Binaural forward and backward masking: Evidence for sluggishness in binaural detection

Abstract

The threshold of a short interaurally phase-inverted probe tone (20 ms, 500 Hz, S pi) was obtained in the presence of a 750-ms noise masker that was switched after 375 ms from interaurally phase-inverted (N pi) to interaurally in-phase (No). As the delay between probe-tone offset and noise phase transition is increased, the threshold decays from the N pi S pi threshold (masking level difference = 0 dB) to the No S pi threshold (masking level difference = 15 dB). The decay in this "binaural" situation is substantially slower than in a comparable "monaural" situation, where the interaural phase of the masker is held constant (N pi), but the level of the masker is reduced by 15 dB. The prolonged decay provides evidence for additional binaural sluggishness associated with "binaural forward masking." In a second experiment, "binaural backward masking" is studied by time reversing the maskers described above. Again, the situation where the phase is switched from No to N pi exhibits a slower transition than the situation with constant interaural phase (N pi) and a 15-dB increase in the level of the masker. The data for the binaural situations are compatible with the results of a related experiment, previously reported by Grantham and Wightman [J. Acoust. Soc. Am. 65, 1509-1517 (1979)] and are well fit by a model that incorporates a double-sided exponential temporal integration window.

The Time Course of Binaural Masking in the Inferior Colliculus of Guinea Pig Does Not Account for Binaural Sluggishness

“…In this experiment, we used a step transition between N0 and N or vice versa, which are comparable to the experiments of Holube et al (1998) and Kollmeier and Gilkey (1990). These experiments showed ERDs of around 55 ms; which are in the middle of the range observed.…”

“…It should be noted, however, that the ERD refers to the equivalent duration of a rectangular averaging window not the duration of the effect. In the experiment of Kollmeier and Gilkey (1990), for example, although the estimated ERD was 55 ms, the smoothing of thresholds was observable over 100 -150 ms, thus given that we did not observe a smoothing over Ͼ30 -60 ms, we can be confident that the neural ERDs are much shorter than the psychophysically measured ones. Whether sinusoidal masker variation or transitions from Nu to N0 would provide measurable and longer time constants is still an open question.…”

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

“…The dynamic task could be viewed as more perceptually demanding than the static task, to the extent that it was based on the interaural envelope configuration as a function of time. It has been shown that temporal resolution of dynamic changes in ITD is relatively poor, leading some to characterize binaural processing as sluggish (e.g., Kollmeier and Gilkey 1990). No such sluggishness has been observed at the level of the IC (Yin and Kuwada 1983;Joris et al 2006).…”

Psychophysical and Physiological Evidence for Fast Binaural Processing

“…Grantham concluded that the time constant of binaural processing was considerably longer than those described for monaural processing (Grantham and Wightman, 1979;Dau et al, 1999). He also attempted to reconcile his results with previous studies by Pollak (1978) who found that listeners could detect the periodic switching between binaural sound sources with periods as short as 1.5-2 ms. More recent quantifications using a masking-period pattern paradigm (Kollmeier and Gilkey, 1990) or a binaural probe configuration (Akeroyd and Summerfield, 1999;Akeroyd and Bernstein, 2001) suggested a considerably longer window of temporal integration for the binaural system than for the monaural system.…”

“…In contrast to this extraordinary neural precision, the binaural system has been described as rather slow in following changes in ITDs as, for example, elicited by a low-frequency sound source moving in space. Previous experiments characterized binaural sluggishness by estimating the capability of the binaural system to detect masked spatially divergent signals (Grantham and Wightman, 1979;Kollmeier and Gilkey, 1990). Grantham and colleagues (Grantham and Wightman, 1978;Grantham, 1982) used a low-pass noise with time-varying ITD or time-varying interaural correlation to estimate the temporal precision of the binaural system.…”