Annie H. Takeuchi
Louis D. Braida
Res. Lab. of Electron., Rm. 36-747, MIT, Boston, MA 02139
Sheft and Yost [J. Acoust. Soc. Am. 91, 2333 (1992)] reported that frequency transposition impaired discrimination of amplitude modulation patterns. They suggested that our failure to supplement speechreading effectively with amplitude envelopes derived from a particular frequency band of speech and carried at a lower center frequency [Grant et al., Q. J. Exp. Psychol. 43A, 621--645 (1991)] might reflect a general auditory limitation on the ability to compare amplitude modulations across carrier frequencies. This study examined the effect of systematic practice on performance in an AXY three-interval amplitude-modulation discrimination task in which all signals were narrow-band noises with bandwidths of 50 Hz and durations of 400 ms. The difference in center frequency between the A stimulus and the X and Y stimuli increased in intervals of 10% to more than an octave. With practice, the decline in discriminability was substantially lessened and some subjects showed almost no decline. This result suggests that even if perception of amplitude modulation is initially dependent on carrier frequency, listeners can learn to compare amplitude modulation patterns across large frequency differences. [Work supported by NIH.]