Abstract:
Dave Green has repeatedly emphasized the paradox in the leaky integrator model of temporal processing and stressed the need for new approaches. Recent experiments at APU on envelope asymmetry, period jitter, and fine-structure regularity reinforce the paradox. When ``damped'' noise with a repeating exponential envelope is time reversed (``ramped'' noise), it alters the envelope and carrier percepts, supporting damped/ramped discrimination for envelope periods from 8--125 ms. The Weber fraction for jitter on the period of a click train peaks around 60 ms; perfectly regular click trains sound irregular in this region reducing jitter detection relative to longer and shorter periods. These experiments suggest a long time constant for the leaky integrator. When iterated rippled noise masks random noise, it is 15 dB less effective than the equivalent random noise; low-level random noise disrupts the fine-structure regularity of iterated noise. This suggests a short time constant, since values over 8 ms remove the fine-structure that appears to underly the timbre discrimination. ``Strobed temporal integration'' offers a potential solution to the primary paradox; the fine-structure of periodic sounds is preserved in an ``auditory image'' which decays relatively slowly thereafter. [Research performed at APU in collaboration with Drs. Akeroyd, Allerhand, Datta, Handel, Irino, Lorenzi, Tsuzaki, and Yost.]