Pure-tone masking patterns in nonsimultaneous masking conditions

The frequency selectivity of the humanauditory system can be evaluated psycho-physically by the masking experimentwhere the stimulus frequency is varied asan independent variable. Classical studieson this issue usually used a simultaneousmasking paradigm where a listener detectsa relatively long probe signal in the pre-sence of a continuous masking stimulus(e.g., Egan & Hake, 1950; Small, 1959;Wegel & Lane, 1924; Zwicker & Feldt-keller, 1967). The masking pattern ob-tained in this way could be considered toreflect the physiological excitation patternelicited in the auditory system by themasker. In this sense it has been calledthe psychophysical excitation pattern(Zwicker, 1975). However it cannot befree from the interaction effects betweena masker and a probe. Of these effectsthe amplitude fluctuation perceived asbeats or roughness, the combination tones,and the two-tone suppression can exertmarked influences on the shape of themasking pattern (see, Greenwood, 1971;Moore & Glasberg, 1981, 1982). In con-sequence one cannot evaluate accuratelythe frequency response characteristics ofthe auditory system from the result ofsimultaneous masking.An alternative approach is forwardmasking where a brief probe is presentedafter the offset of a masker, so the un-desirable interaction effects mentionedabove can be avoided. This paradigm hasbeen often used in recent studies becauseit is expected to provide more accuratemeasures of the frequency selectivity oftheauditory system (e.g., Moore, 1978; Vog-ten, 1978). Moreover one can measuremasking patterns by presenting a briefprobe at different temporal locations be-fore, during, and after a masker, resulting