Synchresis (a word I have forged by combining synchronism and synthesis) is the spontaneous and irresistible weld produced between a particular auditory phenomenon and visual phenomenon when they occur at the same time. This join results independently of any rational logic. Synchresis is responsible for our conviction that the sounds heard over the shots of the hands in the prologue of Persona are indeed the sounds of the hammer pounding nails into them. Synchresis is what makes dubbing, postsynchronization, and sound-effects mixing possible, and enables such a wide array of choice in these processes. For a single body and a single face on the screen, thanks to synchresis, there are dozens of allowable voices — just as, for a shot of a hammer, any one of a hundred sounds will do.
Source: wiktionary