A reexamination of duplex perception evoked by intensity differences

Duplex perception is a term used to describe the simultaneous evocation of phonetic and nonphonetic percepts, a phenomenon held by some to reveal the operation of a specialized module for phonetic perception. In a widely cited experiment by Whalen and Liberman (1987), duplex percepts were created by replacing the third format transition in a synthetic syllable with a sinusoidal tone glide and manipulating the level of the glide relative to the rest of the syllable. We discuss this study, and report four experiments. The first two made a systematic estimate of the "duplexity threshold"--the tone glide level at which a chirp-like sound could be heard as well as the speech-like syllable. In the third and fourth experiments, we used the results of the first to repeat and extend the experimental procedures in the original Whalen and Liberman study. We discuss the differences in outcome, and conclude that our results may be explained without the need to invoke a specialized phonetic module.