A two-dimensional stimulus-classification paradigm was used to examine the ability of listeners to judge the laterality of an interaurally delayed low-frequency target component presented concurrently with a distractor component. Of primary interest was the effect on performance of the frequency difference (Delta f) between the target and distractor. In one set of conditions, the target was fixed at 753 Hz and the distractor was 353, 553, 653, 703, 803, 853, 953, or 1153 Hz (fixed within a block of trails). In a second set of conditions, the distractor was fixed at 753 Hz and the target frequency was 353, 553, 653, 703, 803, 953, or 1153 Hz. The listeners were presented with a target component with an interaural delay that varied from trial to trial, taking on one of ten values, five leading to the left ear and five leading to the right. A distractor component was simultaneously presented with an interaural delay that also took on one of the same ten values. Delays ranged from -90 to (+)90 microseconds in 20-microsecond steps. during a block of 100 trials, each of the possible combinations of target and distractor delay was presented once and only once in a random order. Listeners were instructed to make left-right judgments based on the target delay. Each condition was repeated ten times, and the slopes of the best linear boundaries between left and right responses were used to derive the relative weights given to the target and distractor. The duration of the signals was 200 microseconds. Two of the eight listeners weighted the target heavily when the target and distractor were spectrally remote but gave the two components equal weight when the different in frequency was small. These two listeners yielded similar target weights regardless of which component was designated as the target. One listener gave nearly equal weight to the target and the distractor regardless of Delta f. Five of the listeners gave greater weight to the higher of the two frequencies regardless of which was assigned as the target. This high-frequency dominance is explained in terms of cross-correlation functions based on the composite two-tone waveforms.
Sensitivity to interaural temporal disparities (ITDs) and interaural intensitive disparities (IIDs) was measured as a function of duration in conditions where the center frequency (CF) of the stimuli was constant and, separately, in conditions where the CF of the stimuli was varied on a trial-by-trial basis. Stimuli were bands of noise centered at either 300, 1200, 2400, or 4800 Hz with the bandwidth of the noise being 40% of their CF. The largest effects of shortening duration and varying center CF of the stimuli were degradations of sensitivity to ITDs for stimuli centered at 2400 or 4800 Hz. Overall, the data confirm and extend previous findings which indicate that ITDs and IIDs are processed separately within the central nervous system.
Three listeners used an acoustic pointer to match the intracranial position of dichotic pitches presented with interaural intensitive differences (IIDs). Unlike data reported previously [Raatgever, ‘‘Binaural time processing and time-intensity trading,’’ in Psychophysics, Physiology, and Behavioural Studies in Hearing, edited by G. van den Brink and F. A. Bilsen (Delft U.P., Delft, The Netherlands, 1980), pp. 425–453], the intracranial position of the dichotic image was moved substantially by IIDs. Large effects of IIDs were found in a variety of stimulus conditions, including one investigated by Raatgever. When the dichotic stimuli were not pulsed, but were presented continuously and turned off only when the acoustic pointer was presented, one of the listeners produced data like those previously reported by Raatgever. It appears that intracranial images produced by stimuli which support dichotic pitches, like images produced by other binaural stimuli, can be affected substantially by IIDs. Consequently, in terms of lateralization, it does not appear necessary to maintain a theoretical cleavage between images produced by dichotic pitches (previously thought to be influenced only by ITDs) and images produced by other binaural stimuli. [Work supported by Grant No. 5 RO1 DC00234-13 from the National Institute on Deafness and other Communication Disorders, NIH.]
The present study examined the ability of listeners to detect interaural decorrelation of multicomponent complexes. Just-noticeable correlation differences for a reference correlation of + 1.00 were measured as a function of the number of components in the complex (3,5,9) and bandwidth of the complex (20, 40, 80 Hz). All components were equally spaced and centered at 753 Hz. A 2IFC procedure was used, in which the first interval consisted of a complex with an interaural correlation of + 1.00 (i.e., a diotic complex), and the second interval contained either a diotic complex or an interaurally decorrelated complex. The complexes were decorrelated by generating interaural phase differences (IPDs) in the individual components. The lowest frequency component had an IPD of 0, while the remaining components had equal magnitude IPDs that were of opposite sign for adjacent components. Thus, for each n-component complex, n − 1 components carried an IPD in the decorrelated intervals. The starting phases of the components were randomized between intervals. All of the observed threshold interaural correlations were greater than 0.99 in all conditions. Thresholds were lowest for the 80-Hz bandwidth conditions for three, five, and nine components. At each bandwidth, thresholds increased with increasing numbers of components. [Work supported by NIH.]
Subjects’ thresholds were first determined for detection of an interaural phase shift of a 20-Hz band of equal-amplitude wideband noise. The narrow-band target was centered on 500 Hz, and generated a dichotic, Huggins-type pitch. A diotic band of either 100, 125, 150, or 900 Hz symmetrically surrounded the target band. Interaural phases for frequency components outside of the diotic band were drawn randomly from a rectangular distribution. After thresholds were determined via a tracking procedure, 20 independent samples were generated for each condition at each subject’s threshold. A two-interval forced choice task was used in which each interval was comprised of a 250-ms forward fringe followed by a 250-ms observation period. Sixty trials were presented in a block with each sample presented three times. Order of presentation was randomized across runs and each sample was presented a total of 96 times. P(C) ranged from chance (50%) to over 90% across samples having identical interaural parameters. In conditions where subjects’ thresholds were similar, allowing the same set of samples to be used for two or more subjects, there was a strong inter-subject correspondence with respect to P(C). Possible sources of these sample-specific effects will be discussed. [Work supported by NIH.]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.