In recent years there has been growing interest in masking that cannot be attributed to interactions in the cochlea-so--called informational masking (IM). Similarity in the acoustic properties of target and masker and uncertainty regarding the masker are the two major factors identified with IM. These factors involve quite different manipulations of signals and are believed to entail fundamentally different processes resulting in IM. Here, however, evidence is presented that these factors affect IM through their mutual influence on a single factor-the information divergence of target and masker given by Simpson-Fitter's da [Lutfi et al. (2012). J. Acoust. Soc. Am. 132, EL109-113]. Four experiments are described involving multitone pattern discrimination, multi-talker word recognition, sound-source identification, and sound localization. In each case standard manipulations of masker uncertainty and target-masker similarity (including the covariation of target-masker frequencies) are found to have the same effect on performance provided they produce the same change in da. The function relating d(') performance to da, moreover, appears to be linear with constant slope across listeners. The overriding dependence of IM on da is taken to reflect a general principle of perception that exploits differences in the statistical structure of signals to separate figure from ground.

There has been growing interest in recent years in masking that appears to have its origin at a central level of the auditory nervous system—so-called informational masking (IM). Masker uncertainty and target-masker similarity have been identified as the two major factors affecting IM; however, no theoretical framework currently exists that would give precise meaning to these terms necessary to evaluate their relative importance or model their effects. The present paper offers a first attempt at such a framework constructed within the doctrines of the theory of signal detection.

Evidence is provided suggesting a primary dependence of informational masking (IM) on the stochastic separation of target and masker given by Simpson-Fitter’s da [Lutfi et al. J. Acoust. Soc. Am. 132, EL109-113 (2012)]. The stimuli were synthesized impact sounds of plates played in sequence as masker-target-masker triads. Their spectra varied independently and at random on each presentation as would correspond to changes in plate size. In the 2IFC procedure the listener’s task was to choose the larger-sized target. The effect of spectral uncertainty regarding the masker was examined by measuring d’ performance for different values of the variance in masker size. The effect of spectral similarity of target and masker was examined by measuring performance for different values of the mean difference between target and masker size. The functions relating d’ to da in both cases were identical and of similar slope across listeners. Identical functions were also obtained, though with shallower slopes, when listeners judged the target hit with greater impact force. The results are considered in terms of their implications for the development of a model of IM that emphasizes the statistical properties of signals over loosely defined concepts of target-masker similarity and masker uncertainty.

Informational masking (IM) is the term used to describe masking that appears to have its origin at some central level of the auditory nervous system beyond the cochlea. Supporting a central origin are the two major factors associated with IM: trial-by-trial uncertainty regarding the masker and perceived similarity of target and masker. Here preliminary evidence is provided suggesting these factors exert their influence through a single critical determinant of IM, the stochastic separation of target and masker given by Simpson-Fitter's da [Lutfi et al. (2012). J. Acoust. Soc. Am. 132, EL109-113.]. Target and maskers were alternating sequences of tones or words with frequencies, F0s for words, selected at random on each presentation. The listener's task was to discriminate a frequency-difference in the target tones, identify the target words. Performance in both tasks was found to be constant across conditions in which the mean difference (similarity), variance (uncertainty) or covariance (similarity) of target and masker frequencies or F0s were selected to yield the same value of da. The results are discussed in terms of their implications for the development of a model of IM that emphasizes the statistical properties of signals over loosely defined concepts of masker uncertainty and target-masker similarity.

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