Sensitivity to envelope-based interaural delays at high frequencies: Center frequency affects the envelope rate-limitation

Abstract

Sensitivity to ongoing interaural temporal disparities (ITDs) was measured using bandpass-filtered pulse trains centered at 4600, 6500, or 9200 Hz. Save for minor differences in the exact center frequencies, those target stimuli were those employed by Majdak and Laback [J. Acoust. Soc. Am. 125, 3903-3913 (2009)]. At each center frequency, threshold ITD was measured for pulse repetition rates ranging from 64 to 609 Hz. The results and quantitative predictions by a cross-correlationbased model indicated that (1) at most pulse repetition rates, threshold ITD increased with center frequency, (2) the cutoff frequency of the putative envelope low-pass filter that determines sensitivity to ITD at high envelope rates appears to be inversely related to center frequency, and (3) both outcomes were accounted for by assuming that, independent of the center frequency, the listeners' decision variable was a constant criterion change in interaural correlation of the stimuli as processed internally. The finding of an inverse relation between center frequency and the envelope rate limitation, while consistent with much prior literature, runs counter to the conclusion reached by Majdak and Laback.

Binaural unmasking with temporal envelope and fine structure in listeners with cochlear implants

“…Similar to the CI users in the present study, temporal fine structure encoded in PT did not improve dichotic thresholds of NH listeners beyond dichotic thresholds with constant pulse rates at higher rates but rather made up for higher thresholds at lower constant pulse rates. The fact that CI and NH listeners only benefited from the encoding of temporal fine structure information at low pulse rates is consistent with previous findings that the ITD discrimination of CI users (and NH listeners with amplitudemodulated stimuli) is limited to lower rates (van Hoesel et al, 2009;Bernstein and Trahiotis, 2014;Ihlefeld et al, 2015).…”

“…This value of 100 Hz for the low-pass cutoff frequency is somewhat lower than that used in previous implementations of interaural correlation metrics (Goupell, 2012). The relatively low value for the low-pass cutoff frequency may be due to the high center frequency (9.2 kHz) of the stimuli in the present study; NH listeners can show poorer binaural processing performance with increasing center frequency (Bernstein and Trahiotis, 2014), which a lower low-pass cutoff frequency models. However, because we varied the value of the second-order low-pass filter cutoff frequency to fit the data set and used a relatively small data set, this may have inflated the percent variance explained relative to that which might be found with a larger data set.…”

“…The stimuli were first low-pass filtered with a fourth-order Butterworth filter with a 425-Hz cutoff frequency. The stimuli were then low-pass filtered a second time, this time with a second-order Butterworth filter with a cutoff frequency that varied from 50 to 150 Hz in 10-Hz steps across different iterations of each metric (Bernstein and Trahiotis, 2014). Because the low-pass filtering resulted in no remaining acoustic temporal fine structure (i.e., no carrier at 9.2 kHz), the metrics were that of the temporal envelope (i.e., the pulses) and will be referred to in this regard (e.g., the normalized envelope correlation).…”

Sensitivity to Envelope Interaural Time Difference: Models of Diverse LSO Neurons

“…Considered across listeners and CFs, availability of LSO neurons with high membrane speeds would explain the fact that listeners with the lowest ITD ENV thresholds at 128 and 256 Hz for a 4-kHz carrier frequency were invariably those for whom ITD ENV remained discriminable at higher modulation rates and at higher carrier frequencies. The practical low-pass modulation filter is carrier-frequency dependent (Bernstein & Trahiotis, 2014), and varies across human listeners for the same modulation and carrier frequencies, consistent with our modelling data. This suggests a fundamental determinant of ITD ENV sensitivity might be the ability of different listeners to access fast LSO membrane properties.…”

Sensitivity to Envelope Interaural Time Differences at High Modulation Rates

“…Similarly, Bernstein and Trahiotis (2002) reported a decline in discrimination performance for transposed tones with increasing carrier frequency, with thresholds increasing for modulation rates of 128 and 256 Hz, as the carrier was increased from 4 kHz to 6 kHz or 10 kHz, with some subjects apparently insensitive to envelope ITDs for modulation rates beyond 128 Hz at 10 kHz. Although Majdak and Laback (2009) , employing bandpass filtered pulse trains, reported no such decline in performance in their subjects, this observation was explicitly refuted by Bernstein and Trahiotis (2014) employing apparently identical stimuli and procedures. Interestingly, the effect of center frequency on the low-pass filter is not apparent from studies of monaural listening.…”