in interaural parameters even at a relatively slow rate. The present study evaluated the binaural system's sensitivity to modulation phase rather than to modulation magnitude. The detectability of simultaneous modulations in interaural time and level differences with various relative phases were measured. It was found that for modulation rates up to 10-20 Hz, the detectability varied with the relative phase. This indicates that information about higher rates is lost at or below the level of cue integration.
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ABSTRACT: These experiments tested the hypothesis that detection of frequency modulation (FM) at very low rates depends mainly on temporal information (phase locking to the carrier) for carriers below about 5 kHz, whereas FM detection at higher rates (10 Hz and above) depends mainly on changes in the excitation pattern (a "place" mechanism). In experiment 1, thresholds for detecting FM were measured for a wide range of carrier frequencies (0.25-6 kHz) for modulation rates, fm, of 2, 5, 10, and 20 Hz. Thresholds were determined when FM only was present and when the carriers in both intervals of a forced-choice trial were amplitude modulated at the same rate as the FM with a modulation index of 0.333. The phase of the amplitude modulation (AM) relative to the FM was randomly selected on each trial, in order to disrupt cues for FM detection based on changes in the excitation pattern. For carrier frequencies up to 4 kHz, the deleterious effect of the added AM increased with increasing fm. For the 6-kHz carrier, the deleterious effect was independent of fm. In experiment 2, psychometric functions were measured for detecting combined FM and AM of a 1-kHz carrier, with fm = 2 Hz, as a function of the relative phase of the modulators. The modulation depths for AM and FM were chosen so that each would be equally detectable if presented alone. This was done both in quiet and in the presence of noise designed to mask either the lower or the upper side of the excitation pattern. In contrast to earlier results obtained with fm = 10 Hz [Moore and Sek, J. Acoust. Soc. Am. 96, 741-751 (1994)], only small effects of relative modulator phase were found. Experiment 3, was similar to experiment 2, except that all measurements were done in quiet, and carrier frequencies of 0.25, 1.0, and 6.0 kHz were used. There were no effects of relative modulator phase for the 0.25-kHz carrier, small effects for the 1-kHz carrier, and large effects for the 6-kHz carrier. The pattern of results is consistent with the hypothesis that both temporal and place mechanisms are involved in FM detection. The temporal mechanism dominates for carriers below about 4 kHz, and for very low modulation rates. The place mechanism dominates for high carrier frequencies, and for lower carrier frequencies when stimuli are frequency modulated at high rates.The Journal of the Acoustical Society of America 11/1996; 100(4 Pt 1):2320-31. DOI:10.1121/1.417941 · 1.56 Impact Factor
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ABSTRACT: Detectability and salience of time-varying interaural temporal differences (IATD's) were measured in three experiments by determining observers' ability to follow the temporal fluctuations of a "moving stimulus"--a 3000-Hz low-pass computer-generated noise presented binaurally with a sinusoidally varying IATD. In the first two experiments the peak IATD (deltat the "extent of movement") was manipulated to determine, for different rates of interaural variation (fm), threshold discriminability of the "moving" stimulus from a reference (two-interval forced-choice paradigm). The nonmoving reference was either a dichotic noise stimulus (experiment 1) or a dichotic noise stimulus whose "image width" matched that of the excursions traced by the "moving stimulus" (experiment 2). Threshold deltat's in the two experiments were similar, increasing from 30 microns at fm = 0 Hz to 90 microns at fm = 20 Hz, indicating a "low-pass characteristic" for the binaural system. Thresholds decreased again for fm = 50 Hz, apparently because at these high rates of "movement" observers used other cues than the varying IATD's to perform the task. The third experiment measured the threshold of a binaural click in the presence of a "moving noise" masker as a function of fm and of the instantaneous IATD of the masker when the click was presented. As fm increased, click threshold gradually became independent of the masker's instantaneous IATD, again suggesting a "low-pass" characteristic for the binaural system; additionally, there was some evidence for a lag in the system's response for fm greater than 5 Hz. The data from the three experiments are discussed in terms of results from other studies which have investigated temporal aspects of the binaural system. The possible existence of movement detectors in the auditory system is discussed.The Journal of the Acoustical Society of America 03/1978; 63(2):511-23. · 1.56 Impact Factor
Article: A binaural analog of gap detection[Show abstract] [Hide abstract]
ABSTRACT: The temporal resolution of the binaural auditory system was measured using a binaural analog of gap detection. A binaural "gap" was defined as a burst of interaurally uncorrelated noise (Nu) placed between two bursts of interaurally correlated noise (N0). The Nu burst creates a dip in the output of a binaural temporal window integrating interaural correlation, analogous to the dip created by a silent gap in the output of a monaural temporal window integrating intensity. The equivalent rectangular duration (ERD) of the binaural window was used as an index of binaural temporal resolution. In order to derive the ERD, both the shortest-detectable binaural gap and the jnd for a reduction in interaural correlation from unity were measured. In experiment 1, binaural-gap thresholds were measured using narrow-band noise carriers as a function of center frequency from 250 to 2000 Hz (fixed 100-Hz bandwidth) and a function of lower-cutoff frequency from 100 to 400 Hz (fixed 500-Hz upper-cutoff frequency). Binaural-gap thresholds (1) increased significantly with increasing frequency in both tasks, and (2) at frequencies below 500 Hz, were shorter than corresponding silent-gap thresholds measured with the same N0 noises. In experiment 2, interaural-correlation jnd's were measured for the same conditions. The jnd's also increased significantly with increasing frequency. The results were analyzed using a temporal window integrating the output of a computational model of binaural processing. The ERD of the window varied widely across listeners, with a mean value of 140 ms, and did not significantly depend on frequency. This duration is about an order of magnitude longer than the ERD of the monaural temporal window and is, therefore, consistent with "binaural sluggishness."The Journal of the Acoustical Society of America 06/1999; 105(5):2807-20. DOI:10.1121/1.426897 · 1.56 Impact Factor