Informational masking with small set sizes.

Informational masking refers to interference in the detectability of a sound, or discrimination of some property of a sound, beyond that which can be attributed to interactions at the auditory periphery. In the current experiments the signal to be detected was a tone added to a 6-tone masker, and informational masking was introduced by randomly choosing the frequencies of the tones that comprise the masker. The primary question was whether small numbers of maskers could replace randomly drawn maskers without sacrificing the underlying detection schemes adopted by observers. Similar to the method used by Wright and Saberi [J. Acoust. Soc. Am. 105, 1765-1775 (1999)], detection thresholds were measured for different masker set sizes, where set size refers to the number of 6-tone maskers from which any one masker was drawn. Set sizes of 3, 6, 12, and 24 were tested as well as conditions in which the maskers were chosen at random. In addition, observers' memory for maskers was coarsely evaluated. Large differences in thresholds were found across observers and across different masker sets. Even for set sizes of 24, the memory test suggests some recognition of maskers for some observers. Post hoc analysis of the data included an evaluation of the relative contribution of different frequencies using a single linear model. As a base for comparison, a linear model fitted to each condition was also evaluated. Although the data were fitted better using many rather than one linear model, the reduction in quality of fit was modest. This result suggests substantial consistency in decision strategies regardless of masker set size.