Robert P. Carlyon
Exptl. Psychol., Sussex Univ., Brighton BN1 9QG, England
Much recent research has focused on one's ability to perform simultaneous comparisons between different regions of a sound's spectrum. In particular, it has been suggested that the patterns of modulation at the outputs of different ``auditory filters'' can be compared, and that this ability can be used to group together the commonly varying components of a single source. The case for an across-frequency mechanism that can compare patterns of amplitude modulation (AM) is well established, but that for a corresponding mechanism for frequency modulation (FM) is not. When attempting to identify such a mechanism, it is important to control for the fact that frequency-modulating one component of a harmonic complex out of phase (``incoherently'') from the rest causes it to become mistuned, and that listeners might detect this mistuning rather than the incoherence per se. This presentation reviews existing evidence that (i) for pairs of inharmonically related tones, listeners cannot discriminate coherent from incoherent FM, and (ii) for harmonic sounds, sensitivity to FM incoherence can be predicted from that to the resulting mistuning. New experiments are described that show that recent contradictory evidence, which has been interpreted as revealing an across-frequency mechanism sensitive to FM incoherence, can be accounted for by the existence of within-channel cues.