| |
Abstract:
We investigated the temporal limits of the human auditory
system for identifying direction of frequency modulation (FM): how
rapid can a frequency change be without compromising FM direction
identification? Human subjects binaurally listened to linear FM
sweeps and identified the direction of frequency change at 10 FM
rates. Three frequency ranges were tested: 600-900 Hz (low; typical
range of F1 values), 1000-1500 Hz (mid; range of F2), and 2000-3000
Hz (hi; range of F3). For a given frequency range, each of 20 FM
stimuli (2 FM directions x 10 FM rates) was presented 20 times, in
pseudo-random order, for a total of 400 trials. There was a marked
difference between subjects ability to identify upward and downward
FMs. 90% accuracy in direction identification for upward FMs was
achieved at a rate as fast as 16.7 oct./sec (corresponding to a
stimulus duration of ~25ms). A considerably slower rate, 3.1
oct./sec (duration ~ 160ms), was needed for identifying downward
FMs with an accuracy of 90%. Human listeners are better at
identifying rapid upward FMs than downward ones. The temporal
threshold (fastest rate / shortest duration) for accurate upward FM
identification corresponds to the duration of the order threshold
(~25ms) while the threshold for downward FM is surprisingly slower
(~160ms).
|
