The starting point for the experimental investigation reported in this work is the observation that linguistic units (words, phonemes) do not have an acoustic invariance in the continuous speech. Moreover the a acoustic perception of a word or a phoneme depends on the context in which it is spoken. The experiments were designed to elucidate the interaction of word and context by examining the ways in which context affects the acoustic shape of a given word, as well as the role of context in word perception. The ultimate aim is to throw light on the mechanisms involved in the perception of continuous speech.