C. Formby
Div. of Otolaryngol.---HNS, Dept. of Surgery, Univ. of Maryland School of Medicine, 419 W. Redwood St., Baltimore, MD 21201
M. G. Heinz
Johns Hopkins Univ., Baltimore, MD 21218
S. E. Hargus
J. W. Zeiders
Univ. of Maryland School of Medicine, Baltimore, MD 21201
Detection thresholds were measured for brief band-limited increments and decrements within a broadband noise signal. The signal consisted of three temporal regions, where the first and third regions served as markers for the increment or decrement in the second region. The first and third regions had a flat magnitude spectrum from 0--6000 Hz and were presented at an average N[inf 0]=40 dB/Hz. The second temporal region contained an incremented or decremented frequency band- or notch-width selected from W[inf N]=62 to 6000 Hz, with logarithmic center frequency 2500 Hz and spectrum level S[inf 0]. The temporal increment or decrement was centered within the 500-ms signal. For each W[inf N] condition, detection threshold was measured as a function of increment or decrement duration (P[inf N]=10 to 480 ms) by tracking S[inf 0] adaptively. Increments were detectable for all combinations of W[inf N] and P[inf N], but decrements were consistently detectable only for W[inf N]>500 Hz. Increment and decrement thresholds varied inversely with W[inf N] and P[inf N], ranging from 13 dB for small increment W[inf N] and P[inf N] to 1.5 dB for large W[inf N] and P[inf N]. Temporal integration functions were fitted to the increment detection results. The resulting estimates of integration time constants varied inversely with W[inf N] from 67 to 7 ms. [Research supported by NIH.]