One ear receives an isolated third-formant transition that sounds like a nonspeech chirp.
Normally, there would be peripheral masking in such a binaural listening task but this does not occur.
Instead, the listener's percept is duplex, that is, the completed syllable is perceived and the nonspeech chirp is heard at the same time.
This is interpreted as being due to the existence of a special speech module.
The phenomenon was discovered in 1974 by Timothy C. Rand at the Haskins Laboratories associated with Yale University.