ASA 127th Meeting M.I.T. 1994 June 6-10

4aPP10. Sample discrimination of intensity differences for mixtures of target and context tones.

Boys Town Natl. Res. Hospital, 555 N. 30th St., Omaha, NE 68131

Four listeners were presented with multitone complexes (of fixed frequency and number of tones) in a 2AFC task and asked to indicate which interval had the higher mean tone level. Individual levels of the tones were drawn at random from a Gaussian distribution with a standard deviation of 5 dB, and the distributions for the two intervals differed in mean intensity by 5 dB. Across conditions the number of tones presented varied from 1 to 13. Tones were spaced at equilog intervals from 250 to 4000 Hz, beginning with one tone at 1000 Hz and spreading outward with increasing number. Except for one extremely good listener, the results replicated earlier work by Lutfi [J. Acoust. Soc. Am. 86, 934--944 (1989)], despite the use of different frequencies. Conditions were then repeated adding two flanking context tones whose intensities were drawn from the lower (nontarget) distribution. The context tones degraded performance in all conditions by approximately 0.6d' units. A large increase in the number of context tones reduced performance to chance. Listeners appear unable to apply analytic listening strategies to the task. [Work supported by NIDCD.]