Research into the auditory perception of speech signals has been carried out in two main directions by the Chistovich-Kozhevnikov group in St. Petersburg (Leningrad): modeling of the peripheral auditory analysis and experimental research of how the peripheral auditory representation is processed on the central auditory levels. The main assumptions for those studies were, first, that the output of peripheral auditory analysis represents a sequence of prominent features and events in a speech flow and, second, that the most important role of the central analysis is the allocation and processing of those features and events. A model of processing of the amplitude envelope in speech signals has been developed, in order to extract the socalled on- and off-events. According to the model, positive and negative markers are localized at precisely the time were the model detects amplitude increases and decreases in any of the frequency channels. Experimental evidence about perception of speech-like signals with step-like formant amplitude jumps is presented in the paper. It demonstrates how listeners use those amplitude jumps at different frequencies to attribute a specific phoneme quality of consonants, and how an abrupt change in the amplitude of one of the formants may influence a perceived quality of a following vowel. An attempt is made to interpret the above results on the basis of short-time peripheral adaptation. The important role of auditory processing of amplitude modulation in speech signals are discussed.