Just Noticeable Differences in Dichotic Phase

Abstract

The just noticeable difference in dichotic phase, as a function of sensation level and of frequency, has been determined on a number of listeners with normal hearing. The test tones were transmitted by earphones, and the phase difference between the ears was varied by means of an electronic phase shifter. The psychophysical method used combined paired comparisons and forced choice. The first tone pulse of each pair presented was kept at a constant phase difference at which the subject localized the sound source as equidistant from his ears. The dichotic phase difference of the second pulse was varied irregularly (“randomly”). The results show that the sensitivity to dichotic phase difference is highest (2° of phase) at medium sensation levels, and that the jnd increases with positive acceleration as the sound frequency increases. Around 1300 cps the jnd becomes so great that it cannot be measured. The dichotic time difference calculated from the measured jnd in phase has a minimum near 800 cps.

Binaural jitter improves interaural time-difference sensitivity of cochlear implantees at high pulse rates

“…Listeners bilaterally supplied with cochlear implants (CIs) have been shown to be sensitive to fine structure ITD, but their sensitivity disappears at a pulse rate of a few hundred pulses per second (5)(6)(7)(8). This is in contrast to normal hearing (NH) listeners, who are sensitive to ITD in the fine structure up to much higher frequencies (9,10). The CI listeners' limitation in the ability to process fine structure ITD information at higher rates is disadvantageous with respect to speech coding where such high rates are required.…”

“…As expected, ongoing envelope ITD appears to have contributed little to ITD sensitivity. The results clearly show that introducing binaural jitter makes CI listeners sensitive to fine structure ITD up to rates for which NH listeners show sensitivity to ITD in pure tones (9,10), even though the absolute performance of the CI listeners is considerably lower. Therefore, binaurally jittered stimulation resolves the discrepancy in the rate limitation between CI and NH listeners.…”

Sensitivity to Interaural Time Differences with Combined Cochlear Implant and Acoustic Stimulation

“…In preliminary experiments, no sensitivity to ITD was found at a more apical electrode or lower acoustic frequencies than reported and in most cases our data show best ITD perception performance for acoustic signals with cutoff frequencies of 800−1,600 and 1,600−3,200 Hz. As ITDs in the fine structure of an acoustic signal can only be detected up to about 1.3 kHz (Zwislocki and Feldman 1956), this is indicative for perception of ITD in the envelope instead of in the fine structure of the signals. This is probably related to our finding that ITD perception performance of bimodal subjects is related with the average thresholds of their residual hearing at 1,000 and 2,000 Hz and not with the thresholds at lower frequencies.…”

Neural and Behavioral Sensitivity to Interaural Time Differences Using Amplitude Modulated Tones with Mismatched Carrier Frequencies

“…This result is not altogether unexpected given the nature of ITD stimuli provided by most cochlear implant speech processors. In normal-hearing listeners, the lowest thresholds of 10-20 ms are based on ITD cues conveyed by the fine structure of low-frequency sounds (Zwislocki and Feldman 1956;Klumpp and Eady 1957), whereas thresholds to ITDs in the lowfrequency envelopes of high-frequency carriers tend to be higher, typically 50-100 ms (Henning 1974;Neutzel and Hafter 1981;Bernstein and Trahiotis 1985). With most current cochlear implant speech processors, timing information associated with the fine structure is not provided, so a loss of sensitivity to ITDs is to be expected.…”