Detection and temporal integration of brief band-limited increments and decrements within a broadband noise signal

Abstract

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 N0=40 dB/Hz. The second temporal region contained an incremented or decremented frequency band- or notch-width selected from WN=62 to 6000 Hz, with logarithmic center frequency 2500 Hz and spectrum level S0. The temporal increment or decrement was centered within the 500-ms signal. For each WN condition, detection threshold was measured as a function of increment or decrement duration (PN=10 to 480 ms) by tracking S0 adaptively. Increments were detectable for all combinations of WN and PN, but decrements were consistently detectable only for WN≳500 Hz. Increment and decrement thresholds varied inversely with WN and PN, ranging from 13 dB for small increment WN and PN to 1.5 dB for large WN and PN. Temporal integration functions were fitted to the increment detection results. The resulting estimates of integration time constants varied inversely with WN from 67 to 7 ms. [Research supported by NIH.]