Dichotic pitches as illusions of binaural unmasking. III. The existence region of the Fourcin pitch.

Two experiments explored the existence region of the Fourcin pitch. In each experiment, detectability was assessed by measuring listeners' ability to discriminate pitch changes. In the first experiment, the detectability of the pitch was measured as a function of the number of noises used to generate it. In the second experiment, the pitch was generated using two noises with equal and opposite interaural delays and detectability was measured as a function of the difference between these two delays, and thus of the perceived pitch height. In each case, the experimental results were compared with the predictions produced by a model of binaural unmasking, based on equalization cancellation, that had been designed to recover broadband sounds, such as speech, from interfering noise [Culling and Summerfield, J. Acoust. Soc. Am. 98, 785-797 (1995)]. The model accurately predicted the results from experiment 1, but failed to show an adequate decline in performance for small differences in interaural delay (corresponding to higher perceived pitches) in experiment 2. A revised model, based on similar principles, but using data on listeners' sensitivity to interaural decorrelation, rather than an equalization-cancellation mechanism, was able to predict the results of both experiments successfully.