The role of bottom-up confirmation in the phonemic restoration illusion.

Phonemic restoration is an illusion in which listeners hear spoken words as intact, even though parts of them have been replaced by an extraneous sound. An improved methodology was used to investigate how much the illusion depends upon the bottom-up confirmation of expectations generated at higher levels. A powerful bottom-up factor was phone class of the sound to be restored, and its acoustic similarity to the sound that replaced it. When white noise was the replacement sound, fricatives were better restored than vowels, whereas the pattern reversed with a pure tone replacement. Including a short silence period increased restoration of stop consonants. The data indicate that phonemic restoration depends upon the interplay between the listener's expectations and the acoustic signal.