The term P-center (perceptual center) was introduced to denote the instant at which a syllable or a vowel of speech is perceived (Morton et al. 1976a, Fowler 1979a). One can determine that instant relative to another acoustic event by auditory assessment of the time interval between events and, in particular, from the perceived rhythm. As acoustic events of speech never have an immediate onset but grow relatively slowly, the question is indeed of interest at which instant, relative to a fairly well defined physical onset, the event is perceived.
We have carried out a number of investigations on that question, i.e., both with artificial signals, and speech (, Schütte 1976a, 1978a, 1978b, Köhlmann 1982a, 1984a, 1984b,  p. 406-410). It was shown that even sound impulses that have a sharp onset are not perceived exactly at the instant of onset but with a delay in the order of 10 ms. The data can essentially be described by model that accounts for the rise and decay of auditory excitation (Schütte 1978b, Köhlmann 1984a).
Author: Ernst Terhardt firstname.lastname@example.org - Feb 28, 2000