FURTHER EVIDENCE AGAINST AN ACROSS-FREQUENCY MECHANISM SPECIFIC TO THE DETECTION OF FREQUENCY-MODULATION (FM) INCOHERENCE BETWEEN RESOLVED FREQUENCY COMPONENTS

Previously, Carlyon [J. Acoust. Soc. Am. 89, 329-340 (1991)] argued th at there exists no across-frequency mechanism specific to the detectio n of frequency modulation (FM) incoherence, defined as a difference in FM phase, between pairs of resolved frequency components, Experiments are described which attempted to reconcile this conclusion with the r esults of two recent studies. Wilson et al. [J. Acoust. Soc. Am. 88, 1 333-1338 (1990)] reported that the detection of FM imposed on a target component was impaired by the presence of an FM ''interfering tone,'' and that the size of the effect depended on the FM coherence between interferer and target; Experiment 1 replicated their finding but showe d, by using low-pass and wideband noise, that its dependence on FM coh erence was consistent with the detection of combination tones and of b eating between the interferer and target. Cohen and Chen [ J. Acoust. Soc. Am. 92, 766-772 (1992)] reported that the detection threshold for an FM signal was higher when it was masked by two components modulate d coherently with it than when the masker and signal modulations were incoherent. Experiment 2 showed that, when the masker consisted of eig ht components, thresholds were largely determined by the modulation co herence between the signal and the masker component closest to it in f requency. Experiment 3 presented evidence that Cohen and Chen's findin gs were influenced by harmonicity between the masker and signal, even in conditions which attempted to control it. Experiment 4 replicated a nother of Cohen arid Chen's findings, that when the masker modulation was held constant and the signal FM depth varied, some listeners' thre sholds reached a maximum when the masker and signal FM depths were equ al. By manipulating the frequency ratio between masker and signal, it was shown that this finding, too, could be attributed to harmonicity b etween the signal and one of the masker components. Finally, experimen t 5 replicated Carlyon's (1991) findings at a higher sensation level a nd with a different pattern of modulation than used previously.