Binaural notched-noise masking and auditory-filter shape

Abstract

Thresholds for sinusoids interaurally in phase (S0) and antiphase (Sπ) were measured in the presence of a diotic notched-noise masker (N0) as a function of notch width. The signal frequency was 250, 500, 1000, or 2000 Hz. For all signal frequencies, the difference between N0S0 and N0Sπ thresholds (binaural masking-level difference, BMLD) decreased continuously as the notch width increased. Model simulations showed that this result cannot be accounted for by a model that only processes the output of the auditory filter centered at the signal frequency, even if the nonlinear behavior of the monaural frequency selectivity or interaural differences in the filter shape are considered. The data were predicted well if a detrimental across-channel process was included, either by an addition of portions of the output of adjacent filters to the output of the on-frequency filter or by a notch-width dependent adverse shift in interaural phase in the binaural stage. The strength of this detrimental across-channel process tends to decrease with increasing signal frequencies.

Interaural-phase discrimination in notched noise

“…The filled symbols indicate simulated just-noticeable IPDs. Simulations using the single-channel and across-channel model (see Nitschmann and Verhey, 2013) are denoted by gray and black filled squares, respectively. For details, see text.…”

“…Trial-by-trial feedback was provided. In contrast to the corresponding detection experiment (Nitschmann and Verhey, 2013), all three masker intervals of one trial had the same masker waveform (i.e., the sole difference between the intervals was the signal IPD). For every trial a new noise sample was generated.…”

“…The masking noises (N 0 ) were generated as described in Nitschmann and Verhey (2013). The noise intervals had a duration of 600 ms and were gated using 50-ms raised-cosine ramps at on-and offset.…”

“…The comparison between detection thresholds for sinusoids interaurally in phase (S 0 ) or in antiphase (S p ) masked by a diotic notchednoise masker (N 0 ) suggests a poorer spectral resolution (i.e., wider filters) of the binaural than of the monaural system (Hall et al, 1983;Nitschmann et al, 2010). Which mechanism causes this difference between monaural and binaural spectral resolution is still a matter of debate (Nitschmann and Verhey, 2013;Breebaart, 2013).…”

“…We measured discrimination thresholds of interaural phase differences (IPDs) for sinusoids masked by the same notched-noise masker that we used in the above-cited detection experiments (Nitschmann and Verhey, 2013). The sinusoids were set to be at the same sensation level (3 dB re diotic threshold) across notch widths.…”