Perceptual fusion of tonal and noisy sounds

If stationary noise is added to a tonal, periodic sound, the noise is, to a large extent, perceived as a separate sound coming from a source other than the periodic sound. Perceptual fusion of noise with a periodic sound requires specific conditions. Results will be presented that indicate that the temporal envelope of the noise plays an important role in this matter. In experiments in which this envelope had the same peridocity as the tonal stimulus, perceptual fusion did occur. Furthermore, the energy content of the noise within successive periods of the envelope was made more or less constant. These results were obtained in an experimental setup in which a quantitative measure was obtained for the extent to which the noise integrated with the periodic sound. It will be argued that perceptual fusion as reported here cannot be explained by a peripheral mechanism such as adaptation, but must be the result of a central process which groups components from a wide range of frequency bands into one or more sound images.